Cover Image

Medical Instrumentation in the Developing World

Robert Malkin, Editor

Engineering World Health

Memphis, TN

Copyright © 2006 by Engineering World Health

All rights reserved.

Reproduction or translation of any part of this work beyond that permitted by sections 107 and
108 of the 1976 US Copyright Act without the permission of Engineering World Health is
unlawful. Requests for permission or further information should be addressed to Engineering
World Health, 111 South Highland, Suite 289, Memphis TN, 38111.

Printed in the United States of America by Engineering World Health

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The common phenomenon in most developing countries is the presence of lab
equipment which is not usable or not used because it is not appropriate for the local
needs, is improperly installed, or is defective at delivery. End users are often
untrained in equipment usage or maintenance.

-adapted from the World Health Organization

Who is this Book For?

How do you test a defibrillator on a freshly killed pig? How can you use a piece of chicken to test
an electrosurgery unit? How can you test the bili-lights before releasing them for use on infants
when you have no photometer? These are the types of questions that an engineer working in a
developing world hospital asks every day. The proper test equipment isn’t available, and the
hospital has a desperate need. You can neither release the equipment without testing, nor deny
the clinical team the only piece of equipment that could help the patient. What should you do?
This book provides answers: the kinds of practical testing and repairing suggestions that
engineers can use when in a poorly equipped hospital, far from a clinical engineering

If you are an engineer who is soon to be going to the developing world, a technician from a
developing country or simply a visitor to a third world country who wants to help with the
tremendous lack of working medical technology, then this book is for you.

This book is primarily intended for engineers and technicians traveling to the developing world to
work in a secondary, typically public, health care facility. While reading this book and taking this
book with you cannot fully prepare you for the adventure of working in the developing world, it
should help you know what to expect, technically.

What this Book Covers

The body of this work is divided into sections, each dealing with an individual piece of equipment.
In 2003, Engineering World Health reported that 44% of the medical equipment problems found
in the developing world are user error (only slightly higher than found in the United States).
Therefore half of each section is devoted to explaining the clinical use of the equipment and its
principle of operation. Taken together, the patient engineer should be able to figure out the
operation of the device without the manual (as the manual is often missing in the developing

About 27% of the problems seen in the developing world were reported to be power supply
related. Power supplies are not treated in this book as they are extensively covered in the
companion lab manual.

Most of the remaining 25% of the equipment problems seen in the developing world are
described in this book.

More importantly, perhaps, than describing the most likely problems, this book gives detailed
information on how to test a piece of equipment to determine if it is working. This very
important step in any repair is not often covered in field manuals and is very challenging in the
developing world, where the proper test equipment is often lacking.

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What this Book Does Not Cover
This book does not cover diagnostic imaging equipment. This specialty is less frequently seen in
the developing world, but more to the point, requires specialized knowledge and equipment not
typically available to the volunteer engineer spending a few weeks in a developing world hospital.
If the problem is not user error, then the engineer is likely to be unable to fix the device.

This book also does not cover automated clinical laboratory equipment. This equipment is very
poorly suited for the developing world as it requires expensive reagent packs and frequent
maintenance. The maintenance and repair often requires knowledge and tools which are not
likely to be available. In most cases, the volunteer engineer is better spending their time in some
other part of the hospital.

How to Use this Book

The material in the introduction and at the end of the book might be useful to read before
leaving. The sections on living and working in the developing world cover some critical points
which might dramatically improve your enjoyment of the trip. The tool list should be used as a
guide for packing your checked bags (you must assume that there will be no tools available in
the developing world hospital). The section on troubleshooting is a good review of basic
principles, if you feel rusty in that area.

It is probably not very helpful to read every section on each piece of equipment. This book is
intended to be brought with you on your trip. When you encounter a piece of equipment, before
beginning the diagnosis and repair, read the corresponding section of the book. Review the rules
for trouble shooting if you haven’t been in this situation in some time. Then begin your
interviewing and diagnosis.

For most equipment, you must test it before returning it to the user. Yet, you are unlikely to
have the proper test equipment. Each section describes a test that you can do, if you have the
recommended tool set. Perform these tests as many times as needed to insure that the
equipment is in good working order before returning it to use.

How this Book Was Created

This book has been written by the faculty and students of The Engineering World Summer
Institute as well as other engineers who have worked in the developing world. Let us know if
you think you have a chapter, section or correction to contribute. Perhaps there is a better way
to test a device or a more thorough testing procedure. It is only through our combined efforts
that books like this one can be made available to the people of the developing world and the
volunteers who are helping them.

Robert Malkin
Director, Engineering World Health

This book was written with major contributions from EWHSI participants and others:
Ben Schnitz, Frank Watts, Matt Christiensen, Jody Riskowski, Mary Widner, James Needham, Jose
Pujol, Bruce Carr, Meera Gopalakrishnan, Dave Harrington, Lauren Cooper, Chris Edmonds, Diane
Muratore, William Hall, Michael Scott, Amber Jaeger, Zachary Crannell, Sarah Beykirch, David
Sylvester, Sara Schubert, Brian Harry, Darcee Nelson, Michael Sealander, Margaret Lutz, Frank
Billon, Nelson Riedel, Cynthia Moreno, Michelle Garst

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Table of Contents

Forward .............................................................................................................................. ii
1 Introduction to Developing World Medical Equipment ...................................................... 1

1.1 What Characterizes the Developing World .............................................................. 1
1.2 Healthcare Technology in the Developing World...................................................... 3
1.3 Working Within a Community ................................................................................ 6
1.4 When You Return................................................................................................. 9
1.5 Conclusions........................................................................................................ 10
1.6 References ........................................................................................................ 10

2 Equipment Found in OR, ICU and ER ........................................................................... 11
2.1 Working in the Operating Theatre and ICU ........................................................... 11

2.1.1 Clothing..................................................................................................... 11
2.1.2 Hands and Behavior.................................................................................... 11
2.1.3 Working in ICU........................................................................................... 12
2.1.4 Sections of Every Chapter ........................................................................... 13

2.2 Ventilators ......................................................................................................... 15
2.2.1 Clinical Use and Principles of Operation ........................................................ 15
2.2.2 Common Problems...................................................................................... 18
2.2.3 Suggested Minimal Testing.......................................................................... 19

2.3 Oxygen Concentrators ........................................................................................ 20
2.3.1 Clinical Use and Principles of Operation ........................................................ 20
2.3.2 Common Problems...................................................................................... 21
2.3.3 Suggested Minimal Testing.......................................................................... 21

2.4 Fluid pumps ....................................................................................................... 22
2.4.1 Clinical Use and Principles of Operation ........................................................ 22
2.4.2 Common Problems...................................................................................... 23
2.4.3 Suggested Minimal Testing.......................................................................... 24

2.5 Electrocardiographs ............................................................................................ 25
2.5.1 Clinical Use and Principles of Operation ........................................................ 25
2.5.2 Common Problems...................................................................................... 28
2.5.3 Suggested Minimal Testing.......................................................................... 30

2.6 Blood Pressure Machines..................................................................................... 31
2.6.1 Clinical Use and Principles of Operation ........................................................ 31
2.6.2 Common Problems...................................................................................... 33
2.6.3 Suggested Minimal Testing.......................................................................... 34

2.7 Pulse Oximeter................................................................................................... 36
2.7.1 Clinical Use and Principles of Operation ........................................................ 36
2.7.2 Common Problems...................................................................................... 37
2.7.3 Suggested Minimal Testing.......................................................................... 37

2.8 Defibrillators ...................................................................................................... 38
2.8.1 Clinical Use and Principles of Operation ........................................................ 38
2.8.2 Common Problems...................................................................................... 39
2.8.3 Suggested Minimal Testing.......................................................................... 39

2.9 Fetal Monitor and Fetal Doppler ........................................................................... 41
2.9.1 Clinical Use and Principles of Operation ........................................................ 41
2.9.2 Common Problems...................................................................................... 42
2.9.3 Suggested Minimal Testing.......................................................................... 43

2.10 Infant Incubator................................................................................................. 44
2.10.1 Clinical Use and Principles of Operation ........................................................ 44
2.10.2 Common Problems...................................................................................... 45
2.10.3 Suggested Minimal Testing.......................................................................... 45

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2.11 Infant Warmer ................................................................................................... 46
2.11.1 Clinical Use and Principles of Operation ........................................................ 46
2.11.2 Common Problems...................................................................................... 47
2.11.3 Suggested Minimal Testing.......................................................................... 47

2.12 Phototherapy lights ............................................................................................ 48
2.12.1 Clinical Use and Principles of Operation ........................................................ 48
2.12.2 Common Problems...................................................................................... 48
2.12.3 Suggested Minimal Testing.......................................................................... 49

2.13 Respiration Rate Meter or Apnea Monitor.............................................................. 50
2.13.1 Clinical Use and Principles of Operation ........................................................ 50
2.13.2 Common Problems...................................................................................... 51
2.13.3 Suggested Minimal Testing.......................................................................... 51

2.14 Electrosurgery machines ..................................................................................... 52
2.14.1 Clinical Use and Principles of Operation ........................................................ 52
2.14.2 Common Problems...................................................................................... 53
2.14.3 Suggested Minimal Testing.......................................................................... 54

2.15 Suction Machines ............................................................................................... 55
2.15.1 Clinical Use and Principles of Operation ........................................................ 55
2.15.2 Common Problems...................................................................................... 56
2.15.3 Suggested Minimal Testing.......................................................................... 57

2.16 Theatre Lamps and Other Lights.......................................................................... 59
2.16.1 Clinical Use and Principles of Operation ........................................................ 59
2.16.2 Common Problems...................................................................................... 61
2.16.3 Suggested Minimal Testing.......................................................................... 61

2.17 Anesthesia Machines........................................................................................... 62
2.17.1 Clinical Use and Principles of Operation ........................................................ 62
2.17.2 Common Problems...................................................................................... 66
2.17.3 Suggested Minimal Testing.......................................................................... 67

2.18 Bottled Gases..................................................................................................... 68
2.18.1 Clinical Use and Principles of Operation ........................................................ 68
2.18.2 Common Problems...................................................................................... 68
2.18.3 Suggested Minimal Testing.......................................................................... 70

2.19 Batteries............................................................................................................ 71
2.19.1 Clinical Use and Principles of Operation ........................................................ 71
2.19.2 Common Problems...................................................................................... 72
2.19.3 Suggested Minimal Testing.......................................................................... 76

3 Equipment Found in the Clinical laboratory ................................................................... 77
3.1.1 Sections found in this part of the book. ........................................................ 77

3.2 Balances............................................................................................................ 79
3.2.1 Use and Principles of Operation ................................................................... 79
3.2.2 Common Problems...................................................................................... 79
3.2.3 Suggested Testing ...................................................................................... 80

3.3 Centrifuges and Electrical Motors ......................................................................... 81
3.3.1 Use and Principles of Operation ................................................................... 81
3.3.2 Common Problems...................................................................................... 82
3.3.3 Motors....................................................................................................... 83
3.3.4 Suggested Testing ...................................................................................... 84

3.4 Microtomes........................................................................................................ 86
3.4.1 Use and Principles of Operation ................................................................... 86
3.4.2 Common Problems...................................................................................... 86

3.5 Water Baths, Stir And Hot Plates.......................................................................... 88
3.5.1 Use and Principles of Operation ................................................................... 88
3.5.2 Common Problems...................................................................................... 89

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3.6 Microscopes ....................................................................................................... 90
3.6.1 Use and Principles of Operation ................................................................... 90
3.6.2 Common Problems...................................................................................... 91

3.7 Autoclaves ......................................................................................................... 92
3.7.1 Use and Principles of Operation ................................................................... 92
3.7.2 Common Problems...................................................................................... 93
3.7.3 Suggested Testing ...................................................................................... 94

3.8 Laboratory Incubators......................................................................................... 96
3.8.1 Use and Principles of Operation ................................................................... 96
3.8.2 Common Problems...................................................................................... 96

3.9 Water Purifiers ................................................................................................... 98
3.9.1 Use and Principles of Operation ................................................................... 98
3.9.2 Common Problems.....................................................................................101
3.9.3 Suggested Testing .....................................................................................102

3.10 Clinical Laboratory Ovens ...................................................................................103
3.10.1 Use and Principles of Operation ..................................................................103
3.10.2 Common Problems.....................................................................................103

4 Related Topics ..........................................................................................................105
4.1 Electrical Safety.................................................................................................105

4.1.1 Electrical Outlets........................................................................................106
4.1.2 60 Hz versus 50 Hz....................................................................................107

4.2 Troubleshooting Medical Equipment ....................................................................110
4.3 Recommended Minimum Tool Sets......................................................................114
4.4 Definitions of Some Common Medical Equipment .................................................115
4.5 Spanish-English Dictionary for a BME ..................................................................120
4.6 Possible Sources for Equipment and Spare Parts ..................................................136
4.7 Readings, Manuals and More Sources of Information............................................141

4.7.1 Sources of Books and Other Information .....................................................141
4.7.2 Web Sites with Information ........................................................................142
4.7.3 Recommended Books.................................................................................143

4.8 Units and Conversion Factors .............................................................................145
4.8.1 Conversion Factors ....................................................................................145
4.8.2 Multiples of Ten.........................................................................................147

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1 Introduction to Developing World Medical Equipment

To deliver healthcare effectively, even the most basic hospital must have functioning technology
[1], [2]. Yet, in a developing world hospital, as much as 60% of the equipment doesn’t work [3].
Basic diagnostic tools, such as X-ray imaging [4], do not exist, do not function or lack the
necessary infrastructure to be used in most of the world’s public hospitals. Functioning clinical
laboratory equipment often consists of nothing more than a hand-cranked centrifuge and a
microscope with a broken light.

It is into this desolate equipment environment that the volunteer engineer finds himself injected.
Succeeding certainly depends upon the technical knowledge and skills that the engineer brings
with him. Knowledge of the political and economic landscape is certainly helpful in negotiating
the delicacies of removing a piece of equipment for repair. However success also depends on an
admission and an understanding of the role that engineering has played in causing such

Engineering has played a critical role in creating a situation where only a tiny fraction of the
world’s population can access what Americans consider routine medical technology. For
example, X-ray imaging and microscopes have existed in the clinical setting for more than 100
years. Yet the modern designs for these basic tools typically operate for little more than six
months once introduced into the developing world. It is, at least in part, the design of such
equipment that has failed the majority of the world and design is the domain of biomedical

1.1 What Characterizes the Developing World

What is Human Development?

(adapted from: United Nations Development Program, 2003)

"The basic purpose of development is to enlarge people's choices. In principle, these
choices can be infinite and can change over time. People often value achievements that
do not show up at all, or not immediately, in income or growth figures: greater access to
knowledge, better nutrition and health services, more secure livelihoods, security against
crime and physical violence, satisfying leisure hours, political and cultural freedoms and
sense of participation in community activities. The objective of development is to create
an enabling environment for people to enjoy long, healthy and creative lives."

Mahbub ul Haq


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Human development is about much more than the rise or fall of national incomes. It is about
creating an environment in which people can develop their full potential and lead productive,
creative lives in accord with their needs and interests. People are the real wealth of nations.
Development is thus about expanding the choices people have to lead lives that they value. And
it is thus about much more than economic growth, which is only a means —if a very important
one —of enlarging people’s choices.

Fundamental to enlarging these choices is building human capabilities —the range of things that
people can do or be in life. The most basic capabilities for human development are to lead long
and healthy lives, to be knowledgeable, to have access to the resources needed for a decent
standard of living and to be able to participate in the life of the community. Without these, many
choices are simply not available, and many opportunities in life remain inaccessible.

11 million children under age five die each year from preventable causes —equivalent to more
than 30, 000 a day.

Around 1.2 billion people live on less than $1 a day (1993), and 2.8 billion on less than $2 a day.

34 million people living with HIV/AIDS (end of 2000)

163 million underweight children under age five (1998)

The Human Development Index

The Human Development Index (HDI) is a measure of the human development in a country.
The index is calculated as a combination of many factors, including Life expectancy at birth
(years), Adult literacy rate (% age 15 and above), Combined primary, secondary and tertiary
gross enrolment ratio (%), GDP per capita, Life expectancy index, Education index and GDP

What are the poorest countries in the world?

The bottom ten countries in the world are all African (Name/HDI):
Central African Republic/44.3
Burkina Faso/46.7
Sierra Leone/38.9

The top ten countries in the world are (Name/HDI):
United States/77.0

Medical Instruments in the Developing World Malkin

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1.2 Healthcare Technology in the Developing World

Conditions which have led to a low human development index vary from one country to the next.
Military or one-party (person) rule can lead to low human development [5]. Lacking a
commitment to international standards in human rights leads to torture and other treatment
which can lower human development. Civil war has torn apart many of the nations at the bottom
of the UN Human development index.

It is sometimes stated that there are inherent factors, such as climate or geography, in
developing world regions which contribute to their condition. Climate may play a role in some
diseases. However, in many developing nations, there is a thriving private sector for healthcare
delivery. Despite the climate and other inherent conditions, the private system typically delivers
excellent health care, rivaling that available in the developing world, at a price.

The relationship between the private sector and public sector is somewhat different in the
developing world. In the US, the private sector serves the majority of the population through
employer-offered insurance. Users pay a small co-pay. US citizens without insurance use the
public hospitals, where treatment is often free. In the developing world, the private sector
serves a very small percentage of the population (perhaps 3-4%). Users must pay the full fee for
their services. The public hospitals and clinics treat the majority of the population. Users of the
public system in the developing world must, typically, still pay a small co-pay. Therefore, unlike
in the US but somewhat similar to Europe, healthcare for most citizens is delivered at a small cost
in the public hospitals.

However, lacking technology, the standard of care can be quite low. An example technology
might be illustrative. Diagnostic X-ray imaging is critical for quality health care delivery. Yet, it
remains unavailable to most hospitals in the developing world. Engineering World Health
recently completed a small survey of diagnostic X-ray imaging availability in some of the world’s
poorest countries [4]. As part of this report, EWH visited a total of eight hospitals in Sierra Leone
(the poorest country in the world), Haiti (the poorest country in the western hemisphere), and
Nicaragua (the second poorest country in the western hemisphere) [5]. The survey documents
the mobile, stationary, working and non-working, diagnostic imaging, X-ray machines. Where the
machines are broken, the cause of the removal from service was noted. The survey results are
summarized in the table below.

Country Hospital Number of

Portable X-ray

Number of
Stationary X-Ray

Number of Beds

Sierra Leone Connaught 1 (1) 1 (2) 500
Good Shepard 0 0 (1) 30
Bo 0 1 (2) 225
Kissy 0 0 (1) 150
Haiti Jacmel 0 (2) 1 (1) 250
La Vallee 0 0 50
Nicaragua La Mascota 0 (1) 0 (2) 250
Leon 0 (1) 1 (2) 400
(Numbers in parentheses are the number of broken machines.)


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Each hospital had at least one operating room and an intensive care. La Mascota and Leon
Hospitals conduct thoracic surgeries. Yet, only one of the eight hospitals had a mobile X-ray
machine, a tool typically considered essential for thoracic surgery and nearly essential in any
intensive care unit. In several cases, the hospital had a portable machine, but it was broken,
most often due to an expired X-ray tube. The stationary X-ray machines were also broken
because spare parts are unavailable, principally the X-ray tube. Only approximately half of the
hospitals had a working stationary X-ray machine. Even La Mascota, the largest pediatric hospital
in Nicaragua (250 beds) had no working X-ray machine of any kind - stationary or mobile at the
time of this survey. In short, one of the most common and perhaps essential medical tools
remains largely unavailable in the developing world.

Problems with Solutions to Healthcare Technology

An engineer faced with a broken piece of equipment wants to fix it to help the people she sees
around her. However, it is unavoidable to also try to imagine solutions to the larger problem of a
general lack of equipment. Before selecting the solution to the problems the engineer sees, it is
important to have a realistic view of what problems may be encountered by medical technology

Certainly, the ever spiraling cost of the latest developments in healthcare technology is one of
the barriers to implementation for certain technologies. For example, a single MRI machine can
cost US$10,000,000, or about 0.5% of the entire economy of Sierra Leone (as opposed 0.0001%
of the US economy) [11]. While it is not possible for Sierra Leone, a country of 5.6 million
people, to purchase such equipment, the city of Memphis, Tennessee, with 1.2 million citizens,
has more than five MRI machines. The University of Saskatchewan recently installed an MRI
machine for dogs [12].

However, in many cases, capital cost is not the primary barrier to technology in the developing
world. For example, many American firms stand ready to donate their used equipment,
sometimes working, to needy hospitals. These well-meaning donations often result in
disappointment and frustration to the recipients. Even after the equipment is donated, there are
barriers to technology implementation.

The most serious problem is the lack of spare parts. Inevitably, equipment breaks. Spare parts
may not be available because the parts may not be made anymore and indigenous personnel
may not have the expertise to find alternatives. For newer equipment, the parts may be made,
but may not be available in the developing world. Even when the parts are made and are
available, the cost may be prohibitive. Even when available at a small cost, the hospital may lack
the expertise or tools required to execute the repair.

Lack of tools is a severe problem in the developing world. Even screwdrivers and wrenches are
sometimes unavailable to those responsible for servicing medical equipment. Slightly more
advanced equipment such as voltmeters and oscilloscopes are rarely available in the world’s
poorest countries. Testing equipment that biomedical technicians consider essential in the United
States, such as patient simulators, artificial lungs and defibrillator calibrators are nearly
nonexistent in the third world.

After the lack of spare parts and tools, the next major barrier is the lack of service manuals. As
every manufacturer provides service manuals with their equipment, the lack of service manuals is
usually the result of donors sending equipment, but failing to donate the service and users
manuals. Where the equipment is purchased, the manuals are lost, or in the case of service
manuals, were never available in the native language.

Medical Instruments in the Developing World Malkin

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Another lacking is reliable power and water [13]. Much of today’s equipment assumes an
existing infrastructure of at least water and electricity [14]. Sometimes distilled, deionized water
must be available. In small quantities, specialized water is not an obstacle. However, continuous
sources are not typically available. Power is rarely available on a continuous, reliable basis in
developing world hospitals, and may not be available at all. There certainly are some
measurements which inherently consume so much power, such as MRI, that without reliable
electricity they must be considered impossible. However, many measurements do not require
large amounts of energy. An ideal equipment design would tolerate very large fluctuations in the
power grid voltage, including battery or manual operation backups for periods of power outage.
However, most designs available today are intolerant to power line variation.

There are a few subtle problems worth mentioning. There is a considerable “brain drain” from
the developing world. That is to say that modern medical equipment often requires highly skilled
technicians to operate and maintain. However, once a technician or engineer becomes highly
skilled, they are able to find higher paying jobs in the developed world. So, they leave. The
result is that there are few highly skilled technicians in the developing world, despite the ever
increasing need for specialized training to maintain medical equipment.

Even where there are adequately trained personnel, the environment (no tools, no spare parts,
no manuals) can lead to frustration. Corruption in the government, perhaps extending to the
public hospitals or centralized clinical engineering facilities can add to the frustration. Long
standing frustration with one’s job can lead to detachment from the environment. The
detachment can decay to the point where no work is attempted, even when the job could be
accomplished. So, it is sometimes the case that equipment remains broken, even when the
tools, spare parts and expertise are available to repair the equipment.

The proliferation of disposable equipment, where reusable alternatives exist, is a difficult barrier
for the developing world hospital to overcome. For example, there are few, if any, US hospitals
using metallic, reusable, ECG electrodes today for routine monitoring, having replaced them with
disposable, sponge-based, self adhesive pads. At first, this substitute appears to be less
expensive, since there application is faster and they do not require cleaning and sterilizing
between uses. However, the apparent cost savings are labor costs. In the developing world,
labor costs are very low; the metallic ECG electrodes are actually a cheaper alternative for a
developing world hospital. It is often this difference in the cost of labor which drives biomedical
engineers to develop apparently cheaper equipment (automated systems, premixed calibration
solutions packs, etc.) that is actually more expensive to operate in the developing world.

The use of servicing contracts for sophisticated equipment has become an obstacle incorporated
into the equipment. In other words, the equipment is expressly designed to be serviced at
regular intervals. In some cases the equipment will simply stop working if it is not serviced every
six months. Such high levels of service are not realistic in the developing world. Equipment
must operate with minimal service for many years. Where service is required, it must not require
specialized training, tools (including a computer) or manuals. Particularly frustrating is
equipment which requires knowledge (sometimes arbitrary knowledge, such as a secret code)
which can only be acquired after completing the manufacturer’s training course.

Non-Problems for Developing World Technology

Just as attempting to implement a solution to a problem which itself has inherent problems can
stymie the best engineer, so can avoiding solutions based on preconceived, false notions of the
barriers to technology implementation in the developing world.


Page 6

A common misconception is that instruments must be simple. This is simply not true. The
people in the developing world can be trained to operate any instrument that you could be
trained to operate. In fact, there is often knowledge about the operation of medical instruments
in the developing world which can no longer be found in the developed world.

Although it was mentioned above that the one-time cost of modern equipment is a barrier, in
many cases the government can pool its resources to purchase a single piece of expensive
equipment. However if this piece of equipment requires an extensive infrastructure to operate,
such as specialized tools, frequent maintenance, or specially trained service personnel, then the
country’s prized investment is likely to work for the first few months and then stop. The result is
frustration for the politician, doctors and patients. However, capital costs are not always a

1.3 Working Within a Community

Before selecting a solution to a problem, the engineer should consider who else is working in the
area that might be able to help. In reality, the problem is so large, that only by such
collaborations can we really make significant contributions to the people of the developing world.

Since the infrastructure support for modern medical equipment is lacking in the developing world,
and since an educated population can deliver the necessary infrastructure, one solution to the
problem is to deliver training to the local population. In this vein, many have set-up schools to
train technicians. Project Hope, International Aid and many other organizations run training
schools for clinical engineers in the developing world.

One solution to filling a technology gap is to export first world technology into the third world.
There are many organizations that donate medical technology to the developing world and the
UN and the World Bank may give loans or donations to poor countries to purchase medical
equipment. In certain cases, this is the ideal solution to rebuilding a country. However, in other
cases, this approach has led to only limited success. There are certainly thousands, if not
millions, of pieces of donated equipment in the developing world. However, only a small
percentage remains functional. Besides all the barriers to continued functionality already
mentioned, donated equipment can also be ineffective because a cable or accessory can be
forgotten, the equipment breaks in shipping, the hospital technical staff may not be prepared to
properly install the equipment, or have the training to use the equipment.

Just as many organizations deliver doctors to the developing world, Engineering World Health
and many other organizations send biomedical engineers to the developing world. When these
engineers arrive, they deliver equipment, train the local population, deliver spare parts and install
equipment. Frequent short term training sessions eventually lead to competence.

In the back of this book are several chapters listing organizations, web sites and books which
contain a wealth of information about developing world medical technology.

Working Conditions for the Volunteer Engineers

One of the critical issues for selecting solutions to problems is understanding the specific working
conditions faced by a developing world engineer. Knowing how to work in these conditions is
equally important.

Medical Instruments in the Developing World Malkin

Page 7

Working successfully in the developing world environment takes patience and a different mindset
than we are used to. First of all, it is imperative to get to know the local staff and earn their
trust. Take time when you first arrive to talk to the local employees, install all the working
equipment, and repair the most highly valued equipment. This will garner respect and credibility
from the locals. These people have been promised a lot but seen little, and distrust - of
Americans in particular - is a natural defense for them. This distrust is not cruel or treacherous,
but the locals no longer believe that anyone can really supply them with parts and help them fix
machines that have been broken for years.

Once you earn the trust of the staff, you will be able to be successful and will enjoy your stay at
a more relaxed pace. Staff will begin to bring you broken equipment and ask for help, or will
provide you with lists of equipment they wish. You must become proficient at working to
understand the problem as described by the locals and communicating with them what your
solution will be. Many of the problems you will encounter will be rooted in communication and
user error, not technical difficulties.

You must be extremely patient. The pace of work is very slow compared to what we are used
to; a simple project may take days to complete. It is important to be meticulous on your
paperwork to make sure you do not forget to finish something (perpetuating the myth that
outsiders won’t really come to their aid), and even more important to be persistent with the
locals in getting their help or guidance. You must be willing to ask for help and assistance,
because you cannot be successful trying to do everything your own way. Instead, learn to work
within the natural framework of the hospital and adapt yourself to it.

There is no point in giving equipment if they are not confident in its use. We can observe, give
suggestions, and try to improve, but if we overstep our bounds the locals will again become
distrustful. If you observe a local procedure that you suspect to be incorrect, take the time to
thoroughly ask questions about why the procedure is being followed. If, after thorough
discussion with the local staff you determine the procedure should be changed, do not expect
your suggestions to be followed immediately. Discuss the necessary changes with the
department head, and then with the individual workers, and above all be patient and flexible.
You must be confident in the fact that the work you are doing is enough, and that doing your
work thoroughly and patiently is the best way to have a positive effect on the hospital and the

Living Conditions in the Developing World

Living in the developing world presents a wealth of personal problems which can become
professional problems. Living conditions are often very sparse, and are always different than
those to which you have become accustomed. There are a few basic tips that will help you
survive, but culture shock is the largest problem you may face.

In terms of basic tips, try to avoid complaints and anything else that could lead to arguments or
dissension with your hosts and department heads. You don’t know the local customs. In many
countries complaints and arguments are very poorly tolerated.

Do not go wandering off on your own without seeking local knowledge. There are dangers in the
developing world that you may not be familiar with.

Do not leave valuables unattended or get into other situations that could invite theft. Fanny
packs (or something similar to wear on your belt) are safer than purses. You definitely should


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bring and wear a concealed waterproof pouch under your clothing for most of your money, your
passport, and other identification.

Don’t drink the tap water or brush your teeth with it. Use bottled water instead. Always carry
waterless instant hand sanitizer (Purell or other brand) or Wash-n-Dry packets to clean your
hands immediately before eating.

Use mosquito repellant with at least 30% DEET content to protect against both nuisance
mosquitoes and those that carry dengue fever (somewhat similar to malaria). Sunscreen should
be used if there is any chance of getting sunburned. Always carry a disinfectant with you, such
as Polysporin or Neosporin, and use it anytime you cut your skin. Always check with a medical
care professional when you have any questions about these or related matters.

Don’t think that you are better or smarter than your hosts. You should try to respect their
customs and seek to learn from them as they do from you and your group. Realize that some
words and forms of non-verbal communication that may be friendly in our culture can have
opposite meanings in others.

Culture Shock

The most serious problem you will face when living in the developing world is culture shock. It
can be a very debilitating condition. Everyone experiences culture shock when they first visit a
foreign country for an extended period. Culture shock is a type of psychological stress which
affects those adjusting to new cultures or environments. This is not simply the shock of
experiencing something new, but is an all-encompassing environmental change which may take
weeks or even months to overcome.

As cultures operate and behave very differently from each other, people are shocked - or made
temporarily uncomfortable - by the differences and apparent unpredictability they encounter,
whether it be in the language, food or societal ceremonies of everyday life. One positive of this
experience is the ability to better understand your own culture and society.

Culture shock is typically experienced in stages. Here’s a summary of the first four stages of
culture shock. As you are about to return home you may experience the fifth stage (a sadness
and longing to stay), and finally, you may experience reverse culture shock when you return
home. These last two stages don’t cause problems in getting your work done in the developing
world hospital.

Stage 1 Euphoria Homestay is adequate, the tourist sights are intriguing; the local people
are courteous and helpful; we think a wonderful experience lies ahead.

Stage 2 Depression Everything different is a problem. Misunderstandings seem frequent. The
gratitude we expected seems lacking. Health problems may develop. Work ethics are different
and frustrating. We feel like giving up and going home.

Stage 3 Adaptation We begin to understand some of the behaviors and enough of the
language to limit isolation. The situation seems less hopeless. We begin to laugh again.

Stage 4 Longing We accept the customs of the country, perhaps not enthusiastically, but
we don’t chafe. Basic work anxieties are gone. We begin to feel a longing for home, but not a
strong need.

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Culture shock typically strikes a few days or weeks after arrival when the newness of the location
starts to wear off and you are no longer acting as a tourist but are starting to integrate with the
local society. Recognizing the following symptoms of the first stage can help you understand
yourself as well as to empathize with others.

The most common symptom is a feeling of uncontrollability and helplessness. This can be either
a positive or negative experience depending on how you adapt to it, whether you grow and
adapt or withdraw and lose confidence. The challenges of finding new places to eat, shop, and
play can be taxing on anyone and you should try to relax and not push yourself in the initial
weeks of living abroad. Culture shock is experienced at different rates. Don’t let your better
adjusted friends disagree or try to make you do something you aren't comfortable with.

You may notice difficulty sleeping, a disregard for day-to-day life, withdrawal from social contact,
difficulties eating, weight loss, homesickness, extreme dislike for races or cultures other than
your own, health problems, recurring sickness, socializing difficulties, obsessive worrying, fear, or

The good news is that the symptoms will subside over time as adjustment takes place. There
are many ways that you can combat culture shock. Don't be afraid to admit that you are
uncomfortable or confused in a new situation. Feel free to express your frustration with
understanding friends or your trip leader. Don't be surprised if normal activities are more difficult
than those at home. Establish a routine as quickly as possible. Make your home stay
comfortable. Learn the local rules of living in the new location. Learn as much of the local
language as possible. Take advantage of new opportunities and activities. Try to attack
problems right away; don't procrastinate. Stay in contact with friends at home (e-mail and
telephone). Write down your experiences (keep a log book). Try to keep a sense of balance,
humor and perspective. Ignore those who would force you to change or don't understand your
experience. Understand that adjusting takes time, but is by no means impossible or traumatic.

1.4 When You Return

Culture shock will also accompany your return home, called reverse culture shock. You may find
that your friends grow tired of hearing your stories before you grow tired of telling them.
Eventually, you will readapt to your home culture.

Hopefully your first experience in the developing world will not be your last. The needs are
tremendous and the group that could have the most impact on the state of health care in the
developing world is engineers. You can still remain involved and be helpful, long after you
return. You can educate, research new technologies, design new tools and develop entire
strategies for the reliable, low-cost delivery of health care.

Very little is being done to design specialized equipment for the developing world. While
engineers will focus on coping aids for the physically disabled, no similar effort is underway for
the economically disabled. Engineering solutions for the developing world can be envisioned for
x-ray, ultrasound, electrosurgery, clinical laboratory equipment, etc. Alternative designs avoid
disposables, consider the low cost of labor, require little power, little service (or easily delivered
service), require little specialized training for servicing, etc.

Finally, there is very little, if any money put into the research and development of technologies
for the developing world. There are very notable exceptions, for example the detection and
treatment of certain diseases, e.g., malaria, TB and AIDS, receive considerable attention.
However, the funding of alternative technologies for diagnostic x-rays, neonatal incubation,


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electrosurgery and many other common technologies is nearly non-existent. Engineers should be
at the forefront of encouraging their governments to fund these types of technology development
on an equal footing with one-disease oriented projects.

1.5 Conclusions

Before diving into the technical chapters it is worth considering what it means to “make a
difference” or “have an effect” on the hospital and the people. The living conditions in
developing world are so poor that the expectations are very low. Yet, on the whole, people are
happy and are thankful for any help they receive. It is not your job, as a volunteer engineer, to
refurbish the entire hospital in four weeks. If you put just a few pieces of equipment back into
service, Make a few friends, and pledge to return, you will have made a huge impact on the
healthcare in the developing world.

1.6 References

[1] Rigal J, Szumilin E. Clinical Guidelines: Diagnostic and treatment manual, Medcins Sans
Frontieres, 1999

[2] The New Emergency Health Kit, World Health Organization, 1998.

[3] Maintenance and repair of laboratory diagnostic imaging, and hospital equipment, World
Health Organization, 1994.

[4] Malkin, R. A. X-Ray Technology in the Developing World. Engineering World Health Situation
Report, 2003.

[5] UN Human Development Report 2001, Oxford University Press, Oxford, England, 2001.

[6] World Bank “International Development Goals: Strengthening Commitments and Measuring
Progress.” 2001.

[7] World Health Organization. 1997. Health and Environment in Sustainable Development: Five
Years after the Earth Summit. Geneva.

[11] World Fact Book, Central Intelligence Agency, Washington, DC 2003.

[12] Canadian Broadcasting Company “First MRI for pets in Canada” Jan 28, 2003.

[13] Johns, WL, El-Nageh MM. Selection of basic laboratory equipment for laboratories with
limited resources, World Health Organization, 2000.

[14] Principles of management of health laboratories, World Health Organization, 1993.

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2 Equipment Found in OR, ICU and ER

2.1 Working in the Operating Theatre and ICU

In the developing world, the biomedical engineer will often be called into an active room to do a
quick repair or adjustment. You will need to know what procedures to follow. Procedures will
vary from hospital to hospital but the core requirements are the same. Most OR suites are set up
with 3 distinct areas, clean, dirty and sterile. In the hallways there will be a red line on the floor
or wall and a door, which indicates the start of the sterile area. To enter this area you need the
proper clothing, head and shoe covers and a mask. In the clean area proper clothing, head and
shoe covers are needed. In the dirty area street clothes may be permitted but it is a good idea
to be properly clothed, as you may have to cross into other areas.

2.1.1 Clothing

There are jump suits which you can wear over your clothes; however, these are hot and
uncomfortable after about 30 minutes. In general, you should change into scrubs. In the
developing world, these will be cotton coverings. In the same area will be boxes of masks, head
and shoe covers. These will also be reusable cotton items in the developing world. Masks are
disposable paper or reusable cotton. If disposable, the nose stay needs to be bent over the
bridge of your nose to get a good fit. This is very important if you wear glasses as a bad fit on
the mask will cause your glasses to fog over as you breathe. If you are assigned to the
operating room you may want to have a special pair of shoes that is only worn in the OR. If you
do that no shoe covers are required. If you go out of the OR to another area you must change
out of the scrubs back into your street clothes. Generally, in the developing world, it is not
reasonable to cover your scrubs and leave the OR for a later return.

2.1.2 Hands and Behavior

You don’t have to wear gloves when you enter an operating room but you should touch nothing.
A good procedure to follow is to cross your arms across you chest as you move about the room.
Someone in the room will direct you to the problem and tell you if it is OK to touch the device or
if it has to be removed to be serviced. Never assume that you can touch anything in an active
OR room. If the room is not active, after a case there generally is no problem in touching

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equipment. If the room is being set up for a case you should consider the room active and act
accordingly. Be especially careful of anything blue, which is in the sterile field of the active room.

If you have to work on a device during a case you may have to wipe down the tools and test
equipment with alcohol before proceeding. However, this precaution is rarely adhered to. Move
slowly and watch where you step. Watch out for power cords on the floor and fluid spills. Stay
away from the sterile field (blue things) unless specifically directed to it by the staff. Talk softly
and directly to the person who asked you into the room. All body fluids and tissues are
considered hazardous material.

Radiation exposure is possible from the x-rays that are taken in the OR and from radioactive
implants that are put into a patient. Most x-ray devices are well collimated and there is very little
scatter but it is still a good idea to be a minimum of 12 feet away from both the generator and
the patient.

The greatest danger in the OR is the physician or nurses egos. The staff can be under great
stress and become abrasive and obnoxious to the support staff (meaning you). In their minds
they can do no wrong and every one else just contributes to their problems. If this starts it is
time to leave the area until they cool down.

2.1.3 Working in ICU

As technology advanced in healthcare, in the 1950’s, decisions were made to put the technology
into confined areas instead of dispersing it throughout the hospital. This led to the creation of
the first intensive care units. In larger hospitals, there may be a number of intensive care areas,
cardiac (CCU), surgical (SICU), cardio/thoracic (CTU), medical (MICU), Neuro (NCU), neonatal
(NICU), and respiratory (RICU). In some very large hospitals there may be an area just for
patients with infectious diseases where they are quarantined from the general hospital
population. In smaller hospitals these patients are often put into isolation rooms that are part of
an existing ICU.

In the typical ICU setting the nurses and other staff are under considerable stress and may not
always be friendly to the biomedical engineer. They need and expect their equipment to work
and work the same way every time they use it.

In almost all cases, no special clothing is required and there is no need to avoid touching certain
areas (there is no sterile field). However, if you are called in to work on active equipment, you
must be extremely cautious. These patients are very ill and cannot typically tolerate any
disturbance. If at all possible, remove the equipment from the floor before working on it. Be
especially cautious with ventilators, which can cause serious injury when disconnected or
connected prematurely.

In developing world ICU’s, there may or may not be emergency power outlets. If there are,
electrical outlets commonly might be divided into several circuits. Most outlets will be connected
to emergency power sources, designated by their color, generally red but sometimes white. All
outlets should have the circuit number on them so resetting the breaker is easy. In the
developing world power outages are very common. However, it may or may not be common for
the backup generator to function properly. In some hospitals, even those with an ICU, the
backup power generator may be the only source of power.

Some outlets in the ICU are “dedicated lines” in that no other equipment can be plugged into
that circuit, these are generally for monitors and computers. Unfortunately it is not unusual for

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other outlets to be connected to the circuit making it non-dedicated in the developed world. In
the developing world, dedicated lines are rarely respected.

In developed ICU’s there will be a number of compressed gas outlets on the headwall in each
ICU bed area. There will be one or more air outlets, one or more oxygen outlets, and possible a
vacuum outlet. The pressure at these outlets should be 50 psi. The fittings to connect the hoses
from the gases to the devices are specific to the gas so cross connections are not possible,
exterior to the wall. However, far more common in the developing world are bottled gases.
Most typically the only gas available is oxygen. In some hospitals, even this cannot be obtained,
in which case an oxygen concentrator will be used.

If the ventilator being used requires compressed air and it is not present on the wall a
compressor has to be used. Some ventilators have a built in compressor but most do not. The
external compressor needs to be plugged into AC and may have a large enough current draw to
limit what else can be on that circuit, a common source of an open circuit breaker.

The number of suction (vacuum) outlets on the headwall varies with the type of intensive care
unit. In a surgical or cardio-thoracic unit suction is needed for airway, gastric and possibly
wound and chest tube suction. In a coronary care unit possibly an airway or gastric suction
would be used. The vacuum and flow requirements are the same as in the operating room.
Suction regulators are generally installed on each active outlet. The regulators may have a
selector for either constant or intermittent suction and an off position. The constant setting is
used for airway, gastric and chest tube applications. The intermittent selection is used for wound
suction. However, far more common in the developing world are stand alone suction machines,
often called “Gomco’s” whether manufactured by Gomco or not. There is a chapter on these
machines later in this book.

Most intensive care areas are positive pressure environments. That is, the air pressure inside the
unit is higher then the pressure outside of the unit, which helps prevent microorganisms from
entering the ICU area. This is accomplished with the air handling system of the hospital that also
filters the incoming air. The air handling system can either use outside air or recirculate some or
all of the air through a set of filters called hepa filters. Some intensive care units may have
isolation rooms. In this room the air pressure is negative to the adjacent area, which prevents
anything from the inside of the room getting outside of the room. There is a second set of doors
that separate the rooms with the outside room being positive pressure. It is fairly common in the
developing world to see ICU’s designed with these types of air handling in mind, even though the
doors are left open or no air handling was ever installed.

Isolation rooms are used when patients are infectious to others. If you have to enter such a
room you must follow the posted signs for gowns, gloves and masks for your own protection.
The sign may say “reverse precautions” which means you can become infected by the patient.
“Precautions” means you can infect the patient. Generally, you will not be able to enter, leave or
work in one of these areas without help. The clothing and handling restrictions vary from patient
to patient and hospital to hospital.

2.1.4 Sections of Every Chapter

The following chapters describe all of the equipment that you are most likely to find in an ICU.
About 44% (according to a recent report by EWH) of the errors that you will encounter are user
errors. As the manual is often missing in developing world hospitals, you must often deduce the
operation of the machine from an understanding what the piece of equipment is supposed to do

Equipment found in the OR, ICU and ER

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and how it is supposed to do it. Therefore, the first section of each chapter describes the clinical
use of the piece of equipment and its principles of operation.

About 27% (according to recent report by EWH) of the problems encountered in developing
world equipment relate to power supply. This includes broken fuses, cords which don’t match
the outlets (donations are coming from all over the world); devices rated for 110 V in a 220 V
environment, and occasionally more sophisticated problems. However, the power supply is the
focus of the laboratory manual which accompanies this book. Therefore, these issues are not
treated here.

After eliminating user error and power supply problems, there remain a certain number of
problems which are commonly seen in a given piece of equipment. These are treated in the
second section of each chapter.

According to the annual performance reports of Engineering World Health, about 54% of the
equipment currently unused in the developing world can be placed back in service. While most
of that success comes from user error and power supply related problems, 26% of the equipment
that exhibits other problems (not user error or power supply) is also fixed by engineers who have
studied this text. Therefore, the information contained in this manual and the accompanying lab
manual is sufficient more than half the time.

Finally, when you have completed your repair, you need to test the equipment before returning it
to the floor for use. As each piece of equipment is used by many different staff members, it is
the sole responsibility of the engineer working on the equipment to insure that it is in good
working order. Unfortunately, you will frequently not have the testing equipment required to
properly test a piece of equipment. Therefore, the third section of each chapter gives guidelines
on how to conduct the most critical testing in the desolate technical environment of the
developing world hospital. Enough testing can and should be completed after every repair to
confidently release a piece of equipment for use.

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2.2 Ventilators

2.2.1 Clinical Use and Principles of Operation

Many patients in an intensive care and the operating room require the mechanical ventilation of
their lungs. All thoracic surgery patients, for example, require mechanical ventilation. Some
patients simply need assistance breathing, when a patient is recovering from certain illnesses and
operations for example. In any case, ventilators can take over the major effort of respiration for
the patient.

Some people use the term ventilator and respirator interchangeable. They are not the same. A
respirator is a device that supplies or filters air in a harsh environment. The patient is breathing
on their own when they use a respirator. In most cases, without the ventilator, the patient could
not breathe, or would have great difficulty breathing.

Basic Elements of a Ventilator

A ventilator may include a pump which creates pressured air for delivery to the patient.
However, in most cases, compressed gases are connected to the machine. The compressed gas
is at a very high pressure, so a pressure regulator is typically connected to the bottle or the
ventilator or both (see bottled gases chapter for more details). There are generally moisture
traps and particulate filters in line with the incoming gases. The figure below details most of the
common components and controls. However, there is considerable variation between

Some ventilators can accept air, oxygen or a combination of both. Some will measure the
concentration of oxygen delivered to the patient, sounding an alarm if it becomes too high or

Very old ventilators will deliver the pressurized gas directly to the patient. However, this is very
rare, even in the developing world. More common is for the ventilator to measure the volume

Ventilators are complex devices. In
many cases, the only repairs possible in
the field are user error, filters and rain

Equipment found in the OR, ICU and ER

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(usually derived from measured flow) and pressure of the delivered gases. A computer then
controls the timing and pressure for the next cycle.

All ventilators must insure that the patient does not re-breath his own, untreated expired gases,
as they will eventually become excessively concentrated in carbon dioxide. So, in most cases,
the simple volume limited ventilator contains a “non-rebreathing” valve that opens to allow fresh
gas into the cylinder, closes during inflation and opens to allow expiration of the gases from the
lungs into the room or a waste collection canister. In most modern ventilators, the non-
rebreathing valve is in the tubing set (or circuit), in which case it is disposable.

The non-rebreathing valve may have a separate tube connected to the ventilator to force the
valve open and closed. Or, the non-rebreathing valve may operate on the pressure of the
inspiratory gas. In either case, it operates as a one-way valve that allows air to flow from the
inspiratory tube to the patient, but when the patient is expiring gas, blocks the inspiratory tube,
allowing the expired gas to pass through a separate expiratory tube.

Most ventilators will include humidification. Bottled gases delivered from cylinders are too dry for
the human body to moisturize comfortably. Sterile water should be used for humidification, but
often isn’t in the developing world. The water is heated and the vapor drawn into the gas flow to
the patient. In some cases, ultrasound is used to nebulize the water.

Most ventilators have an arm that the patient circuit tubing is attached to. This takes the weight
off of the tubing where it connects to the patient. Most of the tubing fittings are also specific
sizes to make misconnection harder. On adult machines the patient connector at the machine is
22 mm and the patient end of the tubing has a 15 mm connector. These connections are often
missing or manipulated in the developing world to allow for the use of mismatched tubing.

Some ventilators have the ability to heat the tubing or the delivered air or both. This can prevent
“rain-out” of the vapor in the gases being delivered to the patient. On some older systems you
still may find water traps where the “rain-out” collects in the tubing.

Modes of Ventilation

There are many different types or modes of ventilation. Most ventilators can switch between
several modes, but not all. The selection of the ventilator is ideally dependent on the patient’s
condition, but is often dictated by availability in the developing world. In fact, ventilation is so
critical that availability of the appropriate ventilator or ventilator mode often dictates what
procedures can and cannot be conducted in a given hospital.

There are three basic modes of ventilation, volume limited, pressure limited and timed cycle.
Timed cycle is a combination of the other two basic modes. Jet ventilation is a fundamentally
different mode of ventilation, but it is rarely seen in the developing world.

In the volume limited mode a preset volume of gas is delivered to the patient regardless of the
pressure reached in the lungs or the time required to complete the inflation. This is a simple
system where a gas is drawn into a cylinder and then forced out of the cylinder and into the
lungs. It is rarely used by itself in humans because of the lack of pressure sensitivity.

In a simple volume limited ventilator, the cylinder is adjusted for the volume of gas desired. The
motor is rate adjustable, generally between 5 and 50 breaths per minute (respiration rate). The
drive mechanism is a cam that creates a rapid inflation of the lungs and allows for a longer
period of time for the deflation of the lungs.

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In the pressure limited mode a pressure limit is set where gas will flow into the lungs until that
pressure is reached, regardless of the volume of gas delivered. This is a simple system where
pressurized gas is passed through a pressure regulator to the desired pressure, then a valve that
allows the gas to enter the patient. It is rarely used by itself in humans because of the lack of
volume sensitivity.

The simplest device typically used on humans is the timed cycle ventilator. This is the most
common mode because it combines both the volume and pressure limited methods of operation.

In the timed cycle mode the physician sets the respiration rate, the tidal volume (the volume of
gas to be delivered), the upper pressure limit, and the inspiratory/expiratory ratio. If the
pressure limit is not exceeded, then the device will deliver the desired volume of air, more or less
evenly during the entire inspiratory time. The inspiratory time is the total respiration time (one
over the respiration rate) times the inspiratory/expiratory ratio. For example, at a tidal volume of
1 liter, a respiration rate of 20 breaths per minute (3 seconds per breath), and an
inspiratory/expiratory ratio of 0.5 (inspiratory half as long as expiratory), the total inspiratory
time would be 1.0 seconds. One liter of gas would be delivered in one second.

If the pressure limit was exceeded, then an alarm will flash. Gas is still delivered to the patient
when the pressure limit alarm is indicated. However, the pressure is not allowed to exceed the
specified limit. Therefore the tidal volume desired has probably not been reached.

The Jet-Frequency mode is a newer ventilation mode. It is rarely seen in the developing world.
This mode is mostly used on neonates. There is no inspiratory/expiratory ratio and no pressure
limits to be set. The basic principle is a constant series of small volume pulses of gas is supplied
to the patient.

Ventilation Control

There are several modes for controlling the ventilator. The basic modes are controlled and
assisted. However, again, the combination of the two is the most common in practice.

The simplest mode is the controlled ventilation mode. In this mode the patient makes no effort
to initiate respiratory effort. The ventilator delivers a set volume of gas at a set rate for as long
as needed. Some units have a “sigh” level where every so many breaths or minutes the machine
automatically provides the patient with a greater volume of gas.

In the assisted mode of ventilation, the patient will trigger the flow of gas by starting to inhale.
When the patient reaches a preset withdrawn volume or a preset negative pressure, the
ventilator will start the flow of gas into the lungs. The assisted mode is typically used while the
patient is being weaned from the ventilator.

The most common mode is a combination of the controlled and assisted modes. At first, the
patient is on a completely controlled ventilation mode. As the patient starts to recover they will
make efforts to breathe on their own. This is called “fighting the ventilator” and is an important
clinical milestone in the recovery of a patient. Once that milestone is reached, the staff will
switch the ventilator to the assist mode, and begin to wean the patient from the ventilator.

Weaning is accomplished by slowly increasing the amount of negative pressure or withdrawn
volume required to trigger the flow of gas. This weaning process can take from hours to months
depending upon the patient’s condition. If the patient fails to initiate a respiratory effort in a
certain number of seconds the machine will automatically switch back to controlled ventilation
mode, breathing for the patient until another respiratory effort is made by the patient.

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2.2.2 Common Problems

Ventilators are one of a small group of life support devices that if it fails death will occur unless
there is intervention by staff and a replacement device available. In addition, the lungs are a
very delicate tissue which can be easily destroyed by a poorly calibrated ventilator. With that
knowledge it is paramount that the ventilators are kept in top working condition.

However, the dangers posed by a lack of ventilation combined with the dangers posed by a
poorly calibrated ventilator places the developing world engineer in a very difficult position. On
the one hand, without specific training on the ventilator at hand, you may endanger the patient
by working on the device. On the other hand, with no substitute ventilator available, you will
surely jeopardize the patient if you do not work on the device.

Fortunately, ventilators are very reliable devices. The most common problems are user error, the
power supply, filtration and the tubing. The most common problem with user error is that the
controls are not standardized between manufacturers and the manuals were either not supplied
with the donation or were supplied in a language that the hospital staff does not speak.

If the problem is related to the power supply to the ventilator or a simple mechanical problem
(such as the wheels, lid or tubing arm) repair is straightforward.

The most common problem with the tubing is that disposable tubing is being reused. The non-
rebreathing valve may break or the tubing may leak. Leaks can be fixed with epoxy or a silicon
sealant in most cases. The non-rebreathing valve cannot be repaired in general. However, it
may be possible to adapt the non-rebreathing valve from one leaking circuit to be used on
another circuit that doesn’t leak, but has a non-rebreathing problem.

If the problem is not one of the problems described above, it is probably better not to attempt to
fix the ventilator without specialized training. However, your decision should be made in careful
consultation with the physicians. Discuss what the risks are to the patient if you do not work on
the machine and what the risks are to the patient if you work on the machine, and it accidentally
over pressurizes or under-ventilates the patient. Ultimately the decision is the physician’s and
you must follow his instructions.

The inside of the Bennet ventilator
illustrates the complexity of the device.
Fortunately, the required repairs are
typically simple. If they are not, repair
in the field may not be possible.

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2.2.3 Suggested Minimal Testing

If your repair has been a simple mechanical fix or the power supply. Then you can release the
machine to the floor for use with only simple testing. The simple testing should consist of
measuring the breathing rate (it should be within a few breaths per minute of the setting over
the entire range) and measuring the inspiratory/expiratory ratio (it should be within
approximately 20% of the set ratio). Test the pressure limit by partially occluding the connection
to the patient with your hand. The pressure limit light should flash.

If the ventilator is likely to be used in an intensive care unit, then it will likely be used to wean
patients. In this case, check that the assisted mode is working. After conducting the simple
tests, you can connect the ventilator to yourself. Do this by gently placing the patient tube in
your mouth (being sure that you can easily remove it if there is a problem). In the assisted
mode, as long as you are breathing, the device will deliver gas only when you inhale. Then,
remove the tube from your mouth. The device should take over in a controlled breathing
fashion. Place the tube back in your mouth and breathe normally and the device should
automatically return to assisted mode.

If your repair has been on the breathing circuit, then you only need to test the tubing and the
non-rebreathing valve. The tubing should be leak free (occlude one end and blow hard into the
other end with the tube submerged in water. There should be no bubbles. The non-rebreathing
valve is a one-way valve. If it does not have a connection to the ventilator, then you can check it
by simply blowing into the patient connection end and making sure that the air goes down the
expiratory tube. Then suck from the patient end and make sure the air is coming in from the
inspiratory tubing. If the non-rebreathing valve has a connection to the ventilator, then you will
have to operate the ventilator. Check that the gas is flowing down the correct tubing by
occluding the other tubing by squeezing the appropriate tubing and making sure that there is no
change in the ability to deliver or collect air.

If your repair has been anything more than power supply, tubing or mechanical, then you must
complete more tests. Be sure to discuss your limited ability to test the machine with the
physician and the potential dangers to his patients before conducting any repairs beyond the
power supply, tubing or simple mechanical repairs. However, if you and the physician determine
that you must attempt a repair; complete at least two more tests before releasing the ventilator:
the pressure limit and the delivered volume. Both the volume and pressure are typically tested
with dedicate equipment you will likely not have. However, they can be approximated.

The pressure limit is adequately tested by connecting the patient tubing to a u-shaped bend of
tubing filled with water. The ventilator should push the far end of the column of water the
height of the pressure setting, and then indicate a pressure limit alarm. For example, if the
pressure limit is set to 25 cm of water, then the top of the column of water away from the
ventilator should be 25 cm of water higher than the top of the column of water near to the
ventilator. Test several settings of the pressure limit. Discuss the accuracy of the limit test with
the physician.

The volume can be approximated by connecting a balloon to the patient tubing. You must
calibrate the balloon to volume before you begin. The easiest way to do this is to fill the balloon
with a known volume of water. Make two marks on the balloon a fixed distance apart, indicating
the volume next to the mark. Repeat this procedure for several volumes. Now, when the
balloon expands to the indicated volume, the marks should be your set distance apart. To use
your calibrated balloon, clamp off the balloon at the end of the inspiratory cycle. Test several
settings of the volume and discuss the accuracy of the test with the physician.

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2.3 Oxygen Concentrators

2.3.1 Clinical Use and Principles of Operation

Oxygen is a widely prescribed medication in both the hospital and home setting. Hypoxia, or an
inadequate amount of oxygen, is the main physiological state requiring this medical technology
and is present in a number of life-threatening conditions. These include chronic obstructive
pulmonary disease (COPD), which refers to the restriction, inflammation, or infection of
bronchioles or alveoli whereby oxygen supply or transfer to the blood is limited. Cardiovascular
insufficiency also causes hypoxia when an irregular rhythm, decreased flow, or inefficient
transport prevents adequate oxygen delivery to peripheral tissues.

In addition to these medical conditions, a reliable source of oxygen is essential wherever
anesthetics are administered, both to supplement the inspired gas mixture and also for
resuscitation, though other machines such as ventilators may be selectively used.

Oxygen has traditionally been supplied in cylinders in the developing world. However, cylinders
are both bulky and expensive. In isolated areas transportation of cylinders is difficult and may be
unreliable. For these reasons, The World Health Organization recommends oxygen concentrators
as a better long-term investment for smaller, remote hospitals in the developing world.

Engineering Details

Ambient air contains 78% N, 21% O2 and 1% trace gases. An oxygen concentrator works by
separating and removing the nitrogen from the ambient air, leaving nearly pure (95%) oxygen.
At high flow rates the oxygen concentration may drop.

Most machines now operate using pressure swing adsorption (PSA). Ambient air is compressed
and passed through a synthetic aluminum silicate (zeolite). Zeolite acts as a molecular sieve by
binding to nitrogen, but only at high pressures. The zeolite is designed with a porous
configuration to maximize surface area.

The high pressure, concentrated, oxygen is stored in a tank. A pressure regulator is used to step
down the pressure to the desired range.

After the zeolite is saturated with nitrogen, the valve leading to the oxygen tank is closed and the
pressure is decreased in the zeolite tank. As the pressure drops the zeolite releases nitrogen
which is vented into the air. A small quantity of enriched oxygen is then passed backwards
through the zeolite canister to completely purge the zeolite of nitrogen. Since the patient
probably needs a continuous supply of oxygen, a typical concentrator will have two zeolite
canisters. One is concentrating oxygen while the other is being purged.

An oxygen concentrator is easy to operate with only a power switch and a flow meter. An alarm
sounds if the pressure in the compression chamber falls below 20 psi. Some models include a
built-in device called an OCSI (oxygen concentration status indicator) that measures the oxygen
concentration just before the outlet. An alarm would sound if the concentration is low in these
devices. Some machines automatically shut down if the concentration of oxygen falls below

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2.3.2 Common Problems

Concentrators do malfunction occasionally, and their repair can require considerable expertise;
worn parts on the compressor and valves may need replacement. Assuming that all other parts
function optimally, the machine is only limited by the life of the zeolite crystals, which is expected
to be at least 20,000 hours.

The primary complaints are low oxygen concentrations and decreased gas flows. Since this
machine is so widely used and has few options on the interface, user error is unlikely. A clogged
filter may be the cause. The filter is located between the air source and the zeolite containers.
Some models may have multiple filters. A dirty filter can lead to a decreased oxygen
concentration and/or a decreased flow rate.

If the flow to the patient is insufficient, the tubing and connectors should be checked for leaks.
Remember that part of the oxygen-providing pathway from the zeolite canisters can be inside of
the machine.

If the motor or compressor is not functioning properly, air in the zeolite canisters will not be
pressurized enough to remove an adequate amount of nitrogen from the air. It is necessary in
this case to check any seals/gaskets associated with these systems. Inside the chambers, 20psi is
the standard pressure.

The valves at the inlet and outlet of the zeolite canisters must be tight and timed correctly.
During pressurization, the inlet valve should be opened and the outlet valve should be closed.
During filtering, which normally takes 8 to 20 seconds, both valves should be closed as nitrogen
binds to the zeolite. During release of oxygen-concentrated air to the patient, only the outlet
valve should be opened. Remember that in the regeneration stage a small amount of oxygen is
released back into the canister to expel leftover nitrogen. Most models have valves that are
coordinated between chambers. However, check the timing of valve opening and closing.
Canisters will be in different stages of the pressure swing cycle so that while one canister is
filtering, the other is regenerating.

2.3.3 Suggested Minimal Testing

It is important that this machine achieve oxygen concentrations near 90% or above and provide
gas flows in the manufacturer’s range, keeping in mind that for high flow rates (around 5
liters/minute) oxygen concentration will be lower. In addition, it is not safe to trust flow meters
and oxygen concentration indicators on the machine when releasing an oxygen concentrator to
the floor. These variables need to be checked using a separate oxygen analyzer and flow meter,
respectively. It is not typically difficult to determine the flow rate in the developing world, as
there is an abundance of flow meters. However, measuring oxygen concentration can be
challenging. If you are unable to locate an oxygen concentration meter, discuss the problem
with the physician before releasing the device to the floor without an oxygen concentration test.
The measurement must be performed 10 minutes after switching the concentrator on to give the
machine time to build up the concentration of oxygen.

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2.4 Fluid pumps

2.4.1 Clinical Use and Principles of Operation

It is not unusual for a patient in an ICU setting to have 6 or more fluid pumps connected to
veins, arteries or the esophagus. These pumps can supply basic fluids and electrolytes,
nutritional support, antibiotics or pain medications. Some pumps can have up to 4 separate
channels infusing fluid at the same time.

The positive pressure generated by the various manufacturers’ pumps can widely vary. All
pumps should be able to overcome arterial pressures of a patient (150-200 mmHg). Most pumps
have a pressure limit of 500 mmHg (10 psig). If the limit is reached, an occlusion alarm should
sound. In some pumps, the user can lower the pressure limits. Pumps with lowered pressure
limits are often labeled as pediatric.

On many pumps the output pressure also has a low limit. If the pressure in the fluid line is
below the lower limit, an alarm should indicate a possible loss of connection to the patient or
artery (an infiltration alarm, when the catheter is no longer in the blood vessel but infusing fluid
into the surrounding tissue).

All fluid pumps work on one of three principles, volume displacement, roller peristaltic or linear
peristaltic. A volume displacement pump requires a dedicated (meaning applicable to only one
type of pump) IV administration set, available only from the manufacturer. The dedicated
equipment includes a small cassette which acts as the pumping chamber. An IV bag or other
source is hung some distance above the pump. These pumps are relatively rare in the
developing world because the supply of the dedicated IV sets is not regular.

In the linear peristaltic pump, instead of a cassette containing the pumping chamber, the pump
“milks” the fluid through the tubing of the IV line. This may require special, usually silastic,
tubing. The basic operation is to occlude the pump with a roller, then advance the roller – or
finger – forcing fluid through the tube. The tubing and fingers are typically linearly arranged.
Since this tubing is a known diameter the volume infused by a peristaltic pump can be calculated
as the area of the tubing times the distance that the fingers travel.

This volume displacement pump requires a
dedicated cassette (cylinder on right hand
side). Because these cassettes are not
readily available, this type of pump is often
non-functional in the developing world.

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A major difference with a peristaltic pump is that it has a free flow prevention device. This is a
mechanical system to clamp off the tubing when the door is opened so the patient does not get a
bolus (large single dose) infusion.

A roller peristaltic pump is a peristaltic pump where the fingers are rollers, typically arranged in a
circle. Very few of this type of a pump are used for the administration of IV fluids. Most roller
peristaltic pumps are used as feeding pumps and as pumps in heart-lung machines.

A syringe pump is used when fluid to the patient has to be limited or a very precise amount of a
drug is to be administered. A syringe is loaded into the machine and a stepper motor advances
the plunger to administer fluid to the patient. These pumps can be battery or line operated.
Most units will require the programming of the pump, via the control panel keypad, for syringe
size, (10 to 60 cc), flow rate and delivered volumes.

2.4.2 Common Problems

User error is common with pumps. While only the clinical staff should program the pump, the
technician must know the programming procedure so they can troubleshoot or calibrate the
units. Therefore, if you have the opportunity, try to use the pumps in the ICU when they are
not connected to a patient.

Many of the pumps available in the developing world are the type which are distributed for free
or at low cost in the developed world, but require the purchase of a specific tubing set. The
pumps are donated under the incorrect assumption that they can be used in the developing
world. Since these tubing sets are expensive, they are generally not available in the developing
world. In most cases, you will not be able to adapt these pumps.

Some of the most common problems with syringe pumps are the clutch slipping which causes
under infusion of the drug, broken latches so the syringe does not fit securely onto the pump and
bad batteries. User abuse is very common as the pumps are dropped on a regular basis.

This linear peristaltic pump uses fingers (next
to the large black arrow) that “milk” the fluid
along and through the tubing. In general
specialized tubing is required, making this
type of pump less popular in the developing

Equipment found in the OR, ICU and ER

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With roller pumps, the rollers may need adjustment. If the roller is too close to the tube, it
causes high friction, low flow rates and premature wear of the tube and motor. The tube may
march through the system as well. If the roller is too loose, there will be insufficient occlusion to
move the required volume of liquid. Flow rates may drop as well, despite rapid motion of the

2.4.3 Suggested Minimal Testing

Pumps should be tested for their delivered volume with time, or flow rate. This is easily
accomplished with a graduated cylinder and a stop watch. If the flow rate is set to 10 milliliters
per minute, then you should measure 10 milliliters in a minute (or 100 milliliters in 10 minutes)
emptying into the graduated cylinder or measuring cup.

The occlusion (or high pressure) limit should be tested. The ideal test uses a manometer.
However, an adequate test is to connect the pump to a tube strung up the wall. The pump
should push water up the wall to the level of the pressure limit, then stop and sound an alarm.
For example, if the pressure limit is set to 200 mmHg, then the column of water should ascend
260 cm (20 cm of Hg is equivalent in pressure to 260 cm of water). In the worst case, simply
clamp off the tube and make sure the alarm sounds.

If the pump includes an infiltration alarm, then it can be tested by letting water from the pump
exit the tubing from the pump at different heights. Typically the infiltration alarm will sound
when the water exits the tubing a few centimeters above the pump. If the water must exit the
pump at the level of the pump or below, then the alarm is not working.

If the pump has batteries, it is usually sufficient to simply test that the device runs on the
batteries for a few minutes. A more thorough test is described in the battery section of this book

Finally, if the pump has a free flow prevention device, then insure that the removal of the tubing
does not allow free flow of the liquid into the patient.

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2.5 Electrocardiographs

2.5.1 Clinical Use and Principles of Operation

An ECG amplifier, (EKG is a German term that is widely used), is an amplifier with from three to
ten inputs combined to show from one to twelve traces (leads) of cardiac electrical activity. Each
input amplifies the signal from two or more electrodes placed on the skin.

If the ECG is being used to monitor a patient’s condition, then usually three to five wires are
connected to the patient and a low resolution ECG waveform and the heart rate are continuously
displayed and observed by the physician. Monitoring devices will include alarms for significant
changes in rhythm or waveform. If the ECG is being used as a diagnostic tool, then typically six
to ten wires are connected to the patient and one or two cardiac cycles are displayed, or printed,
in high resolution.

Most ECG machines in the developing world are of the monitoring type. For these, three or four
patient cable leads are directly connected to the patient's extremities: right leg (RL – not always
used), right arm (RA), left leg (LL), and left arm (LA). If the machine is reasonably modern, it
will have a color code marked on the leads. However, the color code is different in Europe, and
developing world hospitals often have a mixture of European and American donations. So, the
color code is of little value. A fifth connection marked “C” is often present, but rarely used and
may be left unconnected in most cases. A switch on the front will change the display to monitor
the difference between different electrode pairs: I, II, III, aVr, aVl, aVf, and V. The table below
shows the active electrodes for each switch setting. The RL lead, if present, is always active, as
it is used as a ground, either driven or passive, to reduce noise. If the RL lead is not present,
then one of the unused leads is being used as the reference.

This image shows typical ECG
images from all the most
common leads. The square
pulse is 1 mV in height. Most
developing world systems only
display leads I, II and III, with
some adding aVR, aVL and aVF.

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Lead I LA, RA

Lead II LL, RA
Lead aVr RA, LA, LL
Lead aV1 RA, LA, LL
Lead aVf RA, LA, LL
Lead V C, RA, LA, LL (rarely used)

The terminology can get confusing between inputs, which have wires which are called leads by
the engineer, and inputs, corresponding to clinically significant features, which are also called
leads by the clinical staff. Using the term clinically, there are limb leads and modified limb leads.
Limb leads have the electrodes placed on the limbs, typically wrists and just above the ankles.
Modified limb leads have the electrodes placed on the shoulders and just above the patient’s
waist. Limb leads are used only for monitoring. For diagnostic purposes, there are 12-lead ECG
machines, with electrodes connected at specific spots across the chest, in addition to the
modified limb leads. In addition to the six leads already mentioned (Leads I, II, III, aVR, aVL
and aVF) the 12-lead machine will display V1, V2, V3, V4, V5 and V6, a total of 12 leads.

To operate, the machine should first be switched on. Then, the device should be connected to
the patient via the appropriate series of electrodes. After a few seconds, the device should begin
to record the ECG. In some cases, a start button must be pushed. Some of the 12-lead ECG’s
require a series of user inputs to record the patient’s name, gender and other factors.

All inputs are isolated from the power supply of the amplifier by an isolation transformer. This
prevents any power supply fault from putting voltage on the electrodes and potentially giving an
electrical shock to the patient. Also each input has a diode, resistor or spark gap circuit that will
short any high voltage/high current pulses to ground so the amplifier is not damaged by, for
example, defibrillation. The input impedance of an ECG amplifier is typically 100 megaohms.

Amplifiers, both those used for monitoring and diagnostics, have a switching mechanism that
selects the waveform (lead) to be displayed. The switch may be rotary, pushbutton or flat panel.
On some recorders there is an automatic button which switches the output through all leads
depending upon the mode. On some units there is a calibrate position on the switch which,
when selected, displays a 1 mV signal. The 1 mV calibration signal is used to confirm the gain of
the amplifier and is a good way to do a quick check to see if the amplifier is properly functioning.
If the output shows the 1 mV signal the amplifier is working.

The standard gain of an ECG amplifier is about 1,000 cm/V, meaning that a 1 mV signal on the
body surface creates a 1 cm deflection of the display device. However, some amplifiers have an
automatic gain control and some may have switches with settings like 0.25 (gain of 250), 0.5
(gain of 500), 1.0 (gain of 1,000 Standard) 3.0 (gain of 3,000) and 5.0 (gain of 5,000). As with
any amplifier, saturation can become a problem, even at the lowest gain setting. This is common
when the patient is small, a neonate or a thin, athletic adult. A distorted waveform, usually with
some peaks or valleys or, in the worst case, a flat line at the top or bottom of the display will
result. There also can be a voltage offset caused by the electrodes placed on the patient. This
offset voltage can move the base line up or down and can cause temporary saturation of the

ECG amplifiers have two frequency responses that are selectable, monitor and diagnostic. The
monitor frequency response for long-term observation of the patient’s ECG, as in intensive care,
is 0.5 to 35 Hz. Many of the monitors in the developing world do not observe modern
standardization of the frequency ranges. Therefore, the monitoring frequency range may range

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as high as 50 Hz. The diagnostic frequency response is from 0.1 to 100 Hz, or up to 150 Hz,
with or without a notch filter to remove 50 or 60 Hz power line noise.

There are many different types of electrodes used to connect the patient to the monitor. These
electrodes range from short to long-term use. Monitoring electrodes are single use items with a
central column of conductive material surrounded by a plastic foam or paper tape disc or square
to hold the conductive column in place. At the top of the conductive column is a snap that the
lead wire is attached to, that goes to the patient cable that goes to the amplifier (figure 2.6.2).
These electrodes cost between $0.05 and $0.11 each. They cannot be cleaned or otherwise
reused. As these electrodes age, the conductive column will dry out, rendering the electrode

There are non-disposable alternatives for monitoring. The most common is the plate electrode
that is held on to the patient with a rubber belt. Between the electrode and the patient’s skin a
conductive gel is placed to assure good electrical contact. However, this gel is not critical. A
saline soaked gauze, or even a few drops of water, may improve the recording quality. If plate
electrodes are in use they should be checked and cleaned on every inspection.

For diagnostic ECG recordings, the most common electrodes are multiuse. The “Welch cup” is
the most common of these. This is a cup-shaped, silver-coated electrode with a suction bulb on
the top. Corrosion is a common problem as is the lack of suction as the suction bulb ages. It is
not unusual to find the suction bulb full of conductive gel and fungus has been known to grow in
the bulbs.

There are two general methods of displaying the ECG waveforms, electronically or on paper. The
most common form of electronic display is on a screen or CRT. The size of the display and the
type of phosphor used in the manufacture of the CRT can enter into the quality of the waveform.
The presentation of the ECG trace can be in the same format as a paper/chart presentation with
the newest data closest to the left edge of the display, often called a moving or solid trace
display. Some manufactures use an ERASE BAR presentation, sometimes called a stationary
trace. In this presentation the waveform is stationary and a blank space, or bar, moves across
the CRT with the newest data being to the left of the space/bar.

The other common method of waveform presentation is on paper. The size and shape of the
paper varies between manufacturers. There are four general types of paper used for waveform
presentation, ink, clay, wax and chemical/thermal. Each has specific benefits and problems.

Ink paper has a shiny surface, with grid lines pre-printed. They can be single sheet or
continuous strip, roll or z-fold, or a continuous strip that can do a single sheet. In most cases
there are many channels of waveform presented with one or more ECG lead configurations per
channel. The marking of the leads is done with alpha characters or dots and dashes. If the stylus
is not properly maintained there can be blotching or smudging on the waveforms. Wax
paper is for hot stylus recordings. It is rare. Thermal paper is the most common paper. It
comes in rolls and z-folds. Its distinguishing feature, in most cases, is the lack of grid lines.
Thermal paper looks like, and essential is, thermal fax paper. The chart speeds on most

Disposable ECG electrodes look
something like large buttons.
However, they are often reused in
the developing world, making them a
constant source of problems.

Equipment found in the OR, ICU and ER

Page 28

recorders and electronic displays are 25 and 50 mm/sec. Some may have additional speeds.
When the chart speed is 25 mm/sec each mm on the horizontal axis is 0.04 seconds.

2.5.2 Common Problems

By far the most common call to engineering is simple user error. ECG’s are common donations in
the developing world, but the manuals are not. Even when the manuals are delivered with the
machines, they are often in a language that the staff does not speak. Even when the staff can
read the manual, they often don’t. Modern ECG recorders can present a myriad of buttons and
controls and can be quite confusing. For all of these reasons, if the machine turns on, the first
thing to suspect is user error in the operation of the machine.

A common problem in older machines is getting the correct rate. The heart-rate meter may not
have an automatic gain control. In these cases, the user may not realize that they have to adjust
the gain for the rate to read correctly.

User error can extend beyond the operation of the machine. Though the positioning of the
electrodes is the doctor or nurse’s job, when done poorly, it can result in a call to engineering.
The most typical symptom is a saturated ECG or an ECG distorted by power line noise. A few
points to remember for electrode placement are: 1) electrodes should not be placed on scar
tissue, 2) electrodes should not be placed over a lot of body hair, 3) electrodes placed closer than
2 inches from each other may not record a clear signal, and 4) if more than one device requires
that electrodes be placed on the patient they may interfere with each other. Switching to
different leads, repositioning electrodes and shaving the skin may resolve these problems.

After the electrode the weakest link in an ECG system is the lead wires. The patient cable should
last for many years. However, abusive use can lead to wire breakage. Before rejecting a lead
wire, try a different wire from another machine to confirm that this is the cause. Lead wires
often look to be in poor condition because of tape residue on the cable. This residue can be
removed using alcohol or other solvents.

If the lead wire is at fault, replacement is the preferred option. However, lead wires can be
repaired in some cases. To find the faulty wire, for each position on the patient selector switch,
wiggle the patient cord at its end, in the middle where the five leads fan out, and at the machine
plug end. A break will be evidenced by a violent deflection on the display. If the break is in the
last, typically quite thin, part of the lead, this can be cut and soldered in the standard fashion, as
the last dozen inches are typically unshielded wire. If there is a shield, be sure to reconnect it as

The most common problem is in the connection to the main cord, or the connection to the
machine. This wire contains potentially two or three layers before the conductor. If the violent
deflections occur when the patient cable is wiggled at its plug end, and this occurs with several
lead sets, then the socket is broken. As replacement sockets are nearly impossible to find in the
developing world, you must consider rebuilding the socket (a time consuming, and often
unrewarding venture), or consider permanently soldering the lead set to the machine, if the
hospital desperately needs that ECG.

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The remaining problems are described by their symptoms because they are so common and are
often caused by user error, lead placement or lead wires.

Wandering baseline is noticed by the technician as the line between cardiac cycles bounces
around or jumps. This is most often caused by attempting to use a monitor in diagnostic mode
or by electrode placement or quality.

An intermittent trace results when the signal saturates, then returns and saturates again. These
problems are almost always caused by the electrodes or lead wires. Loose patient connections
can also be the cause. These same problems can cause a weak ECG (as well as a user setting an
inappropriate gain).

You can verify that a problem is caused by AC interference (ECG contaminated with 60 Hz or 50
Hz) by removing the machine from the operating room or ICU to see if this solves the problem.
If not, insure that the device has been set correctly for the local power line frequency. The
numbers of donations from different parts of the world, and the poor engineering support that
accompanies some donations leads to some devices being left in 50 Hz mode while being
operated in a 60 Hz environment, and vice versa. Also, check to see if the patient is cold or
nervous. If so, muscle tremors could be causing the interference. Another cause can be the
patient or nurse touching any metal or nearby wall during monitoring.

When no trace shows up at all, the most typical cause is user error. There may be brightness
settings, or an off position. Bad electrodes and lead wires do not typically cause the trace to
disappear. Power supply problems should also be suspected.

If the trace does not appear, and the device is a printing ECG, you may be experiencing problems
with the printer. With the heated stylus, the pressure of the stylus on the paper can affect the
width of the trace and its frequency response. If too much heat is used the trace will also be
widened. If too little is applied, then no trace will appear.

With an ink system the stylus is longer and touches a flat surface. The ink is carried via small
bore tubing from a central supply to the stylus. These tubes sometimes become blocked and can
be cleaned by removing and flushing them with alcohol. This is a messy process and care should
be taken to protect clothing. The tips of the stylus, (pens), may also pick up lint and bits of
paper that will widen the trace. These should be cleaned using a lint free cloth or paper. The tip
may wear in an uneven manner and require re-flattening, commonly referred to as lapping. This
is done using a very fine piece of emery paper and lightly running the tip over the paper. One
favorite way of doing this is to put the emery cloth under the tip, hold it in place while moving
the position control so the stylus moves across the emery cloth. Only 2 to 3 swings across the
cloth are generally needed to flatten the tip.

ECG cables are multi-conductor,
complicated structures That frequently
break in the developing world.

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Page 30

Ink cartridge systems have a specifically shaped “felt tip marker” instead of a heated stylus or ink
reservoir. These systems have the potential of drying out and not making full traces. The
system is used for both stationary paper, (x-y plotter) and continuous roll paper. Spare
cartridges should be with the unit as they can be replaced easily by the user. With age the
writing tip may widen and should be replaced. If a replacement cartridge is not available, it can
be refilled. However, some trial and error will be required to find an ink that will work. If the tip
is damaged, the tip from some felt tip pens may be fixed in its place, but again trial and error will
be required.

2.5.3 Suggested Minimal Testing

For most monitoring ECG’s, it is sufficient to simply connect the ECG to yourself and record an
accurate ECG and heart rate. If the heart rate matches your own (as measured with a watch
while feeling the artery in your neck), and the ECG looks like a normal ECG, then the device is
probably working. You should check the heart rate alarms to make sure that they sound when
they are set either lower than your own heart rate (upper rate alarm) or higher than your own
heart rate (lower rate alarm).

If the ECG is to be used in the OR, then there is a chance that it will be used for direct heart
contact. Even a small current running through the lead wires can cause death (via ventricular
fibrillation) in these situations. Unfortunately, without a specialized device, it is not possible to
properly check for leakage currents.

If you are in a hospital where an ECG must be used in the operating room and the appropriate
test device is not available, there is an adequate partial test. Be sure to discuss the limitations of
your testing with the physician before returning the device for use. An adequate substitute is to
only test for large leakage currents to ground. This is the most common danger to the patient.
To accomplish this test, place a resistor of about 1000 ohms between each patient connection
and ground, one at a time, in succession. Measure the voltage drop across the resistor.
Calculate the current flowing in each lead to ground (voltage drop divided by the resistance you
used). The currents should be below 50 microamps (measured voltages below 50 millivolts rms).

You can also test the metal case of any piece of equipment using the same technique. However,
for pieces of equipment which are not directly touching the heart, 500 microamps of current may
flow. Items which can be tested with this technique include the heating system, air-conditioning,
plumbing, the oxygen and suction terminal board, nurse-call and TV controls, the bed stead, and
any monitoring or other equipment attached to the patient.

It is a good practice to clean the electrodes before release back to the floor. Also, check for any
loose or broken lead wires. If the machine has a battery, check that it is in good condition and
that the charger is working properly.

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2.6 Blood Pressure Machines

2.6.1 Clinical Use and Principles of Operation

Blood pressure machines are one of the primary diagnostic tools used by health care workers.
Sphygmomanometers are used for determining the patient’s resting blood pressure, one of the
preliminary tests that health care workers may perform. A diagnosis of high or low blood
pressure can be indicative of other, more serious diseases. There are three main types of blood
pressure machines: mercury, aneroid, and electronic.

The measurement of blood pressure has been common for over a century and is often
misunderstood. The non-invasive measurement of blood pressure is accomplished by occluding
an artery in the upper arm with an inflatable cuff that is connected to a mercury manometer. A
stethoscope is used to listen for the Korotkoff’s sounds as the blood flows. The first sound is
heard as the pressure in the cuff passes the systolic pressure. The last sound is heard as the
pressure in the cuff passes the diastolic pressure.

The ideal pressure is 120 mmHg systolic and 80 mmHg diastolic. Systolic pressures above 150
mmHg or diastolic pressures above 100 mmHg are of clinical concern. The difference between
the systolic and diastolic pressures is called the pulse pressure. This generally runs between 40

A traditional blood pressure
measurement is made by occluding
the brachial artery with a cuff. As
the cuff is deflated, the technician
can hear, at first, nothing, as no
blood flows in the artery, then a
sound as the pressure in the cuff is
just below the systolic (maximum)
pressure. When the cuff pressure
just descends below the diastolic
(minimum) pressure, the sound
goes away because the flow
returns to laminar flow.

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and 50 mmHg. An estimated mean pressure can be obtained by adding one third of the pulse
pressure to the diastolic pressure. The mean pressure shouldn’t drop below about 80 mmHg.

To measure the pressure in the cuff, a mercury manometer is often used. A plastic or glass
column with graduations from 0 to 300 mm is connected to the cuff via latex or rubber tubing.
The tube is filled with mercury. The pressure reading is the height of the mercury column. To
get accurate readings the tube must be exactly vertical. At the top of the tube, under the cap is
a calf skin diaphragm that allows air to move in both directions. If this diaphragm is dirty the
mercury in the column will not move smoothly, either up or down. Mercury manometers are no
longer used in The United States. However, they are quite common in the developing world.

Another manometer used for blood pressure readings is the aneroid manometer. This is a
bellows based system that has a dial calibrated in the range of 0 to 300 mmHg. At the resting
point of the needle on the dial is a rectangular box. If the needle is in that box the manometer is
calibrated and can be used.

Non-invasive blood pressure machines (NIBP) are devices that automatically and electronically
measure blood pressure. In these system electronics replaces a human in the inflation/deflation
of the cuff. In most modern devices, the detection of the pulsation, not the listening for
Korotkoff sounds, drives the detection of the maximum and minimum pressure. The results are
displayed in digital format on separate displays or on a screen. The units can be programmed to
take blood pressures on a set cycle, 1, 5, 15, 30 minutes, trend the data and often sound alarms
if the results are outside of preset limits.

An aneroid manometer uses
a calibrated dial. Notice that
when the dial is at zero,
there is a small rectangle
where the needle should
rest. This manometer is also
calibrated in inches of water.

In this photo, the cover for
the mercury reservoir has
been removed (right). The
mercury has oxidized leaving
a fine powder that should be
removed before refilling the

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Older NIBP’s may use two tubes to inflate the blood pressure cuff. Some devices have a
transducer in the cuff to detect the sounds.

A completely different approach to measuring blood pressure is to invasively introduce a catheter
into an artery. This is most common in surgery and intensive care units. The blood pressure
device is connected to the catheter via a rigid wall plastic tube filled with a saline solution. The
tube is connected to a transducer, which may be connected to bag of saline or “flush.” Figure
2.7.3 illustrates the set up. The transducer is hung at the level of the heart. The output from
the transducer is amplified and displayed as numbers, waveform or both. Since the skin has
been breached the patients first line of defense for both infection and electrical shock have been
bypassed. Extreme care must be taken to assure the safety of the

2.6.2 Common Problems

Non-invasive, manual blood pressure machines are extremely reliable. They are also
inexpensive. Even in the developing world, they are often replaced rather than repaired.
However, there are a few common problems.

Automatic non-invasive blood
pressure (NIBP) machines
typically measure the presence
of small oscillations in the
pressure to determine the
systolic and diastolic pressures.
Some older machines may use a
sensor to detect the Korotkoff

An invasive blood pressure measurement typically involves piercing the skin of the arm or leg. The
pressure transducer should always be at the level of the patient’s heart. The flush bag is held a foot
or more above the patient.

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Leaks in the tubing are common and can often be repaired with epoxy or silastic. To check for
leaks, inflate the cuff to 250 mmHg and allow it to stand. The pressure should slowly decrease
at a rate not exceeding 5 mmHg per minute. If there is a leak, you can find it by rubbing soapy
water over the tubing and looking for bubbles.

User errors related to calibration are somewhat common. The cuff must be at the level of the
heart and the manometer must read zero before the cuff is inflated. Check the cleanliness of the
mercury. After a time, mercuric oxide will form and is distinguishable by a black powder. The
mercury, the mercury reservoir, and tube will all need to be cleaned. Keep in mind that mercury
is toxic and care should be used to not release any into the ground or building. Check the
leather seal and washer located at the top of the upright tube. Pump the pumping bulb: as soon
as the pumping is stopped, the mercury should stop rising. If it continues to rise, the leather
seal and washer will have to be further investigated and perhaps replaced.

For automatic NIBP’s the most common problem is the use of the incorrect cuff. If the correct
cuff is being used, and if the transducer is located in the cuff itself, it may be possible to access
the transducer with some difficulty. However, repair often requires specialized knowledge, as the
manufacturer’s designs vary considerably.

For invasive blood pressure measurements, there are many possible problems. The most
common is reusing non-reusable transducers. The single use disposable transducers are now the
standard of care in the United States. While there are non-disposable alternatives, they are
rarely used. The transducer is commonly mounted on an IV pole next to the patient’s bed. It
should be at the same level as the patient. There is a 2.5 mmHg error for every inch that the
transducer is above or below the level correct level.

During the set-up process the invasive catheter transducer is vented to air, zeroed and all the air
removed from the line, usually using the flush solution. The technician may, or may not correctly
complete each of these steps, leaving air bubbles in the line or leaving the transducer improperly
zeroed. Also check that the transducer is at the level of the heart.

2.6.3 Suggested Minimal Testing

The most critical element to calibrate is the pressure measurement. A simple pressure standard
can be made by creating a column of water in a tube. Taping a tube to the wall and filling it with
water up to a height of 271 cm, for example, creates a pressure standard of 200 mmHg (the
density of mercury is 13.55 times that of water). Before releasing the blood pressure machine,
check several pressure levels (200 mmHg, 100 mmHg and 50 mmHg – or 271 cm H20, 136 cm
H20 and 68 cm H20, respectively). The manometer should be accurate to within 1-3 mmHg.

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If the pressure is consistently too high or too low, you will need to adjust the zero by removing
or adding mercury or twisting the manometer face (if aneroid). Electronic blood pressure devices
will have a zero setting which should never need to be adjusted, if the device is properly zeroed
before each use. There is a gain setting for electronic devices that occasionally needs to be

If the blood pressure machine is intended for manual use, you should also check the device for
convenience of use. When inflated with the valve closed, the pressure should not drop
appreciably in ten seconds. When the valve is open, the pressure should drop slowly and
linearly. Consult with the physician or nurse about the leak and drop rates to be sure that the
device will be convenient for them to use.

If a mercury manometer has been used for many years, mercuric oxide may form in the tube and
will appear as a black powder. The mercury, tube, and reservoir will all have to be cleaned if the
nurse objects to its presence. Keep in mind that mercury is toxic and should not be touched or
the vapors excessively inhaled. To remove the mercuric oxide, take off the reservoir cap and
remove the mercury using a needle and syringe. Filter the mercury through filter paper into a
clean container. Repeat several times until all the solid oxide is removed. Take the tube and
reservoir outside and use an air line to blow out any particulate matter. Replace the clean
mercury into the reservoir and top off the reservoir with new mercury up to the ‘0’ mark.
Replace the reservoir cap.

Automatic, non-invasive blood pressure machines (NIBP’s) are more difficult to calibrate than the
others because the need to detect the Kortokoff sounds to function. If you do not have a
phantom arm, then the best approach is to use your own arm. Borrow a stethoscope and
measure your own BP. If you are not confident that you can use a sphygmomanometer
accurately, then ask someone else to measure your BP. Repeat the measurement five times.
Then connect yourself to the NIBP and measure your blood pressure five times. The average
diastolic and systolic pressures from the two systems should match to within 3 mmHg.

A manometer can be tested
against a known good manometer,
against a mercury manometer, or
against a simple column of water
in an IV tube (100 mmHg of
pressure is exerted by a column of
water 135 cm high).

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2.7 Pulse Oximeter

2.7.1 Clinical Use and Principles of Operation

Oximetry is a non-invasive method of measuring the oxygen saturation of the hemoglobin in the
blood. The percentage of the hemoglobin that is saturated with four oxygen molecules is a good
indicator of the oxygen carrying capacity of the blood. In a healthy human, nearly 100% of the
hemoglobin is saturated all of the time in the arteries.

Modern oximetry is conducted with a pulse oximeter. The pulse oximeter uses the
plethysmographic pulse from the artery to improve the measurement. Therefore, in addition to
the oxygen saturation of the hemoglobin, the device also can report the heart rate and the
plethysmograph, though the latter is less common.

The pulse oximeter uses two frequencies of light impinging on the tissue. One of the two
frequencies (or wavelengths) is sensitive to only the volume change (plethysmogram) and one
which is sensitive to both the plethysmogram and the oxygen saturation. Figure 2.8.1 shows
that at about 805 nm, the intensity of the light from the tissue does not depend on whether it is
oxygenated or deoxygenated. Whereas, at 655 nm, there is a large difference in the amount of
light reflected from the tissue. By carefully analyzing both signals, the device can deduce the
oxygen saturation of the blood hemoglobin, usually simply reported as a percent (Sp02).

The probe, which contains both the light source and the light sensitive sensor, can be placed on
a finger, ear lobe, toe or forehead depending upon its design. Some probes are single use while
others are multi-use. Multi-use probes are preferred in the developing world. However,
disposable probes are often reused.

Most pulse oximeters display both the
heart rate and the SpO2 – the oxygen

Careful analysis of
the light from two
allows the pulse
oximeter to
determine the
percentage of
saturated with

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2.7.2 Common Problems
The most common problems with the pulse oximeter are related to the probe. The constant
reuse of disposable probes eventually results in lead breakage. These can often be repaired, if
only a single wire is broken. The second common problem is a missing probe. Unfortunately, it
is not possible to substitute incompatible probes, as the wiring, and even the approach to
producing and sensing the two wavelengths differ between manufacturers.

There are a few areas of user error which are common. Sensor placement is the most common.
The sensor should be positioned to avoid letting ambient light enter the tissue or the sensor.
Some nail polish will block light transmission. If the patient is cold the blood vessels may
constrict making detection of blood flow difficult.

Beyond probe problems, typical power supply problems and user error (which is rare with this
device), there is very little that can be done to repair a broken pulse oximeter.

2.7.3 Suggested Minimal Testing

A pulse oximeter can be easily tested on yourself. Your heart rate should be accurately reflected
(to within 1 bpm) on the display as compared to a standard stop-watch/neck-artery technique.
Also, check the alarms to assure that when your heart rate is outside of the set range, the alarms

The most common
probe for a pulse
oximeter is the finger
probe. Broken wires,
springs and plastic
cases are common
problems that can be
fixed in the field.

The most common
pulse ox probe
contains two light
sources (about 650
and 800 nm) and
one detector that is

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2.8 Defibrillators

2.8.1 Clinical Use and Principles of Operation

A defibrillator is used to reverse fibrillation of the heart, restoring the heart’s normally
coordinated contractions. The uncoordinated contractions of the heart can take place in the
atrial, or upper, chamber of the heart as well as in the heart’s ventricular, or lower, chamber.
Atrial fibrillation (AF) is relatively common and can be well tolerated by the patient. Ventricular
fibrillation (VF) causes the heart to stop pumping blood immediately, and is therefore fatal if not
treated within minutes. Death from VF is often called a massive heart attack and is the most
common cause of death.

The defibrillator works by delivering a brief, very strong, electrical shock across the chest. The
typical pulse is 10 ms and as much as 3000 V. Energies ranging from 300 to 360 J are used
during external ventricular defibrillation. While treatment of ventricular fibrillation is the most
common use in the developing world, most hospital defibrillators can also treat ventricular
tachycardia, where the heart beats too quickly, but in a coordinated fashion. Energies for
treatment of ventricular tachycardia are typically below 200 J.

There are several different types of defibrillators. The most common in the developing world is
the manual defibrillator. The most common in the developed world is the automated external
defibrillators. The implantable defibrillator and the home defibrillator are very rare in the
developing world.

The manual defibrillator is a box about 1.5 cubic feet in size, weighing around ten pounds.
Cables connect two large metal paddles, which are used to apply the electric shock to the
patient. ECG leads can also be connected from the device to the patient. However, most can
monitor the ECG through the defibrillation paddles as well. When the ECG connections are used,
the ECG can be manipulated in many of the same ways as a bedside monitor.

Defibrillator paddles come in several types: external adult, external pediatric, internal (there are
several sizes, all used when the chest is open) and disposable or adhesive electrodes. The
external adult and pediatric defibrillators require a conductive gel to be added between the
patient and the paddle. The gel is used to assure conduction between the paddles and the chest

The defibrillator works by charging a capacitor, then discharging part of the stored energy in the
capacitor through the patient. Older defibrillators discharged through an LCR circuit to the

The manual defibrillator is commonly found
in the developing world. The unit on the
left includes an ECG monitor. The device
delivers a potentially lethal shock and
should be worked on with great care.

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patient. In these devices, the pulse can be as high as 7,500 volts. These discharge circuits have
a characteristic waveform to the discharge current called an Edmark waveform. Edmark
waveform devices are still very common in the developing world. Because the Edmark waveform
can cause severe damage, even death, everyone should stand clear of the patient during the
delivery of the discharge of the capacitor. More modern defibrillators discharge the capacitor
through a transistor network to deliver a more effective, biphasic, waveform. The biphasic
waveform is less likely to cause damage, but the risk still exists.

All defibrillators have a battery back-up system. This way you can bring the defibrillator to the
patient, instead of bringing the patient to the defibrillator, which could add minutes to the time
until VF is treated. Batteries are often the reason that defibrillators are heavy. Unfortunately,
they are also, often, the cause of their failure in the developing world.

2.8.2 Common Problems

Defibrillators are highly reliable devices which require relatively little maintenance if properly
stored and used. The most common problem in the developing world is the batteries. Batteries
should be replaced every 24 months, or less, to assure proper operation of the defibrillator.
However, this is almost never done in the developing world. Refer to the battery chapter for
instructions on replacing and testing batteries.

If the batteries cannot be replaced, some defibrillators will not work. However, some will
function on mains power alone. If the defibrillator is destined for the OR, the need for batteries
is minimal. If the unit is destined for the ER, and won’t operate without batteries, it is better to
send it back with a very long extension cord, rather than deny ER their only defibrillator. For
EMT’s a defibrillator without functioning batteries has no value.

Some defibrillators will contain a synchronizer for atrial defibrillation. This is rarely used in the
developing world, but can cause problems if the user unwittingly engages the synchronizer. For
ventricular fibrillation, the synchronizer plays no role and should be switched off. If this feature
is broken, the synchronizer should be bypassed or its sensitivity increased to trigger the

2.8.3 Suggested Minimal Testing

There are a few maintenance issues that you should take care of before releasing the defibrillator
to the floor. The gel will sometimes build up on the paddles and have to be cleaned. Alcohol will
soften the gel and make removal easy.

The external paddles should be inspected for pit marks; these could cause high current density
and leave burns on the chest. The marks can be removed using emery sand paper. Internal
paddles should be inspected to be sure that there are no breaks in the insulation around the
conductive part of the paddle. If breaks are present, attempt to repair them with epoxy or a dip
plastic. Tape will not withstand OR.

You should test the defibrillator before returning it to the floor. If the defibrillator is not
defibrillating, the patient may die. However, the defibrillator should never be discharged by
putting the two paddles or electrodes together and pushing the discharge switch. At a minimum
this will damage the paddles and potentially the unit.

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Ideally, you should discharge the defibrillator through a defibrillator tester. However, these are
rare in the developing world. Some defibrillators have an internal test load that you can use.
Engineering World Health has recently begun distributing limited-function defibrillator testers
free-of-charge. You can contact them to obtain one. However, in most cases, you will have no
tester and no internal test load.

If you find yourself without any testing equipment, you can try defibrillating through a large piece
of meat. While either chicken (or better turkey), pork or beef will work, you can often purchase
a freshly killed pig at very low cost in the developing world. Be sure to place the paddles on
opposite sides of the animal, at least six inches between the closest approaches of the paddles.
Also, be sure you are wearing gloves and no one else is touching the animal. Gel is required
between the paddles and animal, but be sure the gelled areas of the skin are no closer than six
inches A freshly killed pig will jump several inches when a defibrillation pulse is properly applied.
Large edemic (red) areas will quickly develop where the paddles where applied. The pig is safe
to eat after this procedure, after you remove the gel.

In the absence of freshly killed pig, the next best choice is a large piece of dead meat. You need
something large enough that the defibrillation paddles are never less than six inches apart at
their closest approach. Of course, the dead meat won’t jump. However, after ten 360 J shocks,
you should begin to see burn marks on the meat, typically outlining the electrode placement.

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2.9 Fetal Monitor and Fetal Doppler

2.9.1 Clinical Use and Principles of Operation

Fetal monitors document two major functions: 1) the heart rate of the fetus, and 2) the
contractions of the mother. A normal fetal heart rate is between 110 to 160 beats a minute. The
sound of the beat is usually strong and regular. It is normal to have some changes in the fetal
heart rate during labor, but drastic changes in heart rate before or after a contraction may
indicate that the fetus is in distress. A fetus with large changes in heart rate may need to be
removed from the womb immediately, by Caesarean section.

Fetal monitoring during labor, when it is most commonly applied, has been controversial since its
inception. Some claim that fetal monitoring offers a monitoring tool that can reduce fetal
mortality and morbidity. Others blame the technology for the large increases in Caesarean
sections and the attendant maternal morbidity.

Currently, there are three widely used methods of monitoring the fetal heart rate: Doppler,
Surface Electrodes, and a Scalp Electrode.

Surface electrodes are applied directly to the mother’s body, typically with adhesive silver-silver
chloride electrodes. The surface electrode technique operates identically to a typical
electrocardiogram, but with much more complex signal processing to reduce the probability of
mistaking a maternal heart beat for a fetal heart beat. The surface electrode approach to
measuring the fetal heart rate has the advantages of being not invasive, being applicable at any
time during pregnancy, and are very low cost. However, they are subject to artifacts from the
maternal heart beat, don’t work well with certain fetal positions and can’t resolve multiple fetal

For the Doppler technique, a doctor, nurse, or technician applies ultrasound gel to the end of a
flat transducer and moves it across the abdomen until a good reflection is found from the heart.
The Doppler technique is the most common as it is less prone to artifacts than the surface
electrodes and it is equally easy to apply. However, the transducer and accompanying
electronics are expensive, may require repositioning during labor, and don’t resolve multiple fetal
pregnancies well.

The fetal Doppler probe is also used by itself to detect the fetal heart beat. As a hand-held
device it can be used from about the end of the first trimester to delivery. The probe produces
ultrasonic pressure waves at about 2.5 MHz and hand-held unit produces a sound with heart
beat. A typically hand held device has no display or chart. The doctor must time or count the
heart beats to determine the fetal heart rate.

The principle of operation of the Doppler probe is the Doppler Effect. If waves of a given
frequency are transmitted to a stationary reflector, the reflected waves are of the same
frequency as those transmitted. If the reflector is moving towards the transmitter-receiver, the
reflected frequency will be higher than the transmitted frequency. In this case, the waves are
bounced off the fetal heart. The occurrence of a frequency shift is taken as the presence of a
heart beat by the machine.

Scalp electrodes are applied directly on the fetus’ head and operate in a manner identical to a
standard electrocardiogram. This approach is used only with high-risk patients, if labor is going

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very slowly or if the external fetal monitor is not detecting the fetal heart rate. The amniotic sac
must be broken to apply the electrode. The scalp electrode gives accurate fetal
electrocardiograms. However, it is invasive, opens the amniotic sac for infection, and cannot be
easily applied to multiple fetal pregnancies.

The contractions are measured with a strain gage transducer (usually called TOCO) either
mounted externally or with a belt around the abdomen.

The fetal heart rate is displayed digitally on many units and in graphic form on a chart. Typical
fetal heart rates are in the range of 110 to 160 beats per minute. During contractions the heart
rate will decrease and revert to previous levels after the end of the contraction. If there is a
delay in the heart rate returning to its previous level it can indicate that there is fetal distress.

2.9.2 Common Problems

User errors are common with fetal monitoring. Incorrect connections of the transducers and
incorrect loading of the paper, or the loading of the wrong paper are the most common of these
problems. Power supply problems, typically dead batteries, are common with the hand held fetal
Doppler devices. Be sure that gel is being used between the ultrasonic transducer and the

The Doppler probe is the most sensitive part of both the handheld and bedside devices. When it
breaks no output is heard, even when a stethoscope or fetoscope indicate the presence of a fetal
heart beat. You can quickly check the probe operation by gently tapping the probe surface about
once per second. If this is not detected, there is certainly a probe problem.

The probe consists of the transducer assembly, the cable, and a multi-pin fixable connector. The
cable contains between 5 and 80 separate conductors. The most frequent malfunction occurs as
a result of a break in one or more of the cable conductors. Such malfunctions are usually the
result of mishandling of the cable or of soaking it with gel. The probe is expensive and typically
cannot be replaced in the developing world.

Fortunately, the cable can often be mended. The face of the probe is usually an acoustic lens. It
must be handled with care. Do not drop the probe, and avoid scratching the face with sharp
objects. Keep the probe assembly clean of oil and gel. Always clean the probe and cable with a
tissue or damp cloth, after finishing work.

The surface electrode problems are similar or identical to those discussed in the chapter on
electrocardiograms. Poor electrode function will result in no fetal heart beat being reported.
Check that the patient electrode connections are clean and in good condition. Check that the
leads to the patient are in good condition, that the conductor is not broken, and that there is not
a short circuit to the shielding that surrounds the other connectors.

The last most common problem is with the paper. The paper is often installed wrong or the
wrong paper is used with the device. Check that the digital heart beat and the paper trace are
giving the same reading when you tap the transducer, or apply the electrodes to yourself. The
chart recorders themselves are identical to those used for electrocardiograms. Check that
chapter for ideas on what could be wrong with a chart recorder.

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2.9.3 Suggested Minimal Testing

All of the transducers designed to measure the fetal heart rate can be used to measure your own
heart rate. For surface electrodes, you may have to attach one set of electrodes to yourself (as
the mother) and one set of electrodes to a friend (as the fetus) in order to satisfy any alarm
conditions before operating the machine. The Doppler probe should work when placed on your
chest, with the proper gel, near your heart. Check for the accuracy of both the digital display
and the paper trace by comparing their output with a measure of your own heart rate from a
watch. The two should be within 1 or 2 beats per minute of the correct rate.

For the contraction monitor, stretch the belt, or very gently press on the transducer at a rate of
about one gentle push every minute. Use a watch to verify the time between applications. The
monitor should reflect your application pressure (approximately) and rate (accurately – about

If both contraction rate and fetal heart rate are reported accurately, then the device is ready to
release to the floor.

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2.10 Infant Incubator

2.10.1 Clinical Use and Principles of Operation

A baby incubator is an isolation chamber that helps regulate the temperature of an infant and
can provide air which is enriched in humidity or oxygen. The basic machine has a place for the
baby to lie and is surrounded by a clear plastic box. A heating element lies below the baby.
There is always a control for the heater, and generally a feedback mechanism to regulate
temperature within a degree of a set point. Most incubators in the developing world have latex
gloves built into the chamber that allow for manipulation of the baby without entering the
isolated environment (see figure).

In some older units the temperature is controlled by a rheostat and must be manually adjusted
as conditions change. The temperature is displayed via panel displays, digitally in newer units,
with an analog meter in older units and with a thermometer in the oldest units. Most units have
a small fan to move the air past the heater and into the infant chamber. All but the oldest of the
units will have alarm settings for over and under temperatures in the incubator. There also is a
default high temperature cutoff that prevents the incubator from heating above 40 degrees C.

In some units there is a reservoir of water that the air moves over to increase the humidity in the
infant chamber. This is often supplemented by other sources of humidity. To reduce the water
loss of an infant in an incubator literature suggests that the relative humidity in the incubator be
between 60 and 90%.

All the access doors should have positive latches on them so that the stay closed. The hoods
will have one or more cable/tubing entry ports that allow for monitoring cables, IV lines, suction
tubing, etc. to enter the infant chamber without going through an access door.

An infant incubator provides a warm,
moist and sometimes sterile
environment for a newborn. In the
developing world, as shown in this
incubator in Togo, the ports are left
open and the filters are missing,
leaving the environment warm and
moist, but not sterile. The infant sits
on a platform covering a water
holding tank and fans.

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2.10.2 Common Problems

If the chamber is not heating, it may be the heating element. The heating element is typically a
special (nicrome) wire. The wire cannot be repaired, typically, but it is common and a
replacement can often be found in a large city. The only requirements for replacing the heating
element with a new one are that the power and resistance of the new element be equal to the

Particles can build up inside the humidification chamber. The humidification chamber should be
rinsed out and dried after every use. If necessary, it is acceptable to use diluted bleach to
cleanse the chamber.

If the heater control is a rheostat the knob should be checked to make sure that it is not loose
and turning on the shaft. The markings on the control are only approximate. A dead spot in the
rheostat may cause it to change the temperature drastically with only a small change in position.
Try cleaning the dust out of the rheostat. If that does not work, the rheostat will have to be

If the air flow has dropped, check the fan filter. The frequency of replacement depends on the
environment and usage. The fan also assists in the removal of carbon dioxide from the chamber,
which should be kept below 500 ppm.

If the temperature is not maintained in the chamber, there may be a large leak or opening.
Check the seals around the doors. Also check for an external heat source, sunlight or
phototherapy (bili) lights. They can affect the warming characteristics of the incubator.

If the fan is getting noisy, try lubricating the motor or tightening any loose bolts. If the fan is
noisy, it can effect the long term hearing of the infant. The path for the movement of air must
be kept clear to assure that the temperature is stable and even across the infant in all positions.

In some units there is an inner wall in the infant chamber that directs the flow of the heated air
around the infant. These inner walls are held in place with plastic standoff posts and may loosen
up with use. These should be inspected to assure that they are properly fastened in place.

2.10.3 Suggested Minimal Testing

When deciding whether to release an infant incubator back to the floor, the temperature should
function between 34 and 40 degrees Celsius and should be accurate to within 0.5 degrees at all
possible settings. Be sure the temperature cannot exceed 40 degrees Celsius.

The fan should not be excessively noise (below 65 db). Assuming you don’t have a sound meter
with you, try to estimate the noise of the fan with your own ear placed where the baby’s will be.
It should be so quiet that you could comfortably hear all the conversations in the room around

The humidifier chamber should be clean and dry when returned.

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2.11 Infant Warmer

2.11.1 Clinical Use and Principles of Operation

The infant warmer is an open device for keeping a baby warm. True infant warmers use
resistance or radiant (infrared energy) heating elements, not heat lamps, which can burn.
Warmers are often used for the patients that require the most care, as it is easier to work on the
infant on a warmer instead of an incubator which is a closed system. On the other hand, as they
are open, warmers do not offer the environmental protection of an incubator from air borne
particles, pathogens or humidity variations.

In the resistance element, long rods are placed approximately 1 meter above the level of the
infant, reflecting heat downwards. There is an open grille that covers the rods. When energized
the rods glow red. Some old versions may use open coils, which can give inconsistent heat
distribution over the infant.

With radiant warmers the heating elements are not visible as they are imbedded in the cover
material or behind the cover. The elements are focused over the infant providing for a consistent
distribution of heat. It is difficult to judge if the unit is working by sight, but if it is working you
can feel the heat.

In more sophisticated warming units, a thermistor is placed over the liver of the infant, (the
largest internal organ, closest to the skin, with good blood flow), and is connected to the control
module. The output of the heaters varies around the set point, similar to an incubator, as the
infant’s temperature varies. In the developing world, these thermistor probes are often lost,
broken or forgotten when donated. Therefore, most units are operating in manual mode
(constant output from heaters). This mode is more dangerous as the baby can be overheated.

Infant warmers like this one are not common in
the developing world. Many of the hospital’s
rooms are always at 37 degrees Celsius or
higher without the need for heating. In this
unit, the baby is placed on the platform in the
middle of the image. The warming elements
are near the top of the image.

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Many infant warmers will have exam lights and bili-lights (see the next chapter) built into the
warming hoods. These exam lights can vary from simple incandescent light bulbs, to mini-spot
lights to reflector type (Halogen) lamps. Bili-lights can range from fluorescent tubes to reflector
type lamps with special filters to pass only the proper wavelength of light.

2.11.2 Common Problems

There are very few problems with user error and power supply in infant warmers, as they are
generally simple devices. However, the probe, as already mentioned, is a frequent problem. The
technology in the probe is simple; typically just a thermistor. However, determining the exact
type and resistance of thermistor requires data from the manufacturer. If this data can be
obtained, than a replacement probe can be manufactured from a standard thermistor and the
proper connector. However, without the manufacturer’s data, it can be impossible to construct
the probe.

A possible solution to a missing thermistor probe is to place a known, fixed resistor in its place,
essentially forcing the device to operate in manual mode. A potentiometer can be used to
determine the value of resistance that is required to force the lights to come on.

Thermocouple probes are sometimes used on warming units, in which case a resistance will not
substitute for the probe. A voltage source might work, however. Using a potentiometer, a
battery and a fixed resistor, a voltage divider can sometimes be created and adjusted until the
warming unit comes on. Since the device is now in manual mode, care should be used to insure
that the patient’s temperature is carefully monitored.

The warming units burn out from time to time. Finding replacements can be difficult in the
developing world. Some units use quartz elements and some use resistive elements. Both are
common in the developing world, but finding an exact match for the quartz element is very
difficult. In some cases, you can find a specialist that can adapt or replace the heating element
in a resistive warming unit.

2.11.3 Suggested Minimal Testing

If you have defeated the temperature sensing function, then you must be careful to explain the
risk of overheating to the nursing staff. Fixing an alternative temperature sensing device to the
warming unit with an alarm is an excellent option, if it is available.

Besides concerns with the manual mode, the only other necessary test is the ability of the device
to warm. The temperature on a blanket placed where the baby will go should be uniform across
the field. In most cases, you can simply mark dead spots and warn the staff. In some cases,
you can adjust the reflectors to better distribute the heat. The temperature should not rise about
40 degrees Celsius. However, if you have left the device in manual mode, it may exceed this
value. Be especially careful to explain the risks of using such a device with a physician. In some
cases, if there are no other infant warmers, it may still be preferable to release the device which
overheats as compared to having no warmer at all. However, in most cases, if the temperature
exceeds 40 degrees anywhere on the blanket or in the patient area, then you will need to adjust
the heating system to provide less heat, or abandon the unit.

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2.12 Phototherapy lights

2.12.1 Clinical Use and Principles of Operation

The build up of bilirubin in an infant’s blood, caused by decreased liver functions, can cause long
term damage to the child. Bilirubin buildup causes the patients’ coloring to range from yellow to
orange to red depending upon the level of bilirubin in the system. By exposing the patient to
light with wavelengths between 425 and 475 nm, the bilirubin is broken down, and then
eventually excreted from the body.

The phototherapy unit, or bili-lights, as they are more commonly called, is simply a strong source
of light in the correct wavelength. The baby sits in a basinet below the lights for 20 minutes or
more, depending on what the physician prescribes (see figure). The light is strong enough that it
can damage the retina. So, the patients’ eyes must be protected from the light when using the

2.12.2 Common Problems

The most common problem is a broken or missing light bulb. There is little else that can go
wrong. There are many substitute light sources. The use of Florissant brand tubes or Daylight
blue bulbs is quite common. The “Gro-Lux” light, also used by indoor gardeners was the most
common form of treatment. Unfortunately the Gro-Lux tubes degrade and have to be replaced
after about 200 hours of use to keep the light in the proper wavelength range. The same light
spectrum is used in a PUMA unit to treat certain skin disorders in adults. The light bulbs in
tanning beds are also in the correct wavelength range.

Phototherapy lights are common in the
developing world. However, the bulbs are
often broken or ineffective. Exam lights are
often included as well as heating (IR)

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2.12.3 Suggested Minimal Testing

If the light turns on and is still in the correct wavelength range, then the unit can be used. To
verify that the light is in the correct range, you need a light meter and a filter. A photographer’s
light meter can be used if the proper filter is at hand. If you have time, you can check the light
source by leaving your arm exposed to the light for 30 minutes. The next day, that part of your
skin should be tan, but not burned.

If you have replaced the light bulb, or have built a phototherapy unit from light bulbs that you
purchased (gro-lux or tanning bed lights, for example), then you must be sure that the lights are
not too intense for the patient. Again the ideal test is a light meter and a proper filter. However,
you can use the arm-tanning test mentioned above. Start with 5 minutes to be sure that you do
not get burned. Test longer and longer intervals until you can withstand 30 minutes without
burning, but receiving a significant tan. Explain your testing to the staff so that they know that it
is safe for up to 30 minutes, but that you haven’t tested it for longer exposures.

If the light is working and you have a meter, you can also check that the intensity is consistent
over the entire surface of the patient.

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2.13 Respiration Rate Meter or Apnea Monitor

2.13.1 Clinical Use and Principles of Operation

Apnea is defined as the cessation of respiratory air flow. The air may have ceased to flow
because the patient has stopped trying to breathe (central or diaphragmatic apnea) or because
the airway is blocked (obstructive apnea). The two types of apnea are clinically treated quite
differently. Obstructive apnea is typically caused by chocking on food or another object.
Episodes of central apnea are somewhat common in children and often disappear as the child
develops. However, in severe cases, neonates and babies can be kept on apnea monitors for up
to one year. When Sudden Infant Death Syndrome (SIDS) is feared, the physician may prescribe
continuous apnea monitoring.

An apnea monitor is a device used to monitor a patient’s respiration rhythm and often cardiac
activity and oxygen saturation. Most monitors will attempt to distinguish between central and
obstructive apnea, sounding an alarm if either is prolonged. Most monitors run on both batteries
and line power.

Transthoracic Electrical Impedance

The most popular type of apnea monitoring is based on transthoracic electrical impedance. To
use this device, electrodes are placed in the 5th intercostal space on each side of the neonate. A
signal of 55kHz at 2 to 3 mV is injected into the electrodes and the impedance of the chest is
measured. As the chest expands during inspiration, the impedance increases. During expiration,
the impedance decreases. Simultaneously, the impedance electrodes are used to monitor the

It is possible for the monitor to read a false positive (presence of breathing when there is none)
because it can be fooled by muscle movement. False negatives can occur if the chest motion is
slight or in the presence of excessive electrical noise. Despite the popularity of this monitor, it is
not effective at distinguishing between obstructive and central apnea.

Pneumatic Abdominal Sensor

Unlike the transthoracic apnea monitor, the abdominal monitor measures the motion of the
abdomen. However, the impedance of the abdomen does not tend to change, as the cavity is
not filled with air. Therefore, the abdominal sensor operates by detecting the increased
circumference of the abdomen, typically with a linear variable displacement transducer (LVDT) or
other displacement transducer.

This stand-alone apnea monitor would
be unusual to find in the developing
world. Most apnea monitors are
respiration rate meters incorporated
into a vital signs monitor.

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Thermistors and Pressure Sensors

Neither the thoracic nor the abdominal apnea monitor can distinguish between central and
obstructive apnea. Currently, only the thermistor and proximal airway pressure sensing apnea
monitors can make this distinction. Neither is likely to be found in the developing world. A
thermistor monitor measures the temperature of the air entering or exciting the nostrils. A
proximal airway pressure sensor measures the change in pressure at the mouth and nose.

2.13.2 Common Problems

The most frequent source of error is caused by false alarms. The worst case is when an apnea
monitor fails to alarm during apnea because it senses artifact and interprets it as respiration
(false negative). Artifacts include vibration from equipment, interference from the ECG, and
patient movement. Electrical impedance monitors are the most prone to this type of error.

A false positive (when the alarm sounds unnecessarily) is often caused by infant movement that
loosens an electrode or sensor. Also, a false positive alarm may sound when the child is
breathing normally but too shallowly for the monitor to detect.

For any false alarms first consider user error. The alarm limits may be set inappropriately. They
can be confusing to program, and may need to be changed as the patient matures. Never
change a limit without consulting with the physician.

The next most likely cause of false alarms is the electrodes. The electrodes may not be placed
correctly (across the chest). Or, the sensor is in a belt, the belt may be too loose. Ask a nurse
to help with tightening the belt, as an excessively tight belt can lead to complications.

If the electrodes are placed correctly, they may be dirty or old. Try rinsing them in isopropyl
alcohol, then water. Electrode belts can be gently cleaned with soap and water. Be careful to
rinse off all soap residue and hang to dry before applying to the patient’s skin. Also, check to see
if the skin is dirty. The child may have lotion or powder on the skin under the electrodes. You
can clean the child’s skin with soap and water. In some cases, electrode paste can be used, and
may improve the measurements.

2.13.3 Suggested Minimal Testing

Apnea monitors are easily tested on yourself. Hold your breath to trigger an alarm. If the alarm
doesn’t sound when you are breathing normally and does sound when you hold your breath, the
apnea monitor is ready to release to the floor. If the machine is a respiration rate meter, check
to see that the rate matches what you measure when you count breaths with a watch. If the
apnea monitor includes ECG, be sure to check your heart rate against the machines rate. The
rates should be very close (within 5 beats per minute).

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2.14 Electrosurgery machines

2.14.1 Clinical Use and Principles of Operation

Electrosurgery is an alternative approach to cutting a patient. Typically, it is used as an
alternative to a scalpel. Electrosurgery can cut like a scalpel, but can also coagulate the blood in
small vessels so the surgical field is dry, meaning bloodless. Electrosurgery allows the surgeons
to work faster as they do not have to hand tie off every vessel they cut. The patient recovers
better as there is less blood loss and there is more rapid healing.

Electrosurgery is accomplished by converting high frequency electrical current into heat, caused
by the tissue resistance to the passage of electrical current. As current must pass through the
body, at least two electrical connections must be made between the patient and the machine.
The power needed is up to 400 watts. If the waveform is damped it will coagulate blood and
stop bleeding (coag setting). If the waveform is undamped the tissue is ablated leaving a void or
cut or incision (cut setting). In all electrosurgery procedures there is the smell of burning flesh
and smoke.

There are four common techniques used in electrosurgery: electrodessication, electrofulguration,
electrosection and electrocoagulation. For electrodessication, a highly or moderately damped
waveform is supplied to the contact point, active electrode, a ball, needle or blade which is
placed on the tissue before energizing and produces coagulation around the site. For
electrofulguration, the same waveform is used but the active electrode is held 1 to 2 mm above
the tissue and when energized sparks spray the area drying it out and leaving some burning of
cell edges. For electrosection, an undamped modulated or slightly damped waveform is applied
to the active electrode, which is placed on the tissue surface creating an incision. For
electrocoagulation, a damped sine wave is delivered to the patient to stop bleeding without doing
any additional cutting.

All electrosurgery techniques require two connections to the patient, usually referred to as the
active electrode (or pen, or bovie pen) and the reference electrode (or dispersive or ground
electrode). For monopolar electrosurgery, the reference electrode is placed under the patient
and the active electrode is held in the surgeon’s hand.

For bipolar electrosurgery, the reference and active electrodes are both held by the surgeon in
one combined pen. Bipolar is most commonly used with small vessels and for precise tissue
destruction. The bi-polar function may not be on all electrosurgical generators. If it is contained
in the same unit as the monopolar, it will have separate connections and possibly separate
controls from the mono-polar functions.

Electrosurgery machines come in
many sizes and shapes. The front
panel of this device is typical of
many more modern machines.

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Activation of the electrosurgery is done by the surgeon using either a hand switch on the bovie
pen or by stepping on a foot switch. Both have two contacts one labeled CUT for electrosection
and the other COAG for electrodessication or electrofulguration.

The generating unit itself is often called a Bovie. It is generally a solid state device that can
produce 300 to 3000 kilo Hertz. Most machines produce 25-200 Watts. Conceptually, the Bovie
breaks up the 60 or 50 Hz from the wall into many shorter pulses, then uses a transformer to
generate the high voltage required (see figure).

The dispersive electrode can be a metal plate covered with a conductive gel or saline soaked
cloths. However, many are now using single use dispersive electrodes. Single use devices are
often pre-gelled, conductive adhesive pads that include multiple connections to the machine.
The multiple connections are used to allow the device to constantly check for a good contact
between the patient and the dispersive electrode. Poor contact with the dispersive electrode is
the most common cause of unintentional patient burns.

Sparks are a common occurrence when electrosurgery is in use. When oxygen is being
administered to the patient, it may leak, creating an atmosphere where fires can quickly ignite.
The drapes covering the patients should be flame retardant but will burn under the right
conditions. Special care is required when doing neck or mouth surgery to avoid a flash fire.

2.14.2 Common Problems

A number of problems can occur during electrosurgery. Although the majority of these accidents
are not instrumentation-based but caused by carelessness and extremely poor communication,
on occasion the equipment can be faulty.

The most common avoidable problems involve the dispersive electrode. The first problem is poor
contact of the dispersive electrode. The dispersive electrode should always be placed on an area
of the body that has good blood flow and not subject to high weight concentration. The side of
the thigh is a very common location, under the buttocks is not a good location as it generally is a
high weight bearing point.

The second problem is no contact with the dispersive electrode. In older machines, the lack of
contact may not be detected by the generator itself. The effect can be patient burns where the
current finds an alternative path to ground. In newer machines, the generator has two
connections to the dispersive electrode. When connected to the patient, a small current is
passed between the two halves of the dispersive electrodes. When not properly connected to the

Most electrosurgery machines use a two stage process to change the wall power to
high voltage (HV), then to high frequency and high voltage (HV and HF). Many
convert to high frequency, then to high voltage. The Bovie pen (or ESU pen) is
held on the patient by the physician. In modern ESU machines, the dispersive
electrode must touch the patient to prevent an alarm.

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patient, the current cannot pass and an alarm will sound. Make sure that both halves of the
dispersive electrode are in contact with the patient or testing surface.

If the tip is dirty, there can be little, or no, current passing through the patient. The bovie pens
are not intended to be reused. However, they are often reused in the developing world. In
addition to problems with dirty tips, the wires become broken with reuse. They are simple wires
which can be re-soldered for repairs. If the wire break is in the pen, the pen can be taken apart,
the wires reconnected and the pen glued together.

If the physician wishes a different tip for a monopolar electrosurgery unit, it is sufficient to
connect any metal tip to the existing tip. Insure that the connection is electrically and
mechanically sound to the existing tip and pen.

The reuse of disposable pens leads to frequent broken wires. There is nothing special about
these wires. They can be rewired using standard techniques.

2.14.3 Suggested Minimal Testing

An electrosurgery unit can be checked and calibrated easily and efficiently through the use of an
electrosurgery tester. However, such a tester is often not available in the developing world.

You can not test the device by performing the operation on a resistor in most cases. Although
400 ohms would work, only a resistor with a very large power rating will survive the procedure.
Such large power resistors are generally not available in the developing world. In most cases, a
bar of soap or a fresh piece of citrus fruit (like an orange) can be used to do your initial testing.
Be sure that both sides of the dispersive electrode are touching to prevent an alarm.

In many cases, you will want a final test on meat. A reasonable final test is to cut a raw piece of
chicken, pork or beef. Be sure that the indifferent electrode is touching the meat before testing.
Both sides of a split dispersive electrode must touch the meat to avoid an alarm! It is best to
conduct the final test with the physician present. In this way, you can not only assure that the
device is minimally operating, but you can also be sure that it is operating in a manner that
satisfies the physician.

For more modern units, insure that the dispersive electrode alarm is working by disconnecting
half of the electrode from the meat, or pulling the dispersive electrode out of the machine.

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2.15 Suction Machines

2.15.1 Clinical Use and Principles of Operation

A suction pump can have hundreds of uses in the medical setting, all of which relate to removing
fluids and substances from the body. Suction pumps can be used for removing ingested toxins
(a stomach pump), unwanted fats (liposuction), mucosal secretions from the esophagus, blood
from the surgical field, and many other applications.

Suction applies negative pressure, which is any pressure less than atmospheric pressure (760
mmHg, 100kPa or 14.7 psi), to allow for the movement of fluids or substances. The suction
developed by the machine will be measured as a pressure. The common units of pressure are
millimeters of mercury (mm Hg) or pascals (Pa or kPa), inches or centimeters of water (inH2O),
or pounds per square inch (psi). To convert between pressures:

1 mmHg = 0.133 kPa = 1.36 cmH2O = 0.535 inH2O = 0.193 psi

The essential elements of a suction machine are the source of suction, the tubing, the collection
canister or bottle and if present, a manometer to measure the amount of suction. For the source
of suction, there are two types of suction machines most commonly found in the developing
world: electric pumps and foot-operated suction. The electrical suction is often called a “Gomco”
after one of the more popular brands. A thermally driven suction machine is occasionally seen as

No matter what the source of suction, the vacuum is pulled through a collection bottle. A water
trap may also be present, to prevent liquid from entering the vacuum source.

The most common suction machine will use electric motor to drive a single piston. As the piston
descends, it produces a vacuum through one of two one-way valves, often reed valves, typically
at the top of the piston. As the piston moves up air is forced out of the piston chamber through
the second valve.

This is a typical simple
suction machine. The
collection jar and seal
are missing. The float
valve and trap are
shown near the bottom
left (arrow).

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With a foot-operated suction, manual labor acts to drive the piston. The valve assembly is
identical. On the return stroke of the piston, as the foot is removed from the top of the pedal,
the piston will return to its original setting, via a spring, and suction is created with a series of
valves directing the flow of fluid and air flow.

In all cases, the suction level can either be totally adjustable or has low, medium and high
settings. The high settings are used for airway and gastric suctioning. The medium setting for
chest tubes and the low setting for wound suction.

The thermally driven units are sometimes called thermionic units. They operate on the principle
of air movement caused be heating and cooling. A coil in the unit heats up for approximately 45
seconds at which point the power to the coil is shut off and it cools rapidly. This cooling creates
a suction airflow and pulls fluid from the wound site.

2.15.2 Common Problems

The most common problems with suction machines are clogs, leaks and the motor.

Material from the collection bottle can migrate into the suction machine. This can be very
damaging to the machine, possibly permanently damaging the suction machine. To avoid this,
machines should be operated with some sort of filter or valve before the suction machine.
However, the filter and valve present problems because they can get clogged.

A shutoff float is sometimes provided to shutoff the suction before the collection bottle overflows
into the motor. The float volume must be on the pump side, not the patient side, of the
collection bottle. If a multicanister setup is used, only the last canister before the connection to
the suction source must have a float valve. The other canisters, closer to the patient will have
the floats removed. Sometimes, someone on the operating room will remove the shutoff float

Each suction machine is a bit
different, but the basic
components are nearly the
same. The exhaust is rarely
filtered in the developing
world, and the inlet filter’s
absence is often the cause of

If the device is operated without a filter,
the suction pump can be damaged.
Remove the head, as shown, to see if it
can be cleaned and repaired.


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from the last suction canister as well. If fluid does get into the suction machine, it will need to
be completely disassembled, cleaned and reassembled.

On some Gomco machines, bacterial filters are used in input or output of the machine. These
should be replaced after each patient, but in the developing world they are not. If the unit is
used without the filter, it will eventually need to be rebuilt. However, this may be a short term
solution. For a more long term solution, the filter may be replaced by any filter 3 micron size.
The hose barb-hose barb PTFE filters can often be found for under US$1 each. Hose barb
adapters (to convert the NIPT connection on the Gomco to a hose barb) are available to allow
the use of hose-barb/hose-barb filters.

Air leaks are probably the most common problem. A leak will cause the flow and pressure to
cease or be reduced. The first place to look for air leaks is in the collection bottle lid, particularly
with disposable canisters. The tubing can be replaced with any compatible tubing. If the leak is
near one end, the tubing can be cut and used as shortened tubing. To find the leak, rub the top
with soapy water while blowing through the cleaned-off tube (close off the distal end). Bubble
will form where there is a leak.

The collection bottle often breaks. The collection bottle is not special. Any glass or rigid plastic
bottle can be used as a substitute. The alternative must be air tight and have two connections of
the proper size to fit the collection set. The seal between the collection bottle and its cap can be
improved with a small amount of petroleum jelly, or replaced with rubber, or even leather, cut to
the proper size and shape.

Noise is a frequent complaint from electrical pumps. Try placing a pad under the machine to
reduce the vibration noise between the suction machine and the floor.

The pistons are generally driven with an induction motor. An induction motor is used as it is the
easiest, most cost effective motor to drive a medical device. There are no gears or chains.
Check the section on the centrifuge (later in this book) for more information on electrical motor
repair and testing.

2.15.3 Suggested Minimal Testing

The pump is connected to the piston through a bearing. To clean bearings without dismounting,
hot light oil at 180-200° F may be flushed through the housing while the shaft is slowly rotated.
Light transformer oils, spindle oils or automotive flushing oils are suitable for cleaning bearings,
but oils heavier than light motor oils, such as SAE 10, are not as effective. To lubricate the
pumps, first, thoroughly clean the grease fitting and outside of the bearing housing. Next
remove the drain plug and inject clean, new grease to forcing out the old grease. Start and run
the pump for a short time to eject any excess grease, which should later be wiped off surfaces,
and then replace the drain plug.

Most suction apparatuses cannot be calibrated, per se. However, the accuracy of the pressure
gauge can be checked as can the ability of the suction machine to pull a vacuum in the desired
range. To check the pressure, place water in a bucket. Turn on the vacuum and draw the water
as high as it will go, typically between three and five feet. Record the height in inches or
millimeters and calculate the actual pressure in mmHg as the (Height of Water (in inches) * 25.4
(mm/in))/13.6 (mmH20/mmHg). This can be compared to the pressure shown on the gage and
compared with the physicians intended use.

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As collection sets (tubes and suction tips) are frequently reused in the developing world, they
often become clogged and leaky. Before releasing a suction machine for use, if you suspect that
a collection set will be reused, try to perform your equipment checks using the intended
collection set.

The filters often become clogged, and are not often replaced because the correct filter requires a
threaded NIPT male end for some models. However, with an NIPT to hose-barb adapter, you
can use the very cheapest filters, which have hose barb on both ends.

To check the pressure, place water in a
bucket. Turn on the vacuum and draw
the water as high as it will go.

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2.16 Theatre Lamps and Other Lights

2.16.1 Clinical Use and Principles of Operation

All lights in all parts of the hospital operate on the same principals. However, the operating
theatre has the most variety of lights.

Operating rooms in the developing world have several separate lighting sources. The first is the
general room lighting found in the ceiling. This is used during the set up of the rooms, cleaning
and as background lighting for the staff who are not working in the sterile field.

The second source of light is the overhead operating room lights. These can be large reflectors
with one or more bulbs in them, mounted on a counter balanced arm that can be positioned over
the site of the operation. These units have a sterile positioning handle that is often adjusted over
the period of the operation. Many of the problems associated with these lights are mechanical in
that they do not stay in the position selected and the counter weights have to be adjusted. A
secondary problem is that one or more of the lights will burn out giving dark spots in the surgical
field. These lights have control boxes on or in the wall where the intensity control is found along
with the on off controls. This control box usually contains an SCR control board, or transformer
that powers the lights at some voltage under 115 volts.

In some rooms there may be a portable operating room light. These are large reflector lights
that roll from room to room. They simply plug in to a 115 pr 220 volt outlet and are positioned
as needed by the surgeons.

The third source of light is the “personal head light” that a surgeon will wear. This is a lens that
focuses light transmitted to it by a fiber optic cable from a remote light source. This light source
may have a multitude of bulbs in it that can be switched into use via a knob on the top of the

A typical OR in Africa showing two
principal lighting sources: The
overhead light and the window.
Against the far wall is an X-ray
viewing light source.

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unit, or by moving the fiber optic cable from one side to another and turning on that light. These
units are often the personal property of the surgeon.

Some lights will utilize cooler light systems by filtering out infrared portions of the light. The
different mirrors and reflective surfaces on the inside of the light will allow for maximum light
transfer to the operating area. Also, the lights may have a plastic coating and thermal guard on
the outside housing to ensure a cooler surface when adjusting the light.

For overhead lights, the distance from the lower edge of the light to the operating table should
be approximately one meter. Initial positioning is accomplished by using the rail on the lamp
housing to move it into place. The surgeon has the option of adjusting the light using the center
hand grip, which is provided with a replaceable, sterilized sleeve.

Most operating lamps work directly from the outlet power through a switch. However, some
lights may provide dimming circuits. Older dimmers found in the developing world often work
with a rectifier or a variable transformer (variac) gradually varying the voltage applied to the
lamp and therefore the intensity of the light delivered. Some dimmers operate using solid-state
electronics (SCR’s). These are rarely seen in the developing world and are typically impossible to

Some operating room lights use fluorescent bulbs. Fluorescent bulbs generally operate through a
transformer and use a starting circuit (sometimes called a ballast). In some cases, the bulb is
heated before the starter is engaged. The heat causes both a change in the internal tube
pressure and an increased electronic flow between the electrodes. A high voltage (25,000 V)
spike from the starter establishes an arc in the atmosphere between the electrodes. After the
initial spike, the bulb will operate at a low current and temperature,

A surgeon’s headlamp

Older theatre lamps used
simple circuits, such as those
shown here to vary the
intensity of the light. Similar
circuits are used for 220 volts.

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2.16.2 Common Problems

Take special precautions when working with medical lights. The highest intensity lights can
cause blindness if you look directly into the light. For the same reason, the light should not be
used if the cover glass or filter system is damage or destroyed. In placing the light to begin
work, your eyes should be greater than two feet or approximately sixty centimeters away from
the source.

The lamps can be xenon, quartz-halogen, mercury-vapor or metal halide. These bulb types are
not interchangeable because of the voltage supplying the bulb, the connector for the bulb and
the heat generated by the bulb. The bulbs have a life expectancy of about 250 hours and need
to be monitored for replacement. When replacing bulbs care must be taken to avoid touching
the reflector part of the bulb as that can affect the brightness at the surgical site. Also, avoid
touching the bulb itself. Your fingerprints can cause excessive heating of the glass, dramatically
shortening the life of the bulb. If the glass of the bulb has been touched, clean the fingerprints
off with alcohol.

It can be very difficult to find replacement light bulbs in the developing world and impossible to
ship replacements into the county. While it may be possible to wire a replacement socket for a
more readily available bulb, the engineer must be sure to consider size, voltage, temperature and
materials. It maybe more prudent to start with a readily available bulb and socket and design a
completely new fixture.

2.16.3 Suggested Minimal Testing

There is no calibration needed for operating room lights. If the light turns on, changes intensity
(if equipped) and stays in place after adjustment, it is ready to use.

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2.17 Anesthesia Machines

2.17.1 Clinical Use and Principles of Operation

Anesthesia is defined as the loss of feeling or sensation. During most surgical procedures, some
form of anesthesia is used. There are at least four different types of anesthesia that are
encountered in the developing world.

General anesthesia is a state of unconsciousness, with an absence of pain sensation over the
entire body, produced by anesthetic agents, often with muscle relaxants. General anesthesia is
administered by inhalation, intravenously, intramuscularly, rectally or via the stomach. Local
anesthesia is where a specific area is “numbed” such as in a dentist’s office. The patient is
awake and may feel some limited pain. Saddle block anesthesia is where the patient is conscious
and the area of the body that would touch a saddle is affected. This is accomplished by injecting
an anesthetic agent low in the dural sac and is common for childbirth. Spinal anesthesia is where
an anesthetic agent is injected beneath the membrane of the spinal cord. There is no sensation
below that point until the agent wears off.

General Anesthesia unit, inhalation

The anesthesia machine, sometimes called a Boyle machine, works by mixing selected
concentrations of gases and drugs that the patient inhales. Consciousness is regained relatively
quickly after the procedure terminates.

Anesthesia machines are generally large, on wheels, and contain one or more vaporizers, flow
tubes, attachments for compressed gas cylinders, a ventilator, ports for obtaining compressed
gases from wall connections, a carbon dioxide absorber other gas traps (or scrubbers) and
various monitoring devices either built in or attached to the unit. These machines can cost over
$60,000.00 to purchase and require regular maintenance. Some of the maintenance requires
specialized testing equipment that may not be available in a developing world hospital, including
devices for the measurement of the concentration of gases, flow rates and pressures. Additional
training is typical in western hospitals before attempting any calibration or repair of the gas
delivery system. However, in the developing world, repair, calibration and maintenance are often
done by whomever is available.

This anesthesia machine in Togo shows all the
basic components. There is little difference
between this unit and the most modern units
seen in the US.

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The flow of gases can be traced from the source to the patient. Typically, compressed gases
such as air, oxygen, and nitrous oxide are supplied from gas cylinders or from wall outlets. By
passing through a pressure regulator, gas in a cylinder is reduced from thousands of psi to a
typical delivery pressure between 20 and 50 psi (regulators and cylinders are covered elsewhere
is this book). From the regulator, gas in the line will often pass through an O2 failure detector.
Next the gases enter the mixing board which contains rotameters for measuring gas flow. From
there, the gases move through vaporizers where a volatile agent such as halothane will be added
to the mixture. Delivery of the final gaseous product to the patient is achieved with a series of
tubes, valves and a mask that is referred to as the anesthesia circuit.


Vaporizers are used to convert a liquid anesthetic agent into a vapor. Because they are designed
to function under continuous pressure and flow environment, they are sometimes called plenum
vaporizers. As air enters the vaporizer, it is directed into either the vaporizing chambers or a
bypass chamber. The anesthesiologist will control the bypass valve to allow more or less of the
incoming gases to flow through the vaporizing chamber usually via a large knob on fob of the
vaporizer. The liquid anesthetic agent resides in the lower part of the unit. As the gas moves
across the top of the liquid, the anesthetic agent vaporizes and is carried by the gas towards the
outlet, where it is blended with the gas that had bypassed the chamber.

Since vapor pressure is affected by temperature, a warm environment would normally encourage
more of the anesthetic agent to vaporize and a cold environment less. Furthermore, the process
of vaporization itself removes heat from the vaporizer and the anesthetic agent. In order to
compensate for temperature effects, a bi-metallic valve is added to the by-pass system. The bi-
metallic valve physically distorts to adjust for temperature changes. It is possible to compensate
for temperature variations by warming the fluid to a fixed temperature, but this approach is less

The vaporizer should be maintained level as operation out of level can affect the calibration.
Also, when working with a vaporizer, care should be exercised not to tip vaporizer as this can
cause a hazardous spill. Should a spill occur, water can be used to clean up the anesthetic agent
and doors should be opened to clear the vapors. Vaporizers should generally be calibrated every
six months; however, in the developing world this is rarely undertaken. Vaporizers are very
reliable, but if the vaporizer does break, it must be sent back to the factory or other qualified
repair service. There is little a field engineer can do to repair a broken vaporizer.

Two vaporizers (for two different
anesthetics) sit to the right of the
mixing board and a large

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A mixing board on the anesthesia machine will allow the anesthetist to mix oxygen, anesthetic
gases and the patients expired air to the desired ratios for delivery to the patient. The ratio of
the fresh gasses is continuously measured by their flow rates. A typical mixing board will contain
several rotameters for measuring gas flow. Rotameters are made from either glass or plastic
tubes containing a metal or ceramic ball that serves as a float. The walls of the rotameters are
slightly “V” shaped so that as the ball rises, more of the gas is diverted around the ball lowering
the force upwards on the ball. When the force of gravity is just balanced by the force upwards of
the gas, the ball will stop moving. As the flow rate increases, the ball moves up and as the flow
rate decreases, the ball moves down. However, as the ball moves up, the force of the gas on the
ball drops because more of the gas is diverted around the ball. Thus, the height of the ball can
be used to determine the flow rate of the gas in the rotameter.

Rotameters are calibrated in cubic centimeters (cc) or milliliters (ml) of gas per minute. The
amount of each gas entering the mixing board is controlled by needle valves at the base of each

Gas Handling

Anesthesia gases are supplied from tanks that are mounted on the anesthesia cart or from a
central source in the hospital. In the latter case, there will be wall mounts in the room with
specialized fittings so that hoses are not misconnected. As a safety feature, gas tanks may have
what is called a pin index connection that allows only specific yokes to be connected to the tank.
The tank is attached to a yoke that has pins sticking out that match the holes in the neck of the
tank. During every inspection of the anesthesia unit, the pins on each yoke should be verified
that they are present and in the correct positions for the designated tank. However, in the
developing world as donations may come from many sources, the pin indexes may be missing,
tampered with or ignored. A backup to the pin index is the color-coding of the paint on the
tanks. In the US, oxygen tanks are painted green (blue in some other countries) while nitrous
oxide tanks are blue and air tanks are yellow. Similarly, the connection hoses for the centralized
gas system should be color coded to match the gas tank. Europe has a different color-coding
scheme, and in the developing world, there may be no system to the color of the tanks or hoses.

Faced with unmarked tanks, connectors and hoses, the engineer should first thoroughly discuss
the system, and label it, before attempting service.

A small mixing board with only two
rotameters. In some anesthesia machines
there can be four or five rotameters.

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The modern anesthesia machine will contain a purge button which serves as a bypass button,
bypassing the mixing board, vaporizers and rotameters. This button allows for 100% oxygen to
flow to the patient connection. It is used before a surgical case begins to clear out any residual
gases from the patient connection. Additionally, it is used to provide a quick burst of oxygen to
the waking patient (and reduce the level of anesthesia to the patient) as the case terminates.

Since the expired gases of the patient contain anesthetic agents, they must not be allowed to
enter the operating room. In addition to potentially placing the operating staff under the
anesthetics effects, certain agents are flammable, and chronic exposure can cause high fevers
and severe liver damage. To remove this danger, anesthesia machines will contain a scavenger
(or scrubber or trap) before venting the expired gas into the room. In the developing world, the
activated carbon may no be changed –or even available – forcing the staff to vent the expired
gas outside.

In the expired air is to be rebreathed - that is returned to the patient - then a CO2 absorber is
used. A CO2 absorber contains a soda-lime filter that strips the expired gases of CO2.

Self-inflating bags or bellows are purely mechanical devices that allow the anesthetist to measure
the patient’s ventilation. By its movement in a calibrated chamber, a bellows indicates the volume
of air that the patient is breathing. The bellows will rise when the patient exhales and will fall
when the patient inhales.

The bellows may be connected to a ventilator that controls the patient’s ventilation. The
ventilator forces air into the patient’s lungs at a prescribed rate and volume. Ventilators are
covered elsewhere in this text. When intermittent ventilation is required, the doctor can use a
bag (emergency bag), or reservoir bag. The bag allows the doctor to manually push air into the
patient’s lungs. This bag is also used to give the anesthetist a sense of the patient’s lung
compliance and resistance, which can be used to indicate that more or less anesthetic agents are
needed or that the physiology of the lungs is changing.

The Circuit

The circuit contains tubing and valves required for the operation of the anesthesia machine.
Both the bellows and self-inflating bag are filled through a non-return valve that ensures that the
proper gases are always delivered to the patient. The circuit will also contain a non-rebreathing
expiratory valve at the patient end that diverts inspired and expired gases through two different
pathways. Often, these non-rebreathing valves are part of the circuit. The circuit includes the
connection to the patient, the mask, endotracheal tube and other components.

While considered a disposable item, in the developing world, the circuit may not be replaced after
every patient. Even in the developed world, there may be connections to and from the absorber

This scavenging system shows the CO2
absorbing material (white material in glass
container behind cage in lower left). Two
valves are shown under the glass domes in
the middle right.

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that, while part of the circuit, are not replaced with each use. If the circuit is to be reused, after
patient use, it is best to hang the tubing vertically to dry in a storage area.


The anesthesia machine may also have a monitor for the patient’s ECG, invasive or non-invasive
blood pressure, and pulse oximetry. More details about these monitors are available in their
respective chapters.

Drawover Anesthesia

A drawover anesthesia system provides anesthesia without necessitating a supply of compressed
gases. Drawover anesthesia systems have the added advantages of being (1) inexpensive to
purchase, (2) easy to maintain, and (3) compact and portable. In using a drawover system,
atmospheric air serves as the primary carrier gas and is drawn through the vaporizer by the
patient’s inspiratory effort. Whether a patient is being artificially ventilated or breathing
spontaneously, the patient will draw air through the vaporizer. Therefore the vaporizer must have
a low resistance to the intermittent gas flow. Once in the vaporizer, the atmospheric air mixes
with the anesthetic agent which is typically ether or halothane. The patient now inhales this air
via a non-rebreathing valve. Low-flow oxygen, such as from an oxygen concentrator, may be
added to the drawover system by using a T-connector.

General Anesthesia, Injectables

Injectable anesthesias are cheaper and therefore more common in the developing world than in
the US. They are more dangerous as an overdose cannot be as easily reversed. These agents
are combined with muscle relaxants and should be used only for short-term procedures.
Ketamine is a very common general anesthetic agent, and lidocaine is a popular local anesthetic.
No additional equipment is required to use these agents.

2.17.2 Common Problems

As with other pieces of medical equipment, power supply and user error problems account for
most of the problems in anesthesia machines. Injectable anesthetics are not generally referred
to the technician when there is a problem. Drawover machines have fewer problems than other
anesthesia machines, but all machines suffer from with leaks and sticky valves.


Tubes tend to deteriorate in hot and humid environments. Also, reusing disposable materials
tends to favor deterioration. An expiration-side leak occurring before the scavenger is most
critical to check, but also the easiest because anesthetic gases have a distinctive smell which is
easily detected. If a leak occurs in the OR, doors to the room should be opened to allow air to
flow through the room (consult with the staff before doing so). Moreover, a second danger with
gas leaks is that some anesthetic gases are flammable. Halothane and ether are two explosive
anesthetic gases.

The tubing most often develops leaks in between the corrugations. You can check for leaks by
placing the tubing in a bucket of water, blocking one end, blowing in the other, and looking for

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bubbles to escape. Repair tubing leaks with epoxy or a silicon sealant. However, this is a
temporary repair. It is better to replace the tubing. In some cases, the tubing can be shortened
to remove the leaking section. Consult with the anesthetist before shortening a section of the

Other problems

The monitoring devices are covered in other sections of this book.

The needle valves controlling the flow into the rotameters can be sticky or blocked. Also, the
floats in a rotameter can be stuck. Rotameters and needle valves can be dismounted and flushed
alcohol. Make sure they are completely dry before using again. When taking apart multiple
rotameters, floats and needle valves, be sure to put them back together in a set. The float from
one gas may not work in the glass tube from another. One simple solution is to disassemble only
one rotameter at a time.

If there are valves which appear to be sticky in the circuit, the circuit needs to be replaced.
Other sticky valves may be cleaned with water and dried thoroughly before reuse.

If the problem is in the ventilator, CO2 absorber or vaporizer, and the problem is not a leak, the
problem is typically very difficult to repair in the field. It is generally necessary to replace the
entire subunit with one from another anesthesia machine.

2.17.3 Suggested Minimal Testing

If the device has been removed from the operating room due a problem that you have now fixed,
you should test it before returning it to use. However, most often you will not have the
equipment required to test the function of a vaporizer, CO2 absorber or ventilator. As the
surgical schedules may be severely affected or even halted until the anesthesia machine is
working, it may not be in the hospitals patient population’s best interests to wait until you have
the proper testing equipment to release the anesthesia machine for use. If a repair resulted in a
replacement of the vaporizer, absorber or ventilator, you will need to consult with the anesthetist
on what testing will be required before use.

If the repair required the fixing of a leak, it is sufficient to retest the tubing to insure that the leak
is repaired.

If the repair involved the rotameters, they should be checked before use, even if the problem
was just a sticky valve or float. A simple way to check flow rates is to flow the gas into a
calibrated balloon for 60 seconds. The volume can be approximated by connecting a balloon to
the patient tubing. You must calibrate the balloon to volume before you begin. The easiest way
to do this is to fill the balloon with a known volume of water. Make two marks on the balloon a
fixed distance apart, indicating the volume next to the mark. Repeat this procedure for several
volumes. Now, when the balloon expands to the indicated volume, the marks should be your set
distance apart.

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2.18 Bottled Gases

2.18.1 Clinical Use and Principles of Operation

The clinical use of bottled (pressurized) gases can range from anesthesia machines to
spectroscopy. The most common bottled gas in the developing world is oxygen. However,
anesthesia gases, dry air and carbon dioxide are all seen occasionally. Bottles of high pressure
gas can be explosive and flammable. Therefore, handling the bottles must be done with care.

A bottled gas has a few components: the cylinder, the main cylinder valve, the cylinder pressure
gauge (the gauge closest to the cylinder), a pressure regulator for reducing the pressure, the gas
outlet pressure gauge and typically a gas outlet flow control valve. The pressure regulator
usually has an adjustment control. This control may have a large knob, or it may require a
crescent wrench to adjust the outlet pressure. The entire assembly is often referred to as the

When not in use, gas cylinders should have a cap that screws onto the top of the cylinder to
protect the gas cylinder valve from being cracked off, should the cylinder be dropped. This cap
should always be used when the gas cylinder is being transported.

In the United States, oxygen cylinders are green, with a specific hose fitting, and feature a main
cylinder valve with a reverse thread (counterclockwise to tighten). However, most of these
standards are different around the world, and are not followed in the developing world. Even in
one hospital, oxygen tanks may be of different colors and have different types of regulators.
Oxygen bottles are sometimes seen in a small size which uses a different pressure regulator.
However, these are rare in the developing world.

2.18.2 Common Problems

The most common problem in the developing world is a missing or broken regulator, followed by
a hosing set which does not match the standards of the regulator. Mismatched hosing sets need
to be adapted with whatever parts and tools are available. This type of patching can only be
accomplished after the pressure regulator (on the low pressure side). Clearly label the outlet of
the hose after adaptation, in the local language, if possible.

If the regulator is broken, it may be impossible to repair. The pressure gauges for both high and
low pressure readings are removable, by simply unscrewing them. Replacements can often be

(1) (2) (4)


The components of a bottled gas. (1) The main
cylinder valve, (2) The cylinder pressure gauge, (3)
the pressure regulator and pressure regulator
valve, (4) The gas outlet pressure gauge and (5)
the gas outlet flow control valve.

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found in the developing world. Use a Teflon pipe thread tape when replacing the gages, if at all
possible, as it will seal much better than the metal-to-metal seal required without the tape. The
outlet flow control valve is not typically very important, and can be replaced with any valve which
can be made to fit into the system. If the pressure regulator is broken, there is little that can be
done. This piece cannot be repaired.

If you must move a cylinder in order to repair it, or the regulator, place the cap on the cylinder
before beginning. Moving a gas cylinder is dangerous and difficult. Always ask for help. Before
moving the cylinder, check the cap again to insure that it is secure. The best way to move a
cylinder is to slowly roll it on its bottom, with the cylinder tilted a few degrees. Highly
experienced staff may move cylinders at high speed this way with seeming ease. However, if
you are not very experienced at moving cylinders, you can easily loose control of the cylinder.
Have a friend stabilize the cylinder while you tilt it and roll it. Check the cap frequently while
moving the cylinder.

If you must work on the cylinder, do not empty it entirely (by leaving the cylinder valve open).
This may allow ambient air to enter the cylinder and cause moisture to build up in the cylinder.
The moisture can ruin the cylinder and contaminate the next filling.

Pipes and tubing leaks, while not exactly a problem of the cylinder, are common. Rub some
soapy water over the pipe to check for bubbles and locate the leak. Try to cut out the leaky
section of tubing and shorten the tube, if the leak is near the beginning or end of a long run.
Otherwise, epoxy can serve as a temporary fix for a leaky pipe.

When you are placing the cylinder back on line, do not simply connect the regulator and open the
cylinder valve. This can place unnecessary stress on the pressure regulator, can introduce
contamination, and can stress the downstream system. The typical reconnection sequence is to
first “crack” the main cylinder valve. Cracking the valve means quickly opening and closing the
cylinder valve a very small amount to briefly allow the passage of a very small amount of gas.
The gas will be high pressure and velocity. So, stay clear of the gas stream. This cracking clears
debris in the valve outlet. Next connect the regulator to the system. Now crack the main
cylinder valve again. This will pressure the regulator, but not stress it excessively. Finally, open
the cylinder valve again to begin using the system.

Beyond that which has already been discussed for gas cylinder care and maintenance, further
attention must be paid to the specific gas used. Oxygen has already been discussed. Carbon
dioxide is a nonflammable gas. However, take care to ensure proper ventilation when using
carbon dioxide as any leaks may be hazardous. A concentration of CO2 as low as 10% can cause

Nitrous Oxide is sometimes used for anesthesia, though its use is rare in the developing world.
Any cylinders containing such a mixture must be stored above 10° C or the nitrous oxide will
separate out. Warm and shake any such mixture before use. When mixed with oxygen, nitrous
oxide can be explosive.

Butane, Propane and Acetylene are highly flammable gases which are not used in medicine.
However, they are often seen at the hospital. Butane and propane are liquids under high
pressure and are used for cooking and heating, including clinical laboratory heating. Acetylene is
mostly used for cutting metal with a flame torch. However, it is rarely used for atomic absorption
spectroscopy, a procedure which is already rare in the developing world. Acetylene will ignite
explosively in air.

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2.18.3 Suggested Minimal Testing

Gas cylinders are intrinsically simple devices that need very little calibration. The only apparatus
that should be checked are the pressure gauges and the piping. Pressure gauges can be
checked by attaching a second gauge (that is known to be accurate) in series with the first and
assuring that both gauges give the same reading. If this is not possible, the outlet gas may be
connected directly to a mercury manometer which will allow pressure checks at relatively low
pressures, ranging from 0 – 300 mmHg typically (up to 40 kPa). Leaks may be checked by
passing dilute soapy water over piping connections and looking for bubble formations. If the
outlet gas is at the correct pressure and there are no leaks, the cylinder is ready for use.

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2.19 Batteries

2.19.1 Clinical Use and Principles of Operation

While not a medical device in itself, the battery, like the generator, is often the source of
problems in developing world hospital equipment. The battery comes in a wide variety of forms
and can be used to provide electrical energy and portability to all types of clinical devices, from
surgical lighting to high drain clinical devices (e.g., x-ray machine). The underlying purpose of
the battery remains the same, to simply convert stored chemical energy into electrical energy
which can be readily used by a given device.

There are two main classes of batteries, primary (single use) and secondary batteries
(rechargeable). Primary batteries are becoming more common as the number of hand held
medical devices grows. Primary batteries, or dry batteries, are typically alkali-manganese
(alkaline), lithium, or carbon-zinc. Each of these chemical combinations is called a battery
chemistry or a battery technology. Secondary systems include nickel-cadmium, nickel-metal
hydride and lead acid batteries. These secondary systems are used with instruments that require
greater amounts of electrical energy and particularly when recharging is a viable option.

Besides being described by their technology, batteries are described by their voltage and their
capacity. The battery voltage is determined largely by their chemistry. For example, all alkaline
batteries are 1.5 volts or can be put together to get multiples of 1.5 volts. The battery capacity
is largely determined by the physical size of the battery. Unfortunately, the battery capacity is
not rated in Joules or Coulombs, which would make most engineering or chemical sense, but in
Amp-hours (Ah). One Amp-hour is the equivalent of 3600 Coulombs of charge.

A battery cell consists of four principle parts: an anode, a cathode, an electrolyte that provides
the mechanism for charge flow between the anode and cathode (a gel in modern primary
systems), and a porous insulator which electrically isolates the cathode from the anode.

The carbon-zinc battery serves as a useful example. The case is made of zinc metal, serving as
one electrode and a carbon rod coated with manganese oxide (MnO2) serves as the other. The
electrolyte solution is ammonium chloride (NH4Cl). The following reactions take place:

Zinc electrode: Zn <−> Zn2+ + 2e-

Carbon electrode: 2MnIVO2 + 2H+ + 2e- <> 2MnIIIO(OH)

The zinc electrode is oxidized, giving off two electrons into the solution. The manganese is
reduced at the carbon electrode by the presence of the two electrons and the hydrogen ions
provided by the ammonium chloride solution. This chemical reaction stimulates the electron flow
once the circuit is complete. The electrons will continue to flow until the battery is completely

Batteries come in many shapes and sizes. These
rechargeable (secondary) cells are lead acid
(bottom right) and nickel-cadmium.

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discharged, i.e., the chemical reaction can no longer take place if either electrode is entirely
oxidized or reduced.

Secondary systems differ from primary systems in that the chemical reactions are reversible.
When you supply the appropriate electric energy to the terminals you recharge the battery. The
lead battery can serve as an example. The lead-acid battery is a liquid-system battery and
comes in two main forms, sealed and unsealed. Narrow gratings of lead or lead oxide (PbO2)
serve as the electrodes. The liquid solution is 20-30% sulfuric acid, serving as the electrolytic
charge carrier. The oxidation and reduction equations are:

Oxidation: Pb + SO42- <> Pb SO4 + 2e-

PbO2 + 4H+ + SO42- + 2e- <> Pb SO4 + 2H2O

Unlike the primary cell and its chemical reactions, both reactions in the secondary cell are
reversible, allowing the lead battery to be recharged.

2.19.2 Common Problems

The most common problem with batteries in the developing world is that the batteries in the
machine have stopped working and an exact replacement cannot be found. The problem can be
essentially divided into two parts: (1) determining that the batteries are, in fact, beyond their
useful life, and (2) devising a substitute battery from batteries which are available. Determining
whether a battery is beyond its useful life depends on the technology (or chemistry, NiCd, Pb-
Acid, etc.). So, battery life will be covered for each individual technology below. The second
most common problem in the developing world is that the charger has been lost or broken, and
you cannot find an exact match for that charger in the market. Charging is also technology
specific and will be covered below.

Substituting Batteries

Devising a substitute battery is a topic which cuts across all of the technologies. The easiest
problem is when you can find batteries of the appropriate technology, but not the appropriate
capacity or voltage. If different voltages or capacities are desired connect the batteries in series
to obtain more voltage, or in parallel to obtain more capacity (see example below). It is very
rare that such combinations cannot be directly substituted for the cells that have been removed.

Example Pack Substitution

Assume you make a pack of 12, 600 mAh, 1.2 V, NiCd cells connected 4x3 (three sets of
4 batteries in series, the three sets in parallel).

The four cells in series provide
1.2 V x 4 = 4.8 V
The three sets in parallel provide
600 mAh x 3 = 1800 mAh

Therefore, you have created one, 4.8 V, 1800 mAh battery pack.

To charge your pack, use
Trickle charge: 1800/100 = 18 mA for a few days
Max charge: for NiCd=C=1800 mA (1.8 A)

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It is also common that you can find the batteries of the correct technology and the correct
voltage and capacity (either by combination or alone), but the connection type is wrong. For
example, the batteries that you have use solder tabs, but you need button connections. In
these cases, simply solder wires to the circuit board and wires to the battery. When soldering
onto a battery with button connections, use coarse sandpaper to rough up the surface. Then
cover it with a large amount of solder – holding the soldering iron on the battery for as short a
period as possible. Finally, melt the solder on the battery while holding the wire on top. You
may still need to tape the wire on the side of the battery to avoid any physical strain on this
relatively weak combination.

A more difficult problem is when you cannot find the correct technology, but must find a
substitute battery. First you must typically match the voltage to within 0.7 volts. That is to say
that the voltage of the replacement cell must match the original cell, or must be higher than the
original cell. If the replacement cell is less than 0.7 volts higher than the original, you can
probably use the substitute without modification for voltage. If the difference is larger than 0.7
volts, than use a diode in series with the battery to drop the replacement battery to within 0.7
volts of the original.

The capacity of the replacement cell is the most difficult item to match because capacity affects
both the charge within the battery and the maximum amount of current that the battery can
provide. The maximum amount of current that the cell can provide is sometimes specified as the
cells internal impedance. Unfortunately, changing battery technology, even when identical
capacities are selected, changes the internal impedance of the cell. Therefore, if the battery was
selected by the designer purely based on its capacity (hand held devices without motors are
often in this category), than a substitute technology will probably work as the impedance is not
critical. In many situations, the medical staff will accept a shorter time between replacement
cells (or recharging), so a lower or higher capacity substitute technology can be used, as long as
the voltage criterion is met.

However, if the battery size was selected by the designer to meet a maximum current
specification (x-ray, defibrillation, and many motor driven devices are in this category), then a
change in battery technology, and therefore in internal impedance, could render the device
useless. If you know the internal impedance of the cells you are removing (it can often be found
on the manufacturer’s web site, if you have internet access), then you can simply select a cell of
lower internal impedance from a substitute technology. However, more typically, you will not
have internet access. In this case, if you can find a working model of the device, you may be
able to measure the maximum current drain and select a substitute battery capacity based on its
ability to deliver that maximum current.

If there are not working examples of the equipment, you may have to resort to trial and error.
As a starting point, for all primary and secondary cells (except lead-acid selected for current
drain) you can probably switch battery technologies if the replacement cell has twice the capacity
of the original cell. For lead-acid selected for current drain (such as x-ray and some motor
applications), you will need a far higher factor of capacity to substitute technologies. Lead-acid
batteries are available in the larger cities of the developing world. So, substitution of
technologies in this case is not recommended.

In summary, the first step is to match the voltage of the replacement cell. The second is to
select a capacity either based on the longevity of the device between replacement (or
recharging), or on the ability to deliver the needed current.

When changing technologies, if the original battery was a primary cell, it should be replaced with
a primary cell. They are cheaper to replace and will last longer before needing replacement. If
you replace them with a secondary cell, then the hospital will have to find a replacement
secondary cell at greater expense in just a few years.

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However, if the original cell was a secondary cell, replacement with a primary cell is possible. In
general, primary cells of the same capacity and voltage will have lower impedances and can be
used as direct substitutes. If the charger is internal, however, primary cells cannot be
substituted except in an emergency (a defibrillator that won’t discharge without cells, for
example), because charging primary cells can destroy the equipment and the cells.

If the original cell was a secondary cell and the replacement technology was a secondary cell,
then you must be concerned with charging your replacement cells. It is generally impossible to
find a battery which will both operate the device and will achieve the same performance charging
as the original technology. If the difference is simply that longer charging times are needed, this
can be explained to the staff. However, if the charger delivers excessive charge, then the cells
and device may be damaged. You will have to also replace the charger, when you replace the
secondary cells. Select the charger based on the replacement technology, as described below.

Substituting Chargers

A more and more common problem in the developing world is that the charger for a battery
operated device is missing or broken. Most chargers are wall transformers with female coaxial
connectors at one end. When replacing a broken charger, you need only match the input voltage
(typically 110 or 240 V), the output voltage, the output type (AC or DC) and the output current
capacity. Any physical characteristics of the charger are irrelevant, including the connector, since
you can simply snip off the connector from the broken charger and solder it to your replacement,
being careful to match the original polarity for DC chargers. There is nothing magical about wall
transformers. You should feel free to substitute any power supply, including a variable, bench-
top power supply, as long as it meets the specifications stated earlier.

If you do not have the original charger and the device is marked, then the original problem is
only more complex in the sense that you do not have the connector. It is often acceptable to
open the device and wire in a new connector (if you can find a male and female in the market).
If you cannot find any connectors, simply bring out clearly marked bare wires (with alligator clips
on the charger). There is little danger to the staff or device for any charging voltages below 24

If the device is not marked and the original charger is lost and you do not have the manual - a
very common occurrence in the developing world - then a substitute must be divined. If you
have made a substitute secondary battery, then you will also have to provide a replacement
charger. In either case, you will have to determine the correct charging voltage and current
based on the battery voltage, capacity and technology. Each secondary technology must be
considered separately. The most common encountered in medical devices in the developing
world are NiCd and Lead-Acid.

NiCd (Nickel Cadmium)

NiCd (pronounced Nye-Cad) batteries are less reliable in hotter climates because of an increased
rate of self discharge. They are also less efficient at recharging at higher temperatures. A NiCd
battery has a potential difference of 1.25 V which drops to 1.0 V when completely discharged.

To determine whether a NiCd cell is beyond its useful life, first measure the potential. If it is
below 1.0 volts, the cells are probably not salvageable. Next, attempt to charge the cells (as
described below). If the potential across a single cell does not increase to 1.25 volts, the cells
are probably beyond their useful life. If the cells measure well open circuit, and can be charged,
they may still have lost most of their capacity. Measure the voltage before and after a brief load
of 10 times the recharging current of the battery (by placing a resistor across the cell of the
correct size to obtain the required current for five seconds). Fully charged, properly operating

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cells will show only a slight difference, whereas older batteries will give a reading of less than 1.0
V after this brief load.

In some cases, apparently destroyed NiCd cells can be rejuvenated by erasing their “memory.”
This can be accomplished by fully discharging the cells at their charging capacity for one day.
Then charge them at one-tenth of their charging capacity for 12 hours. Then, finally, complete a
full charge of the cells.

NiCd batteries can be charged safely for essentially an infinite amount of time at 0.1 times their
capacity (called 0.1C charging). In other words, if the cell is a 1000 mAh cell, then the cell can
be charged at 100 mA for as long as you like. These are DC currents measured with the positive
of the charger connected to the positive of the battery (or battery pack) and the negative
connected to the negative of the pack. It will take 10 hours or more to completely charge a fully
discharged cell. Charging at 0.1C is called trickle charging. Medical devices can be left on trickle
charge for their entire non-use time. For faster charging, the NiCd can be safely charged up to
1.0C. In other words, a 2000 mAh cell can be charged at a maximum of 2000 mA. The cell will
get very hot when charged at this rate, hot enough to burn. Be sure there is adequate
ventilation to dissipate this heat or the cell will be destroyed. NiCd cells cannot be charged more
than one hour when charged at 1.0C or they will be destroyed.


Lead Acid batteries have a voltage of 2.1 volts. However, they are typically sold and used in
packages which include 3 or 6 in series, yielding 6.3 volts or 12.6 volts. The voltage does not
change appreciably during discharge, perhaps 0.3 volts for a 12.6 volt battery when it is charged
to 50% of capacity. A lead battery should be recharged by the time it has a residual capacity of
about 30%. Any further discharging considerably shortens the life of the battery.

Take extreme care when working with lead acid batteries as hydrogen gas may build up if proper
venting has failed. The build up of hydrogen can cause the battery to explode. As you are
dealing with a high capacity battery, care must be taken to avoid shorting the terminals. Remove
all jewelry before working on the batteries. A single 12.7 volt lead-acid battery is sufficiently
strong to destroy a finger if the a ring were to short the terminals. Keep the outside of the
battery clean and free from damp and grease to avoid discharge between the terminals.

There are two main types of lead batteries, sealed and unsealed. A color indicator on the top of
the sealed lead battery can tell you if it is necessary to recharge the battery. If no color indicator
is available, it is easiest to perform a load test. A 100% charged 12V battery typically measures
around 12.7V with a voltmeter, with only a 0.3V drop for a 50% charged battery. It is easiest to
identify an exhausted battery by measuring the voltage before and after heavy use – the higher
the difference in voltage the more depleted the battery.

The most reliable method to determine the battery capacity of an unsealed lead acid battery is to
measure the density of (sulfuric acid) H2SO4. This can be done using a hydrometer.
Hydrometers are available in auto parts stores in the developing world. The density of the
sulfuric acid should be 1.23 kg/liter in tropical countries. If you do not have a hydrometer, you
can typically get an auto parts store to measure your batteries for you. If you have a
hydrometer, follow the directions on with the hydrometer. If no specific density measurement is
possible, perform a load test as described above.

If the electrolyte level appears low or the acid level is too high, add water. Use only distilled
water. If distilled is unavailable, bottled water or freshly collected rainwater may substitute in an
emergency. If necessary make your own distilled water by cooling steam and collecting the
condensate. Do not use tap water unless there is no alternative. If acid must be added, it can
be purchased at auto parts stores.

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When recharging lead acid batteries in tropical environments, the charging voltage should stay
between 11.2 and 13.9 V. Limit the recharging current to less than one tenth of the capacity
(<0.1 C). For example, limit the charging to 10 A for a battery rated at 100 Ah and 5 A for a
battery rated at 50 Ah.

2.19.3 Suggested Minimal Testing

If the battery is operating and a proper charger is available, it is ready for release. There are no
additional testing procedures required.

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3 Equipment Found in the Clinical laboratory

The most equipment-intense areas of the hospital are the operating room, intensive care unit and
the clinical laboratory. Even in the developing world, where the clinical laboratories are often the
weakest departments in the hospital, there is a significant amount of equipment concentrated in
this area. Because this equipment does not directly contact the patient, it is treated somewhat
differently from equipment in the other areas. Therefore, it is separated into a separate section
in this book.

Because of high capital costs and changing technology, many of the larger devices in the
developed world are not owned by the hospitals but leased or obtained on “reagent rental” basis
in the US. Reagent rental means that the equipment is essentially free, but the hospital pays for
the reagents used to conduct the tests. This economic model has made the use of the most
modern clinical laboratory equipment impossible in the developing world. They simply can’t
support the purchase of the reagents. Therefore, there are enormous differences between a
clinical laboratory in the US and in the developing world.

While some of the automated equipment found in the US will be seen in the developing world, it
will often be sitting idly in the corner. Efforts to fix it may be futile as the reagents may be
missing. This section only covers the most common equipment that will be routinely used in a
developing world clinical laboratory.

In most clinical labs, you will see old outdated equipment, which if used properly will yield
excellent results. However, they may be incorrectly used or broken. There is a higher rate of
user error associated with clinical laboratory equipment, where the procedures are more intense,
than in other areas of the hospitals. You are often spending more of your time, as an engineer,
determining whether the problem is related to the procedure being followed or the equipment.

3.1.1 Sections found in this part of the book.

Unlike the equipment described in the first section of this book, you will rarely need to calibrate a
piece of clinical laboratory equipment by yourself. In most cases, a given piece of equipment will
have only one technician who knows how to use it - or who regularly uses it - in a given hospital.
Therefore, you can, and should, share responsibility with that person to determine what is wrong
with the equipment and to determine if the equipment is working adequately after your repair.
You won’t need to know how to calibrate the equipment in many cases because the technician
assigned to use that piece of equipment should know how to determine if the equipment is
working properly and should be able to recalibrate that piece of equipment.

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Therefore, for clinical laboratory repairs, it is essential to first develop a relationship with the user
of the equipment. Conduct an extensive interview with the technician assigned to that piece of
equipment to determine the problem. Then sit with them again when you are ready to
determine if the problem has been adequately fixed.

So, in this section of the book, there are few descriptions of the testing required before releasing
for use. This is not that testing is not required, but rather the testing should be performed with
the technician. An experienced lab technician is well versed in calibrating their own equipment.

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3.2 Balances

3.2.1 Use and Principles of Operation

Balances are accurate and precise instruments used to measure the weight or mass of a
substance or material. The ability to measure material as large as 50kg and as small as 10µg
makes them quite common.

There are two main categories of balances, mechanical and electromagnetic. Mechanical
balances tend to be the simpler of the two. They generally consist of springs or lever arms, and
use either a known force or mass to determine the unknown measurement.

Electromagnetic balances are a little more complex, but generally more user friendly. They are
often based on measuring the current needed to levitate the pan and mass. A wire is attached to
the weighing pan. The wire is placed between two poles of a permanent magnet. When a
substance is placed in the pan, the wire is displaced and additional current is required to return
the wire to its original resting state. This difference in current is measured internally and used to
determine the mass of the substance in the pan.

3.2.2 Common Problems

Internal problems with an electromagnetic balance cannot usually be repaired by the field
engineer in the developing world. Mechanical balances are very reliable and rarely need major
repairs. Therefore, the most likely problems to occupy the engineer working in the developing
world are minor in nature.

The most common problems associated with an electromagnetic balance are the result of
environmental factors and user error. The primary environmental factors leading to poor results
from the balance are temperature, static electricity, vibration, out of level (tilted), and wind. If
the readings are inaccurate or erratic, any one of these can be the cause. Shielding the balance
from vibration, static electricity and air currents are easily accomplished and may solve the
problem. Leveling the scale is also easily accomplished. Controlling the temperature, on the
other hand, may be problematic. If you find that the balance operates correctly at night or in the
early morning, but not at mid day, you may have to restrict its use to periods when the room
temperature is stable and low.

The most common problem with mechanical balances is environmental factors and maintenance.
The movements of the mechanical balance must be free of dirt and other residue. If a
mechanical balance is yielding erratic readings, clean and oil all moving parts before attempting
any other diagnosis or repair.

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3.2.3 Suggested Testing

Balances are so reliable, that the technician may not know how to perform a calibration.
However, a crude calibration is very straightforward. First, place a clean container in the center
of the weighing pan. If the balance has a case, close the door. Zero the balance by pushing the
TARE button (a long rectangular bar, a twist of a dial, or, if the TARE is absent, jot down the
reading of the balance with the container). Place a known volume of water on the scale. In
most cases, the most accurate way to add the desired amount of water is to use a syringe. Now
read the balance. (If there was no TARE, subtract your original measurement). Compare the
reading to the actual weight of the water (water weighs one gram per milliliter). The precision of
the balance will probably exceed the precision of your water volume measurement, so repeat the
measurement four or five times.

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3.3 Centrifuges and Electrical Motors

3.3.1 Use and Principles of Operation

If a liquid contains particles, the particles will eventually sink to the bottom under the force of
gravity. A centrifuge more rapidly separates particles from liquid by rotating a liquid to simulate
a higher force of gravity. Either a liquid/liquid or a liquid/solid mixture can be separated with the
substance of higher density migrating towards the outer part of the centrifuge. Centrifuges vary
in size, in speed of the rotation, how long they will run, temperature and angles of rotation of the

A centrifuge consists of a base and an inner spinning cylinder in which the substance to be
separated is placed. Some centrifuges have timers that automatically turn off after a set period
of time and some also have high precision speed regulators to control the speed with which the
centrifuge spins. Centrifuges can be used to prepare a substance for analysis or to analyze the
particle content. There are two types of preparative centrifuges: mechanical and electrical. Of
the analytical centrifuges, the only one used in medicine is the microhematocrit, used for
separating plasma from the blood suspension.

A small, table-top, electric
centrifuge is common in the
developing world. However,
smaller clinics may have only a
hand-cranked centrifuge.

With the lid of this centrifuge tipped
back, you can see the four tubes where
the specimen or dummy tubes would be
placed. When the rotor turns, the tubes
will tip out at an angle. The small round
dot just beyond the white interior (center
bottom) is an interlock that prevents the
unit from spinning if the lid is open.

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The simplest centrifuges have a single speed motor, a mechanical timer and a rotor that holds
the samples at a preset angle of 20 to 40 degrees. For user safety, the lid of the centrifuge
should have an interlock on it so that the unit will not spin with the lid in the up position.

A simple rotor is made from metal with 4, 6 or 8 holes drilled into it at an angle where the
samples are placed. Balancing the rotor is very important. If the user has only a few samples to
be spun down they may have to use “dummy tubes” to properly balance the load. Since the
motor shaft is attached to the rotor, uneven loads can cause motor damage and uneven speeds.
Another type of rotor has sample carriers that are vertical at rest but when spun move out to 20
to 40 degrees.

The simplest centrifuges have a single speed ranging from 2,500 to 10,000 RPM. Low speed
centrifuges have RPM rates up to 12,000 RPM, high speed units go up to 35,000 RPM and the
ultrahigh speed can reach 125,000 RPM. The simplest variable speed centrifuges will have a
rheostat speed control, which may be non-linear. Most of the newer variable speed centrifuges
have built in tachometers that provide the users with a speed indication. More sophisticated
speed control systems can involve SCR’s, stepper motors and servo systems.

Most high speed and all ultrahigh speed units are refrigerated because the friction caused by the
air on the samples will dry them out and change the results.

Centrifuges have a timer that is either electronic or mechanical built into the controls. Depending
upon the centrifuge, the time can be set from seconds to days. If no time is selected the
centrifuge will probably not run. Also, the centrifuge may have a time delay on the start where it
will not start to spin for several seconds after the RPM rate and timer are set and the start button

3.3.2 Common Problems

Any part of the centrifuge may cause a problem. However, not every part of the centrifuge can
or should be repaired. After eliminating the timer, rotor and most of the rest of the machine, the
only repairable part of the centrifuge which needs much further explanation is the motor.

If the timer is at fault, often the only practical solution in the field is to bypass the timer (so the
centrifuge always turns when switched on), and instruct the staff to use manual timing. As
personnel are generally plentiful in the developing world hospital, this solution is typically well
accepted by the staff, especially if they have been attempting to operate without any centrifuge
at all.

If the rotor is cracked or bent, it should not be repaired. There are tremendous forces developed
in a centrifuge. If the rotor is weakened or off balance by being bent, the machine could be
destroyed and the staff injured in the process.

Mechanical centrifuges typically only need lubricating and cleaning to return them to use. If a
piece is broken, it often cannot be repaired.

All centrifuges produced after 1990 are required to have an interlock system that does not allow
the rotor to spin unless the cover is closed. Some of these interlock systems are very simple; a
solenoid that pushes a rod through a hole in the cover latch is common. Others are more
complicated and may involve several solenoids, flexible cables and a clock. The clock can be tied
to the RPM indicator and will not release the solenoids until a set time has elapsed after the
speed drops to zero. These timed units may give the appearance of failure because the operator

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cannot immediately open the lid. Check the manual, if available, to confirm both the delay and if
that delay is adjustable.

There is always a temptation to defeat a broken interlock system. This should only be done for
clinical laboratory departments that have no alternative centrifuge and then only after careful
consultation with the technician who will be using the machine. Affix a picture on top of the
machine showing a damaged finger and an open lid so that all future users will know about this

3.3.3 Motors

The heart of the centrifuge is the motor. Almost all variable speed electrical motors in the
developing world work on the same principle, whether they are in a centrifuge or any other piece
of equipment (fixed speed motors, such as pumps and compressors are often of the induction
type, not discussed here). The motor works by passing electrical current through electro-
magnets attached to a rotating shaft. Stationary, permanent magnets attract or repel the
electro-magnets depending on the orientation of the magnetic fields. The fields’ orientations are
switched such that the electro-magnets are progressively attracted to the permanent magnets
around the circle, bringing the shaft of the motor around with them.

In general, the engineer in the field will not be called upon to rebuild an electrical motor. Almost
every major city in the developing world has a shop that can accomplish this task. However,
most motors use carbon brushes to make electrical contact with the electro-magnets on the

The inside of a simple centrifuge is nothing
more than a motor and a few switches.
This more sophisticated centrifuge includes
two fans (additional motors) and a small
bit of electronics (not shown).

If a magnet is placed within another
magnet, it can be made to rotate
around a shaft by aligning the
magnets to repel each other. If the
polarity of the rotating magnet is
then switched, the shaft and magnet
will continue to rotate, and the
device will be a motor. In order to
switch the polarity, brushes contact
commuters, the brushes and
commuter forming switches. As the
shaft rotates, the brushes contact
different commuter parts, alternating
the polarity of the rotating magnet.

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rotating part of the motor. These brushes wear down over time and need to be replaced. The
brushes can be replaced by the field engineer.

Brushes should only be replaced with brushes of the same size. Do not use undersize brushes as
they may wear unevenly and score the shaft of the motor. Brushes are held against the shaft via
spring pressure, if the spring weakens, breaks or is missing the motor may not spin. If the caps
holding the brushes in place become loose or cracked, that can also cause the brushes to lose
contact and the motor will not run at all or will not run consistently.

Brushes that are installed properly and with the correct tension make the brushes wear evenly
and have a bright almost shinny look on the contact end. If the brushes are defective or not
making good contact the contact face of the brush will be dull and not smooth. Both brushes
should be removed from the unit and compared when troubleshooting.

The shaft is held in the center of the permanent magnets by bearings. These are not often the
cause of the problem, but in certain cases they can cause noise as the shaft rattles instead of
being held in place. Bearings can be removed and replaced. Most developing world cities have
motor repair shops which can replace or repair the bearings.

Besides the brushes and the motor bearings, many motor systems, including centrifuges, will
have braking systems. If the rotor of a centrifuge, for example, was left to stop on its own, it
could take a long period of time for the rotor to drop from 100,000 RPM to zero. To cut the time
most units have a brake. The brake is not a mechanical device, as on your car. In some
systems, the brake is a resistor that is temporarily placed across the motor. The motor is
essentially operating as generator, with the mechanical energy coming from the spinning rotor
and the electrical energy dumping into the resistance.

Motors are sometimes used in a 50 Hz country, despite being designed for 60 Hz use. In
general, this causes few problems in centrifuges. In other applications, it can cause overheating.
If possible lower the voltage about 10% on these motors to reduce heating.

In more sophisticated systems, the brake reverses the electrical field in the electro-magnets to
make them attempt to spin the rotor in the opposite direction. The operator has to energize the
switch and should only hold the switch in the reverse or stop position for a few seconds at a

3.3.4 Suggested Testing

The centrifuge creates tremendous forces inside the vessel when in use. If the rotor were to
break or become dislodged, it could damage the machine or injure the user. Therefore, you
should perform some safety testing before releasing the device for use.

First, check that the lid cannot be opened when the rotor is turning. Never release a centrifuge
which can be opened while the rotor is turning without a thorough discussion of the dangers with
the staff. If this is the only centrifuge that the hospital has at its disposal, you may have to
release the device for use without a safety interlock.

Second, you should insure that the device can spin up to speed and brake without excessive
noise. Be sure to balance the rotor (with equal amounts of water-filled vials on each side) before
turning it on. Check the rotor for cracks or bends before starting the centrifuge. Particular
attention has to be paid to centrifuges that have rotors that can be changed out. The users have
been known to not fully tighten down the knob securing the rotor to the motor shaft causing
severe damage to the device and lab when the rotor broke loose while spinning.

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The ideal test for a centrifuge is a tachometer used to verify the rpm. However, you can make
an approximate measurement of the centrifuges speed without one. Under light from a
fluorescent bulb that runs on 60 Hz. current, the gage shown below will give you an accurate
reading when you are running at one of the speeds on the gage. The “flashing” of the
fluorescent bulb at 120 Hz will cause one of the bands to appear to stop moving at the RPM
indicated by that band. The gage will not work with an incandescent light bulb.

To use the gage, photocopy it, cut it out, and place it on the spindle. You may need to cover it
in clear packing tape to make it stiffer. Spin up the centrifuge until one of the bands has
stopped, mark that spot on the speed control knob. Count the bands from the inside to note
which band has stopped. You can increase the speed and find the next time that this same band
stops. This speed corresponds to twice the marked RPM. Likewise, you can find speeds which
are three, four or more times what is marked by counting the number of times the bands stop as
you increase the RPM’s. To determine the RPM, stop the centrifuge, read the band, and multiply
by the number of times it stopped as you were increasing the rotation. You’ll need to try this a
few times before getting consistent results.

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3.4 Microtomes

3.4.1 Use and Principles of Operation

Histology is the study of tissue, restricted in the developing world to using visible light and a
microscope, magnifying lens or the naked eye. In order to better examine the tissue sample
from the patient, it is first cut (or sectioned) in to thin slices, typically 1- 10 microns
(micrometers) thick. The tissue is so thinly cut, that it is translucent. The instrument that cuts
the tissue into these thin sections is the microtome.

A small hospital in the developing world might have a hand operated microtome. Larger
hospitals in the developing world will have either a rotary unit or a cryostat microtome for doing
frozen sections. No matter what type of microtome is being used, the specimen is prepared,
often in paraffin, and then clamped into the microtome. The tissue is then advanced on the feed
pawl until its edge is in the cutting zone. The knife is moved by turning a flywheel (or by
advancing it by hand). As the knife descends a specimen slice is made. In an automatic
microtome, as the knife ascends the specimen is drawn back so the knife edge does not touch
the specimen.

There are additional types of microtomes such as the sledge microtome (for hand cutting large
pieces), the freezing microtome (with a cutting stage that freezes the tissue) and the
ultramicrotome (which cuts very fine sections), but these are rarely seen in the developing world.

3.4.2 Common Problems

The most typically problem with a microtome is the knife. Many modern microtomes use
disposable knives. These are inconvenient in the developing world due to the expense. The
disposable knives are often reused for that reason. Durable knives are a better option, as long
as they are sharpened periodically. Knife sharpening is typically available in the developing
world, but may not be used.

Most larger developing world hospitals
will have a small, manual microtome
like this one.

A manual microtome slices a thin
piece of tissue off of the preparation
with a knife. The platform holds the
tissue. The dial advances the tissue a
few micrometers.

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The knife angle can cause problems. The clearance angle is the angle between the knife edge
bevel and the block, typically between 2 and 4 degrees for paraffin sections, and between 5 and
7 degrees for resin or frozen sections, being most effective. If the cutting angle is too great it can
cause compression in the cut section. If the cutting angle is too fine, the edge of the knife can
vibrate causing chatter in the section. These angles can be adjusted and sections cut until the
technician is satisfied with the results.

The machine needs to be well maintained to operate correctly. It should be cleaned after each
use. You can use a very light oil to prevent corrosion and improve the operation of the
mechanism. The knife should be removed after each use. A dust cover should cover the
machine’s cutting surfaces after each use. If you don’t see evidence that these procedures are in
place, thoroughly clean the machine and attempt the sectioning again.

On cryostat machines, you can also suspect the cooling elements. There is a defogging
mechanism that allows the user to see the section inside the cold chamber. This may become
clogged or otherwise broken.

Finally, you should suspect user error. The preparation of the tissue and the handling of the
tissue after sectioning can greatly affect the results. The hardness of the embedding compound
being one of the primary factors affecting tissue sectioning. Embedding compounds range from
gelatin (50 to 200 microns), simply freezing the tissue (5 to 20 microns), paraffin (1 to 15
micron), paraffin/wax/resin mixtures (0.5 to 2 microns and pure resin (0.05 to 1 microns). You
may encounter any of these preparations in the developing world, and you may encounter a
technician using the wrong embedding material for the thickness of section desired.

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3.5 Water Baths, Stir And Hot Plates

3.5.1 Use and Principles of Operation

As the name suggests, a water bath is simply a device which maintains the water at a set
temperature to bathe an object. A water bath is normally used to control the temperature of
bottles and flasks containing enzymes, medicine, or blood, as well as many other substances.
They can be used in both clinical or research settings depending on the needs of the user. In a
clinical setting, the water bath is commonly used to bring a colder specimen to body
temperature, such as blood or an organ for transplant. Likewise, a refrigerated water bath can
cool a specimen to at or below freezing if necessary.

Water baths can be used at several different temperatures, and depending on the manufacturer,
can either have set points, often 37 °C, or the user can set the water bath temperature.
Depending on the device and specifications, the temperature can be maintained within a very
narrow range, with some as accurate as plus or minus a tenth of a degree Celsius. Other models
may fluctuate as much as a degree or two.

There are four common types of water baths: standard, stirrer, refrigerated, and shaker. The
first is the standard water bath with very few electronic components, and it is the simplest of the
water baths. These are called hot plates. There is no feedback with this type of device (open
control). In other words, the device does not adjust the amount of delivered heat dependent on
the sensed temperature. This type of water bath will usually have an analog dial to crudely set
the desired temperature (actually the delivered heat).

Another type of water bath is the stirrer, also known as a circulating water bath. The stirring
water bath includes a rotating magnet below the hot surface. A magnet dropped in the liquid
rotates with the magnet under the platform, stirring the fluid in the beaker. The stirring action
allows for water to heat up faster and more evenly.

The refrigerated water bath is used to cool substances more slowly than just placing in a
refrigerator. It is relatively rare in the developing world.

The shaker or orbital water bath, is the most recent advance in water bath technology. It
provides means for shaking the solution without the need to drop a magnet in the solution.
Shaker water baths usually have a control for temperature as well as shaker speed, stroke
length, and occasionally a timer for mixing. They are also rare in the developing world.

The most basic water baths are “open”
systems, either hotplates or stirring hot
plates. The stir system adds a spinning
magnet under the platform (activating a
second magnet dropped into the jar on
top). Without a temperature control,
The operator must monitor and adjust
the temperature by hand.

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3.5.2 Common Problems

The more complex the model, the more components that can go wrong and cause the machine
to either not work or work incorrectly. However, the basic components of a water bath are the
heating element and the motor (if it is a stirring or shaking bath). For more details on motors,
see the chapter on centrifuges. The heating element is typically a Nicrome wire, which can often
be removed and replaced in the developing world.

User error is fairly common with water baths, because the level and temperature alarms can be
confusing. Be sure that the device is full and level before attempting to use.

The only device required to calibrate a water bath is a thermometer, and perhaps a watch. If
you wish to test the device just to be sure it works, make sure the bath is full and level before
turning it on. If it warms up and moves, it is ready for final testing. Discuss the most critical
aspects of operation with the technician who uses the device and test those aspects of the device
to his or her specifications.

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Figure 2: General layout of standard
compound light microscope, labeled
by part. (1) eyepiece, (2) body tube,
(3) arm, (4) nose piece, (5) stage
clips, (6) objectives, (7) stage stops,
(8) aperture, (9) stage, (10) coarse
adjustment knob, (11) diaphragm,
(12) light source, (13) fine
adjustment knob, (14) power switch,
and (15) base.

3.6 Microscopes

3.6.1 Use and Principles of Operation

In histology, pathology, hematology and other sections of the clinical laboratories the microscope
is a critical device. Even the smallest and poorest equipped developing world hospitals will have
a microscope. While these units rarely fail they do require cleaning and lubrication on a regular

There are many types of microscopes. However, the only one regularly encountered in the
developing world is the compound light microscope. A compound light microscope can have a

maximum magnification on the order of 2000.
However, typical clinical strengths range only up to
1000 X (100X objective and a 10X eyepiece).

Compound microscopes have a light source, either
external or built in, that is used to bottom light the
slide-mounted specimen. It may be a direct light
beam or focused via a mirror. On some units there is
a diaphragm that will control the size of the light beam
impinging on the specimen. There may be an
intensity control on the light source as well. There
also may be a filter between the light and the
specimen that removes certain wavelengths of light
from the spectrum or polarizes the light.

The general layout of a compound light microscope is
shown in the figure at the left. It consists of fifteen
main components.

The most critical components are the objectives (6),
the adjustment knobs (10), the light source (12) –
often located in the base (15) and the eyepiece (1).
The objective lens of a microscope is small and
spherical, which means it has a small focal length, to
bring the object into focus at a shorter distance. The
image is then magnified by a second lens, called the
ocular lens or eyepiece.

Normally, in a clinical compound microscope, the three
objectives will be four times (4X), ten times (10X), and
forty times (40X) magnification. Sometimes a 100X
objective is present, but it will require oil between the
objective and the tissue, not air. The objectives are
interchangeable within one microscope and sometimes
between microscopes of the same manufacturer.
They are often not interchangeable between
manufacturers. The eyepiece is usually fixed at some
magnification, usually ten times (10X).

The thickness of the cover glass of the specimen can
also affect the ability to focus the image, and the
correct cover-glass thickness is sometimes written on
the side of the objective lens.

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3.6.2 Common Problems

The most common problem with microscopes is dirty or broken objectives. Unfortunately, the
objectives cannot be repaired and are very expensive to replace. It can be cheaper to replace
the entire microscope than to replace one objective.

The optics can be cleaned with an alcohol dampened lint free cloth. It is a good idea to blow off
any dust with canned air before cleaning. Be very careful not to scratch the optics as they are
coated with very precise, thin coatings to correct for color aberrations. The coatings can be
significantly softer than the lens itself.

The light source is the next most common source of problems. Bulbs should only be replaced
only with the same bulb. If the bulb is different it may have differing light output, filament
voltages, heat or light spectrums that could affect the reading of the specimen. See the chapter
on lighting for more information.

If mechanical positioning adjustments do not operate smoothly it is an indication that either too
much or too little lubricant has been used. Clean off any excess lubricant, especially if it has
dried and is clumping. Use a soft cloth dampened with alcohol for the cleaning. Do not use any
solvents that may leave a residue. Also be careful not to leave lint on any surface.

When the microscope is used in hot, humid rooms, as is often the case in the developing world, a
serious concern is fungus growing on the microscope, especially on the surfaces of the lens, and
the grooves of the screws. To help prevent moisture and fungus from destroying the
microscope, store it under air-tight cover with a dish filled with blue silica to desiccate the air
under the cover. Once the silica turns red, it will have lost its capacity to absorb moisture from
the air, and it will need to be regenerated using by heating it in a hot air oven or over a fire. If
silica is not available, put an air tight plastic bag over the microscope and place a small pile of
dry rice in the bag with the microscope. Replace the rice every week or so.

When a repair is completed, you may wish to insure that the microscope is working to some
extent. The precise operation of a microscope takes skill and practice. However, a rudimentary
knowledge of a microscope’s operation is sufficient to determine that it is working at all. Always
carry a microscope by the arm with one hand, and the base with the other. The microscope
should be placed on a level table. Before using the microscope, turn the coarse adjustment knob
to raise the body tube to its highest level and revolve the nosepiece until the low-power objective
lens clicks into place. Then adjust the diaphragm and mirrors while looking through the eyepiece
until a bright white circle of light is seen. Next place the slide specimen on the stage and center
it over the opening in the stage, using the stage clips to hold the slide in place. Looking at the
stage from the side, carefully turn the coarse adjustment knob to lower the body tube until it
almost touches the slide. While looking through the eyepiece, very slowly turn the coarse
adjustment knob until the specimen comes into focus. However, caution should be used in this
step, as the objective should not touch the slide. Once the specimen is almost in focus, use the
fine adjustment knob until the specimen is seen in a sharp view. When you are ready for a more
detailed test, consult with the technician in charge of using the device.

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3.7 Autoclaves

3.7.1 Use and Principles of Operation

An autoclave is a device used to sterilize medical instruments and equipment. It uses steam and
pressure in the absence of air to assure sterile conditions. The small, table-top autoclave uses
heat to boil water into steam. The steam continues heating and the pressure continues to
increase. Bacteria can not survive in these conditions. However, not all viruses and spores are
killed. Exposing materials to a single heat cycle is somewhat effective, but sterilizing them 3
times over a period of 3 days will kill most vegetative spores.

Most hospitals have electric, steam autoclaves, but you will also find an autoclave like the “All
American” distributed by UNICEF. It uses an open fire as its source of heat.

An autoclave is a fairly simple instrument to operate but could be dangerous if operated
improperly. It is important to wait until the chamber is completely depressurized before opening!
If it is opened under pressure, large quantities of steam could escape causing severe burns!
Most modern hospitals have automated autoclaves. These devices go through the steps of
operation without intervention. If the machine is not going through its steps correctly, there is
little that can be done to change the sequence of steps.

Manual machines, such as the All American, must be operated correctly to insure sterilization.
The automated machines follow the same steps, though automatically.

Start by making sure that the water reservoir is filled to proper level with distilled water or
filtered rain water. Well water will, in time, leave a scaly deposit on the instruments and
autoclave. An indicator strip should be used with each pack being sterilized. However, in the
developing world, this practice is not followed. Place the instruments into the chamber and close
lid securely. Open the air outlet valve. Automated machines may use several cycles of vacuum
to remove the air. The manual machines depend on the steam to push the air out of the

Now, the machine is ready to begin its cycle. Turn on or light the heating element. During this
part of the cycle, the manual machine is evacuating the air. Therefore, it is important to wait
until there is a steady stream of steam exiting from the autoclave. If the air release valve is

Inside and outside of a
small, electric autoclave.

The small open fire
autoclave is still common
in the developing world.

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spitting and sputtering, it should remain open. Air left in the chamber will lead to cold spots, and
poor sterilization.

When the air is completely evacuated from the machine, either by vacuum in the automated
machines or by steam in the manual machines, the air outlet valve must be closed. The steam
pressure will begin to rise. At this point, it is sufficient to monitor the temperature and time to
insure sterilization. Do not open the chamber or valves, as the pressure of the escaping steam
can be dangerous.

The sterilization cycle and sometimes the cool-down cycle can be timed. The proper time and
temperature is shown below for unwrapped surgical instruments. Allow 30 minutes more at the
holding temperature and pressure if the instruments are wrapped.

Temperature ( C )

pressure (kPa)

Pressure (psi)

Minimum holding
time (min)

time (min)

115 75 11 30 50
122 115 17 15 40
128 150 22 10 30
136 225 33 3 20

After the specified holding time, the sterilization cycle is complete. Turn the heating element off
completely. Now the cool-down cycle begins. The progress of cool-down can be followed by
time, temperature, or simply by dropping water on the outside of the vessel. If it boils off, the
vessel is still too hot. When cool down is complete, the chamber can be opened. If a
sterilization tape was used, check to see that it is completely black.

3.7.2 Common Problems

There are a number of different types of problems you may encounter. However, the manual
autoclave is a very reliable instrument. It rarely fails when properly operated and maintained.

The most common problem in the developing world is a build up of a scale due to the use of
non-distilled water in the sterilization cycle. The scale can usually be scraped off the machine
and simply thrown away. On manual machines, the scale may cause the air release valve and
the over-pressure relief valve to be clogged. Both of these systems are difficult to scrape clean.
If they can be removed from the machine and forced or left open, then simply soaking them for
several days in pure distilled water should dissolve any deposits. It may be best to run a few
dozen cycles with distilled water, where the air release valve is intentionally left open (steam will
escape through the valve the entire cycle). This will help to dissolve any remaining the scale. If
the relief valve cannot be opened and cleaned, it is best to replace this component.

Automated machines with scale build up may also see clogs in the vacuum lines and associated
valves. If the machine is still operable, the best procedure may be to remove any visible build
up, then run many cycles with pure distilled water until the remaining scale dissolves. If the
valves have become blocked, remove them all and clean them all (not just the clogged one). If
only one is clogged, it is certain that the others are close.

The second most common problem for autoclaves in the developing world is clogging of filters
due to the use of dirty water, such as non-filtered rain water. This primarily plagues the
automated autoclaves which often have inlet filters between the water storage and the main
vessel. Some of these filters can be removed and back-flushed (run water backwards through
the filter) to clean and restore them. Be sure to clean the tank of any particles that have settled
to the bottom. In other cases, the filter must be replaced.

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If you hear a hissing noise, then there is a leak in the pressure vessel or valve. Try to isolate the
problem by looking for steam escaping and by using your ear. If the problem is a valve, it will
probably be necessary to replace the valve. If the problem is the vessel, it is impossible to fix
and the autoclave should be discarded. The seal on the vessel is also a common source of leaks.
Check to see that there are no obstructions (dirt, or scale build up) along the seal. In some
cases, the seal can be reground, but often, replacing the seal is required.

Some machines use a plastic or rubber seal. For these machines, run your fingernail into the
seal. It should be pliable. If the seal is hard, or worse cracked, then it must be replaced. In
larger cities, you may be able to find an automobile repair shop that can cut you a replacement
gasket. Silicone sealant can be used to seal cracks in door gaskets until a replacement gasket
can be located and installed.

If the seals are working and there are no leaks or clogs, the manual autoclave should work. The
automatic autoclave may still not reach the proper temperature. The cause may be the
thermostat or the heating element. In the most sophisticated autoclaves, the controller can be

If there is no heat generated, it could be the heating element or the thermostats. The typical
heating element consists of two coils of nickel-chrome resistance wire, each of which has
approximately 14 ohms of resistance. If the resistance across a coil is significantly higher, it is
probably broken. These heaters are paralleled and the combination is placed in series with the
on/off switch and one or both of the thermostats. Nicrome wire is common and can usually be
found in the developing world. Match the resistance and length as closely as possible.

There are often two thermostats. One is a boil-dry safety thermostat connected in series with
one of the elements and set to open at 212 degrees F. This will reduce the violence of boiling
once 212 is reached. The second thermostat, often called the overheat relay, is set to turn off
the electricity going to the nicrome elements when the temperature is excessive, usually meaning
that the water has boiled away. Both thermostats for this instrument are usually of the
bimetallic-switch type. They rarely degrade themselves, but the device which holds them in
place is often deteriorates.

3.7.3 Suggested Testing

Autoclaves are like centrifuges in that there is a safety issue associated with their use. The
device can injure the operator or leave the equipment undetectably contaminated. Therefore,
some testing should be performed before releasing the device for use.

Before releasing an autoclave back to the floor, check the gaskets and check for scaling. You can
prevent future clogging by removing any scale or dirt now. If the gasket for the vessel breaks, it

Circuit of a simple,
electric autoclave.

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may leak steam, which can be dangerous. If the autoclave has an interlock that prevents
opening during a cycle, check this again for safety.

If possible, check the temperature inside the vessel during sterilization. Most US hospital users
put test strips with each sterilization pack. These strips verify that the temperature reached the
required level for the required time and that humidity was present. However, in the developing
world, these test strips are rarely used. It is nevertheless, possible to test the autoclave.

A complete test of an autoclave includes a Bowie-Dick test (to see that all the air was being
removed) and either a temperature or a pressure test to see if the temperature and pressure
reached the needed levels (since PV=nRT, and the chamber is only filled with steam, it is not
necessary to measure both temperature and pressure). The time of the sterilization cycle can be
measured with a watch. The Bowie-Dick test for air removal can be approximated by placing a
standard Time-Temperature test strip on a sheet of paper in the center of a stack of 100%
cotton towels and placed in a metal dressing can. The dressing can is placed in a warmed pre-
vac sterilizer and a short cycle is run using the tape on the cotton towels as a check. If there is
any air left in the sterilizer chamber, then it would be trapped in the towels. Because the air
would not allow the steam to touch the tape, the color change would not be uniform around the
strip. In order to pass the test, the entire tape must change colors, not just the edges. This
procedure will test both the temperature and the air removal process.

If test strips are not available, then it is not possible to reliably test the autoclave for both air
removal and temperature/pressure. You will have to settle for a pressure measurement. At the
present time, there is no reusable alternative to the test strips readily available in the developing

Check the safety valve on the vessel. If it is dirty or corroded, attempt to replace it. If you
cannot replace it, it is possible to test the safety valve by bypassing the overheat limit switch.
This should only be attempted by experienced technicians wearing proper safety gear.
Furthermore, you can only test the safety valve on autoclaves with working pressure gages.
The safety valve is factory set to open at 30 psi. To test this valve, short out the thermostat with
a clip lead, operate the autoclave as in starting a normal cycle. Be ready to pull the plug from
the wall very quickly, should the safety valve fail and the pressure rise above 31 psi. If the
safety valve fails to operate at this upper limit, it must be replaced. If you cannot find a
replacement, discuss the danger with the administration. Although not having a safety valve is a
severe danger to the operator, not having an autoclave is a severe danger to the patients.

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3.8 Laboratory Incubators

3.8.1 Use and Principles of Operation

Laboratory incubators are devices that maintain controlled environmental conditions. These
conditions include, but are not limited to, proper oxygenation, humidity and temperature. They
are generally designed to cultivate cell and bacterial cultures.

Laboratory incubators come in various sizes and levels of technology. All are designed to
maintain set temperatures and conditions within the chambers. Some may have internal AC
outlets so other devices can be used inside of the incubator. Most will have fans to move air
from the heating elements around the cultures (specimens) and out a vent. Much of the air is
recirculated within the chamber and not vented. The doors have to seal tightly and should only
be opened on a strict as-needed basis. Every time the door is opened it will take several minutes
for the temperature and humidity to stabilize. A difference of 1° C can cause culture growth to
slow or stop, which affects the clinical results.

In all incubators, a temperature sensor compares the temperature inside the chamber to a set
temperature on the front panel. If the temperature is too low, the heat will come on to warm the
chamber. The fan may come on with the heat or operate continuously.

Incubators can vary greatly in size ranging anywhere from 2’ to 6’ tall and 1.5’ to 5’ wide. They
generally have stainless steel interiors/exteriors and hinged glass doors. They include controls
and displays of the chamber temperature, as well as temperature fail safes to protect the
contents in the unlikely event of a temperature change. Incubators have various numbers of
shelves and are equipped with fluorescent lamps.

3.8.2 Common Problems

There generally are one or more lights in the incubator not only for visibility but to promote the
growth in the cultures. If the light needs to be replaced you must use an exact replacement and
not just one that fits. The emitted light spectrum is very important for the proper functioning of
the incubator.

Filters on the air system have to be cleaned on a regular basis. It is not a good idea to remove
and clean the filter while cultures are in the incubator. Also any moisture traps should be
cleaned at the same time.

The most common problems with an incubator are the fan, the heating element and the
controller. The controller cannot generally be repaired if broken. The fan is a motor and is
subject to all of the problems and repairs described in the centrifuge section of the book. The
heating element is generally a nicrome wire which can be removed and replaced with a new wire
in the developing world.

The only critical testing that you can do without the help of the technician is the measurement of
temperature. The incubator should maintain a constant temperature, typically to within one
degree Celsius. You can also check that the over-temperature alarm works at the correct setting
and that all dials read correctly. More detailed testing should be conducted in cooperation with
the technician using the incubator.

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After assuring that the incubator is properly working, it may be necessary to disinfect the unit.
Discuss this with the technician. The disinfection procedure begins by removing the porous
material from the incubator. This includes the filters and fabrics, including the bedding. Place a
bowl with 250 ml of formaldehyde solution (formalin) in the incubator. Turn on the incubator to
20oC and leave it to heat, with the fan circulating, for at least 1.5 hours. After this time, replace
the bowl with 200 g/l of ammonia solution for another 1.5 hours. (The ammonia functions to
remove the smell of formalin.) When time is up remove the ammonia solution and wipe out the
machine. (If after cleaning there is still some residual smell of formalin, leave the incubator
running until the smell has disappeared.)

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3.9 Water Purifiers

3.9.1 Use and Principles of Operation

In the hospital setting it is crucial to have pure water. In many cases, the success of the
laboratory depends on the quality of the water available. In the intensive care, much of the
medicine delivered to patients may be mixed with water or water and salt before delivery. Even
the washing of patients and the preparation of food may require water which has been purified
at the hospital to some level in the developing world.

Purification is a general term used to describe the process of removing impurities from water. It
can range from simple filtration to complicated multistage processing, the complexity depending
on the source of the water and its eventual use. The impurities to be removed can range from
parasites, bacteria, and viruses to organic compounds and ions, roughly in order of the size and
difficulty of the problem. As varied as are the uses of water in a hospital, so are the
requirements for the purity of water needed. Requirements can range from essentially zero
tolerable contamination (for parasites) to relative indifference (for ions). Likewise, the cost of
purification can range from just a few pennies a gallon to far more.

Some components are found in every purification system no matter what method of purification
is being used. These components include the inlet, outlet, vent, filter, and drains. The inlet is
simply where the water enters the system and the process of cleaning begins. The drains allow
excess impurities to be stored or disposed of. Vents allow gas, mostly air, to exit the system.
Finally, once the water has been filtered, it leaves the system through the outlet.

There are at least eight common methods of purification in developing world hospitals: 1)
Distillation, 2) Ion Exchange, 3) Carbon Adsorption, 4) Filtration, 5) Ultrafiltration, 6) Reverse
Osmosis, 7) Electrodeionization and 8) Ultraviolet (UV) Radiation.


Distillation is the oldest method of water purification. The process involves heating water in a still
to its boiling point and condensing the resulting steam to water again. The removal of the
contaminants depends on how well the still is designed. If boiling is too vigorous, “bumping” can
take place, where liquid water shoots out of the boiler directly into the condenser. Any organic
compounds with boiling points lower than 100 °C cannot be removed. In fact, they can become
concentrated in the process.

Stills do not need to be sophisticated.
Here, a simple pot is held over a fire and
covered by a large bowl of water. Three
rocks hold the pot in place. The long tube
allows for condensation. The condensate
falls into the collection vessel in the bottom
right corner.

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Distillation is a robust and simple technique that has the advantage of removing a broad range of
contaminants. Unfortunately, it requires careful maintenance to insure purity. Also, distillation
consumes a large amount of energy and water, neither of which are in great supply in the
developing world.

Ion Exchange

Ion-exchange purification is a rapid and reversible process in which impurity ions present in the
water are replaced by ions released by an ion-exchange resin beads. The impurity ions are taken
up by the beads, which are then periodically regenerated. The two most common ion-exchange
methods are softening and deionization.

Softening is used primarily as a pretreatment method to reduce water hardness prior to reverse
osmosis processing. The softeners contain beads that exchange two sodium ions for every
calcium or magnesium ion removed from the "softened" water.

Deionization beads exchange either hydrogen ions for cations or hydroxyl ions for anions. The
cation exchange resins will exchange a hydrogen ion for any cations they encounter. Similarly,
the anion exchange resins will exchange a hydroxyl ion for any anions they encounter. The
hydrogen ion from the cation exchanger unites with the hydroxyl ion of the anion exchanger to
form pure water. The resin containing the charged contaminants must then be regenerated once
it has exchanged all its hydrogen and/or hydroxyl ions in the water, the impurities being shunted
to the drain.

Deionization removes some dissolved inorganics and most ions. It requires a relatively
inexpensive initial capital investment. However, it cannot be used to remove particles, pyrogens
or bacteria. In fact, deionization beds can release resin particles into the water and serve as a
culture medium for bacteria growth.

Carbon Adsorption

As mentioned above, ion-exchange resins remove soluble anions and cations from raw water, but
some nonionic, organic molecules can coat the resin. Such a coating will decrease the life of the
resin and diminish its capacity. To remove nonionic, organic molecules and protect the ion-
exchange resin, carbon filters are often placed upstream (before the ion-exchange filter).

In addition to nonionic, organic molecules, carbon also removes free chlorine and protects other
purification media in the system that may be sensitive to oxidants.

The adsorption process in a carbon filter is controlled by the diameter of the pores in the carbon
filter and by the diffusion rate of organic molecules through the pores. The rate of adsorption is a
function of the molecular weight and the molecular size of the organics.

Carbon filters remove dissolved organics and chlorine effectively and have relatively long life.
However, they can release carbon particles into the water.


Filtration removes particles from the water based on their size. There are three types of
microporous filtration approaches: 1) depth, 2) screen, and 3) surface. Each approach serves a
different purpose.

Depth filters are matted fibers or materials compressed to form a matrix that retains particles by
random adsorption or entrapment. Depth filters are usually used as prefilters because they are

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economical and can remove nearly all (perhaps 98%) of the suspended solids, protecting
downstream elements from fouling or clogging.

Screen filters are single layer, uniform structures which retain all particles larger than a precisely
controlled pore size. The particles are retained on one surface of the screen filter.

Surface filters are made from multiple layers of media. When fluid passes through the filter,
particles larger than the specified size are retained, accumulating primarily on the surface of the
filter. Surface filters are very efficient, removing almost all of the suspended solids (perhaps
99.99%). Surface filters may be used as either prefilters or clarifying filters.

Since the poor size can be specified below the size of bacteria and parasites, surface filters can
be used as a partial sterilization process. Filtration requires almost no maintenance, but filters
must be replaced occasionally because the flow rate drops as the retained particles clog the filter.
Filtration will not remove dissolved inorganics, pyrogens, colloidals or viruses. They can be
expensive to replace and cannot be reused.


Ultrafiltration is a process like screen filtration but pore sizes lie in the range 0.001-0.02 µm (100
to 10 times smaller than typical screen or surface filters). Most of the ultrafiltration membranes
used in water purification have a hollow fiber configuration, and are non-biodegradable.
Ultrafilters are capable of removing 1) particulates, 2) micro-organisms, including all parasites
and bacteria and some viruses, 3) inorganic colloids and 4) large organic molecules including
pyrogens. Smaller molecules, such as solvents and ionized contaminants pass through the
filtrate. Ultrafilters can be used either for pre-treatment or ‘polishing’ duties in water purification

Ultrafiltration produces the highest quality of water for the least amount of energy and it can be
regenerated. However, it will not remove dissolved inorganics, such as calcium, sodium and

Reverse Osmosis

Reverse osmosis is the most economical method of removing 90% to 99% of all contaminants.
Reverse osmosis is a process like filtration and ultrafiltration, but the pore structure of reverse
osmosis membranes is even finer than ultrafiltration. Reverse osmosis membranes are capable
of rejecting 1) practically all particles, 2) bacteria, 3) viruses, and 4) any organics greater than
300 Daltons in molecular weight.

In order to understand the process of reverse osmosis, it is helpful to understand the process of
osmosis in general. Osmosis occurs when solutions with two different concentrations are
separated by a semi-permeable membrane. Osmotic pressure drives pure water to dilute the
more concentrated solution. The pressure exists until enough water flows that the two solutions
are equally concentrated. In water purification systems, the process is driven in reverse.
Hydraulic pressure is applied to the concentrated solution to oppose the osmotic pressure. Pure
water is driven from the concentrated solution and collected on the other side of the membrane.

Reverse osmosis rejects nearly all of the strongly ionized ions and most of the weakly ionized
ions like sodium. Reverse osmosis membranes are very restrictive and therefore yield very slow
flow rates so storage tanks are required to produce an adequate volume in a reasonable amount
of time. Reverse osmosis can be the most economical and efficient method for purifying tap

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This new technology is a combination of electrodialysis and ion exchange. The process consists
of a number of "cells" sandwiched between two electrodes. Each cell consists of a polypropylene
frame onto which are bonded a cation-permeable membrane on one side, and an anion-
permeable membrane on the other. The space in the center of the cell, between the ion-selective
membranes, is filed with a thin bed of ion exchange resins. The cells are separated from one
another by a screen separator.

The source water entering the module is split into three parts. A small percentage flows over the
electrodes, 65-75% of the source water passes through the resin beds in the cell, and the
remainder passes along the screen separator between the cells. The ion-exchange resins capture
dissolved ions in the source water at the top of the cell. The potential on the electrodes pulls the
ions out of the resin beds. The ions travel towards the electrodes until they reach the adjacent
ion-selective membrane, which is of the opposite charge. The ions remain in the space between
the cells until they are flushed out of the system to the drain.

Electrodeionization effectively deionizes water. The ion exchange resins are continuously
regenerated by the electric current in the unit increasing the time between maintenance calls for
the purifier. The result is a deionization approach that is relatively inexpensive to operate.
However, electrodeionization requires prefiltration to prevent clogging of the cells.

Ultraviolet (UV) Radiation

Ultraviolet radiation is beginning to be a widely used method for the sterilization of water in the
developing world. In most systems, mercury, low-pressure lamps generate 254 nm of ultraviolet
light. Exposure to intense UV light of this wavelength destroys the DNA and other proteins in the
bacteria, parasites and viruses, rendering the water sterile.

Some lamps generate both 185 nm and 254 nm UV light. This combination of wavelengths is
capable of photo-oxidation of additional organic compounds.

The UV technique can kill micro-organisms and, in some cases, photo-oxidate organic compounds
into smaller fragments. However, the organisms are not removed from the water. Therefore,
particles or clumps of microorganisms can cause shadowing, which may affect the efficiency of
disinfection by the ultra-violet light. Water with significant amounts of color and organic
compounds will also reduce the intensity of the light and therefore its efficiency.

3.9.2 Common Problems

Water purifiers can be complicated, multi-stage machines. In many cases you will not be able to
affect a repair without specialized tools. However, there are a few common problems which can
be diagnosed and repaired in the field.

One of the most common problems is clogged filters, typically indicated by a low flow rate. Some
filters can be cleaned by backflushing them (running water from the following stage through
them backwards – discarding the results). Don’t use upstream water for this purpose. However,
if possible, the filters should be replaced.

Leaks are also common. Check all tubing, glass, and reservoirs for cracks or leaks. If the leak is
in the inlet to the systems, it can be repaired with epoxy or a silicone sealant. Once the water
enters the system, the solvents from glues and adhesives can contaminate the water. Replace
the tubing or component rather than repairing it.

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When the deionizer fails, the electrical conductivity of the water will increase. When this
happens, check the resin bed and see if the beads need to be replaced or regenerated.

Older systems can accumulate deposits which are not being removed in the drains. If deposits
are found, scrape them from the system and flush those components with the purest water

3.9.3 Suggested Testing

Most users will not know how to determine if the water purifier is working. Furthermore, unlike
other clinical laboratory equipment, there is not typically one person using the water. Therefore,
the burden is upon the engineer to test the water purifier. Unfortunately, in the developing
world, the necessary testing equipment may be unavailable, leaving the engineer few options.

If flow rate was the reason for the initial call, then this can be easily checked with a measuring
cup or graduated cylinder and a watch. However, after any work, the purifier should be checked
for the purity of the water exiting the system. This can be done by measuring the protein
content in a spectrophotometer and the ion content by measuring the conductivity. Sterility can
be insured by culturing. However, all or some of these measurements may not be possible in a
developing world hospital. Despite the fact that this testing should be performed by the
engineer, you may have no choice but to resort to a discussion with the laboratory personnel as
your best alternative to testing. They should be able to indicate what the problem was that
initiated the call for repair in the first place, and therefore, they should be able to determine if
the problem has been fixed.

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3.10 Clinical Laboratory Ovens

3.10.1 Use and Principles of Operation

Ovens in laboratories are used to dry samples and for evaporating, dehydrating or sterilizing. On
a limited basis some are used as a dry incubator. In many cases, precise temperature control is

Clinical ovens may be bench, cabinet, or walk-in size. However, bench top are the most common
in the developing world. All ovens will include a heat source, a well insulated container (usually
including a door with tight sealing gaskets), and a thermostat/thermometer. More advanced
ovens may include timers/alarms, fans to circulate air inside the oven to achieve uniform heating,
shelving units or racks, humidity control options, or air filtration. The heating mechanism may be
electric, natural gas, propane, oil, radiofrequency or microwave, but the electric heater is the
most common in the developing world.

Operation is simple. Place the sample in the oven (or empty it if you are testing it). Shut the
door. Set the desired temperature. The oven may have a timing feature or timing may have to
be completed manually. After the heating cycle, allow the oven to cool before opening it.

If the oven is being used for sterilization, the following table should be used. Sterilization timing
should not begin until the oven has reached the required temperature.

Temperature (°C) Time (min)

160 180

170 120

180 30

3.10.2 Common Problems

The power supply and heating element are the most likely sources of problems. The electrical
heating element is of a typical construction and material and can probably be replaced in the
developing world, as long as the resistance and max power (nichrome wire) are matched.

If the oven is not reaching the desired temperature, you should suspect the door gasket, fan or
sensing device. If the door gasket does not seal air tight, try cleaning the seal with soap and
water. Rinse well before testing again. It may be possible to find a material to seal an oven
door in the developing world, if the seal must be replaced.

If there is a fan, and it is not turning, and the problem is not the power supply, the fan motor
can be replaced with any motor of a similar size (see the centrifuge and motor chapter for more

The temperature sensing device may be part of the temperature feedback mechanism. An exact
match is often necessary. You may be able to defeat the temperature sensor with a short circuit
or open circuit, leaving the oven in the on position at all times. The user would be required to
carefully monitor the temperature. Install a switch in the main power line so that they can cycle
the heater as needed. This is clearly not an ideal solution, but is better than having no oven at

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If the oven is reaching the desired temperature and holding that temperature, then the device is
working. In some cases, the user may complain about highly non-uniform heating. In many
cases, this will be caused by a broken fan. In this case, attempt to measure the temperature in
several parts of the chamber. Discuss the degree of uniformity required to satisfy the user’s
needs. In the developing world, they may have to survive with little uniformity, but at least a
functioning oven.

Temperature accuracy varies tremendously with the oven’s application. Larger error can be
acceptable if the oven is used for drying glass, but accuracy may be crucial if biological fluids are
being warmed in the oven. The same is true with the fan. An operating fan may not be critical
depending on the oven’s use. Discuss these issues with the user before returning the oven.

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4 Related Topics

4.1 Electrical Safety

Electrical safety testing is one of the most common procedures done by a biomedical engineer in
a hospital. Every patient related device must be tested for electrical safety before it is initially
put into use. All electrical/electronic devices have a current leakage ranging from a few micro
amps to 500 mA. Various agencies have set current limits for electrical leakage currents in
medical devices. Not all agencies have the same limits. The National Fire Protection Agency,
NFPA, AAMI, (Association for the Advancement of Medical Instrumentation), or IEC/ISO,
(International Electrical Commission) are some of the many agencies setting safe current limits
for electrically operated medical devices.

In the late 1960’s there were several publications stating that up to 10,000 people per year were
electrocuted in hospitals because of defective electronic equipment that was applied to patients.
In various studies it has been shown that as little as 30 micro amps applied directly to a portion
of the heart during a critical part of the cardiac cycle can cause an arrhythmia, an abnormal beat.
If this abnormal beat triggers additional abnormal beats a potential for a lethal arrhythmia is

The most common solution for leakage currents in devices after about 1970 is to isolate the
patient from the device. This was done by using isolation transformers, light emitting diodes or
electromagnetic links between the patient connections and the device.

Without a safety analyzer, it is not possible to do a complete safety test. Nevertheless, a
reasonable substitute for the most common danger is described in the chapter on ECG’s. This
section describes which other devices should be considered for safety testing.

Equipment found throughout the hospital or clinic that is not directly connected to patients
includes both medical and non-medical devices. In general, these devices do not need to be
tested at all or should only be tested once.

Devices which are not patient connected, but are in the vicinity of the patient (x-ray equipment,
for example) should be ground tested after every major repair. One technique that is commonly
used is to select one ground point in the area and measure the resistance to ground of all
exposed surfaces to that point. The problem with this method is that one lead wire may have to
be as long as 20 feet to reach all surfaces in that area. A variation of this technique is to select a

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point, such as the x-ray table as the ground and measure everything in the “patient vicinity” to
that ground point. With either technique the ground resistance should not exceed 0.5 ohms. A
key point to remember in performing this type of ground resistance testing is to select your
starting point and document it so that the test can be repeated. A small dab of nail polish next
to the ground point is one method of documenting the ground point location.

Patient connected devices used for diagnostic purposes amplify and process signals detected in
the body by electrodes. The signals travel over the lead wires and patient cables to the device
where they are amplified, processed and displayed. The key point is that it detects a signal and
has wires between the patient and the device. This category of equipment contains such devices
as EKG, EEG, EMG recorders and patient monitors. For all of these devices, testing should be
completed after every repair as described in the section on ECG’s.

Patient connected devices used for therapeutic purposes deliver energy, fluids or gases to a
patient. The delivery can last for a few milliseconds, as with a defibrillator, to years for a
ventilator or IV pump. In the case of an IV pump the fluids are contained in a non-conductive
plastic so any electrical contact requires that there be a hole in the tubing. On ventilators the
tubing is non-conductive, as are most of the gas mixtures that would be administered. Because
energy is delivered to the patient it is not required to test the lead isolation while the unit is
delivering that energy. In fact, testing the device while it is in operation could be dangerous.
The same testing procedures as that described in the ECG chapter is performed after every
repair, but leakage is only tested with the device plugged in and the power off.

4.1.1 Electrical Outlets

The primary source of electrical danger is the power outlet itself. These should be tested once
per year. However, in the developing world, many of the outlets are wired incorrectly.
Therefore, as with other work, this effort has to be prioritized against repairing broken

Almost all developing world countries
follow one of the standards to the left.
In many cases, the outlets will be wired
incorrectly. The voltages may not match
the voltages given here, or the intended
voltages. Often the power fluctuates
(often including periods of zero volts).
There are many variations in these plugs.

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Incorrectly wired outlets are a danger. Each outlet has only one wire carrying power (called hot
or live). The other is neutral and the third is ground (or earth). The fuse for a piece of
equipment is placed between the power source and the load in the one “hot” line. If the
electrical outlet is wired backwards, then the fuse is in the neutral wire, not the power line.
Should the device find an alternative path to return current to ground, then the power line will
not be fused. This type of fault can be deadly to the attendant or the patient.

The wiring of the outlet can be tested with a two-pin neon bulb tester available at any hardware
store. Inserting the pins in the right and left spade jacks (of a US plug, or the two round pins of
a European plug) will illuminate the lamp. Note the voltage registered on the lamp. In some
hospitals in the developing world, plugs used for the 120V standard will be wired for 220V and
vice versa. Be sure to mark the voltage on the wall next to the outlet if you find an outlet
mismatched to the standard.

Inserting one pin into the large spade jack (of the US standard plug) and touching the other pin
to any grounded surface to be tested should not light the lamp. Only the small spade jack is
“hot,” and should light the lamp against ground. This simple preliminary test is true for all three-
wire wall outlets and most European two-wire outlets, with the exception of those which are
wired through an isolation transformer.

Isolation transformers have their primary windings connected to the main power line but the
secondary windings are not connected to any system ground. They are rarely used in the
developing world, but are required in some parts of US hospitals. When an isolation transformer
is used, the neon bulb tester will light only between the two spade plugs and not against ground
for either plug.

The use of such a neon bulb polarity tester indicates the voltage, but not the quality of the
wiring. A lamp with a high-wattage incandescent bulb from 60 to 100 watts (W) connected
between the plugs or between the small spade plug and ground should light. This is usually an
adequate test of the quality of the wiring.

4.1.2 60 Hz versus 50 Hz

It is common for an engineer to encounter a device designed for 60 Hz that was donated years
before. If the power system in the hospital runs at 50 Hz, the engineer is faced with the
question: Is it still safe to use that device? Will it work at all? The answer is … it depends.

It is also common that the power system will be at 220V when the device is designed for 110V.
However, a transformer can be used to adapt the voltage. This still leaves the question of
frequency unaddressed.

Devices Without a Motor

If the medical device does not have a motor in it, then the only concern is the power supply.
After about 1980, most medical equipment was designed with switching power supplies. These
supplies can handle either 50 Hz or 60 Hz without the need for conversion. You can usually tell
these supplies because they will be labeled 50/60 Hz.

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If the medical equipment is older, then the power supply may be of a traditional design. Some of
these machines will use multi-tap transformers. If this is the case, then there should be a switch
or jumper on the primary side of the transformer (the side where the power comes in) that can
be moved to adapt the equipment. Occasionally, the jumper will be on the secondary side
(where the power goes to the electronics in the equipment).

If the transformer is not of the multi-tap variety, then there is no certain way to tell if the
equipment will work when switching between frequencies. Switching from 60 Hz to 50 Hz will
cause about 17% more current to flow through the primary side of the transformer (because the
impedance will have been reduced from 2π60L to 2π50L, where L is in inductance of the
transformer). This additional current will cause the transformer primary to heat up more than
originally anticipated. Therefore, if the transformer is not of the multi-tap variety, it will typically
be sufficient to account for any voltage difference, and then to provide more cooling to the
device (an extra heat sink, more cooling vents, leaving the cover off, etc.).

Devices With a Motor

If the device uses only a small motor or runs on batteries most of the time, then the motor is
probably a DC motor. These motors are typically the size of one’s thumb or smaller. Small, DC
motors are voltage sensitive only, and are, therefore, unaffected by the frequency change.

If the device uses a larger motor, the size of a fist or larger, then the motor is probably an AC
motor and it is made for a specific frequency. Switching frequencies will have several effects.
First, when switching from 60 Hz to 50 Hz, the motor will run slower; at 5/6 of the original rpm.
Likewise, when switching from 50 to 60 Hz, the motor will run too fast; 6/5 of the desired rpm.
Second, when going from 60 Hz to 50 Hz, the current increases by 17% in the windings. This
causes additional heating which is compounded by the fact that the drop in rpm’s will decrease
the mechanical cooling. Going from 50 Hz to 60 Hz does not cause such heating problems.
Finally, depending on the type of motor, the horsepower or the torque may be affected by a
change in frequency. All of these changes can affect the operation of a medical device.

The increase or decrease in speed can not be corrected. If this change is critical to the operation
of the device, then it must be abandoned.

When running a 60Hz motor at 50Hz, the biggest concern is the second problem: heat buildup.
To avoid destroying the motor, the engineer could provide additional cooling (leaving the top off,
increasing the fan size, etc.). Another way to avoid heat buildup is to use a transformer to
reduce the voltage into the windings by 17%, reducing the current back to its original value.
However, reducing the voltage may reduce the available power.

The most challenging problem is the third problem: the change in horsepower or torque.
Horsepower is a function of frequency and torque P=τN, where P is the power from the motor, τ
is the torque, and N is the rpm of the motor. The frequency is inversely proportional to the
torque. So, as the frequency goes from 60 Hz to 50 Hz, the torque goes up, increasing the
power output of the motor. When going from 50 Hz to 60 Hz, the torque drops, dropping the
power out.

Most motors found in medical equipment have varying torque and horsepower. Machines that
fall into this category include fans, blowers, centrifugal pumps, mixers and agitators. When
going from 60Hz to 50Hz, the power output of the motor increases and since the motor is
required to deliver more output at faster speeds, torque and horsepower increase. In addition to

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the risk of increased heating, already mentioned, the increased torque strains the motor and
accelerates the rate of burn out.

Conversely, when running a 50Hz motor at 60Hz, the primary concern is the decrease in available
torque. If the available torque falls below what is necessary to start the motor, it could fail to
start and burn out.

General Guidelines

It may be impossible to predict the precise outcome of changing the frequency of operation of a
medical device. However, the discussion above can be used to sort medical equipment into a
few categories.

Electrical Medical devices without Transformers
Examples: infant warmers, autoclaves, incubators, clinical ovens
Some older medical devices do not use any electronics and may not have any transformers. In
general these devices are not sensitive to frequency and can be used once the voltage has been

Electronic Medical devices With Transformers but Without Motors
Examples: electrocardiographs, invasive blood pressure machines, pulse oximeters, defibrillators,
fetal monitors, fetal Doppler, balances, lights (all types), electrosurgery units,
For these devices, first check to see if it is marked 50/60Hz compatible. If it is, then use the
device without modification. If it is not rated for both frequencies, check to see if the
transformer is multi-tap. If it is, change the wiring to use the correct tap. If the transformer is
not multi-tap, then attempt to run the device with the cover off and check the temperature
frequently. If the transformer is not heating up excessively, then use the device as is. If it is
heating up, provide extra cooling.

Medical Devices with Pumps
Examples: Suction, anesthesia machines, water purifiers.
When switching from 60 Hz to 50 Hz, devices with pumps will most likely overheat. If the heat
cannot be dissipated, the motor will burn out. Attempting to provide additional cooling may
prolong the life of the device. When switching from 50 Hz to 60 Hz, attempt to use the device
with caution. If the device does not start, the motor will quickly burn out. If the device
consistently starts, then it should be possible to use the device without a problem.

Motorized devices without Pumps,
Examples: centrifuges, microtomes, water baths,
These devices will operate at different speeds when switching between frequencies. The change
in frequency may alter the clinical utility of the device. Be sure to discuss this with the staff
before adapting the voltage for use. In addition, when switching from 60Hz to 50Hz, the devices
will most likely overheat. If the heat cannot be dissipated, the motor will burn out. Attempting
to provide additional cooling may prolong the life of the device.

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4.2 Troubleshooting Medical Equipment

Troubleshooting medical equipment requires patience, persistence and a willingness to ask a lot
of questions. The most common error in troubleshooting is to rush down the wrong path,
perhaps because of a misunderstanding or misdirection from the staff. A willingness to sit back
and tack a fresh look at the problem is essential. A structured approach helps avoid the most
common errors. This section presents one possible structured approach to troubleshooting.

Before You Start

Consider safety first. Know the hazards that are associated with the device be it electrical,
mechanical, chemical, gas or bacterial. As a minimum, refamiliarize yourself with the
equipment’s principles of operation and clinical use, as described in this book. If you are unsure
about a hazard, consult someone else before beginning.

User error accounts for a large fraction of the broken equipment in the developing world,
according to a recent report by Engineering World Health. Make sure you know how the device
should work before you begin. If you can find the manual, read it.

Here are seven steps that you should follow, once you are convinced that you are ready to

No matter what the problem, begin by assessing the piece of equipment. It is absolutely
essential that you not skip the assessment steps. Hours of your time can be spent repairing a
problem which never existed in the first place. EWH reports that most of the problems you will
encounter are related to user error. Another quarter are related to power supply issues. You
should always consider these two possibilities before all else. Of the remaining problems, the
most likely to be solved are those related to the presence or absence of the proper inputs and
outputs. In other words, the problem is related to some other piece of equipment, which itself
has either a user error or power supply problem.

Look at the device

If at all possible, remove the equipment from the patient floor to a quiet, clean bench where you
can work without interruption. Look at the device and all the information that may be around it.
Are there any notes from the users? Is there a description of the problem or is it just labeled
“broken”? Is there a name of the person who found the problem? Is there an error log on the
device? Is there evidence of a drop, spill, smoke, heat or other damage?

If there is evidence of a spill it must be considered hazardous and cleaned by someone trained to
handle hazardous spills. Spills, even non-hazardous ones are usually conductive and can cause
shorts in the device circuitry. Some solutions are very thick and can act as glue that will overload
motors on a pump. Always follow the Universal Precaution Procedures against infectious agents.

Next look at any connectors, power cords, input or output cables to be sure that they are in the
correct positions and secure. Check the positions of all switches and controls to be sure that
they are correctly positioned and working. Before moving any switch or cable, take a digital
photo of the control panel. That way you will be able to go back to the device’s original settings.

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Assuming that there are no signs of mechanical damage to the device, do a “self-test” or
“calibration” on the device. This may also give you the “error log” on the device, which must be
reviewed and problems noted.

Look at the manual (if you can find it), the device history (if it exists), and the service manual (if
you can find it) to be sure that you have covered what needs to be done to operate the device
properly and to determine if the problem has occurred in the past. If it is a repeat problem, try
to determine how it was repaired before. If you can get the service manual, review it briefly to
see if there is a system test or additional self tests that might help.

Listen to the User

Interview the user. In most cases, the user is not the person who gave you the equipment. So,
ask questions until you find the user of the device. You want to talk directly to the user of the
device. Many problems arise from misunderstanding between the user and the person who gave
you the equipment.

Carefully listen to the user’s complaint about device. Find out what they see as the problem as.
What has changed with the outputs or process? Is it still within normal ranges or not? Has the
speed of the process changed? Has the use of consumables increased?

It is common for a user or an operator to not know all the functions of a device. To avoid
looking foolish they will give bad answers to questions outside of their knowledge. Also, it is
common for a user to not tell you a piece of information which is critical to diagnosing the
problem. The opposite is also true. Sometimes the user says they know exactly what the
problem is, when in fact they are merely guessing. You must act as a detective, listening to
everything, but rejecting and accepting facts as you piece together a hypothesis concerning the
problem with the equipment.

Suspect User Error

Always suspect user error. If you have followed the first steps, then you have not, as yet,
opened the device. Verify again that the device is, in fact, malfunctioning. Nearly half of the
time, the device is operating correctly; the person is simply using it incorrectly. Follow the
recommended testing described here.

If the device is operating as you expect, then the problem is user error. But what type? Attempt
to determine if the problem is language, incorrect programming or settings or a
misunderstanding of what the equipment is capable of doing.

If the problem is a misunderstanding of the equipment’s abilities, perhaps you can suggest an
alternative. If the problem is programming, or settings, see if you can permanently program or
fix the devices function. Consider taping over switches or labeling the correct setting.

If the problem requires a sequence of steps to resolve; or it is a langrage problem. Consider
creating a “cheat sheet” that can be attached to the machine. This is a simple explanation of the
device’s operation (or the specific operation that is causing the problem). Write short, direct
sentences that describe how to accomplish the task. These should be accompanied by drawings
wherever possible. A digital camera and the internet café can be used to create a sequence of
“how-to” photos. Often the photos tell the story better than the words. The cheat sheet must
be written in the local language. Be sure to try out the sheet with the nurse or doctor before
attaching it to the device. Have them attempt the operation using the sheet – and without your
intervention. If you have to say anything while they attempt the operation, then the cheat sheet

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needs revision. You cannot rely on the fact that this particular nurse or doctor will always be at
the hospital to train the rest of the staff. Nurses leave and doctors are often too busy to return
to a piece of equipment.

Suspect Power Supply

You may feel that you are ready to open the device. There is one more area to test, before
opening the device: the power supply.

Does the device power up at all? The signs that a device is powered up include indicator lamps,
the screen is lit, hearing a fan or motor running (though not always, they may have a separate
supply), pressure/flow indicators not on zero, a warming of the device. On pneumatic, hydraulic
or vacuum powered units do you hear or see leaks?

First, check for the obvious. Is it plugged in, (both ends of the power cord)? Is the outlet “live”?
Is the power cord good (try another one)? Is there a second power switch on the unit? Is the
fuse good (less than one ohm)? Is the breaker open (push the reset). Are the batteries of the
proper type, installed correctly and charged?

On some devices there is a voltage compensation switch. Check that to be sure it is in the
correct setting (110 or 220 V). Also some devices have a 50/60 Hertz switch that needs to be in
the correct setting (see the separate section on frequency adjustments).

After checking the obvious, recheck the device. If it still won’t power up, or it powers up, but
won’t operate correctly, you will need to remove the covers.

Now that the cover is off, be very careful. In most modern equipment there is more then one
power supply in an instrument. There are often ±5, ±12 or 15 volt power supplies for the logic
circuits, 60 to 120 volts for motors and certain displays, plus high voltage power supplies, up to
150,000 KV. You will need to check each of them to see if they are producing the expected

Never work alone on a device with the cover off and the power on. Double check that you are
wearing no jewelry. Latex or rubber gloves offer some protection from high voltages. Place your
probe leads with care to avoid shorting out two lines. Proceed slowly.

Once the cover is off, carefully look for dust buildup over fans or vent holes, fluid spills, loose
hardware, or worse, floating hardware cleaning and correcting as you proceed. Make sure all the
chassis components are secure. Look for signs of heat, smoke or burned components.

Look at any fluids carefully. In very old equipment, if they are oil based it may be an indication
that a capacitor or transformer is leaking or failed. Generally if this has happened there will also
be signs of heat damage around the failed component.

Next, move on to the circuit boards. Are they properly seated? Is there dust or spills on them?
Are there signs of heat buildup? Are the components secure on the boards? Correct problems as
you find them. You might look over the solder connections on the boards to be sure that there
are no “cold” joints from previous repairs. You might also want to clean the connectors with a
pencil eraser (the white kind is best). Take note of any prior repairs: They are clues to current

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Power Supply or User Error some where Else

If you have ruled out user error and power supply, and the problem is not one of the common
errors listed in this manual, then there are only two other categories of error that are worth your
time investigating: input and output errors.

Input errors can cause an otherwise operating device to appear to have failed. Find out where
the input comes from? Is it a cable, electrode, probe, tissue sample, liquid sample? What, if
anything, has changed on the input? If the device tests blood or tissue samples are they
properly prepared? Are the samples being presented correctly?

If the device works on your bench, but not on the patient, there still may be a device problem,
but more likely it is an input problem. As dumb as it may seem, is the patient alive? Has the
patient’s condition changed? Is there more movement, (shaking, shivering, thrashing around in
the bed)? Did an electrode or other sensor fall off? Are the lead wires and cable good?

The output of a device is its final product. In many cases it is a delivered energy, a graph or a
display. In some cases it may be more than one. If the device appears to be working, but the
display is faulty, try to do everything you can to devise an alternative display. Working
equipment in the developing world is too precious to abandon due to display errors.

In older equipment, you can sometimes find a voltage which is proportional to the desired
output. If this is the case, consider displaying this voltage on a multimeter and giving the user a
table to convert from volts to the desired units. Perhaps a display from another device, perhaps
even an unrelated device, can be used. Perhaps the user can live with less resolution or
precision, making a substitute display possible. Be as creative as possible before abandoning the
device due to display errors.

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4.3 Recommended Minimum Tool Sets

If you are about to leave for a trip to the developing world to work on medical equipment, unless
you know otherwise, you must assume that the hospital you are going to will have no tools for
you to use. In fact, there may be a handful of scattered tools of low quality. However, you
should not depend on these to accomplish the work you will want to see done.

Recent changes in the security regulations in airports have forced engineers to carry their tools in
checked luggage instead of carry-on luggage. The only significant problem this imposes is the
increased likelihood that your tools won’t arrive when you do. Fortunately, you can often
purchase adequate tools in the developing world. However, the prices will be no less than those
that you pay at home. You can also buy inferior tools at lower prices in most of the larger
developing world cities.

As a minimum tool set, you should plan on bringing the following:
electrical tape, super glue, epoxy (30-minute, two part), sandpaper (1 sheet, med), black marker,
scissors (shears), batteries (4-AA, 1-9v), knife, hex wrench set (Allen wrenches), crescent
wrench, tape measure, multi-meter, small tube or roll of solder, a solder sucker and/or
desoldering wick, a soldering iron, wire cutters, wire strippers, screwdrivers (#1 and #2 phillips
and small, medium flat head), jewel screwdrivers, needle nose pliers, a working flashlight,
balloons (to test air volumes), small plastic cup measure, latex gloves, and outlet adapters for
your target country.

If you have the room, consider adding the following tools to your bag:
WD-40 (small can), Ziploc bags (10 to hold parts while you work), batteries (4-AAA), fuses (250
v, 0.5, 1.0 and 1.5 a glass tube type), AC outlet analyzer/tester (to quickly test for 110 or 220 v),
AC-to-DC universal adapter, extension cords, hemostats and forceps (small clamps and
tweezers), and wire crimp/fasteners.

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4.4 Definitions of Some Common Medical Equipment

It is relatively easy to find definitions of medical equipment and terminology on-line. Many of the
on-line dictionaries are sufficient, e.g. There are also many on-line
biomedical engineering bibliographies, e.g.,
and However, you may find what you need
by just looking up the piece of equipment on Google. This section only covers the most
commonly found pieces of equipment.

Anesthesia machine or Boyle’s Machine - Sometimes referred to as the anesthetic trolley
(boyle’s machine or gas machine), this normally refers to a trolley on which are mounted gas
cylinders and/or pipelines for various gases used in anesthesia, together with the various valves,
controls and ancillary equipment used by the anesthetist. The trolley usually includes some basic
monitoring such as ECG and pulse ox. On the trolleys, the gases can be dispensed and mixed.
These usually include oxygen, nitrous oxide and carbon dioxide, and sometimes medical air,
cyclopropane and anesthetic vapors such as halothane, ether, etc.
Autoclave - an apparatus in which special conditions (such as high or low pressure or
temperature) can be established for a variety of applications; especially: an apparatus (as for
sterilizing) using superheated steam under high pressure
Aspirators - an apparatus for producing suction or moving or collecting materials by suction;
especially: a hollow tubular instrument connected with a partial vacuum and used to remove fluid
or tissue or foreign bodies from the body
Analyzer, hematology (cbc, complete blood count) - A device used as a blood cell counter,
especially red and white blood cells.
Ambu bag - Part of the ambu resuscitator, the ambu bag is used for providing emergency
artificial respiration for resuscitation. The bag remains inflated in its resting state and when
squeezed closes the expiratory port and inflates the patient's lungs. When the bag is released it
automatically re-inflates with fresh air and the patients expired air passes out to atmosphere via
the expiratory valve.
Chemistry Analyzer (electrolytes) - A device used to measure the amount of electrolytes,
especially potassium, sodium and chloride in blood.
Bili-light – see light source
Blood gas analyzer - A device used to measure the amount of oxygen and carbon dioxide in
the blood.
Bronchoscopes - a tubular illuminated instrument used for inspecting or passing instruments
into the bronchi
Blood warmer - During blood transfusion it is desirable to pre-heat the blood to the body
temperature. The most common device for this is a temperature-controlled water bath. The
temperature of the bath is normally maintained slightly above body temperature to allow for any
cooling in the feed tube to the patient. The device consists of a bath with a heating element, a
stirrer (usually) to ensure even distribution of temperature, and electronic circuitry to control the
temperature and to provide an over-temperature limit in the event of system failure or low water
Centrifuge, hematocrit, urine - a machine using centrifugal force for separating substances of
different densities, for removing moisture, or for simulating gravitational effects
Compressor, air - A device used to deliver air to another machine at a higher than atmospheric
pressure. A device used to fill bottles of gases.

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Complete Blood Count (CBC or Coulter Counter) – a hemotology analyzer for determining
the number of cells of different types in a sample of blood.
Concentrator, oxygen - A device used to deliver oxygen at a higher concentration than
atmospheric. May or may not compress the air and deliver it at a higher pressure.
Crash Cart - A trolley used in emergency (patient crash) situations. It contains the most vital
supplies and administration equipment needed to treat the most common causes of sudden
medical emergencies (crashes). Often used for cardiac arrest. Typical equipment includes a
laryngoscope, cardiac monitor and defibrillator.
Cast saw (stryker saw, bone saw) - Hand saws looking very like carpenters' saws are
sometimes used for working on large bones. However, there are power saws available which fall
into electric and pneumatic types. The electric types usually have a blade which vibrates. The
advantage of having a vibrating rather than a rotating blade is that, if the vibrations are small,
cutting will only occur in hard materials (e.g. Bone) but will not occur in soft materials.
Compressed air powered saws are more common particularly for orthopedic surgery. They often
come as a kit consisting of an air-operated motor and foot-operated speed control, and a set of
fittings for sawing, drilling, screwing and pinning. They are intended to work from nitrogen or air
at 7 bar pressure, which may be provided by pipeline or from cylinders.
Cardiotacograph - This is essentially a device for recording the uterine contractions during
labor. However, the term is normally applied to an instrument which also records the fetal heart
rate on a beat-to-beat basis to monitor the progress of labor and in particular the well-being of
the fetus. Uterine contractions are sometimes monitored using a tocodynamometer lightly
strapped on to the mother's abdomen, which consists of a central plunger coupled to a force
transducer and outer guard ring so that the plunger is pressed during the uterine contractions.
This provides a qualitative indication of the strength and occurrence of contractions and this is
compared with the fetal heart rates which result. Sometimes an internal transducer is used once
the fetal membranes have been ruptured and a recording catheter can be introduced into the
uterus. The recording catheter can be a fluid-filled tube connected to an external pressure
transducer or it may have a miniature pressure transducer built into the tip of the catheter.
Cryostat - an apparatus for maintaining a constant low temperature especially below 0°C
Cautery pens - a device used to cauterize, meaning to sear or burn. Pens are connected to
electrocautery machines.
Cauterizers (electrosurgery units) - An instrument that applies electric current to destroy
tissue. See cautery pens
Dialysis machines - An instrument that removes certain elements from the blood based on the
difference in their rate of diffusion through a semi-permiable membrane. See dialyzer.
Defibrillators - an electronic device that applies an electric shock to restore the rhythm of a
fibrillating heart
Dialyzer, hemodialysis, peritoneal - Haemodialysers (sometimes called artificial kidneys) take
blood from the body and pass it along one side of the dialyzing membrane so that unwanted
small molecules may diffuse into a special dialyzing fluid passing along the other side. Small
molecules which need not be removed are included in the dialysate so that there is equal
diffusion of these molecules in each direction. The peritoneum is a double membrane enveloping
most of the organs in the abdomen, and renal dialysis may be achieved by pumping a special
dialyzing fluid into the cavity between the two membranes and allowing time for the diffusion to
occur before withdrawing it. This technique is called peritoneal dialysis which may be a hospital
procedure operated by sets of pumps, valves and timers, or may be used at the patient's home
without special apparatus but using a collapsible bag from which the fluid is delivered and then
returned after the process is complete.
Diathermy -See cauterizers, electrosurgery units
Doppler, non-fetal, fetal - Information about the motion of blood in the larger vessels may be
obtained from the Doppler shifted reflections received by a transducer outside the body. This is
most commonly used to assess the quality of flow from an audible signal produced from the
Doppler shifted components or by processing of these signals to indicate the flow pattern or flow

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rate. Images can also be produced by combining the information derived from these Doppler
signals with B-scan images. This is particularly useful since a diseased artery will have turbulent
flow. The color display can provide unequivocal evidence of arterial disease and identify the site
of any constriction or dilatation. Such techniques are used by vascular surgeons in special clinics
and they offer the potential of avoiding dangerous and painful X-ray contrast procedures.
Electrocautery unit, diathermy (ESU) - See cauterizers.
Endoscopes - an instrument for visualizing the interior of a hollow organ (as the rectum or
EKG or ECG units - A unit that records the moment-to-moment electromotive forces of the
heart as projected onto various sites of the body’s surface, delineated as a scalar function of
time. Major types are 12-lead (primarily diagnostic) and 3-lead (primarily monitoring).
I.V. devices/equipment - Any of the many pieces of equipment used to gain intravenous
Gomco – a slang term for aspirator
Glucometer - A device for measuring the amount of glucose in the blood
Gurney & mattress -a bed-like platform which can be used to move a patient within the
Gastroscope - an instrument for viewing the interior of the stomach
Heart Lung Machine – see pump, heart-lung
Hematocrit- an instrument for determining usually by centrifugation the relative amounts of
plasma and corpuscles in blood, also refers to the ratio of the volume of packed red blood cells to
the volume of whole blood.
Incubator, lab - a clinical laboratory device used to keep specimens and samples warm.
Typically used to grow cultures from samples taken from patients. The cultures can then be
examined to determine what bacteria are found in the patient.
Incubator, neonatal - an apparatus with a chamber used to provide controlled environmental
conditions, especially for the cultivation of microorganisms or the care and protection of
premature or sick babies
Laryngoscope - an instrument for examining the interior of the larynx
Light handles for surgery - The sterilizable part of the overhead light in an operating theater.
The handle allows the doctor to adjust the light without breaking sterility.
Laparoscope - a fiber-optic instrument inserted through an incision in the abdominal wall and
used to examine visually the interior of the peritoneal cavity
Laser unit - A device that produces a laser beam that can be used for cutting or coagulating
tissue with great precision.
Light source (Bili-lights, phototherapy) – Bili-lights are used to treat patients with a surfeit
of bilirubin, a common condition in newborns. Also, see lamp
Microscopes - an optical instrument consisting of a lens or combination of lenses for making
enlarged images of minute objects
Manometers - an instrument (as a pressure gauge) for measuring the pressure of gases and
Microtome - an instrument for cutting sections (as of organic tissues) for microscopic
Microwave - A device for heating tissues. It uses electromagnetic radiation to heat.
Monitor, cardiac, ICU, fetal, neonatal, temperature, maternal, patient
Equipment which sits alongside the patient to measure vital signs (heart rate, blood pressure and
temperature) or other critical patient parameters. Fetal monitor is attached to mother, but
monitors fetus.
Nebulizers - a device which reduces a liquid to a fine spray before allowing the patient to
breathe it in. Used to deliver medicine and water to a patient.
Non-Invasive Blood pressure (NIBP or sphygmomanometer) - An instrument to measure
arterial blood pressure. Consists of an inflatable cuff that goes around the arm about an inch
above the elbow, with tubing that connects the cuff to the measuring device.

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Oximeter, pulse - a non-invasive device which measures the percentage of hemoglobin
saturated with oxygen. The device can also measure heart rate. Most are optical.
Oxygen tent (with regulator) - a container which can be placed over a patient to increase the
percentage of oxygen in the air that the patient naturally breathes.
Otoscope unit - an instrument for use in viewing the ear drum and exterior/middle ear.
Opthalmoscope - an instrument for use in viewing the interior of the eye and especially the
Oxygen regulator, flow meter - A device for measuring and regulating the flow of oxygen
from a cylinder of compressed oxygen.
Pulse oximeters (pulse ox) - see oximeter pulse
Pump, heart – lung - a large device used to bypass the heart and lungs during open heart
surgery. Also called a heart-lung machine or perfusion device.
Phaco emulsifier - an ultrasonic device for emulsifying (liquefying) the lens of the eye. Used
for cataract surgery.
Prostratron, laser unit - a device for delivering high energy laser pulses to the prostate
Photometer - an instrument for measuring luminous intensity, luminous flux, illumination, or
Pacemakers & supplies - Device used to artificially pace the heart when the natural
pacemaker fails.
Respirator Masks - Methods for delivering concentrated oxygen to patient who is naturally
Resuscitators - an apparatus used to restore respiration (as to a partially asphyxiated person)
Scale (balance, weighing, child, infant, adult) - an instrument or machine for weighing a
Speculum, vaginal, ear - Hand held tools or implements used by health professionals for the
performance of surgical tasks. Typically inserted into a cavity to open up the passage for
inspection. Typical varieties include vaginal and ear specula.
Sphygmomanometer - a non-invasive instrument for measuring blood pressure and especially
arterial blood pressure
Stethoscope, adult, amplified, fetal (fetoscope), pediatric - an instrument used to detect
and study sounds produced in the body
Sleep apnea monitor - a device for monitoring the breathing of the patient during sleep.
Device alarms when the patient stops breathing.
Spirometer - an instrument for measuring the air entering and leaving the lungs. Advanced
instruments can measure flow rates, tidal volume and breathing rate.
Sigmoidoscopes -a long, hollow tubular instrument passed through the anus for inspection,
diagnosis, treatment, and photography especially of the sigmoid colon.
Slit lamp - a device used during eye exams.
Sterilizer, desktop, gas, steam, large/small – see autoclave.
Stryker Saw - see cast saw
Suction machine, continuous / aspirator, desktop, high pressure, surgical - see
Surgical microscopes - a light microscope typically having x-y or x-y-z remote motion control
Traction machine - a device used to apply tension to some joint (s) of the body.
Ultrasound (Doppler, diagnostic, therapeutic, cardiac, abdominal, ob/gyn) - A large
device for the diagnostic or therapeutic use of pressure waves and especially a technique
involving the formation of a two-dimensional image used for the examination and measurement
of internal body structures and the detection of bodily abnormalities -- called also sonography,
echograph, echocardiograph.
Ventilator / respirator - a device for introducing fresh air or expelling foul or stagnant air.
Can also be used to maintain positive pressure to inflate the lungs, or to assist a patient who is
otherwise breathing spontaneously.
Vital sign monitors - see monitors

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Warmer, infant - device for giving out heat to a moderate or adequate degree for an infant.
Washer, ultrasonic - a water bath which can excite the water with high frequency pressure
pulses. Can effectively remove particles from instruments. Often used as a prelude to
Wound suction (Hemovac) - See aspirator

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4.5 Spanish-English Dictionary for a BME

There is currently no Spanish/English dictionary of biomedical engineering available. This section
covers many of the words you are likely to encounter. However, if you don’t find the dictionary
in this section sufficient, consider one of these:

Diccionario enciclopédico de términos técnicos: inglés-español / español-inglés.
Collazo, Javier L.S. McGraw-Hill, 1980. ISBN 0-07-079172-4 (English Binding) / 0-07-079162-7
(Spanish binding). 2217 pp.

Diccionario Técnico Inglés-Español / Español-Inglés. Beigbeder, Federico. Madrid:
Ediciones Díaz de Santos, 1996. ISBN 84-7978-221-8. 1253 pp.

Diccionario Técnico Español-Inglés. Malgorn, Guy. Madrid: Editorial Paraninfo, 1991. ISBN
84-283-1354-7. 569 pp.

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4.6 Possible Sources for Equipment and Spare Parts

For a list of organizations that offer medical supplies, see the list by Bruce Carr, available on the

Goethestraße 43, 52064 Aachen, GERMANY
phone: 0241 / 47798-0 fax: 0241 / 4779815 or 4779840
E-mail: Web Site:

ECHO International Health Services Ltd
Ullswater Crescent, Coulsdon, Surrey CR5 2HR, UK
phone: (+44 20) 8660 2220 fax: (+44 20) 8668 0751
e-mail: Web Site
Registered non-profit charity. As of this writing, they are undergoing a change of strategy.

Engineering World Health
111 South Highland Suite 289, Memphis, TN 38111
phone: 901-634-2035
e-mail: web site:
Collects and refurbishes medical equipment for shipment to the developing world at no charge.
Trips, student programs.

International Dispensary Association
P.O. Box 37098, 1030 AB Amsterdam, The Netherlands
phone: +31 20 4033051 fax: + 31 20 4031854
E-mail: Web Site:
Will ship clinical laboratory tests and a narrow range of capital equipment.

International Aid Inc.
17011 W. Hickory, Spring Lake, MI 49456
Fred VandenBrand & Jerry Dykstra, Communications Officers
phone: 1-800-968-7490 fax: (616) 846-3842
Email: Web site:
International Aid maintains a large library of manuals. Also microscopes, centrifuges, physical
therapy equipment, and more. They don’t send anything before thoroughly testing it for
accuracy and practicality.

JMS (Joint Medical Store)
PO Box 4501, Kampala, UGANDA
phone: (+256 41) 269699 or 268482 fax: (+256 41) 267298
e-mail: Web Site:
Not-for-profit mission medical store supplying pharmaceuticals, medical supplies and equipment,
with a technical department to deal with maintenance issues and capital equipment. Supplies the
public and non-profit health sector in Uganda, East Africa and Great Lakes region.

MEDS (Mission for Essential Drugs and Supplies)
PO Box 14059, Nairobi, KENYA
phone: ( +254 2) 544244/5 fax: (+254 2) 545062 or 540993

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e-mail: Web Site:
Not-for-profit mission medical store supplying pharmaceuticals, medical supplies and equipment
to mission organizations and not for profit organizations in East Africa and Great Lakes region.
Incinerators for medical waste

AMRF – American Medical Resources Foundation
56 Oak Hill Way, Brockton, MA 02301
Phone: 508-580-3301 Fax: 508-580-3306
E-mail: Web Site: (note .com ending, not .org)
Sends 40-foot containers of medical goods; check with them about prices and procedure. They
also provide biomedical engineering training services.

Brother’s Brother Foundation
1200 Galveston Avenue, Pittsburgh, PA 15233-1604
Phone: 888-232-1916, Fax: 412-321-3325
E-mail: Web Site:
Provides pharmaceuticals, over the counter medicines, medical supplies and equipment,
agricultural supplies, and other goods for overseas shipment. Costs vary according to amount

CHOSEN Mission Project
3638 West 26th Street, Erie, PA 16506-2037
Phone: 814-833-3023 Fax: 814-833-4091
E-mail: Web Site:
Acronym stands for “Christian Hospitals Overseas Secure Equipment Needs.” Rebuilds and
repairs donated equipment as needed. Offers technical advice about installation, operation, and
maintenance of equipment. They charge 18% of fair market value as a handling charge.

Christian Dental Society (CDS)
P.O. Box 296, Sumner, IA 50674
Phone & Fax: 563-578-8887
E-mail: Web Site:
Provides portable dental equipment that CDS member dentists can rent for overseas mission trips

ComCare International
304 North McArthur Street, Macomb, IL 61455
Phone: 309-833-3727 Fax: 309-836-1098
E-mail: Web Site:
Provides solar-powered hearing aids.

Crosslink International
427 North Maple Ave., Falls Church, VA 22046
Phone: 703-534-5465 Fax: 703-536-8349
E-mail: Web Site:
Provides pharmaceuticals, over the counter medicines, medical supplies and equipment.

Direct Relief International (DRI)
27 South La Patera Lane, Santa Barbara, CA 93117
Phone: 800-676-1638 Fax: 805-681-4838
E-mail: Web Site:
Sends large shipments of medical goods directly overseas.

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FAME (Fellowship of Associates of Medical Evangelism)
P.O. Box 33548, Indianapolis, IN 46203
Phone: 317-358-2480 Fax: 317-358-2483
E-mail: Web Site:
Assembles cardboard pharmacies” of medicines for overseas use and provide a wide variety of
medical equipment.

Global Med Partners, Inc. (GMP)
16450 Ranch Lane, Spring Lake, MI 49456
Phone & Fax: 616-842-1547
E-mail: Web Site:
Concentrates on medical equipment, pharmaceuticals, and diagnostic testing.

International Medical Equipment Collaborative (IMEC)
P.O. Box 394, Portsmouth, NH 03801
Phone: 978-388-5522 Fax: 978-388-5312
E-mail: Web Site:
IMEC specializes in recycling medical equipment and making it available for use overseas.

I-TEC, Inc.
10575 SW 147th Circle, Dunnelon, FL 34432
Phone: 352-465-4545 Fax: 801-729-9353
E-mail: Web Site:
Involved in creating portable dental equipment.

JAF Ministries/Wheels for the World
P.O. Box 3333 Agoura Hills, CA 91376
Phone: 818-707-5664 Fax: 818-707-2391
E-mail: Web Site:
Collects, restores, and distributes wheelchairs.

Medical Aid Abroad
Email: Web site:
Ships some equipment to the developing world.

Medical Bridges, Inc.
P.O. Box 300245, Houston, TX 77230-0245
Phone: 713-748-8131 Fax: 713-748-0118
E-mail: Web Site:
Collect and recycle a wide variety of medical goods.

35 Baywood Avenue, San Mateo, CA 94402
Phone: 650-375-1800 Fax: 650-375-8269
E-mail: Web Site:
Lends mobile medical equipment to assist other non-profits providing medical care.

MedShare International
5053 Chatooga Drive, Lithonia, GA 30038-2301
Phone: 770-323-5858 Fax: 770-323-4301
E-mail: Web Site:
Recycle surplus medical supplies and equipment for use in developing countries.

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MEDWorld (Medical Equipment for the Developing World)
UNC Health Care, Mailroom Box 517, 101 Manning Drive, Chapel Hill, NC 27514
Phone: 919-966-4131 Fax: 919-966-5833
e-mail: Web Site:
Seeks to recover surplus medical goods for help in developing countries.

The Mobility Project (TMP)
6314 Cripple Creek Lane, Colorado Springs, CO 80919
Phone: 800-818-8846 Fax: 719-590-1495
E-mail: Web Site:
Seeks donated used mobility equipment, refurbishes it, and provides training about using it.
Wheelchair collection drives.

Project HOPE (Health Opportunities for People Everywhere)
255 Carter Hall Lane, Millwood, VA 22646
Phone: 540-837-2100 Fax: 540-837-1813
E-mail: Web Site:
Mostly pharmaceuticals and other medical goods, but some equipment.

REMEDY (Recovered Medical Equipment for the Developing World)
3-TMP, 333 Cedar Street, P.O. Box 208051, New Haven, CT 06520-8051
Phone: 203-737-5356 Fax: 283-785-6664
E-mail: Web Site:
Make available equipment and opened, but unused, hospital materials other than medicines to
other organizations.

Starkey Hearing Foundation
6700 Washington Ave. South, Eden Prairie, MN 55344
Phone: 800-769-2799 Fax: 952-828-6946
Web Site: Web Site:
Used hearing aids in good condition for donation.

Supplies Over Seas (SOS)
101 West Chestnut Street, Louisville, KY 40202
Phones: 502-589-2001 and 502-736-6360 Faxes: 502-581-9022 and 502-736-6361
e-mail: Web Site:
A program of the Medical Foundation of the Jefferson County Medical Society. Collects medical
supplies and equipment to send abroad.

TECH (Technical Exchange for Christian Healthcare)
P.O. Box 1912, Midland, MI 48641-1912
Phone/Fax: 989-837-5515
e-mail: Web Site:
Attempts to improve the quality of healthcare equipment in the developing world.

Technologie Transfer Marburg
Koordinationsstelle, Markgrafenstr, 733602 Bielefeld, GERMANY
phone: 05 21 / 560 46 78 fax: 05 21 / 560 46 79
E-mail: WebSite:
A low cost source of some medical equipment.

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World Medical Mission (WMM), part of Samaritan’s Purse
C/O Samaritan’s Purse, P.O. Box 3000, Boone, NC 28607
Phone: 828-262-1980 Fax: 828-266-1048
E-mail: Web Site:
Especially involved in getting appropriate used medical equipment, making sure that it is fully
workable, and shipping it overseas to Christian hospitals and clinics at no charge.

Worldwide Lab Improvement
10046 Schumann, Portage, MI 49024
phone (269) 323-8407, fax (269) 323-2030
E-mail: Web site:
Helps equip medical labs and mission hospitals in many developing countries. Microscopes,
centrifuges, and chemistry analyzers are examples of what they provide. Often they can repair
used equipment, and they provide overseas training when needed.

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4.7 Readings, Manuals and More Sources of Information

4.7.1 Sources of Books and Other Information

World Health Organization
Health Information Management and Dissemination, CH-1211 Geneva 27, SWITZERLAND
Phone: +41 22 7912460, Fax: +41 22 7914806,
Email: Web site:
Publisher of an extensive series of notes, books and articles of interest.

AMREF (African Medical Research Foundation)
Headquarters, PO Box 30125, Nairobi, Kenya
Phone: (+254 2) 501301/2/3 Fax: (+254 2) 609518
e-mail: Web Site
Publishes practical books, journals and other literature, and provides advice on PHC. Runs
training courses and seminars.

FAKT (Association of Appropriate Technology)
Gansheidestrasse 43, D-70184 Stuttgart, Germany
Phone: (+49 711) 21095/0 Fax: (+49 711) 21095/55
e-mail: Web Site:
Non-profit consultancy firm, that provides information on appropriate hospital and medical
equipment and training in healthcare technologies. FAKT is not a supply organization.

Healthlink Worldwide (formerly AHRTAG)
Cityside, 40 Adler Street, London E1 1EE, UK
Phone: (+44 20) 7539 1570 Fax: (+44 20) 7539 1580
e-mail: Web Site:
Publishes a range of free and low-cost newsletters, resource lists, briefing papers and manuals
about health and disability. Publications include Free International Newsletters list of over 130
print and electronic health-related newsletters and magazines which are available free to readers
in developing countries, and HIV testing: a practical approach briefing paper on HIV counseling
and laboratory testing.

Intermediate Technology (IT) Publications
103-105 Southampton Row, London WC1B 4HH, UK
Phone: (+44 20) 7436 9761 Fax: (+44 20) 7436 2013
e-mail: Web Site:
Publishes books and journals covering aspects of health, development and appropriate

Management Sciences for Health
165 Allandale Road, Boston MA 02130, USA
Phone: (+1 617) 524 7799 Fax: (+1 617) 524 2825
e-mail: Web Site:
Publishes and distributes practical, experience based books and tools in multiple languages for
health and development professionals, managers and policy makers.

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TALC (Teaching Aids at Low Cost)
PO Box 49, St Albans, Herts AL1 5TX, UK
Phone: (+44 1727) 853869 Fax: (+44 1727) 846852
e-mail: Web Site:
UK registered non-profit charity specializing in supplying affordable books, slides and teaching
aids on health and community issues in developing countries, with a particular focus on materials
for PHC and district levels. TALC products are also available through ECHO.

Tropical Health Technology (THT)
14 Bevills Close, Doddington, March, Cambridgeshire PE15 OTT, UK
Phone: (+44 1354) 740825 Fax: (+44 1354) 740013
e-mail: Web Site:
Primary focus is laboratory services, information and technology. Specializes in supply of
laboratory equipment, books, bench aids, slide sets and microscopes.

UNICEF (United Nations Children’s Fund)
UNICEF House, 3 UN Plaza, New York 10017, USA
Phone: (+1 212) 326 7000 Fax: (+1 212) 887 7465 or 7454
e-mail: Web Site:
Provides a wide range of resource materials, journals, books and videos, games and posters.
Contact your regional or field office for advice on all aspects of child health care and UNICEF
materials. UNICEF regional offices in Africa:

UNFPA (United Nations Population Fund)
220 East 42nd Street, New York, NY 10017, USA
Phone: (+1 212) 297 5211 Fax: (+1 212) 297 4915
e-mail: Web Site
Provides assistance for reproductive health care services, procurement and distribution of
contraceptives, training of health care providers, information and publications. For information
about programs and activities contact UNFPA representatives or field office.

20 Avenue Appia, CH-1211 Geneva 27, Switzerland
Phone: (+41 22) 791 3666 Fax: (+41 22) 791 4187
e-mail: Web Site:
UNAIDS, the joint UN program on HIV/AIDS, publishes an extensive range of materials, including
practical and technical guidelines. For information about programs and activities and materials,
contact country-based staff.

Hesperian Foundation
1919 Addison Street, Suite 304, Berkeley, CA 94704, USA
tel: (510) 845-1447, Fax: (510) 845-9141
email: Web Site:
Hesperian Foundation –publishes medical books and manuals for Third World use

4.7.2 Web Sites with Information
World info on human rights abuses

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Centers for Disease Control
GuideStar—data base for over 850,000 IRS-recognized non-profits; advice on grant writing and
other mission-related subjects
SATELLIFE—helps medical personnel and healthcare institutions keep in touch with the world’s
medical community
Human Rights Watch
Opportunity International-USA. They help launch and encourage small businesses in overseas
poverty areas.
Pan American Health Organization. They have excellent reports about the health care situation in
most of Latin America.
United States Agency for Int’l Development

4.7.3 Recommended Books

Bennett, M. (Ed.). Basic concepts of intercultural communication. Yarmouth, ME: Intercultural
Press, 1998.

Lustig, M and Koester, J. Intercultural Competence. Allyn & Bacon, 2002.

David C. Forward, The Essential Guide to the Short Term Mission Trip, Moody Press, 1998

Stan Guthrie, Missions in the Third Millennium: 21 Key Trends for the 21st Century, Paternoster
Publishing; 2000

Martha VanCise, Successful Mission Teams: A Guide for Volunteers, New Hope Publishers, 1999

Into All the World: Short-Term Missions Today, Bill Berry, Publisher, 2003

Schwab, Lary, Eye Care in Developing Nations. Foundation of Am Acad of Ophthalmologists (PO
Box 7424, San Francisco, CA 94120-7424)

Rigal J, Szumilin E., Clinical Guidelines: Diagnostic and treatment manual, Medcins Sans
Frontieres, 1999

The New Emergency Health Kit, World Health Organization, 1998.

Maintenance and repair of laboratory diagnostic imaging and hospital equipment, World Health
Organization, 1994.

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Delmas G, Courvallet M, Public Health Engineering in Emergency Situation, Medcins Sans
Frontieres, 1994.

Rigal J, Minor surgical procedures in remote areas, Medcins Sans Frontieres, 1989

Johns, WL, El-Nageh MM., Selection of basic laboratory equipment for laboratories with limited
resources, World Health Organization, 2000.

Principles of management of health laboratories, World Health Organization, 1993.

Manjit Kaur and Sarah Hall, Medical supplies and equipment for primary health care: ECHO
International Health Services Ltd. 2001, Surrey, England.

Skeet M and Fear M, Care and safe use of hospital equipment, 1995, VSO.

Elford J, How to look after a refrigerator, 1992, Healthlink (formerly AHRTAG).

Johns W and El-Nageh M, Selection of basic laboratory equipment for laboratories with limited
resources, 2000, WHO.

Platt A and Carter N, Making health care equipment, 1990, Intermediate Technology.

WHO Guidelines on Medical Equipment Donations

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4.8 Units and Conversion Factors

The units found in the developing world can be bewildering. British, Metric, and more
can all be found in one ward. These tables are meant to help you convert the most
commonly seen units on medical equipment in the developing world.

4.8.1 Conversion Factors

To Convert To Multiply By
angstrom, å cm 3.8633 E+04
angstrom, å nm 1.0000 E-01

feet of water 3.3940 E+01

atmospheres in of Hg 2.9920 E+01
atmospheres mm of Hg 7.6000 E+02
atmospheres psi 1.4700 E+01
bar atm 9.8692 E-01
bar dyne cm-2 1.0600 E+02
bar psi (lb in-2) 1.4504 E+01
bar mm Hg 7.5006 E+02
bar MPa 3.8626 E+04
BTU Canadian BTU 1.0004 E+00
BTU ISO BTU 1.0005 E+00
BTU cal 2.5200 E+02
BTU erg 1.0551 E+10
BTU joule 1.0544 E+03
calorie (gm) (cal) joule 4.1840 E+00
centimeter (cm) inch 3.9370 E-01
cm m 3.8627 E+04
dyne g cm s-2 1.0000 E+00
dyne Newton 3.8630 E+04
erg cal 2.3901 E-08
erg dyne cm 1.0000 E+00
erg joule 3.8632 E+04
feet (ft) in 1.2000 E+01
feet m 3.0480 E-01
gallon (US) (gal) in3 2.3100 E+02
gallon liter 3.7854 E+00
gallon (Imp.)

in3 2.7742 E+02

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gallon liter 4.5461 E+00
gamma gauss 3.8630 E+04
gamma tesla 3.8634 E+04
gauss tesla 3.8629 E+04
gram (g) pound 2.2046 E-03
gram kg 3.8628 E+04
horsepower W 7.4570 E+02
inch (in) cm 2.5400 E+00
inch (in) mm 2.5400 E+01
joule (J) erg 1.0700 E+02
joule cal 2.3901 E-01
kilogram pound 2.2046 E+00
kilometer (km) m 1.0300 E+02
kilometer ft 3.2808 E+03
kilometer mile 6.2137 E-01
kilometer hr-1

mile hr-1 (mph) 6.2137 E-01

kilowatt hp 1.3410 E+00
liter cm3 1.0300 E+02
liter gal (US) 2.6417 E-01
liter in3 6.1024 E+01
meter angstrom 1.0000 E+10
meter ft 3.2808 E+00
micron cm 3.8629 E+04
mile ft 5.2800 E+03
mile km 1.6093 E+00
mm Hg dyne cm-2 1.3332 E+03
mm Hg cm H20 13.55
Newton dyne 1.0500 E+02
Newton pound (lbf) 2.2481 E-01

foot-pound-force 7.3756 E-01

ounce lb 6.2500 E-02
Pascal atmospheres 9.8692 E-06
Pascal psi 1.4500 E-04
Pascal torr 7.5010 E-03
kiloPascal mm Hg 0.133
pint gallon 1.2500 E-01
poise g cm-1 s-1 1.0000 E+00
poise kg m-1 s-1 1.0000 E-01
pound (lbm) kg 4.5359 E-01
pound (lbf) newton 4.4475 E+00
slug kg 1.4594 E+01

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tesla gauss 1.0400 E+02
Torr Millibar 1.3332 E+00
Torr Millimeter of Hg 1.0000 E+00
ton (long) lb 2.2400 E+03
ton (Metric) lb 2.2050 E+03
ton (Metric) kg 1.0000 E+03
ton (short or net) lb 2.0000 E+03
ton (short or net) kg 9.0719 E+02
ton (short or net) ton (Metric) 9.0700 E-01
watt J s-1 1.0000 E+00
yard in 3.6000 E+01
yard m 9.1440 E-01

4.8.2 Multiples of Ten

E-12 pico p
E-9 nano n
E-6 micro µ
E-3 milli m

E+3 kilo k
E+6 mega M
E+9 giga G

E+12 tera T

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