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EquipmentPacket:AnesthesiaMachineUMDNS#:10134DateofCreation:September8,2015Creator:CompliedbyCassandraStancoforEngineeringWorldHealth(EWH)EquipmentPacketContents:Thispacketcontainsinformationabouttheoperation,maintenance,andrepairofanesthesiamachines.PartI:ExternalFromthePacket: 1. AnIntroductiontoAnesthesiaMachines(PowerPoint)PartII:IncludedinthisPacket: 1. OperationandUse:a. BriefOverviewofAnesthesiaUnits(p.3)b. PrinciplesandUseofAnesthesiaMachines(p.4-10)c. IntroductiontoPulseOximetry(p.11-14)2. DiagramsandSchematics:a. Figure1:ComponentsofaGasSupplySubsystem(p.16)b. Figure2:ScavengingSubsystem(p.17)c. Figure3:PatientVentilationandScavengingSystems(p.18)d. Figure4:AnesthesiaMachineOverview(p.19)e. Figure5:PinIndexSystem(p.19)f. Figure6:SafetyValves(p.20)g. Figure7:ConnectorsandTheirSafetyMechanisms(p.20)h. Figure8:OxygenFailureWarningDevices(p.21)i. Figure9:SafeandUnsafeFlowMeters(p.22)j. Figure10:WHOSpecificationforAnesthesiaVentilators(p.23-27)3. PreventativeMaintenanceandSafety:a. HowtoCheckAnestheticEquipmentBeforeUse(p.29-31)b. AnesthesiaMachineSafetyChecklist(p.32)c. AnesthesiaMachinePreventativeMaintenanceChecklist(p.33)4. TroubleshootingandRepair:a. AnesthesiaMachineTroubleshootingTable(p.35)b. RisksAssociatedwithAnesthesiaMachines(p.36)5. ResourcesforMoreInformationa. ResourcesforMoreInformation(p.38)b. Bibliography(p.39)

1. Operation*and*Use**of*Anesthesia*Machines****Featured*in*this*Section:***)*Malkin,)R.)“Anesthesia)Machines,”)From)the)publication:)Medical)Instruments)in)the)Developing)World.)Engineering)World)Health,)2006.))))WHO.)“Anesthesia)Unit,”)From)the)publication:)Core(Medical(Equipment.)Geneva,)Switzerland,)2011.)) ))Wikipedia.)“Pulse)Oximetry.”)Wikipedia,)pgs.)1a4.)Retrieved)from:)* *
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n Health problem addressed

Anesthesia units dispense a mixture of gases and vapors and
vary the proportions to control a patient’s level of consciousness
and/or analgesia during surgical procedures.

Product description
An anesthesia system comprises of a gas delivery platform,
a data analysis and distribution system, and physiologic and
multigas monitors (optional in most units), which indicate levels
and variations of several physiologic variables and parameters
associated with cardiopulmonary function and/or gas and
agent concentrations in breathed-gas mixtures. Manufacturers
typically offer a minimum combination of monitors, alarms, and
other features that customers must purchase to meet standards
and ensure patient safety.

Principles of operation
Because O2 and N2O are used in large quantities, they are usually
drawn from the hospital’s central gas supplies. Vaporizers add a
controlled amount of anesthetic vapor to the gas mixture. An
automatic ventilator is generally used to mechanically deliver
breaths to the patient. The ventilator forces the anesthesia gas
mixture into the patient’s breathing circuit and lungs and, in a
circle breathing system, receives exhaled breath from the patient
as well as fresh gas. A scavenging system captures and exhausts
waste gases to minimize the exposure of the operating room
staff to harmful anesthetic agents. Scavenging systems remove
gas by a vacuum, a passive exhaust system, or both.

Operating steps
A mask is placed over the nose and mouth. The anesthesia
unit dispenses a mixture of gases and vapors and varies the
proportions to control a patient’s level of consciousness
and/or analgesia during surgical procedures. The patient is
anesthetized by inspiring a mixture of O2, the vapor of a volatile
liquid halogenated hydrocarbon anesthetic, and, if necessary,
N2O and other gases.

Reported problems
One of the greatest dangers of anesthesia is hypoxia, which
can result in brain damage or death, though the administration
of concentrated O2 (100%) may be toxic. Gas with excessive
CO2 concentration, an inadequate amount of anesthetic agent,
or dangerously high pressure may cause hypoventilation,
compromised cardiac output, pneumothorax, and asphyxiation.
Contamination of the anesthesia breathing circuit may lead to
nosocomial infections.

Use and maintenance
User(s): Anesthesiologist, nurse anesthetist,
medical staff

Maintenance: Biomedical or clinical engineer/
technician, medical staff, manufacturer/

Training: Initial training by manufacturer,
operator’s manuals, user’s guide, some
manufacturers offer offsite training or remote

Environment of use
Settings of use: Hospital (surgery),
ambulatory surgery centers

Requirements: Uninterruptible power source,
O2 fail-safe and hypoxic mixture fail-safe
systems, gas cylinder yokes for O2 if central
supplies fail, internal battery (for units with
automatic ventilators) capable of powering
the unit for at least 30 minutes

Product specifi cations
Approx. dimensions (mm): 1,500 x 700 x 700

Approx. weight (kg): 130

Consumables: Anesthetic agents, tubing,

Price range (USD): 5,000 - 100,000

Typical product life time (years): 8-10

Shelf life (consumables): Variable

Types and variations
Cart mounted, ceiling mounted, wall mounted,

Anesthesia Unit
10134 Anesthesia Units 47769 Anaesthesia unit, mobile

Other common names:
Anesthesia machines; Anaesthesia apparatus; Gas-machine, anesthesia

Equipment found in the OR, ICU and ER

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.

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.

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 whoever is available.

Malkin, R. “Anesthesia Machines,” From the publication: Medical Instruments in

the Developing World. Engineering World Health, 2006.

Principles and Use of Anesthesia Machines


Medical Instruments in the Developing World Malkin

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.

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

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.

Malkin, R. “Anesthesia Machines,” From the publication: Medical Instruments in

the Developing World. Engineering World Health, 2006.


Equipment found in the OR, ICU and ER

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.

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

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.

Malkin, R. “Anesthesia Machines,” From the publication: Medical Instruments in

the Developing World. Engineering World Health, 2006.


Medical Instruments in the Developing World Malkin

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 not
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.

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.

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
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

Malkin, R. “Anesthesia Machines,” From the publication: Medical Instruments in

the Developing World. Engineering World Health, 2006.


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.

Malkin, R. “Anesthesia Machines,” From the publication: Medical Instruments in

the Developing World. Engineering World Health, 2006.


Equipment found in the OR, ICU and ER

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 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 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 circuit.

Malkin, R. “Anesthesia Machines,” From the publication: Medical Instruments in

the Developing World. Engineering World Health, 2006.


Medical Instruments in the Developing World Malkin

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

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.

Malkin, R. “Anesthesia Machines,” From the publication: Medical Instruments in

the Developing World. Engineering World Health, 2006.


Pulse oximetry 1

Pulse oximetry

Pulse Oximeter

Pulse oximetry (or ~ oxymetry in the UK) is a non-invasive
method allowing the monitoring of the oxygenation of a patient's

A sensor is placed on a thin part of the patient's body, usually a
fingertip or earlobe, or in the case of a neonate, across a foot, and a
light containing both red and infrared wavelengths is passed from
one side to the other. Changing absorbance of each of the two
wavelengths is measured, allowing determination of the
absorbances due to the pulsing arterial blood alone, excluding
venous blood, skin, bone, muscle, fat, and (in most cases)
fingernail polish.[1] Based upon the ratio of changing absorbance
of the red and infrared light caused by the difference in color between oxygen-bound (bright red) and
oxygen-unbound (dark red or blue, in severe cases) blood hemoglobin, a measure of oxygenation (the per cent of
hemoglobin molecules bound with oxygen molecules) can be made.

Pulse oximetry data is necessary whenever a patient's oxygenation may be unstable, as in intensive care, critical care,
and emergency department areas of a hospital. Data can also be obtained from pilots in unpressurized aircraft,[2] and
for assessment of any patient's oxygenation in primary care. A patient's need for oxygen is essential to life; no human
life thrives in the absence of oxygen (cellular or gross). Although pulse oximetry is used to monitor oxygenation, it
cannot determine the metabolism of oxygen, or the amount of oxygen being used by a patient. For this purpose, it is
necessary to also measure carbon dioxide (CO2) levels. It is possible that pulse oximetry can also be used to detect
abnormalities in ventilation. However, detection of hypoventilation is impaired by the use of supplemental oxygen,
as it is only when patients breathe room air that abnormalities in respiratory function can be detected reliably.
Therefore, the routine administration of supplemental oxygen may be unwarranted if the patient is able to maintain
adequate oxygenation in room air, since it can result in hypoventilation going undetected.

In 1935 Matthes developed the first 2-wavelength ear O2 saturation meter with red and green filters, later switched to
red and infrared filters. This was the first device to measure O2 saturation.

In 1949 Wood added a pressure capsule to squeeze blood out of ear to obtain zero setting in an effort to obtain
absolute O2 saturation value when blood was readmitted. The concept is similar to today's conventional pulse
oximetry but was hard to implement because of unstable photocells and light sources. This method is not used
clinically. In 1964 Shaw assembled the first absolute reading ear oximeter by using eight wavelengths of light.
Commercialized by Hewlett Packard, its use was limited to pulmonary functions and sleep laboratories due to cost
and size.

Pulse oximetry was developed in 1974, by Takuo Aoyagi and Michio Kishi, bioengineers, at Nihon Kohden using
the ratio of red to infrared light absorption of pulsating components at the measuring site. Susumu Nakajima, a
surgeon, and his associates first tested the device in patients, reporting it in 1975.[3] It was commercialized by Biox
in 1981 and Nellcor in 1983. Biox was founded in 1979, and introduced the first pulse oximeter to commercial
distribution in 1981. Biox initially focused on respiratory care, but when the company discovered that their pulse
oximeters were being used in operating rooms to monitor oxygen levels, Biox expanded its marketing resources to

Pulse oximetry 2

focus on operating rooms in late 1982. A competitor, Nellcor (now part of Covidien, Ltd.), began to compete with
Biox for the US operating room market in 1983. Prior to its introduction, a patient's oxygenation could only be
determined by arterial blood gas, a single-point measurement that takes a few minutes of processing by a laboratory.
(In the absence of oxygenation, damage to the brain starts within 5 minutes with brain death ensuing within another
10–15 minutes). In the US alone, approximately $2 billion was spent annually on this measurement. With the
introduction of pulse oximetry, a non-invasive, continuous measure of patient's oxygenation was possible,
revolutionizing the practice of anesthesia and greatly improving patient safety. Prior to its introduction, studies in
anesthesia journals estimated US patient mortality as a consequence of undetected hypoxemia at 2,000 to 10,000
deaths per year, with no known estimate of patient morbidity.

By 1987, the standard of care for the administration of a general anesthetic in the US included pulse oximetry. From
the operating room, the use of pulse oximetry rapidly spread throughout the hospital, first to the recovery room, and
then into the various intensive care units. Pulse oximetry was of particular value in the neonatal unit where the
patients do not thrive with inadequate oxygenation, but also can be blinded with too much oxygen. Furthermore,
obtaining an arterial blood gas from a neonatal patient is extremely difficult.

By 2008, the accuracy and capability of pulse oximetry had further improved, and had allowed for the adoption of
the term high resolution pulse oximetry (HRPO).[4] [5] [6] One area of particular interest is the use of pulse oximetry
in conducting portable and in-home sleep apnea screening and testing.[4] [7]

In 2009, the world's first Bluetooth-enabled fingertip pulse oximeter was introduced by Nonin Medical, enabling
clinicians to remotely monitor patients’ pulses and oxygen saturation levels. It also allows patients to monitor their
own health through online patient health records and home telemedicine system.[8]

Pulse oximetry measures solely of oxygenation, not ventilation, and it is not a substitute for blood gases checked in a
laboratory because it gives no indication of base deficit, carbon dioxide levels, blood pH, or bicarbonate HCO3-
concentration. The metabolism of oxygen can be readily measured by monitoring expired CO2. Saturation figures
also give no information about blood oxygen content. Most of the oxygen in the blood is carried by hemoglobin. In
severe anemia, the blood will carry less total oxygen, despite the hemoglobin being 100% saturated.

Falsely low readings may be caused by hypoperfusion of the extremity being used for monitoring (often due to the
part being cold or from vasoconstriction secondary to the use of vasopressor agents); incorrect sensor application;
highly calloused skin; and movement (such as shivering), especially during hypoperfusion. To ensure accuracy, the
sensor should return a steady pulse and/or pulse waveform. Falsely high or falsely low readings will occur when
hemoglobin is bound to something other than oxygen. In cases of carbon monoxide poisoning, the falsely high
reading may delay the recognition of hypoxemia (low blood oxygen level). Methemoglobinemia characteristically
causes pulse oximetry readings in the mid-80s. Cyanide poisoning can also give a high reading because it reduces
oxygen extraction from arterial blood (the reading is not false, as arterial blood oxygen is indeed high in early
cyanide poisoning).

Pulse oximetry only reads the percentage of bound hemoglobin. Hemoglobin can be bound to other gases such as
carbon monoxide and still read high even though the patient is hypoxemic. The only noninvasive methodology that
allows for the continuous and noninvasive measurement of the dyshemoglobins is a pulse co-oximeter. Pulse
co-oximetry was invented in 2005 by Masimo and currently allows clinicians to measure total hemoglobin levels in
addition to carboxyhemoglobin, methemoglobin and PVI, which initial clinical studies have shown may provide
clinicians with a new method for noninvasive and automatic assessment of patient fluid volume status.[9] [10] [11]

Appropriate fluid levels are vital to reducing postoperative risks and improving patient outcomes as fluid volumes
that are too low (under hydration) or too high (over hydration) have been shown to decrease wound healing, increase
risk of infection and cardiac complications.[12]

Pulse oximetry 3

See also
• Oxygen sensor

• Oxygen saturation

• Pulse oximeter

• Capnography, measuring of carbon dioxide (CO
) in the respiratory gases

• Sleep Apnea

• Integrated Pulmonary Index

External links
• iPleth: Pulse oximetry on a cell phone for the developing world [13]

[1] Brand TM, Brand ME, Jay GD. Enamel nail polish does not interfere with pulse oximetry among normoxic volunteers (http:/ / www. ncbi.

nlm. nih. gov/ entrez/ query. fcgi?cmd=Retrieve& db=pubmed& list_uids=12212998) J Clin Monit Comput. 2002 Feb;17(2):93-6.
[2] WAGNER Jessica L. ; RUSKIN Keith J. Pulse oximetry : Basic principles and applications in aerospace medicine. Aviation, space, and

environmental medicine 2007, vol. 78, no10, pp. 973-978

[3] John W. Severinghaus, MD,and Yoshiyuki Honda, MD: HISTORY OF BLOOD GAS ANALYSIS. VII. PULSE OXlMETRY "History of Pulse
Oximetry" (http:/ / www. masimo. com/ Nellcorfiction/ PDF_FF/ History of Pulse Oximetry. pdf)

[4] http:/ / www. sleepreviewmag. com/ issues/ articles/ 2008-04_10. asp

[5] http:/ / www. maxtecinc. com/ assets/ docs/ pulsox/ ml187. p300iDataSheet. pdf

[6] http:/ / www. anesthesiology. org/ pt/ re/ anes/ fulltext. 00000542-200809000-00004. htm

[7] http:/ / www. post-gazette. com/ pg/ 08009/ 847751-114. stm

[8] "Tekne Awards Announced" (http:/ / www. startribune. com/ blogs/ 65775732.

html?elr=KArks7PYDiaK7DUdcOy_nc:DKUiD3aPc:_Yyc:aUU). Star Tribune. . Retrieved 2009-10-23.
[9] Keller G, Cassar E, Desebbe O, Lehot JJ, Cannesson M (2008). "Ability of pleth variability index to detect hemodynamic changes induced by

passive leg raising in spontaneously breathing volunteers" (http:/ / www. pubmedcentral. nih. gov/ articlerender. fcgi?tool=pmcentrez&

artid=2447559). Crit Care 12 (2): R37. doi:10.1186/cc6822. PMID 18325089. PMC 2447559.
[10] Cannesson M, Delannoy B, Morand A, et al. (April 2008). "Does the Pleth variability index indicate the respiratory-induced variation in the

plethysmogram and arterial pressure waveforms?". Anesth. Analg. 106 (4): 1189–94, table of contents. doi:10.1213/ane.0b013e318167ab1f.
PMID 18349191.

[11] Cannesson M, Desebbe O, Rosamel P, et al. (August 2008). "Pleth variability index to monitor the respiratory variations in the pulse
oximeter plethysmographic waveform amplitude and predict fluid responsiveness in the operating theatre". Br J Anaesth 101 (2): 200–6.
doi:10.1093/bja/aen133. PMID 18522935.

[12] Ishii M, Ohno K (March 1977). "Comparisons of body fluid volumes, plasma renin activity, hemodynamics and pressor responsiveness

between juvenile and aged patients with essential hypertension". Jpn. Circ. J. 41 (3): 237–46. PMID 870721.
[13] http:/ / ecem. ece. ubc. ca/ research. htm#iPleth

Article Sources and Contributors 4

Article Sources and Contributors
Pulse oximetry  Source:  Contributors: Academic Challenger, Almazi, Apollo the Archer, Ariel., Beelaj., Bemoeial, Chewkoh, Choij,
Clannum, CoyneT, Curps, Dana boomer, Darkwolf325, Davidruben, Dforester, Dkazdan, Doctortomwiki, Draeco, DreamsReign, DuLithgow, ESkog, Elkman, Everyking, Folajimi, FrancoGG,
GK tramrunner, Hu12, Inoculatedcities, IronLung2533, Jaksmata, Jengod, Jfdwolff, Jgoldman, Joe Brigen, JoeBrigen, Karensams, Kbdank71, Kintetsubuffalo, Lukobe, M.clare.smith, Mccallusa,
Medicaltechwriter, Moxy, Mr Bungle, NellcorPro, Nono64, Orangemarlin, Piano non troppo, ProspectHCH, Rdarwin, Rettetast, Rich Farmbrough, Rjwilmsi, Rsabbatini, SarekOfVulcan,
Scientificone, Smuseby, TaintedMustard, Ujalm, VEA Tim, VanGore, WhatamIdoing, Wiki Jibiki, WikiScience1, Wormholio, 84 anonymous edits

Image Sources, Licenses and Contributors
File:Pulse oxi.JPG  Source:  License: GNU Free Documentation License  Contributors: Tom Mallinson

Creative Commons Attribution-Share Alike 3.0 Unported
http:/ / creativecommons. org/ licenses/ by-sa/ 3. 0/

*2.*Diagrams*and*Schematics*of*Anesthesia*Machines****Featured*in*this*Section:*****Chan,)A.)Biomedical(Device(Technology:(Principles(and(Design.)Charles)C.)Thomas)Publisher:)USA)(2008).) ))Subrahmanyam,)M.)and)Mohan,)S.)“Safety)Features)in)Anesthesia)Machine.”)Indian(Journal(of(Anesthesia,)Vol.)57,)No.)5)(2013),)p.)472a480.)**WHO.)“Anaesthesia)Ventilator.”)From)the)publication:)“WHO)Technical)Specifications)for)61)Medical)Devices.)WHO.)Retrieved)from:)* * *

Chan, A. Biomedical Device Technology: Principles and Design.

Charles C. Thomas Publisher: USA (2008).

Figure 1: Components of a Gas Supply and Control



Chan, A. Biomedical Device Technology: Principles and Design.

Charles C. Thomas Publisher: USA (2008).

Figure 2: Scavenging Subsystem


Chan, A. Biomedical Device Technology: Principles and Design.

Charles C. Thomas Publisher: USA (2008).

Figure 3: Patient Ventilation and Scavenging Systems


The high, intermediate and low-pressure systems of the anaesthesia machine

Figure 2

The pin index system and its components

Figure 3

Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia

Machine.” Indian Journal of Anesthesia, Vol. 57, No. 5 (2013), p. 472-480.

Figure 4: Anesthesia Machine Overview

Figure 5: Pin Index System


Safety valves

Figure 4

Different connectors and their safety mechanisms

Figure 5

Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia Machine.” Indian Journal

of Anesthesia, Vol. 57, No. 5 (2013), p. 472-480.

Figure 6: Safety Valves

Figure 7: Connectors and Their Safety Mechanisms


Non-interchangeable screw thread

Figure 6

Oxygen failure warning devices

Figure 7

Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia Machine.” Indian Journal

of Anesthesia, Vol. 57, No. 5 (2013), p. 472-480.

Figure 1: Components of a Gas Supply and Control


Figure 8: Oxygen Failure Warning Devices


Potential unsafe and safe arrangements of flow meter tubes

Figure 8

Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia Machine.” Indian Journal

of Anesthesia, Vol. 57, No. 5 (2013), p. 472-480.

Figure 9: Safe and Unsafe Flow Meter Tubes


12/20/15 WHO_TS_61_MDs_web.xlsx 02

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i Version No. 1ii Date of initial version 6/13/12iii Date of last modification 6/18/14iv Date of publicationv Done by WHO working group1 WHO Category / Code (under development)2 Generic name Anaesthesia ventilator3 Specific type or variation (optional) Alone or as a part of anesthesia machine4 GMDN name Anaesthesia ventilator5 GMDN code 348516 GMDN category 02 Anaesthetic and respiratory devices 7 UMDNS name Ventilators, Anesthesia8 UMDNS code 101459 UNSPS code (optional)10 Alternative name/s (optional) Ventilator; Anaesthesia unit ventilator; Anesthesia ventilator11 Alternative code/s (optional) MS 42251; S 10145; S 3632512 Keywords (optional) Anesthesia machines, Anesthesia Units, Acute Care, Respired/Anesthetic
13 GMDN/UMDNS definition (optional)

A mains electricity (AC-powered) stand-alone, automatic cycling device used to assist and control alveolar ventilation during general anaesthesia, and is compatible with inhaled anaesthetic agents. It has fewer functions and is less complex to operate than an intensive care ventilator, but adequately meets the patient's ventilation needs for oxygen (O2) and carbon dioxide (CO2) exchange to maintain normal blood gas concentrations. The device provides a mechanical means to deliver the breathing gas to the patient in a controlled pattern, and is equipped with alarms to warn of changes in respiration or the onset of unsafe operating conditions.
14 Clinical or other purpose Provides a mechanical means to deliver the breathing gas to the patient in a controlled pattern, and is equipped with alarms to warn of changes in respiration or the onset of unsafe operating conditions. Ventilators designed to use positive pressure to deliver a prescribed mixture of respiratory and anesthetic gases and vapors to the patient's lungs during surgical procedures that require general anesthesia15 Level of use (if relevant) District Hospital, Provincial Hospital, Specialized Hospital, General Hospital16 Clinical department/ward(if relevant) Surgery (Operating theatre, Operating room)17 Overview of functional requirements Dispenses a controlled mixture of anaesthetic agents (externally supplied), oxygen and air to the patient, gives artificial respiratory support as necessary, fully alarmed with all necessary monitors for continuous operation in operating theatre environment, includes compressor, nebulizer and humidifier, reusable, sterilizable patient masks and connectors, suitable for all ages and body weights of patient, provides port for linkage with ************* anaesthetic delivery system.

MEDICAL DEVICE SPECIFICATION(Including information on the following where relevant/appropriate, but not limited to)



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Detailed requirements The unit must be able to measure O2 concentration, airway pressure, and the volume of expired gas. Trend display facility for at least the last 8 hours, with minimum 5 minutes resolutionAutomatic compliance and leakage compensation for circuit and tubes. Closed circuit system with possibility to work in open circuit.Externally supplied anaesthetic gas, oxygen and air mixture ratios fully controllable (mixing system selector for Air-O2 and N2O-O2 gasses mixture management) Expiratory block should be autoclavable and no routine calibration required.Should have the ability to calculate intrinsic PEEP Volume, occlusion pressure and inflection points. Circle breathing circuit to be included, with CO2 absorption chamberNebuliser to deliver particle size of < 3 micron and to be used in both offline and online modes.Automatic patient detection facility preferable. Minimum oxygen enrichment not lower than 25%.Inlet gas supply (O2 / N2O) pressure range at least 35 to 65 psi. Gas supply gauges required, with scales allowing easy reading. Gasses pressure system continuous control with accuracy of at least +/- 10%.At least four analog rotameters (two for oxygen, one for air and one for N2O) with programmed parameters visualization. Digital rotameters are not accepted.Rotameters flow rate range not smaller than 0.0 to 10.0 l/min and resolution at least of 0.2 l/min. Minute volume 2 to 25 L/minute. Tidal volume 20 to 1500ml. Respiratory rate 5 to 70 cycles/minute. Respiratory rate 5 to 70 cycles/minute. I/E ratio 2/1 to 1/4. Inspiration pressure 0 to 80mbar. Peak inspiratory flow 0 to 60 L/minute. Trigger sensitivity 0 to 20mbar. At least the following safety systems:a) oxygen-N2O gasses mixture guaranteed with not less than 25% of Oxygen;b) oxygen leakage or low pressure alarm with simultaneous stop of N2O gas delivery; c) adjustable Pressure Limiting (APL) valve to prevent from too high pressure gas delivering; d) compressed Air leakage or low pressure alarm with automatic passage of the units using air to the oxygen alimentation;e) system safety measure to prevent from the Air and N2O simultaneous delivery.Units should have a power-loss alarm, and the battery backup should have an automatic low-battery alarm. All units should include a backup battery to guard against power loss.


Displayed parameters Facility to measure and display on screen:a) 3 traces against time: pressure, volume and flowb) 3 two-axis displays: Pressure-Volume, Flow-Volume and Pressure-Flowc) Status indicators for ventilator mode, battery life, patient data, alarm settings, clock etc.d) Airway pressure (Peak and Mean).e) Tidal volume (Inspired and Expired).f) Minute volume (Inspired and Expired).g) I:E ratioh) inspiration and expiration timesi) Spontaneous Minute Volumej) Respiratory rate (spontaneous and mechanical)k) Total Frequency.l) Oxygen concentrationm) End tidal CO2 with capnographyn) FiO2 dynamic.o) Intrinsic PEEP and PEEPi Volume.p) Plateau Pressure.q) Resistance and Compliance. r) Blood pressure
20 User adjustable settings Units should have a power-loss alarm, and the battery backup should have an automatic low-battery alarmAlarms for all measured and monitored parameters, including circuit disconnection and gas failure.
21 Components(if relevant) External anaesthetic gas supply connection to be secure but easy to fit and releaseMovable arm holder for supporting patient breathing circuitWhole unit to be mounted on wheeled base, with brakes when in useScreen to be mounted flexibly to enable easy, ergonomic viewingIf O2 / N2O supplied by bottle, holders for bottles to include secure locking mechanismIf O2 / N2O supplied by bottle, bottles to have ******** type connector22 Mobility, portability(if relevant)23 Raw Materials(if relevant)

Electrical, water and/or gas supply (if relevant) Electrical source requirements: Amperage:______; Voltage:______. Power input to be ************* fitted with ********** compatible mains plug.Voltage corrector / stabilizer to allow operation at ± 30% of local rated voltage.Resettable overcurrent breaker required on both live and neutral supply lines.Voltage corrector / stabilizer to allow operation at ± 30% of local rated voltage.An internal battery capable of powering the unit for at least 30 minutes. Compliance with ____ electrical standards and regulations.


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Accessories (if relevant) Breathing circuits (two sets)Reusable masks (two sets each of small, medium and large), textured for easy fit.Filters sufficient for 100 patients’ use Rechargeable batteries with:a) autonomy of at least 1 hours;b) visual alarm in case of low battery;c) automatic passage from line alimentation to battery operating modes;d) system integrated battery charger.26 Sterilization process for accessories (if relevant)27 Consumables / reagents (if relevant)

Spare parts (if relevant) Medical units select them according to their needs, ensuring compatibility with the brand and model of the equipment. 1 reusable ECG sensors and connectors set.1 reusable adult and or pediatric oxygen saturation sensor and connector set.1 reusable adult and or pediatric invasive pressure transducer and connector set.1 reusable adult and or pediatric non-invasive pressure transducer and connector set.1 rectal temperature transducer and connector set.1 adult and or pediatric cardiac output connector set.1 CO2 sensor.29 Other components (if relevant) Some anesthesia units require stand-alone physiologic monitors (modular approach) and/or anesthetic agent monitors, while others have integrated monitors (preconfigured approach)

30 Sterility status on delivery (if relevant) N/A31 Shelf life (if relevant) N/A32 Transportation and storage (if relevant) N/A33 Labelling (if relevant) N/A
34 Context-dependent requirements Capable of being stored continuously in ambient temperature of 0 to 50 deg C and relative humidity of 15 to 90%.Capable of operating continuously in ambient temperature of 10 to 40 deg C and relative humidity of 15 to 90%.
35 Pre-installation requirements(if relevant)36 Requirements for commissioning (if relevant)37 Training of user/s (if relevant) Training of users in operation and basic maintenance shall be providedAdvanced maintenance tasks required shall be documentedSupplier to perform installation, safety and operation checks before handoverLocal clinical staff to affirm completion of installation.38 User care(if relevant) Casing to be splash proof and cleanable with alcohol or chlorine wipes39 Warranty Two year warranty should be provided by the supplier40 Maintenance tasks Advanced maintenance tasks required shall be documented41 Type of service contract Service contract is recommended in case no in-house service experience is avialable to ensure that preventive maintenance will be performed at regular intervals.Pricing for service contracts should be negotiated before the system is purchased.42 Spare parts availability post-warranty43 Software / Hardware upgrade availability Routine software updates should be provided
44 Documentation requirements User, technical and maintenance manuals to be supplied in ************** languageCertificate of calibration and inspection to be providedList to be provided of equipment and procedures required for local calibration and routine maintenanceList to be provided of important spares and accessories, with their part numbers and costContact details of manufacturer, supplier and local service agent to be provided






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45 Estimated Life Span 8 to 10 Years46 Risk Classification Class C (GHTF Rule 11-1); Class II (USA); Class III (EU, Japan, Canada and Australia)47 Regulatory Approval / Certification


International standards ISO 13485:2003 Medical devices -- Quality management systems -- Requirements for regulatory purposes (Australia, Canada and EU)ISO 14971:2007 Medical devices -- Application of risk management to medical devices IEC 60601-1:2012 Medical electrical equipment - Part 1: General requirements for basic safety and essential performanceIEC 60601-1-1:2000 Medical electrical equipment - Part 1-1: General requirements for safety - Collateral standard: Safety requirements for medical electrical systemsIEC 60601-1-2:2007 Medical electrical equipment - Part 1-2: General requirements for basic safety and essential performance - Collateral standard: Electromagnetic compatibility - Requirements and tests ISO 4135:2001 Anaesthetic and respiratory equipment -- VocabularyISO 5356-1:2004 Anaesthetic and respiratory equipment -- Conical connectors -- Part 1: Cones and socketsISO 5356-2:2012 Anaesthetic and respiratory equipment -- Conical connectors -- Part 2: Screw-threaded weight-bearing connectorsISO 5358:1992 Anaesthetic machines for use with humansISO 5360:2012 Anaesthetic vaporizers -- Agent-specific filling systemsISO 5361:2012 Anaesthetic and respiratory equipment -- Tracheal tubes and connectorsISO 5362:2006 Anaesthetic reservoir bagsISO 5364:2008 Anaesthetic and respiratory equipment -- Oropharyngeal airwaysISO 5366-1:2000 Anaesthetic and respiratory equipment -- Tracheostomy tubes -- Part 1: Tubes and connectors for use in adultsSO 5366-3:2001 Anaesthetic and respiratory equipment -- Tracheostomy tubes -- Part 3: Paediatric tracheostomy tubesISO 5367:2000 Breathing tubes intended for use with anaesthetic apparatus and ventilatorsISO 7376:2009 Anaesthetic and respiratory equipment -- Laryngoscopes for tracheal intubationISO 7396-2:2007 Medical gas pipeline systems -- Part 2: Anaesthetic gas scavenging disposal systemsISO 8835-7:2011 Inhalational anaesthesia systems -- Part 7: Anaesthetic systems for use in areas with limited logistical supplies of electricity and anaesthetic gasesISO 9170-2:2008 Terminal units for medical gas pipeline systems -- Part 2: Terminal units for anaesthetic gas scavenging systemsISO 9360-1:2000 Anaesthetic and respiratory equipment -- Heat and moisture exchangers (HMEs) for humidifying respired gases in humans -- Part 1: HMEs for use with minimum tidal volumes of 250 ml


International standards ISO 9360-2:2001 Anaesthetic and respiratory equipment -- Heat and moisture exchangers (HMEs) for humidifying respired gases in humans -- Part 2: HMEs for use with tracheostomized patients having minimum tidal volumes of 250 mlISO 11197:2004 Medical supply unitsISO 11712:2009 Anaesthetic and respiratory equipment -- Supralaryngeal airways and connectorsISO 15001:2010 Anaesthetic and respiratory equipment -- Compatibility with oxygenISO 10524-1:2006 Pressure regulators for use with medical gases -- Part 1: Pressure regulators and pressure regulators with flow-metering devicesISO/TS 18835:2004 Inhalational anaesthesia systems -- Draw-over vaporizers and associated equipmentISO 21969:2009 High-pressure flexible connections for use with medical gas systemsISO 23328-1:2003 Breathing system filters for anaesthetic and respiratory use -- Part 1: Salt test method to assess filtration performanceISO 23328-2:2002 Breathing system filters for anaesthetic and respiratory use -- Part 2: Non-filtration aspectsISO 23747:2007 Anaesthetic and respiratory equipment -- Peak expiratory flow meters for the assessment of pulmonary function in spontaneously breathing humansISO 26782:2009 Anaesthetic and respiratory equipment -- Spirometers intended for the measurement of time forced expired volumes in humansISO 26825:2008 Anaesthetic and respiratory equipment -- User-applied labels for syringes containing drugs used during anaesthesia -- Colours, design and performanceISO 27427:2010 Anaesthetic and respiratory equipment -- Nebulizing systems and componentsISO 80601-2-12:2011 Medical electrical equipment -- Part 2-12: Particular requirements for basic safety and essential performance of critical care ventilatorsISO 80601-2-13:2011 Medical electrical equipment -- Part 2-13: Particular requirements for basic safety and essential performance of an anaesthetic workstationISO 80601-2-55:2011 Medical electrical equipment -- Part 2-55: Particular requirements for the basic safety and essential performance of respiratory gas monitors


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Reginal / Local Standards ASTM F1101-90(1996) Standard Specification for Ventilators Intended for Use During AnesthesiaASTM F1208-89(2005) Standard Specification for Minimum Performance and Safety Requirements for Anesthesia Breathing SystemsASTM F1850-00(2005) Standard Specification for Particular Requirements for Anesthesia Workstations and Their ComponentsASTM F2002-01 Standard Terminology Relating to Anesthesia and Respiratory EquipmentJIS T 7201-1:1999 Inhalational anaesthesia systems -- Part 1 Anaesthetic machines for use with humans JIS T 7201-2-1:1999 Inhalational anaesthesia systems -- Anaesthetic and respiratory equipment -- Conical connectors -- Part 2-1 Cones and sockets JIS T 7201-2-2:1999 Inhalational anaesthesia systems -- Anaesthetic and respiratory equipment -- Conical connectors -- Part 2-2: Screw-threaded weight-bearing connectors JIS T 7201-3:2005 Anaesthetic reservoir bags JIS T 7201-4:2005 Breathing tubes intended for use with anaesthetic apparatus and ventilators JIS T 7201-5:1999 Inhalational anaesthesia systems -- Part 5: Anaesthetic circle breathing systems JIS T 7211:2005 Breathing system filters for anaesthetic and respiratory use -- Part 1: Salt test method to assess filtration performance JIS T 7212:2005 Breathing system filters for anaesthetic and respiratory use -- Part 2: Non-filtration aspects

50 Regulations US regulations 21 CFR part 820 21CFR section 868.5160 gas-machine, anesthesia JP regulations MHLW Ordinance No.169 34851000 Anaesthesia ventilator (Japan)

3.*Preventative*Maintenance*and*Safety*of*Anesthesia*Machines****Featured*in*this*Section:******Pescod,)D.)Developing(Anesthesia(Textbook,(Version(1.6.)(2007).)Retrieved)from:) *Strengthening)Specialised)Clinical)Services)in)the)Pacific.)User(Care(of(Medical(Equipment:(A(first(line(maintenance(guide(for(end(users.)(2015).)* *


15. CHECKING THE EQUIPMENT It is the responsibility of the anaesthetist to check all anaesthetic equipment and drugs before giving an anaesthetic. There must always be alternative equipment to ventilate the patient’s lungs if the anaesthetic machine or oxygen supply fails. A self-inflating resuscitation bag does not need a source of oxygen. It should be available whenever an anaesthetic is given. Airway Equipment An alternative method of ventilating the patient must always be available. Ideally the anaesthetist would have at least two laryngoscopes of different sizes. The light should be checked. Oropharyngeal (and nasopharyngeal) airways should be available in different sizes. A flexible stylet and gum elastic bougies are excellent aids for intubation. The anaesthetist should have several different sized masks and an appropriate sized endotracheal tube (plus one size smaller and one bigger) available. A laryngeal mask may be used as the airway or as an excellent alternative airway if endotracheal intubation is difficult (secondary plan). Emergency airway equipment (e.g. laryngeal masks, intubating laryngeal masks, percutaneous tracheostomy, fibreoptic laryngoscopes) should be kept together in a labelled container in a central area. Suctioning Suction equipment should be available. It consists of a pump to generate a vacuum, a reservoir and tubing. The reservoir must be large enough to hold the aspirated fluid but not too large. (The larger the reservoir the longer it will take to achieve a vacuum). The minimal flow rate should be 35 l/min of air and generate at least 600 mmHg (80 kPa) negative pressure. Suction may be powered by electricity, compressed gas or by hand/foot. Continuous Flow Anaesthetic Machine (Boyle’s machine) The anaesthetic machine can be considered in thee parts: high pressure (pipeline, cylinders, pressure gauges and regulators), low pressure (oxygen failure alarm, antihypoxic device, flowmeters, vaporisers, pressure release valve, and common gas outlet) and the breathing system. Cylinders and Pipelines Cylinder and pipeline gases are too highly pressurised (5,000 kPa to 14,000 kPa) for safe flow regulation. Regulators are used to decrease the pressure to a safe level. Pressurised gases must never be connected directly to the breathing system. (1 atmosphere = 760 mmHG = 98 kPa = 14 psi. 1 psi =6.9 kPa).

How to Check Anesthetic Equipment Before Use

Pescod, D. Developing Anesthesia Textbook, Version 1.6. (2007). Retrieved from: http://



Cylinders should be checked regularly for faults. Full and empty cylinders should be kept separately. Cylinders must be handled carefully. They are heavy and oxygen cylinders are a fire risk. Different gases are supplied at different pressures. Oxygen is stored at 14,000 kPa. A standard D cylinder contains 400 litres, an E cylinder 680 litre and an F cylinder 1400 litres. The gauge pressure on an oxygen cylinder will decrease at a rate proportional to the amount of oxygen used. When half the contents of a cylinder are used, the gauge pressure will be half of the original pressure. A second oxygen cylinder must always be available and checked. Oxygen is available as “industrial” or “medical” grade. The same process is used to produce both grades of oxygen and it is safe to use “industrial” grade oxygen if “medical” grade oxygen is unavailable. Nitrous oxide cylinders are filled with liquid nitrous oxide. The gauge pressure of a nitrous oxide cylinder will not change as the nitrous oxide is used until all the liquid is depleted. Once the gauge pressure of a nitrous oxide cylinder starts to fall the cylinder is nearly empty. A full C cylinder of nitrous oxide contains 450 litres, a D cylinder 900 litres, an E cylinder 1800 litres and an F cylinder 3600 litres. In order to ensure that the correct cylinder is attached to the yoke of the anaesthetic machine a series of pins on the machine yoke is made to fit an identical pattern of indentations on the cylinder. This is a pin-index system. Flow Meters Gases from the cylinders and pipeline pass though flow meters. The flow meters are made for a specific gas. They are not interchangeable. Flow meters have a spindle valve in the base to control flow and a bobbin or a ball in a vertical tube. The bobbin should spin. After the gases pass though the flow meters the different gases are joined together. Oxygen is added last to reduce the chance of giving a hypoxic mixture. New anaesthetic machines link the flow of nitrous oxide to the flow of oxygen to prevent less than 25% oxygen being given (anti-hypoxic device). Anaesthetic machines without an anti-hypoxic device should have an oxygen analyser. Oxygen Failure Alarm The anaesthetic machine should have an oxygen failure warning device. An anaesthetist should not use an anaesthetic machine that does not have an oxygen failure warning device or a broken device. If there is no alternative the anaesthetist must check the oxygen gauge pressure every 5 minutes. The cylinder must be changed when the cylinder pressure is less than quarter full. There are a variety of alarms. Older models depend on batteries to power a red light and nitrous oxide to power a whistle (Bosun oxygen failure alarm). The anaesthetist must check that the batteries are working. Other devices do not rely on batteries and will shut off the nitrous oxide. Some have a reserve supply of oxygen.
Pescod, D. Developing Anesthesia Textbook, Version 1.6. (2007). Retrieved from: http://



Vaporisers A horizontal pipe (back bar) on the anaesthetic machine connects the flow meters to a common gas outlet. The breathing systems are connected to the common gas outlet. Vaporisers are usually mounted on the back bar. Some older vaporisers may be free-standing and are connected to the common gas outlet. The anaesthetist must check that the vaporisers are connected in the correct direction. Vaporisers are made for a specific volatile anaesthetic agent. Filling a vaporiser with the incorrect volatile anaesthetic agent will produce the wrong concentration. Some vaporisers have a special filling system to ensure that they are filled with the correct agent. If a vaporiser does become contaminated with the incorrect agent it should be emptied, washed out several times with the correct agent and then blown though with oxygen or air until all smell has been eliminated. On some anaesthetic machines it is possible to connect more than one vaporiser to the back bar. Newer anaesthetic machines have a mechanism to prevent more than one vaporiser being turned on at the same time. Turning more than one vaporiser on at the same time will produce dangerous concentrations of volatile anaesthetic gases. The vaporisers made for the back bar are for use with compressed gas. They have a high internal resistance. They must not be used for drawover anaesthesia. The anaesthetist must check that the vaporiser is filled with the correct agent, correctly fitted to the back bar and that it easily turns on and off. The vaporiser should be left in the off position. (A Boyle’s bottle should have both the lever and the plunger pulled up. Check that filling ports are closed). Vaporisers must never be tilted or turned upside down. This will produce dangerous concentrations of the agent when it is turned on. Oxygen Flush/Pressure Relief Valve At the end of the back bar there may be an emergency oxygen flow button (oxygen flush) and a pressure relief valve. Anaesthetic machines should have an emergency high flow rate (20 to 35 litres/min) supply of oxygen that bypasses the flow meters and the vaporisers. The anaesthetist should check the oxygen flush by pressing the spring-loaded button. The pressure relief valve is located downstream from the flow meters and the vaporiser. It protects the anaesthetic machine and vaporisers from high pressures. It does not protect the patient.

Pescod, D. Developing Anesthesia Textbook, Version 1.6. (2007). Retrieved from: http://



Checking the Anaesthetic Machine Always have an alternative resuscitation device (e.g. self-inflating bag). Check that cylinders are full and attached to the anaesthetic machine. There must always be a reserve supply of oxygen. Never use a machine if there is no reserve supply of oxygen. Turn off all cylinders. Turn on all flow meters. There should be no flow. Check the flow meters for cracks. Turn on the oxygen cylinder. There should only be flow in the oxygen flow meter. The bobbin should spin. Repeat with each oxygen cylinder. Set the oxygen flow to 4 litres/min. Turn on the nitrous oxide cylinder. Check that there is flow in the nitrous oxide flow meter (the bobbin should spin) and that the oxygen flow meter is still at 4 litres/min. Turn off the oxygen supply and push the oxygen flush button. The oxygen failure alarm should sound. Turn on the oxygen cylinder again. The oxygen failure alarm should go off. Check that all vaporisers are full and correctly fitted. The controls should operate thoughout their full range without sticking. Turn off the vaporisers. If the anaesthetic machine is fitted with a pressure relief valve it should be tested by occluding the common gas outlet whilst gas is flowing. (Never do this test if a pressure relief valve is not fitted). Attach the breathing system. Check that it has been correctly assembled. Close the APL valve, occlude the end and fill with gas. Squeeze the reservoir bag to ensure there are no leaks. Open the valve and ensure the breathing system empties. Check all airway equipment, suction equipment and drugs.

Pescod, D. Developing Anesthesia Textbook, Version 1.6. (2007). Retrieved from: http://

Anesthesia Machine Safety Checklist


User Care of Medical Equipment – First line maintenance for end users


User Care Checklist – Anaesthesia Machines and Ventilators



9 Remove any dust, dirt, water, waste matter, tape and paper


9 If any leak is audible, check with soapy solution

9 Check all seals, connectors, adapters and parts are tight

9 Check all moving parts move freely, all holes are unblocked


9 Report any faults to technician immediately

9 After checks, depressurize system and replace all caps / covers



9 Clean inside and outside with damp cloth and dry off

9 Remove dirt from wheels/any moving parts


9 Check connections for leakage with soap solution and dry off

9 Check all fittings and valves for proper assembly

9 Replace soda lime if it has changed colour

9 Replace any deteriorated hoses and tubing

9 If seal, plug, cable or socket are damaged, replace


9 When next used, check pressure gauges rise

9 When next used, check there are no leaks

Every six months
Biomedical Technician check required

*4.*Troubleshooting*and*Repair*of*Anesthesia*Machines****Featured*in*this*Section:*****Chan,)A.)Biomedical(Device(Technology:(Principles(and(Design.)Charles)C.)Thomas)Publisher:)USA)(2008).) ))Strengthening)Specialised)Clinical)Services)in)the)Pacific.)User(Care(of(Medical(Equipment:(A(first(line(maintenance(guide(for(end(users.)(2015).)* *

User Care of Medical Equipment – First line maintenance for end users


Troubleshooting – Anaesthesia Machines and Ventilators

Fault Possible Cause Solution


Equipment is not running

No power at mains socket

Electrical cable fault

Check power switch is on.
Replace fuse with correct voltage
and current rating if blown.
Check mains power is present at
socket using equipment known to
be working. Contact electrician
for rewiring if power not present.

Refer to electrician for repair


No gas output

No O2 pressure in cylinder / gas

Check pressure gauges for gas
pressure (about 4 bar or 4 kg/cm2)

Restore gas supply or replace gas

Replace O2 cylinder and/or N2O
cylinder in case of low pressure.


O2 failure, power failure or
breathing alarm not working

Alarm battery is low.

Alarm device is not working

Call biomedical technician to fix
the problem.


Machine has leaks

Poor seal
(commonly occurring around
tubing connections, flow valves
and O2 / N2O yokes)

Cylinders not seated in yokes

Clean leaking seal or gasket,
replace if broken. If leaks remain,
call technician for repair.

Refit cylinders in yokes and
retest. If leaks remain, call
technician for repair.


Flowmeter fault

Over tightening of the needle
valve or sticking of the float / ball

Refer to biomedical technician


Electrical shocks

Wiring fault

Refer to electrician immediately

Risks Associated with Anesthesia Machines

Chan, A. Biomedical Device Technology: Principles and Design.

Charles C. Thomas Publisher: USA (2008).


5.*External*Resources*for*More*Information*about*Anesthesia*Machines****Featured*in*this*Section:***** Developing)World)Healthcare)Technology)Laboratory.)“Routing)to)Clear)Blockage)in)a)Tube.”)Biomedical(Technician(Assistant((BTA)(Skills.)DHT)laboratory,)Duke)University,)2011.)***Malkin,)Robert.)“Bottled)Gasses:)Operation)and)Use.”)Medical(Instrumentation(in(the(Developing(World.)Engineering)World)Health,)2006.)* *)

* Resources*for*More*Information:** *Internal*Resources*at**For*more*information*about*anesthesia*machines,*please*see*these*resources*in*the*BMET*Library!*) 1. Malkin,)Robert.)“Bottled)Gasses:)Operation)and)Use.”)Medical(Instrumentation(in(the(Developing(World.)Engineering)World)Health,)2006.)** 2. Developing)World)Healthcare)Technology)Laboratory.)“Routing)to)Clear)Blockage)in)a)Tube.”)Biomedical(Technician(Assistant((BTA)(Skills.)DHT)laboratory,)Duke)University,)2011.)) **** *

Anesthesia*Machine*Bibliography:**Chan,)A.)Biomedical(Device(Technology:(Principles(and(Design.)Charles)C.)Thomas)Publishers,)2008.)))Developing)World)Healthcare)Technology)Laboratory.)“Routing)to)Clear)Blockage)in)a)Tube.”)Biomedical(Technician(Assistant((BTA)(Skills.)DHT)laboratory,)Duke)University,)2011.))*Malkin,)R.)“Anesthesia)Machines,”)From)the)publication:)Medical(Instruments(in(the(Developing(World.)Engineering)World)Health,)2006.))))Malkin,)R.)“Bottled)Gasses:)Operation)and)Use.”)Medical(Instrumentation(in(the(Developing(World.)Engineering)World)Health,)2006.)))Ministry)of)Health)and)Family)Welfare,)New)Delhi.(Medical(Equipment(Maintenance(Manual:(A(first(life(maintenance(guide(for(end(users.)Ministry)of)Health)and)Family)Welfare,)2010.)))Pescod,)D.)Developing(Anesthesia(Textbook,(Version(1.6.)(2007).)Retrieved)from:) )Subrahmanyam,)M.)and)Mohan,)S.)“Safety)Features)in)Anesthesia)Machine.”)Indian(Journal(of(Anesthesia,)Vol.)57,)No.)5)(2013),)p.)472a480.)))WHO.)“Anesthesia)Unit,”)From)the)publication:)Core(Medical(Equipment.)Geneva,)Switzerland,)2011.))) WHO.)“Anaesthesia)Ventilator.”)From)the)publication:)“WHO)Technical)Specifications)for)61)Medical)Devices.)WHO.)Retrieved)from:) Wikipedia.)“Pulse)Oximetry.”)Wikipedia,)pgs.)1a4.)Retrieved)from:)

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