1. ANESTHESIA MACHINE ,
ELECTRICAL COMPONENTS,
HIGH PRESSURE SYSTEM ,
INTERMEDIATE PRESSURE
SYSTEM
MODERATOR: DR. H. SAHARIA
( ASST. PROFFESOR)
PRESENTER: DR. KUNAL AGARWAL (PGT)
DEPT OF ANESTHESIOLOGY & CRITICAL
CARE .GMCH
24 TH -NOV-2012

2. Anaesthesia
machine: a short
introduction
Anaesthesia gas machine is a device which delivers a
precisely known but variable gas mixture,including
anaesthetizing and life sustaining gases. The most common
type of anaesthetic machine in use in the developed world
is the continuous-flow anaesthetic machine, which is
designed to provide an accurate and continuous supply of
medical gases (such as oxygen and nitrous oxide), mixed
with an

3. Contd..
accurate concentration of anaesthetic vapour (such as
isoflurane), and deliver this to the patient at a safe
pressure and flow. Modern machines incorporate a
ventilator, suction unit, and patient-monitoring devices

4. HISTORY…
• The original concept of Boyle's machine was
invented by the British anaesthetist H.E.G.
Boyle in 1917.
• Prior to this time, anaesthetists often carried
all their equipment with them, but the
development of heavy, bulky cylinder storage
and increasingly elaborate airway equipment
meant that this was no longer practical for
most circumstances.
• The anaesthetic machine is usually mounted
on anti-static wheels for convenient
transportation.

5. • Originally boyle introduced nitrous oxide-oxygen
anaesthesia through this machine and it was a two gas
system with watersight-feed type of flowmeter.
• In 1920,modification was made by incorporating a
vaporising bottle to flowmeters.
• A second vaporising bottle and bypass controls were
further added in 1929.
• In 1933 dry bobbin type of flowmeter was introduced in
place of watersight-feed type.
• In 1937 rotameters displaced dry-bobbin type of
flowmeters.

6. • The basic design has been called upon to perform
more complicated functions since 1990, with the
advent of computer-controlled monitors into the
operating room, especially pulse oximetry,
capnography, and gas analysis.
• Our gas machines have become top-heavy with the
monitors we have added to their basic design.
• But despite numerous modifications the modern
apparatus retains many of the features of the
original Boyle's machine.

7. PHYSICAL TERMS AND UNITS
 Flow - Flow is the measure of volume per unit time. In
anaesthesia , common units are liters per minute ( L min -1 )
 Force - is that property which when applied to a mass causes
acceleration , or a change in the direction of motion. i.e. F =
ma
 Pressure - is the intensity of force over a defined area such
that:
 Pressure = total force (F) / total area (A) =force per unit area.
 Pressure retains some traditional units in common use such
as pounds per square inch (p.s.i.) , millimeters of mercury (mm
Hg), centimeters of water(cm H2O) , and atmospheres).
 1 bar = 100 kPa = approx. 760 mmHg = approx. 1000cm H20
= approx 14.7 p.s.i.

8.  Gauge pressure – describes the pressure above atmospheric
pressure.
 Absolute pressure includes atmospheric pressure.
 The pressure in a full O2 cylinder can be quoted as137 bar
gauge pressure or 138 bar absolute pressure.
 Critical temperature - The temperature , above which a gas
cannot be liquefied , however much pressure is increased is
known as its critical temperature. It is 36.5 oC for nitrous
oxide and -118oC for O2
 Filling Ratio – To prevent cylinders , the contents of
which are normally in liquid form , from being
overfilled , a filling ratio (or filling density) is
specified. This is the ratio of the total weight of gas
in a cylinder to the weight of water that the cylinder
would hold at 160C. For nitrous oxide it is 0.67- 0.75.
Note that the filling ratio is not the proportion of the
cylinder occupied by liquid.

9. STANDARDS FOR ANESTHESIA
MACHINES AND WORKSTATIONS
 Standards for anesthesia machines and workstations
provide guidelines to manufacturers regarding their
minimum performance, design characteristics, and safety
requirements. During the past 2 decades, the progression
of anesthesia machine standards has been as follows:
 1979: American National Standards Institute, Z79.8-19793
 1988: American Society for Testing and Materials, F1161-
884
 1994: ASTM F1161-94 (reapproved in 1994 and
discontinued in 2000)5
 2005: International Electrical Commission (IEC), 60601-16
 2005: ASTM F1850-00 (reapproved)2

10. CONTD…..
To comply with the 2005 ASTM F1850-00 standard, newly
manufactured workstations must have monitors that
measure the following parameters:
 continuous breathing system pressure,
 exhaled tidal volume,
 ventilatory CO2 concentration,
 anesthetic vapor concentration,
 inspired oxygen concentration,
 oxygen supply pressure,
 arterial hemoglobin oxygen saturation
 arterial blood pressure,
 and continuous electrocardiogram.

11. CONTD….
 The anesthesia workstation must have a prioritized alarm
system that groups the alarms into three categories: high,
medium, and low.
 These monitors and alarms may be enabled automatically
and made to function by turning on the anesthesia
workstation, or the monitors and alarms can be enabled
manually and made functional by following a pre-use
checklist.

13. APL valve

14. SYSTEM COMPONENTS
Electrical
Components
Many components of modern anesthesia machines are powered by
electricity. Turning the machine ON enables these devices.

15. MASTER SWITCH
On most anesthesia machines, a master (main power) switch
activates both the pneumatic and electrical functions.
On most machines, when the master switch is in the OFF
position, the only electrical components that are active are
the battery charger and the electrical outlets.
Master switch. Turning the master switch to
the ON position activates both pneumatic
and electrical functions of the machine as
well as certain alarms and safety features.

16. POWER FAILURE INDICATOR
Most machines are equipped with a visual and/or audible
indicator to alert the anesthesia provider to the loss of mains
power .
The machine will usually give an indication when mains power is
lost.

17. RESERVE POWER
Since electricity is crucial for many machine functions, a
backup source of power for the occasional outage is
necessary.
The anesthesia provider should check the battery status
during the preuse checkout procedure.
While some older anesthesia machines used replaceable
batteries, most new machines use rechargeable batteries.
The duration of battery backup depend on the power usage.
A noninterruptible power source may be added to the
anesthesia machine for a longer backup .
An extra source of power may
be attached to the anesthesia
machine to extend the life of
the electrical power in the
machine

18. ELECTRICAL OUTLETS
 Most modern anesthesia machines have electrical outlets.
 These are intended to power monitors and other devices.
 As a general rule, these outlets should only be used for
anesthesia monitors.
 Other appliances should be connected directly to mains
power.
 If the power requirements exceed that for which the outlet was
designed, a circuit breaker will be activated .
Convenience electrical outlets on the back of the anesthesia machine.
These should be used only for anesthesia monitors and not for general
operating room use.

19. CIRCUIT BREAKERS
There are circuit breakers for both the anesthesia machine
and the outlets .
When a circuit breaker is activated, the electrical load should
be reduced and the circuit breaker reset.

20. DATA COMMUNICATION
PORTS
 Most modern anesthesia machines have data
communications ports.
 These are used to communicate between the anesthesia
machine, monitors, and the data management system.

21. MEDICAL GAS
CYLINDERS

22. COMPONENT OF
MEDICAL GAS
CYLINDERS
 BODY
 constructed of steel alloy containing molybdenum(0.15% -
0.25% ) & / chromium (0.8%-1.1%)
 alloys added for strength ,minimize wt. & wall thickness.
 Cylinders that have marked „3AA‟ are manufactured by using
steel.
 The marking „3AL‟or „3ALM‟ indicates that the cylinders made
from aluminium.
 Aluminum cylinders are MRI compatible
 Cylinders have flat or concave bases .
 The other end may taper into a neck that is fitted with tapered
screw threads that attach to the valve.

23. CONTD…
VALVE
 filled and discharged through a valve
 it is attached to the neck
 made of bronze or brass
PORT
 The port is the point of exit for the gas.
 It should be protected in transit by a covering.
 When installing a small cylinder on an anesthesia machine, it is
important not to mistake the port for the conical depression on the
opposite side of the valve.
 The conical depression is designed to receive the retaining screw
on the yoke. Screwing the retaining screw into the port may
damage the port and/or index pins.

24. CONTD…
STEM
 Each valve contains a stem, or shaft, that is rotated during
valve opening or closing.
 To close the valve, the stem seals against the seat that is
part of the valve body.
 When the valve is opened, the stem moves upward,
allowing gas to flow to the port.

26. CONTD…..
1. PACKED VALVE:
 here, stem is sealed by a resilient packing such as Teflon,
which prevents leaks around the threads.
 -This type of valve is also called direct acting, because
turning the stem causes the seat to turn.
 -In a large cylinder valve, the force is transmitted by
means of a driver square. This type of valve is capable of
withstanding high pressures.

27. 2. DIAPHRAGM VALVE
 -The disks, or diaphragms, separate upper and lower stems,
which may be permanently attached to the diaphragms.
 -The upper stem is actuated by a manual or automatic
means, and the lower stem shuts or permits flow through the
valve.
-This type of valve has the following advantages:
• -can be opened fully using a one half to three
quarters turn
• -The seat does not turn & therefore less likely to
leak
• -No stem leakage can occur because of
diaphragm.

28. CONTD…

29. CONTD….
Handle or Handwheel
A handle or handwheel is used
to open or close a cylinder
valve. It is turned
counterclockwise to open the
valve and clockwise to close it.
This causes the stem to turn.
A handle (cylinder wrench) is
used to open a small cylinder
valve. Handles come in a
variety of shapes

30. CONTD….
PRESSURE RELIEF DEVICES :
Every cylinder is fitted with pressure relief (safety
relief/safety) device whose purpose is to vent the cylinders
content to atmosphere if the pressure of enclosed gas
increases to dangerous level.
TYPES
● rupture disc
● fusible plug
● combination of both
● pressure relief valve(spring loaded)

31. CONTD….
Rupture disc:
-non reclosing device held against an orifice.
-when predetermine pressure is reached the disc ruptures &
allow the cylinder content to be discharged.
-it protects against excess pressure as a result of high temp or
overfilling.

32. CONTD..
FUSIBLE PLUG
The fusible plug is a thermally operated, nonreclosing
pressure relief device with the plug held against the
discharge channel.
It offers protection from excessive pressure caused by a high
temperature but not from overfilling.
The yield temperature is the temperature at which the fusible
material becomes sufficiently soft to extrude from its holder
so that cylinder contents are discharged.

33. pressure relief valve(spring loaded)
Figure 1.6 Pressure relief valve. When the set pressure is exceeded, the pressure
in the cylinder forces the spring to the left, and gas flows around the safety valve
seat to the discharge channel

34. NONINTERCHANGEBLE SAFTEY
SYSTEMS
PIN INDEX SAFTEY SYSTEM
Fig :Pin Index Safety System. The bottom figure shows the six positions
for pins on the yoke.
The pins are 4 mm in diameter and 6 mm long, except for pin 7, which is
slightly thicker.
The seven hole positions are on the circumference of a circle of 9/16 inch
radius centered on the port.

35. Indian standard specification for
yoke type valve connection for
oxygen & nitrous oxide:
-two line one mid-horizontal & other
vertical drawn over the yoke
-meeting point taken as center of gas
inlet hole
-hole is drawn as diameter of 7mm
which is fitted to with BODOK SEAL
-distance between center & lower
part of yoke is 20.6mm.
-from the center a circle is drawn
with a radius of 14.3mm. In that arc
pins numbering 1 to 6 are
positioned.
The pin should be diameter of 4.75
mm & 6mm long

37. PISS
oxygen air N2O CO2 nitrogen

38. PIN INDEX SYSTEM
OXYGEN 2,5
NITROUS OXIDE 3,5
CYCLOPROPANE 3,6
AIR 1,5
NITROGEN 1,4
NITROUS+OXYGEN 7
CARBON DIOXIDE 1,6

39. Bodok seal
-cylinders are fitted with yoke with a
sealing washer called BODOK SEAL
-it is made up of non combustible
material and has a metal periphery
which
make it long lasting.
-it should be less than 2.4mm thick
prior to compression.
-only one seal should be use between
the valve & yoke

40. SIZE OF CYLINDERS
Cylinder classified using a letter code
A type cylinders are smallest
However AA (smaller than A) also available.
SIZE D & E is the cylinder most commonly
used

42. TYPICAL MEDICAL GAS CYLINDRES,
VOLUMES, WEIGHT
cylinde Cylinder wt .(lb) Air CO2 oxygn NITROUSO
Dimensions XIDE
r size (O.D. × Length
EMPTY
(litres) (litre (litres)
in Inches) (litres)
s)
A 3X7 0.23 76 189
B 3 1/2 x 13 5 370 200
D 4 1/2 x 17 11 375 940 400 940
E 41/4 x 26 14 625 1590 660 1590
M 7 x 43 63 2850 7570 3450 7570
G 8 1/2 x 51 97 5050 1230 13800
0
H 91/4 X 51 119 6550 6900 15800

43. COLOUR OF CYLINDER
GAS USA INTERNATIONAL
oxygen Green White Shoulder&
Black Body
Carbon dioxide Gray Gray
Nitrous Blue Blue
oxide
helium Brown Brown
Nitrogen Black Black
Air Yellow Gray Body ,Shoulder
black/white quartered

44. CONTENT AND PRESURE
FIG:A nonliquefied gas such as oxygen will show a steady decline
in pressure until the cylinder is evacuated. Each cylinder,
however, will show a steady decline in weight as gas is
discharged.

45. CONTENTS AND PRESSURE
FIG:The relationship between cylinder weight, pressure, and contents. A gas
stored partially in liquid form, such as nitrous oxide, will show a constant
pressure (assuming constant temperature) until all the liquid has evaporated, at
which time the pressure will drop in direct proportion to the rate at which gas is
withdrawn.

46. PNEUMATIC SYSTEM

47. PNEUMATIC SYSTEM
 Gases are supplied under tremendous pressure for the
convenience of storage and transport.
 The anaesthesia machine receives medical gases from a
gas supply; controls the flow of desired gases reducing
their pressure, to a safe level.
 Gases used during ventilation must be supplied to the
patient in a controlled way to avoid any harm to the
patient.

48. PNEUMATIC SYSTEM
 So the pressure inside a source ( cylinder or
pipeline ) must be brought to a certain level
before it can be used for the purpose of
ventilation.
 And it needs to be supplied in a constant
pressure, otherwise the flow meter would need
continous adjustment.
 This is achieved by bringing down the pressure
of a gas supply in a graded manner with the help
of three pressure reducing zones .
 Thus the pneumatic part of the machine can be
conveniently divided into three parts:high
,intermediate and low pressure systems.

49. MACHINE COMPONENTS
High-pressure circuit
oxygen cylinder 2200 psi >> 45 psi
N2O cylinder 750 psi >> 45 psi
Intermediate-pressure circuit
oxygen cylinder 45 psi
N2O cylinder 45 psi
>>14-26 psi (low)
oxygen pipeline 50 psi
N2O pipeline 50 psi

50. CONTD..
Low pressure system: from flow control valve to
common gas outlet.

51. Intermediate Low Pressure Circuit
High Intermediate

52. • Receives gasses from the high
pressure E cylinders attached to the
back of the anesthesia machine (2200
psig for O2, 745 psig for N2O)
• Consists of:
– Hanger Yolk (reserve gas
cylinder holder)
– Check valve (prevent reverse
flow of gas)
– Cylinder Pressure Indicator
(Gauge)
– Pressure Reducing Device
(Regulator)
• Usually not used, unless pipeline gas
supply is off

53. HANGER YOKE ASSEMBLY
The Hanger yoke assembly
1) Orients and supports the cylinder
2) Provides a gas-tight seal
3) Ensures uni-directional gas flow
The workstation standard recommends that there be at
least one yoke each for oxygen and nitrous oxide.
If the machine is likely to be used in locations that do not
have piped gases, it is advisable to have a double yoke,
especially for oxygen.

54. Hanger-yoke assembly

55. HANGER YOKE ASSEMBLY
The hanger yoke assembly is composed of several
parts:
1)Body, which is the principal framework and
supporting structure
2) The retaining screw, which tightens the
cylinder in the yoke
3) The nipple, through which gas enters the
machine
4) The pin index system, which prevents
attaching of incorrect cylinder

56. HANGER YOKE ASSEMBLY
5) The washer, which helps to form a seal between the
cylinder and the yoke
6) The filter, to remove dirt from the gas in the cylinder
7) Check valve assembly, to ensure unidirectional
flow of gas

57. BODY
 It is threaded into the frame of the machine.
 It provides support for the cylinder(s).
 Commonly the swinging gate type is used.
 When a cylinder is mounted onto or removed from a yoke,
the hinged part can be swung to side.

58. RETAINING SCREW
 It is threaded into the distal end of the yoke.
 Tightening the screw presses the outlet of the cylinder
valve against the washer and the nipple so that a gas tight
seal is obtained.
 The cylinder is then supported by the retaining screw, the
nipple, and the index pins.
 The conical point of the retaining screw is shaped to fit the
conical depression on the cylinder valve.

59. NIPPLE & INDEX PINS
Nipple
 It is a part of the yoke through which the gas enters the
machine.
 It fits into the port of the cylinder valve.
 If it is damaged, it may be impossible to obtain a tight seal
with the cylinder valve.
Index Pins
 These are situated below the nipple.
 These help to prevent mounting of incorrect cylinder to
yoke.
 The holes into which the pins are fitted must be of a
specific depth.
 If they extend too far into the body of the yoke, it may be
possible to mount a incorrect cylinder.

60. WASHER & FILTER
Washer
 It is placed around the nipple to effect a seal between the
cylinder valve and the yoke.
 A broken or curled washer should not be used.
 No more than one washer should be used.
Filter
 It is used to prevent particulate matter from entering
the machine.
 It is to be placed between the cylinder and the pressure
reducing device.

61. CONTD..
Swinging gate–type
yoke. Note the
PLACING CYLINDER IN washer around the
YOKE. THE CYLINDER IS nipple and the index
SUPPORTED BY THE FOOT
AND GUIDED INTO PLACE pins below.
MANUALLY

62. CHECK VALVE ASSEMBLY
 It allows gas from a cylinder to enter the
machine but prevents gas from exiting the
machine when there is no cylinder in the yoke.
 It allows an empty cylinder to be replaced with a
full one without having to turn off the `in–use`
cylinder.
 Prevents transfer of gas from one cylinder to the
other with a lower pressure in a double yoke.

63. CHECK VALVE ASSEMBLY CONT…..
 It consists of a plunger that slides away from the
side of the greater pressure.
 It is not designed to act as a permanent seal for
empty yoke and may allow small amount of gas
to escape.
 As soon as a cylinder is exhausted it should be
replaced by a full one or a dummy plug.

64. CHECK VALVE ASSEMBLY

65. CYLINDER PRESSURE INDICATOR
 It is made up of Bourdon tube which is a metal tube bent
into a curved, sealed, and linked to a clock like
mechanism.
 The other end of the tube is connected to the gas source
and a increase in pressure of gas inside the tube causes it
to straighten.
 Through a clock like mechanism these motions are
transmitted to the indicator.
 Gauges are requried to be calibrated in kPa but psi may
also be used.
 Now-a-days digital pressure indicators has also come up.

66. CYLINDER PRESSURE INDICATOR
(BOURDEN TUBE)

67. CYLINDER PRESSURE GAUGE
 Each hanger yoke or a group of hanger yoke should be
provided with a gauge that will display the pressure of
the cylinder.
 The indicator may be located near the cylinder or on the
front panel of the machine.
 The indicator is circular, the lowest pressure indication
must be between the 6 o`clock and the 9 o`clock position
on a clock face.
 The scale must be at least 33% more than the maximum
filling pressure.
 It must be clearly and permanently marked with the name
or chemical symbol of the gas it monitors and should be
identified by the color assigned to that gas.

68. PRESSURE REDUCING DEVICE
(REGULATOR)
 The pressure in a cylinder varies. The anesthesia machine
is fitted with devices (reducing valves, regulators,
reducing regulators, reduction valves, regulator valves) to
maintain constant flow with changing supply pressure.
 These reduce the high and variable pressure found in a
cylinder to a lower (40 to 48 psig, 272 to 336 kPa) and
more constant pressure suitable for use in an anesthesia
machine.
 The machine standard requires reducing devices for each
gas supplied to the machine from cylinders.
 Separate yokes for the same gas may be connected to
one reducing device.

69. INTERMEDIATE
PRESSURE SYSTEM

70. INTERMEDIATE PRESSURE
SYSTEM
Begins at the regulated cylinder supply source at 45 psig
,includes the pipeline sources at 50 to 55 psig and extends to
the flow control valve.
Depending on manufacturer & specific
machine design,second stage regulators may be used to
decrease the pipeline supply pressures to the flow control
valves to even lower pressures as 14 or 26 psig with in the
intermediate pressure circuit.

71. Receives gasses from the
regulator or the hospital
pipeline at pressures of 40-
55 psig
Consists of:
• Pipeline inlet connections
• Pipeline pressure indicators
• Piping
• Gas power outlet
• Master switch
• Oxygen pressure failure
devices
• Oxygen flush
• Additional reducing devices
• Flow control valves

72. MASTER SWITCH (PNEUMATIC
COMPONENT )
 The pneumatic portion of the master switch is located in
the intermediate pressure system downstream of the
inlets for the cylinder and pipeline supplies
 The oxygen flush is usually independent of this switch.
 The master switch may be a totally electronic switch that
when activated controls the various pneumatic
components in the anesthesia machine.
 When the master switch is turned off ,the pressure in the
intermediate system will drop to zero

74. PIPELINE INLET CONNECTIONS
 THE PIPELINE INLET CONNECTION IS THE ENTRY
POINT FOR GASES FROM THE PIPELINES.
THE ANESTHESIA WORKSTATION STANDARD
REQUIRES PIPELINE INLET CONNECTIONS FOR
OXYGEN AND NITROUS OXIDE.
MOST MACHINES ALSO HAVE AN INLET
CONNECTOR FOR AIR.
THESE INLETS ARE FITTED WITH THREADED NON
INTERCHANGEABLE DIAMETER INDEX SAFETY
SYSTEM (DISS) FITTINGS

75. Each inlet must contain a unidirectional (check) valve to
prevent reversed gas flow from the machine into the piping
system (or to atmosphere if no hose is connected).
Problems have been reported with this check valve.
Each pipeline inlet is required to have a filter with a pore
size of 100 μm or less. The filter may become clogged,
resulting in a reduction in gas flow

76. PIPELINE INLET CONNECTIONS

77. PIPELINE INLET CONNECTIONS

78. PIPELINE PRESSURE INDICATORS
 Indicators to monitor the pipeline pressure of each gas are required
by the anesthesia workstation standard.
 They are usually found on a panel on the front of the machine and
may be color coded for the gases that they monitor
 Some machines have digital pressure indicators. The pipeline
pressure is displayed either continuously or on demand
 On some newer electronic machines, LEDs indicate pipeline
pressure.
 A green LED indicates that the pipeline is connected and the
pressure is adequate.
 If the LED is OFF, the pressure is inadequate or the pipeline is not
connected.
 If the transducer is inoperable, the LED is dark. A digital pressure
can be displayed on the screen to augment the information from the
LEDs.

80. PIPELINE PRESSURE INDICATORS
 The workstation standard requires that the indicator be on
the pipeline side of the check valve in the pipeline inlet.
 If the indicator is on the pipeline side of the check valve, it
will monitor pipeline pressure only. If the hose is
disconnected or improperly connected, it will read “0” even if
a cylinder valve is open
 If the indicator were on the machine (downstream) side of the
check valve, it would not give a true indication of the pipeline
supply pressure unless the cylinder valves were closed. If a
cylinder valve is open and the pipeline supply fails, there will
be no change in the pressure on the indicator until the
cylinder is nearly empty.

81. PIPELINE PRESSURE INDICATORS
 The indication of an adequate pressure on the pipeline
indicator does not guarantee that gas is not being drawn
from a cylinder. If for any reason the gas pressure coming
from a cylinder via a pressure regulator exceeds the
pipeline pressure and a cylinder valve is open, gas will be
drawn from the cylinder. Therefore cylinder valves should
always remain closed when the pipeline supply is in use.
 Pipeline pressure indicators should always be checked
before the machine is used. The pressure should be
between 50 and 55 psig (345 and 380 kPa). The indicators
should be scanned repeatedly during use.

82. PIPING
 Piping is used to connect components inside the machine.
It must be able to withstand four times the intended
service pressure without rupturing.
 The anesthesia workstation standard specifies that leaks
between the pipeline inlet or cylinder pressure reducing
system and the flow control valve not exceed 25
mL/minute. If the yoke and pressure reducing system are
included, the leakage may not exceed 150 mL/minute.
 Piping cross connections inside the machine have been
reported. Disconnections in the piping may occur but are
rare

84. OXYGEN PRESSURE FAILURE DEVICES
 One of the most serious mishaps that occurred with early
machines was depletion of the oxygen supply (usually
from a cylinder) without the user awareness.
 The result was delivery of 100% anesthetic gas.
 Numerous inventions have been devised to prevent this
problem.
 Among these are devices that shut off the supply of gases
other than oxygen (oxygen failure safety device) or alarm
when oxygen pressure has fallen to a dangerous level
The anesthesia workstation standard requires that whenever
the oxygen supply pressure is reduced below the
manufacturer-specified minimum, the delivered oxygen
concentration shall not decrease below 19% at the common
gas outlet.

85. OXYGEN FAILURE SAFETY DEVICE
 The oxygen failure safety valve (oxygen failure safety device,
low pressure guardian system, oxygen failure protection
device, pressure sensor shutoff system or valve, fail safe,
pressure sensor system, nitrous oxide shut off valve) shuts off
or proportionally decreases and ultimately interrupts the
supply of nitrous oxide if the oxygen supply decreases.
 On many modern machines, the air supply is also cut off .
 When the pneumatic system is activated, oxygen pressure
reaches the oxygen failure safety device, allowing other gases
to flow. Turning OFF the pneumatic system causes oxygen in
the machine to be vented to atmosphere. The resulting
decrease in oxygen pressure causes the oxygen failure safety
device to interrupt the supply of other gases to their flow
control valves.

86. OXYGEN SUPPLY FAILURE ALARM
 The anesthesia workstation standard specifies that whenever
the oxygen supply pressure falls below a manufacturer-
specified threshold (usually 30 psig (205 kPa)), at least a
medium priority alarm shall be enunciated within 5 seconds.
It shall not be possible to disable this alarm.
 Because both the oxygen failure safety device and alarm
depend on pressure and not flow, they have limitations that
are not always fully appreciated by the user.
 In OHMEDA machines, the alarm is actuated at around 28
psig (190 kPa). On DRAGER machines, the threshold is
between 30 and 37 psig.
 Alarms may be either electronic or pneumatic (directs a
stream of oxygen in a resorvoir through a whistle).

87. CONTD…
 They aid in preventing hypoxia caused by problems
occurring upstream in the machine circuitry (disconnected
oxygen hose, low oxygen pressure in the pipeline, and
depletion of oxygen cylinders)
 These devices do not offer total protection against a hypoxic
mixture being delivered, because they do not prevent
anesthetic gas from flowing if there is no flow of oxygen.
 Equipment problems (such as leaks) or operator errors (such
as a closed or partially closed oxygen flow control valve) that
occur downstream are not prevented by these devices.
 They do not guard against accidents from crossovers in the
pipeline system or a cylinder containing the wrong gas.

89. GAS POWER OUTLET
 One or more gas power (auxiliary gas) outlets may be
present on an anesthesia machine. It may serve as the
source of driving gas for the anesthesia ventilator or to
supply gas for a jet ventilator. Either oxygen or air may be
used.
 In the past, the power outlet was usually present when the
ventilator was an add-on part of the anesthesia machine,
and one of several different ventilators could be used.
 However, with modern anesthesia machines, the ventilator
is an integral part of the machine and the breathing
system and is connected to the ventilator with internal
piping. Therefore, the power outlet is not found in many
anesthesia machines today.

90. GAS SELECTOR SWITCH
SOME MACHINES HAVE A GAS SELECTOR SWITCH THAT PREVENTS
AIR AND NITROUS OXIDE FROM BEING USED TOGETHER. TWO
TYPES OF SWITCHES ARE SHOWN.

91. SECOND-STAGE PRESSURE
REGULATOR
 Some machines have pressure regulators in the intermediate
pressure system just upstream of the flow indicators.
 Ohmeda uses a second-stage O2 pressure regulator which
receive gas from either the pipeline or the pressure regulator
and reduce it further to around 26 psi (177 kPa) for nitrous
oxide and 14 psi (95 kPa) for oxygen.
 The purpose of this pressure regulator is to eliminate
fluctuations in pressure supplied to the flow indicators
caused by fluctuations in pipeline pressure (ensures
constant oxygen flowmeter input until supply pressure is
less than 12-16 psi)
 By reducing the pressures below the normal fluctuation
range, the flow will remain more constant. Not all anesthesia
machines are equipped with this device.

92. OXYGEN FLUSH
 The oxygen flush (oxygen bypass, emergency oxygen bypass) receives
oxygen from the pipeline inlet or cylinder pressure regulator and directs a
high unmetered flow directly to the common gas outlet.
 It is commonly labeled “02+.”
 On most anesthesia machines, the oxygen flush can be activated regardless
of whether the master switch is turned ON or OFF.
 The anesthesia workstation requires that the oxygen flush be a single-
purpose, self-closing device operable with one hand and designed to
minimize unintentional activation. A flow between 35 and 75 L/minute must
be delivered.
 An oxygen flush consists of a button and stem connected to a ball. The ball
is in contact with the seat. When the button is depressed the ball is forced
away from the seat, allowing the oxygen to flow to the outlet. A spring
opposing the ball will close the valve when the button is not depressed.
 The button is commonly recessed or placed in a collar to prevent accidental
activation.

93. CONTD…….
 Oxygen flush activation may or may not result in other gas flows
being shut off and may result in either a positive or negative
pressure in the machine circuitry, depending upon the design of the
inlet and the flush line into the common gas line.
 This pressure will be transmitted back to other structures in the
machine, such as flow indicators and vaporizers, and may change
the vaporizer output and the flow indicator readings.
 The effect caused by oxygen flush activation will depend on the
pressure generated, the presence or absence of check valves in the
machine, and the relationship of the oxygen flush valve to other
components.
 The anesthesia workstation standard requires that the connection of
the flush valve delivery line to the common gas outlet be designed
so that activation does not increase or decrease the pressure at the
vaporizer outlet by more than 10 kPa or increase the vapor output by
more than 20%.

94. CONTD…..
Reported hazards associated with the oxygen flush include
 Accidental activation and internal leakage resulting in an
oxygen-enriched mixture being delivered.
 The flush valve may stick in the ON position obstructing the
flow of the gases from the flowmeters.
 Barotrauma and awareness during anesthesia have resulted
from its activation.
 Oxygen flush activation during inspiration delivered by the
anesthesia ventilator will result in delivery of high tidal
volumes and possible barotrauma. Ventilators that exclude
fresh gas flow from the breathing system during inspiration
will not present this problem

95. FLOW ADJUSTMENT CONTROL
 The flow adjustment controls regulate the flow of oxygen,
air, and other gases to the flow indicators.
 There are two types of flow adjustment controls:
mechanical and electronic.
 The anesthesia workstation standard requires that there
be only one flow control for each gas. It must be adjacent
to or identifiable with its associated flowmeter.

96. MECHANICAL FLOW CONTROL VALVE
 The mechanical flow control valve (needle valve, pin valve, fine
adjustment valve) controls the rate of gas flow through its
associated flowmeter
 Some also have an ON-OFF function. On some machines, the ON-
OFF function is controlled by the master switch.
 Mechanical flow control valves are used with both mechanical and
electronic flowmeters

97. MECHANICAL FLOW CONTROL VALVE
COMPONENTS
Body. The flow control valve body screws into the anesthesia
machine.
Stem and Seat.
The stem and seat have fine threads so that the stem moves
only a short distance when a complete turn is made.
When the valve is closed, the pin at the end of the stem fits into
the seat, occluding the orifice so that no gas can pass through
the valve. When the stem is turned outward, an opening between
the pin and the seat is created, allowing gas to flow through the
valve. The greater the space between the pin and the seat, the
greater the volume of gas that can flow.

98. To eliminate any looseness in the threads, the valve may be
spring loaded. This also minimizes flow fluctuations from
lateral or axial pressure applied to the flow control knob.

99. CONTD
It is advantageous to have stops for the OFF and MAXIMUM
flow positions. A stop for the OFF position avoids damage to
the valve seat. A stop for the MAXIMUM flow position
prevents the stem from becoming disengaged from the body.
Control Knob :
The control knob is joined to the stem. If it is a rotary style
knob, the oxygen flow control knob must have a fluted profile
and be as large as or larger than that for any other gas. All
other flow control knobs must be round. The knob is turned
counterclockwise to increase flow. If Other types of flow
control valves are present, the oxygen control must look and
feel different from the other controls.

100. Flow Control Knobs

101. CONTD…..
 When a machine is not being used, the gas source (cylinder
or pipeline) should be closed or disconnected.
 The flow control valves should be opened until the gas
pressure is reduced to zero and then closed.
 If the gas source is not disconnected, the flow control valve
should be turned OFF to avoid the fresh gas desiccating the
carbon dioxide absorbent and to conserve gas.
 Before machine use is resumed, the control valves should be
checked to make certain that they are closed.
 Sometimes, a flow control valve remains open after the gas
is bled out or opened when the machine is cleaned or moved.
 If the gas supply to an open flow control valve is restored
and the associated flow indicator is not observed, the
indicator may rise to the top of the tube where its presence
may not be noticed.
 Even if no harm to the patient results, the sudden rise may
damage it and impair the flow meter accuracy.

102. REFERENCES
Understanding Anesthesia Equipments
• DORSCH & DORSCH
Clinical Anesthesiology
• MORGAN
Drugs and Equipments in Anesthesia Practice
• ARUN K PAUL

103. thanks