The document discusses the key components of an anesthesia machine, including the high pressure system that receives gases from cylinders, the intermediate pressure system that receives gases from regulators or pipelines, and the low pressure system that extends from flow meters to the common gas outlet. It describes important safety features like fail-safe valves that prevent hypoxic mixtures if oxygen pressure drops, as well as limitations of such devices. The document also covers vaporizers, flow meters, and other parts that deliver medical gases and anesthetic agents.

1. Introductory LectureIntroductory Lecture
Series: The AnesthesiaSeries: The Anesthesia
MachineMachine
PORNSIRI WANNADILOKPORNSIRI WANNADILOK

2. ObjectivesObjectives
 Anesthesia MachineAnesthesia Machine
 VentilatorsVentilators
 Scavenging SystemsScavenging Systems
 System CheckoutSystem Checkout

3. vaporizer
bellow
Corrugated
tube
Soda lime
Flow
meter
ventilator
APL valve
Scavenging
system

4. The Anesthesia MachineThe Anesthesia Machine
High Intermediate Low Pressure Circuit

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

6. E Size Compressed GasE Size Compressed Gas
CylindersCylinders
CylinderCylinder
CharacteristicsCharacteristics
OxygenOxygen Nitrous OxideNitrous Oxide Carbon DioxideCarbon Dioxide AirAir
ColorColor WhiteWhite
(green)(green)
BlueBlue GrayGray Black/WhiteBlack/White
(yellow)(yellow)
StateState GasGas Liquid andLiquid and
gasgas
Liquid and gasLiquid and gas GasGas
Contents (L)Contents (L) 625625 15901590 15901590 625625
Empty WeightEmpty Weight
(kg)(kg)
5.905.90 5.905.90 5.905.90 5.905.90
Full Weight (kg)Full Weight (kg) 6.766.76 8.808.80 8.908.90
Pressure FullPressure Full
(psig)(psig)
20002000 750750 838838 18001800

7. Hanger YolkHanger Yolk
 Hanger Yolk: orientsHanger Yolk: orients
and supports theand supports the
cylinder, providing acylinder, providing a
gas-tight seal andgas-tight seal and
ensuring aensuring a
unidirectional gas flowunidirectional gas flow
into the machineinto the machine
 Index pins: Pin IndexIndex pins: Pin Index
Safety System (PISS)Safety System (PISS)
is gasis gas
specificspecificpreventsprevents
accidentalaccidental
rearrangement ofrearrangement of
cylinders (e.g..cylinders (e.g..

8. Pressure ReducingPressure Reducing
DeviceDevice
 Reduces the high and variable pressures found in aReduces the high and variable pressures found in a
cylinder to a lower and more constant pressurecylinder to a lower and more constant pressure
found in the anesthesia machine (45 psig)found in the anesthesia machine (45 psig)
 Reducing devices are preset so that the machineReducing devices are preset so that the machine
uses only gas from the pipeline (wall gas), when theuses only gas from the pipeline (wall gas), when the
pipeline inlet pressure is 50 psig.pipeline inlet pressure is 50 psig.
This prevents gas use from the cylinder even if theThis prevents gas use from the cylinder even if the
cylinder is left open (i.e. saves the cylinder forcylinder is left open (i.e. saves the cylinder for
backup if the wall gas pipeline fails)backup if the wall gas pipeline fails)

9. Pressure ReducingPressure Reducing
DeviceDevice
 Cylinders should be kept closedCylinders should be kept closed
routinely. Otherwise, if the wall gasroutinely. Otherwise, if the wall gas
fails, the machine will automaticallyfails, the machine will automatically
switch to the cylinder supply withoutswitch to the cylinder supply without
the anesthetist being aware that thethe anesthetist being aware that the
wall supply has failed (until thewall supply has failed (until the
cylinder is empty too).cylinder is empty too).

10. Intermediate PressureIntermediate Pressure
SystemSystem
 Receives gasses from theReceives gasses from the
regulator or the hospitalregulator or the hospital
pipeline at pressures of 40-pipeline at pressures of 40-
55 psig55 psig
 Consists of:Consists of:
– Pipeline inlet connectionsPipeline inlet connections
– Pipeline pressurePipeline pressure
indicatorsindicators
– PipingPiping
– Gas power outletGas power outlet
– Master switchMaster switch
– Oxygen pressure failureOxygen pressure failure
devicesdevices
– Oxygen flushOxygen flush
– Additional reducing devicesAdditional reducing devices
– Flow control valvesFlow control valves

11. Pipeline InletPipeline Inlet
ConnectionsConnections
 Mandatory N2O and O2,Mandatory N2O and O2,
usually have air andusually have air and
suction toosuction too
 Inlets are non-Inlets are non-
interchangeable due tointerchangeable due to
specific threading as perspecific threading as per
the Diameter Index Safetythe Diameter Index Safety
System (DISS)System (DISS)
 Each inlet must contain aEach inlet must contain a
check valve to preventcheck valve to prevent
reverse flow (similar to thereverse flow (similar to the
cylinder yolk)cylinder yolk)

12. Oxygen Pressure FailureOxygen Pressure Failure
DevicesDevices
 Machine standard requires that an anesthesiaMachine standard requires that an anesthesia
machine be designed so that whenever the oxygenmachine be designed so that whenever the oxygen
supply pressure is reduced below normal, thesupply pressure is reduced below normal, the
oxygen concentration at the common gas outletoxygen concentration at the common gas outlet
does not fall below 19%does not fall below 19%

13. Oxygen Pressure FailureOxygen Pressure Failure
DevicesDevices
 AA Fail-Safe valveFail-Safe valve is present in the gas lineis present in the gas line
supplying each of the flowmeters except O2.supplying each of the flowmeters except O2.
This valve is controlled by the O2 supplyThis valve is controlled by the O2 supply
pressure and shuts off or proportionatelypressure and shuts off or proportionately
decreases the supply pressure of all otherdecreases the supply pressure of all other
gasses as the O2 supply pressuregasses as the O2 supply pressure
decreasesdecreases
 Historically there are 2 kinds of fail-safeHistorically there are 2 kinds of fail-safe
valvesvalves
– Pressure sensor shut-off valve (Ohmeda)Pressure sensor shut-off valve (Ohmeda)
– Oxygen failure protection device (Drager)Oxygen failure protection device (Drager)

14. Pressure Sensor Shut-Pressure Sensor Shut-
Off ValveOff Valve
 Oxygen supply pressureOxygen supply pressure
opens the valve as longopens the valve as long
as it is above a pre-setas it is above a pre-set
minimum value (e.g.. 20minimum value (e.g.. 20
psig).psig).
 If the oxygen supplyIf the oxygen supply
pressure falls below thepressure falls below the
threshold value the valvethreshold value the valve
closes and the gas incloses and the gas in
that limb (e.g.. N2O),that limb (e.g.. N2O),
does not advance to itsdoes not advance to its
flow-control valve.flow-control valve.

15. Oxygen FailureOxygen Failure
Protection DeviceProtection Device
(OFPD)(OFPD)
 Based on a proportioning principle rather than aBased on a proportioning principle rather than a
shut-off principleshut-off principle
 The pressure of all gases controlled by the OFPDThe pressure of all gases controlled by the OFPD
will decrease proportionately with the oxygenwill decrease proportionately with the oxygen
pressurepressure

16. Oxygen Supply FailureOxygen Supply Failure
AlarmAlarm
 The machine standard specifies thatThe machine standard specifies that
whenever the oxygen supply pressurewhenever the oxygen supply pressure
falls below a manufacturer-specifiedfalls below a manufacturer-specified
threshold (usually 30 psig) a mediumthreshold (usually 30 psig) a medium
priority alarm shall blow within 5priority alarm shall blow within 5
seconds.seconds.

17. Limitations of Fail-SafeLimitations of Fail-Safe
Devices/AlarmsDevices/Alarms
 Fail-safe valvesFail-safe valves do notdo not preventprevent
administration of a hypoxic mixture becauseadministration of a hypoxic mixture because
they depend on pressure and not flow.they depend on pressure and not flow.
 These devicesThese devices do notdo not prevent hypoxia fromprevent hypoxia from
accidents such as pipeline crossovers or aaccidents such as pipeline crossovers or a
cylinder containing the wrong gascylinder containing the wrong gas

18. Limitations of Fail-SafeLimitations of Fail-Safe
Devices/AlarmsDevices/Alarms
 These devicesThese devices prevent hypoxia from someprevent hypoxia from some
problems occurring upstreamproblems occurring upstream in thein the
machine circuitry (disconnected oxygenmachine circuitry (disconnected oxygen
hose, low oxygen pressure in the pipelinehose, low oxygen pressure in the pipeline
and depletion of the oxygen cylinder)and depletion of the oxygen cylinder)
 EquipmentEquipment problems that occur downstreamproblems that occur downstream
(for example leaks or partial closure of the(for example leaks or partial closure of the
oxygen flow control valve)oxygen flow control valve) are not preventedare not prevented
by these devices.by these devices.

19. Oxygen Flush ValveOxygen Flush Valve
(O2+)(O2+) Receives O2 from pipelineReceives O2 from pipeline
inlet or cylinder reducinginlet or cylinder reducing
device and directs high,device and directs high,
unmetered flow directly tounmetered flow directly to
the common gas outletthe common gas outlet
(downstream of the(downstream of the
vaporizer)vaporizer)
 Machine standard requiresMachine standard requires
that the flow be betweenthat the flow be between
35 and 75 L/min35 and 75 L/min
 The ability to provideThe ability to provide jetjet
ventilationventilation
 HazardsHazards
– May cause barotraumaMay cause barotrauma
– Dilution of inhaled anestheticDilution of inhaled anesthetic

20. Second-Stage ReducingSecond-Stage Reducing
DeviceDevice
 Located just upstream of the flowLocated just upstream of the flow
control valvescontrol valves
 Receives gas from the pipeline inlet orReceives gas from the pipeline inlet or
the cylinder reducing device andthe cylinder reducing device and
reduces it further to 26 psig for N2Oreduces it further to 26 psig for N2O
and 14 psig for O2and 14 psig for O2
 Purpose is to eliminate fluctuations inPurpose is to eliminate fluctuations in
pressure supplied to the flowpressure supplied to the flow
indicators caused by fluctuations inindicators caused by fluctuations in
pipeline pressurepipeline pressure

21. Low Pressure SystemLow Pressure System
 Extends from the flow control valves toExtends from the flow control valves to
the common gas outletthe common gas outlet
 Consists of:Consists of:
– Flow metersFlow meters
– Vaporizer mounting deviceVaporizer mounting device
– Check valveCheck valve
– Common gas outletCommon gas outlet

22. Flowmeter assemblyFlowmeter assembly
 When the flow control valveWhen the flow control valve
is opened the gas enters atis opened the gas enters at
the bottom and flows up thethe bottom and flows up the
tube elevating the indicatortube elevating the indicator
 The indicator floats freely atThe indicator floats freely at
a point where thea point where the
downward force on itdownward force on it
(gravity) equals the upward(gravity) equals the upward
force caused by gasforce caused by gas
molecules hitting the bottommolecules hitting the bottom
of the floatof the float

23. Arrangement of theArrangement of the
Flow-Indicator TubesFlow-Indicator Tubes
 In the presence of a flowmeterIn the presence of a flowmeter
leak (either at the “O” ring or theleak (either at the “O” ring or the
glass of the flow tube) a hypoxicglass of the flow tube) a hypoxic
mixture is less likely to occur ifmixture is less likely to occur if
the O2 flowmeter isthe O2 flowmeter is downstreamdownstream
of all other flowmetersof all other flowmeters
 In A and B a hypoxic mixtureIn A and B a hypoxic mixture
can result because a substantialcan result because a substantial
portion of oxygen flow passesportion of oxygen flow passes
through the leak, and all nitrousthrough the leak, and all nitrous
oxide is directed to the commonoxide is directed to the common
gas outletgas outlet
** Note that a leak in the oxygenNote that a leak in the oxygen
flowmeter tube can cause a hypoxicflowmeter tube can cause a hypoxic
mixture, even when oxygen ismixture, even when oxygen is
located in the downstream positionlocated in the downstream position

24. Proportioning SystemsProportioning Systems
– MechanicalMechanical
integration of the N2Ointegration of the N2O
and O2 flow-controland O2 flow-control
valvesvalves
– AutomaticallyAutomatically
intercedes to maintainintercedes to maintain
a minimum 25%a minimum 25%
concentration ofconcentration of
oxygen with aoxygen with a
maximum N2O:O2maximum N2O:O2
ratio of 3:1ratio of 3:1

25. Limitations ofLimitations of
Proportioning SystemsProportioning Systems
 Machines equipped with proportioningMachines equipped with proportioning
systems can still deliver a hypoxic mixturesystems can still deliver a hypoxic mixture
under the following conditions:under the following conditions:
– Wrong supply gasWrong supply gas
– Defective pneumatics or mechanics (e.g.. TheDefective pneumatics or mechanics (e.g.. The
Link-25 depends on a properly functioningLink-25 depends on a properly functioning
second stage regulator)second stage regulator)
– Leak downstream (e.g.. Broken oxygen flowLeak downstream (e.g.. Broken oxygen flow
tube)tube)
– Inert gas administration: Proportioning systemsInert gas administration: Proportioning systems
generally link only N2O and O2generally link only N2O and O2

26. VaporizersVaporizers
 A vaporizer is an instrument designedA vaporizer is an instrument designed
to change a liquid anesthetic agentto change a liquid anesthetic agent
into its vapor and add a controlledinto its vapor and add a controlled
amount of this vapor to the fresh gasamount of this vapor to the fresh gas
flowflow

27. Classification ofClassification of
VaporizersVaporizers
Methods of regulating output concentrationMethods of regulating output concentration
Concentration calibrated (e.g. variable bypass)Concentration calibrated (e.g. variable bypass)
Measured flowMeasured flow
Method of vaporization
Flow-overFlow-over
Bubble throughBubble through
InjectionInjection
Temperature compensation
ThermocompensationThermocompensation
Supplied heatSupplied heat

28. Generic BypassGeneric Bypass
VaporizerVaporizer
 Flow from the flowmetersFlow from the flowmeters
enters the inlet of theenters the inlet of the
vaporizervaporizer
 The function of theThe function of the
concentration control valveconcentration control valve
is to regulate the amountis to regulate the amount
of flow through the bypassof flow through the bypass
and vaporizing chambersand vaporizing chambers
Splitting Ratio = flow though vaporizingSplitting Ratio = flow though vaporizing
chamber/flow through bypasschamber/flow through bypass
chamberchamber

29. Factors That InfluenceFactors That Influence
Vaporizer OutputVaporizer Output
 Flow RateFlow Rate: The output of the vaporizer is: The output of the vaporizer is
generallygenerally lessless than the dial setting at very low (<than the dial setting at very low (<
200 ml/min) or very high (> 15 L/min) flows200 ml/min) or very high (> 15 L/min) flows
 TemperatureTemperature: Automatic temperature: Automatic temperature
compensating mechanisms in bypass chamberscompensating mechanisms in bypass chambers
maintain a constant vaporizer output with varyingmaintain a constant vaporizer output with varying
temperaturestemperatures
 Back PressureBack Pressure: Intermittent back pressure (e.g.: Intermittent back pressure (e.g.
positive pressure ventilation causes apositive pressure ventilation causes a higherhigher
vaporizer output than the dial setting)vaporizer output than the dial setting)

30. Factors That InfluenceFactors That Influence
Vaporizer OutputVaporizer Output
 Atmospheric PressureAtmospheric Pressure : Changes in: Changes in
atmospheric pressure affect variable bypassatmospheric pressure affect variable bypass
vaporizer output as measured by volume %vaporizer output as measured by volume %
concentration, but not (or very little) asconcentration, but not (or very little) as
measured by partial pressure (loweringmeasured by partial pressure (lowering
atmospheric pressure increases volume %atmospheric pressure increases volume %
concentration and vice versa)concentration and vice versa)
 Carrier GasCarrier Gas: Vaporizers are calibrated for: Vaporizers are calibrated for
100% oxygen. Carrier gases other than this100% oxygen. Carrier gases other than this
result in decreased vaporizer output.result in decreased vaporizer output.

31. The Circuit: CircleThe Circuit: Circle
SystemSystem
 Arrangement is variable,Arrangement is variable,
but to prevent re-breathingbut to prevent re-breathing
of CO2, the following rulesof CO2, the following rules
must be followed:must be followed:
– Unidirectional valvesUnidirectional valves
between the patient andbetween the patient and
the reservoir bagthe reservoir bag
– Fresh-gas-flow cannotFresh-gas-flow cannot
enter the circuit betweenenter the circuit between
the expiratory valve andthe expiratory valve and
the patientthe patient
– Adjustable pressure-Adjustable pressure-
limiting valve (APL)limiting valve (APL) cannotcannot
be located between thebe located between the
patient and the inspiratorypatient and the inspiratory
valvevalve

32. Circle SystemCircle System
 Advantages:Advantages:
– RelativeRelative stabilitystability of inspired concentrationof inspired concentration
– Conservation of respiratoryConservation of respiratory moisture and heatmoisture and heat
– Prevention of operating roomPrevention of operating room pollutionpollution
– PaCO2 depends only on ventilation, not freshPaCO2 depends only on ventilation, not fresh
gas flowgas flow
– Low fresh gas flows can be usedLow fresh gas flows can be used
 Disadvantages:Disadvantages:
– ComplexComplex design = potential for malfunctiondesign = potential for malfunction
– HighHigh resistanceresistance (multiple one-way valves) =(multiple one-way valves) =
higher work of breathinghigher work of breathing

33. The Adjustable PressureThe Adjustable Pressure
Limiting (APL) ValveLimiting (APL) Valve
 User adjustable valveUser adjustable valve
that releases gases tothat releases gases to
the scavenging systemthe scavenging system
and is intended toand is intended to
provide control of theprovide control of the
pressure in thepressure in the
breathing systembreathing system
 Bag-mask VentilationBag-mask Ventilation::
Valve is usually leftValve is usually left
partially open. Duringpartially open. During
inspiration the bag isinspiration the bag is
squeezed pushing gassqueezed pushing gas
into the inspiratory limbinto the inspiratory limb
until the pressure reliefuntil the pressure relief

34. Scavenging SystemsScavenging Systems
 Protects theProtects the
breathing circuit orbreathing circuit or
ventilator fromventilator from
excessive positive orexcessive positive or
negative pressurenegative pressure..

35. Scavenging SystemsScavenging Systems

36. Checking AnesthesiaChecking Anesthesia
MachinesMachines
8 Categories of check:
 Emergency ventilation equipment
 High-Pressure system
 Low-Pressure system
 Scavenging system
 Breathing system
 Manual and automatic ventilation system
 Monitors
 Final Position

37. The end