Anaesthetic MachinesAnaesthetic Machines

Anaesthesia MachineAnaesthesia Machine

““An Anaesthesia Machine is a device An Anaesthesia Machine is a device which is used to deliver a precisely which is used to deliver a precisely known but variable gas mixture known but variable gas mixture including anaesthetic & life including anaesthetic & life sustaining gases to the patients sustaining gases to the patients respiratory system”respiratory system”

HistoryHistory

Original Continuous-flow Anaesthetic Original Continuous-flow Anaesthetic Machine was designed by Boyle in Machine was designed by Boyle in 19171917

Most current anaesthetic machines Most current anaesthetic machines are derived from Boyles Machineare derived from Boyles Machine

Boyles Anaesthetic MachineBoyles Anaesthetic Machine

http://www.nda.ox.ac.uk/wfsa/html/u06/u06_015.htm

Functions of AnaesthesiaFunctions of Anaesthesia

It ensures that the patient does not It ensures that the patient does not feel pain & minimizes patient feel pain & minimizes patient discomfort.discomfort.

It provides the surgeon with It provides the surgeon with favourable conditions for the work.favourable conditions for the work.

Why do we need an Why do we need an anaesthetic machine?anaesthetic machine?

Supply compressed gasesSupply compressed gases Measure flow of gasesMeasure flow of gases Add vapours in known concentrationsAdd vapours in known concentrations Deliver vapours and gases to patient Deliver vapours and gases to patient

via breathing systemvia breathing system Scavenge wasteScavenge waste

Components of the Anaesthetic Components of the Anaesthetic MachineMachine

Gas suppliesGas supplies Pressure gaugesPressure gauges Pressure reducing valvesPressure reducing valves RotametersRotameters VapourisersVapourisers Common gas outletCommon gas outlet High flow oxygen flushHigh flow oxygen flush Pressure relief valvePressure relief valve Oxygen supply failure alarmOxygen supply failure alarm

Breathing Breathing systemsystem

VentilatorVentilator ScavengingScavenging SuctionSuction Monitoring Monitoring

devices devices

Basic Components of Anaesthetic Basic Components of Anaesthetic MachineMachine

Fundamentals of AnaesthesiaFundamentals of Anaesthesia

Gas Supply - PipelinesGas Supply - Pipelines

Central supply pointCentral supply point OO22, N, N22O, air, medical vacuum O, air, medical vacuum

suppliedsupplied Pipelines throughout hospitalPipelines throughout hospital Outlets – colour and shape codedOutlets – colour and shape coded Pipelines permanently fixed to Pipelines permanently fixed to

machine (Non-Interchangable Screw machine (Non-Interchangable Screw Thread – NIST)Thread – NIST)

Gas CylindersGas Cylinders

Essentials of Anaesthetic EquipmentEssentials of Anaesthetic Equipment

YokeYoke

Each Anaesthesia Machine has atleast Each Anaesthesia Machine has atleast one yoke for an oxygen cylinder but one yoke for an oxygen cylinder but most are provided with two.most are provided with two.

To prevent incorrect placement of tank To prevent incorrect placement of tank into wrong yoke, two pins located in the into wrong yoke, two pins located in the yoke must fit into corresponding holes yoke must fit into corresponding holes drilled into the tank neck.drilled into the tank neck.

Pressure RegulatorsPressure Regulators

Reduce pressure to protect machineReduce pressure to protect machine

Maintain constant supply to Maintain constant supply to compensate for changing cylinder compensate for changing cylinder pressures.pressures.

Pressure GaugesPressure Gauges Pressure gauges to measure pipeline and Pressure gauges to measure pipeline and

cylinder pressurescylinder pressures OO22, N, N22O and air gauges on front of machineO and air gauges on front of machine For OFor Oxygen,operating range of gauge isxygen,operating range of gauge is

0 to 150Kg/cm²0 to 150Kg/cm²

Bourdon GaugeBourdon Gauge

RotametersRotameters Measure flow rate of gas passing through Measure flow rate of gas passing through

themthem Calibration (accuracy +/- 2.5%)Calibration (accuracy +/- 2.5%)

ComponentsComponents: flow control: flow control

(needle) valve, tapered tube, (needle) valve, tapered tube,

bobbinbobbin

Back BarBack Bar

Horizontal part of machine between rotameters Horizontal part of machine between rotameters and common gas outletand common gas outlet

Vapourisers mounted here so volatiles can be Vapourisers mounted here so volatiles can be added to fresh gasesadded to fresh gases

Pressure ranges 0-30 kPa (1 kPa at outlet end) Pressure ranges 0-30 kPa (1 kPa at outlet end)

Non-return pressure relief valve downstream of Non-return pressure relief valve downstream of vapourisers set at 35 kPa – prevents barotrauma vapourisers set at 35 kPa – prevents barotrauma to rotameters, vapourisers and patientto rotameters, vapourisers and patient

VapourisersVapourisers Add controlled amount inhalational agent, after Add controlled amount inhalational agent, after

changing it from liquid to gas, to fresh gas flowchanging it from liquid to gas, to fresh gas flow Design depends on SVP, boiling point and MAC Design depends on SVP, boiling point and MAC

of volatile being used – variable bypass or of volatile being used – variable bypass or measured flow vapourisermeasured flow vapouriser

Accurate delivery of anaesthetic agent Accurate delivery of anaesthetic agent regardless of time, gas flow and temperatureregardless of time, gas flow and temperature

Antispill mechanismAntispill mechanism Colour coded keyed filling devicesColour coded keyed filling devices Safety interlock deviceSafety interlock device

Variable Bypass VapouriserVariable Bypass Vapouriser

Essentials of Anaesthetic EquipmentEssentials of Anaesthetic Equipment

Measured Flow VapouriserMeasured Flow Vapouriser

http://www.frca.co.uk/article.aspx?articleid=100151

HumidificationHumidification

Dry gases supplied by the anaesthesia Dry gases supplied by the anaesthesia machine may cause clinically machine may cause clinically significant desiccation of mucus. This significant desiccation of mucus. This may contribute to retention of may contribute to retention of secretion & the mucus flow may secretion & the mucus flow may cease.cease.

Two Types of Humidity:Two Types of Humidity: Absolute Humidity.Absolute Humidity. Relative Humidity .Relative Humidity .

Safety Features of Anaesthetic Safety Features of Anaesthetic MachinesMachines

Non interchangable Non interchangable pipeline outletspipeline outlets

Colour coded pipelines Colour coded pipelines and cylindersand cylinders

Pin index systemPin index system Pressure gauges for Pressure gauges for

gasesgases Colour coded Colour coded

rotametersrotameters Oxygen rotameter on Oxygen rotameter on

left, protrudes, ridgedleft, protrudes, ridged

Oxygen/nitrous oxide Oxygen/nitrous oxide interlink deviceinterlink device

Emergency oxygen Emergency oxygen flushflush

Oxygen failure Oxygen failure warning devicewarning device

Keyed vapouriser Keyed vapouriser fillersfillers

Pressure relief valvePressure relief valve Anaesthetist to Anaesthetist to

check the machinecheck the machine

Oxygen Failure Warning Oxygen Failure Warning DeviceDevice

Upstream of rotametersUpstream of rotameters

Specifications (British Safety Standard):Specifications (British Safety Standard): Audible alarm >60db, 1m from machine, >7 Audible alarm >60db, 1m from machine, >7

secondsseconds Activated when OActivated when O22 supply falls to 200kPa supply falls to 200kPa Power supply from OPower supply from O22 supply pressure supply pressure Alarm can’t be switched off/reset until OAlarm can’t be switched off/reset until O22

supply restoredsupply restored Coupled to gas cut off valve – opens machine Coupled to gas cut off valve – opens machine

circuitry to aircircuitry to air

Emergency Oxygen FlushEmergency Oxygen Flush

Non-locking buttonNon-locking button Bypass rotameter block and back barBypass rotameter block and back bar Delivers flow > 30 l/minDelivers flow > 30 l/min Pressure ~ 400 kPaPressure ~ 400 kPa

Risks:Risks: BarotraumaBarotrauma AwarenessAwareness

ReferencesReferences

R.S KhandpurR.S Khandpur

Pinnock et al (2003) Fundamentals of Pinnock et al (2003) Fundamentals of Anaesthesia. CambridgeAnaesthesia. Cambridge

Anaesthesia UK (2005) Temperature Anaesthesia UK (2005) Temperature Measurement Measurement www.frca.co.uk/article.aspx?articleidwww.frca.co.uk/article.aspx?articleid=100325=100325

Anaesthesia UK (2004) Precision Vapourisers Anaesthesia UK (2004) Precision Vapourisers http://www.frca.co.uk/article.aspx?articleid=1001http://www.frca.co.uk/article.aspx?articleid=10015151