Anaesthetic Machine Anatomy - University Of Bristol

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Anaesthetic MachineAnatomyYear Group: BVSc3 Document Number: CSL A00

Equipment list:Anaesthetic Machine AnatomyEquipment for this station: Anaesthetic machineName labelsFunction labelsConsiderations for this station: Do not attempt to attach cylinders or connect theoxygen pipeline, this machine is for reference only andis NOT a working machine.The first time you try to complete this task it may beworth refreshing your memory of the anaestheticmachine by reading the section of this booklet marked‘Answers’.Anyone working in the Clinical Skills Lab must read the ‘CSL I01 Induction’ andagree to abide by the ‘CSL I00 House Rules’ & ‘CSL I02 Lab Area Rules’Please inform a member of staff if equipment is damaged or about to run out.

Clinical Skills:Anaesthetic Machine Anatomy1Using the name labelsprovided, name each part ofthe anaesthetic machine(match/stick the white squarevelcro tab to the yellowsquare tab).4You will need to lift the lidto find all of thecomponents!2On the bottom of the namelabel, place a function label(match the circular tabs).3On some of the functionlabels there are additionalquestions.Place the correct answers inthe space provided (matchthe semi-circular tabs).5Once you have placed all ofthe labels, use theinformation on the followingpages of this booklet tocheck your answers.Here are some online resources and tutorials that you may find useful:1. nes/player.html2. 1LY0eAzrIrE

ANSWERS:Anaesthetic Machine AnatomyANSWERSThe following pages contain the answers i.e. the nameand function of each part of an anaesthetic machine

Clinical Skills:Anaesthetic Machine AnatomySchematic Diagram of an Anaesthetic MachinePressure regulatorPipelineoxygen (O2)O2 flushPressure gaugeCheck valveO2 failure alarmand reservoirCommongas outletOxygen(O2)FlowmeterN2O cut-offVaporiserNitrousoxide(N2O)Pipelinenitrous oxide(N2O)N.B. This diagram is simplified to aid in the understanding of the components.Anaesthetic machines have additional regulators and check valves to those shownabove. Ensure you know the functions of each of the components named in the diagram.

Clinical Skills:Anaesthetic Machine Anatomy1Gas source: Cylinders(not included on thismachine - do NOT attach)4The yoke also prevents acylinder being attached tothe wrong inlet via the PinIndex Safety System.The yoke for each gas typehas 2 protruding pins thatmatch 2 holes on therespective gas cylinders.The placement of the pins(and holes) vary for eachgas, with a potential 6 pinpositions, shown above.2Cylinders attach via a yoke.The yoke: Supports the cylinder Provides a gas-tight seal(Bodok seal) Allows unidirectional flowfrom the cylinder to themachine Prevents the cylinder beingattached to the wrong inlet(pin index system)53The yoke contains a Bodokseal. The Bodok seal consistsof a non-combustibleneoprene washer with acopper ring.It ensures a gas-tight sealbetween the yoke and thegas cylinder.6Yoke pin positions for anoxygen cylinder.Example pins on gascylinders: Oxygen (O2) has a pin indexof 2 & 5 Nitrous oxide (N2O) has apin index of 3 & 5

Clinical Skills:Anaesthetic Machine Anatomy789Schrader socketsGas source: Pipeline(do NOT attach the oxygenpipeline included on thismachine to the wall outlet)10Flexible pipelines have threecomponents:1. Schrader probeThis prevents misconnectionto the wrong gas service.Each gas probe has aprotruding index collar witha unique diameter - this onlyfits the Schrader socket forthe same gas type.Some practices use apipeline system.Piped gas is drawn from acentral source and fed into alabelled and colour-codedpipeline distributionnetwork which terminates inself-closing Schrader socketsat the wall.112. Flexible hosepipeModern hoses are colourcoded for each gas: Oxygen – white Nitrous oxide – blue Medical air – black & whiteFlexible pipelines connectthe terminal outlet to theanaesthetic machine.123. Non-InterchangeableScrew Thread (NIST)This comprises of a nut andprobe with a unique profilefor each type of gas.It includes a one-way valve toensure unidirectional flow.When a pipeline is used, it isgood practice to have reservecylinders available as a backup.

Clinical Skills:Anaesthetic Machine Anatomy1314SpringPressure regulator:Gas from cylinders is atvery high pressure( 10,000 kPa)This pressure needs to bereduced to a safe levelthat will not damage theanaesthetic machine(approximately 400 kPa)15Pressure gauges:The pressure gaugesindicate the pressure ofgas in kPa.If using cylinders, use thepressure gauge todetermine when thecylinder is nearly empty(low pressure on gauge)and needs changing.DiaphragmValveInlet fromcylinderHIGHPRESSUREOutlet tomachineLOWPRESSURE16Oxygen (O2) is stored as a gas inthe cylinder. The pressure isproportional to the volume of gasin the cylinder. As the cylinderempties, the pressure gaugedrops in a linear fashion.Nitrous oxide (N2O) is both liquidand gas in the cylinder. As N2O isused, liquid vapourises into thegaseous form and the pressureremains constant. Once the liquidis used up, the pressure fallsquickly. As soon as the pressuregauge decreases, be aware thatthe cylinder is nearly empty.The pressure regulator: Reduces the cylinderpressure to a suitablesupply pressure Compensates as thecylinder content decreasesThis ensures a safe deliveryof gas at a manageablepressure, whilst smoothingany fluctuations of pressurefrom the gas supply.17On this machine the pressuregauges can be identified forboth the cylinders and thepipeline supply.

Clinical Skills:Anaesthetic Machine Anatomy18Inlet19AlarmValveReservoirOutletCheck valve:The check valve is a one wayvalve that prevents backflowof gas to the atmosphere orbetween cylinders on onemachine.20O2 failure alarm:An alarm sounds when thepressure in the oxygensupply falls below 200 kPa.In this machine there is areservoir of air used tosupply the whistle alarm.O2O2N2O inputN2O outputN2O inputNitrous oxide cut off:The flow of N2O is dependent onoxygen pressure. When the O2pressure falls past a certainthreshold, the nitrous oxide supplyis cut off. This threshold is between130 kPa to 70 kPa, depending onthe machine.This prevents the administration ofa hypoxic gas mixture.N2O output

Clinical Skills:Anaesthetic Machine Anatomy21Flowmeter:Flowmeters measure theflow rate of a gas passingthrough them. They consistof:1. A flow control valve2. A tapered transparenttube3. A lightweight rotatingbobbin or ball24221. Flow control valves Reduce gas pressure from420 kPa to just aboveatmospheric pressure(1 atm or 100 kPa). Allow fine adjustment ofgas flow through theflowmeters by manualadjustment.25232. A tapered tube Gas enters the tube whenthe valve is open.3. A bobbin or ball The bobbin floats withinthe tube as the gas flowpasses around it. The higher the flow, thehigher the bobbin rises.26N2O flowmeterO2 flowmeterLinkGas flow rate:To adjust the gas flow rate ofa particular gas, rotate therespective flow controlvalve.Take care when adjustingthese valves, the mechanismis delicate and can be brokenby using too much force orclosing the valve too firmly.Read the gas flow rate from: The TOP of the bobbin(not the dot) The MIDDLE of the ball (ifa spherical ball is used inplace of a bobbin)Some flowmeters have a built inhypoxic guard: The O2 and N2Ocontrol valves are linkedmechanically. Either valve can beadjusted independently but thelink maintains a minimal ratio ofO2 : N2O.If you turned on the N2O alone,the O2 flowmeter is alsooperated so that 100% N2O isnot delivered. If you turn the O2off, the N2O is also turned off. Inthis way O2 can never beadministered at less than 20-25%

Clinical Skills:Anaesthetic Machine Anatomy27Occasionally old anaesthetic machines havean uncalibrated vaporiser. These are simpleand inexpensive but have been replaced bycalibrated vaporisers as the vapour producedvaries depending on temperature, gas flowrate and back pressure from a ventilator.Gas enters the chamber, picks up vapour andthen exits the vaporiser. It is difficult tocontrol the concentration of agent that isdelivered. As the agent vaporises it will cool.The saturated vapour pressure will fall andso less agent is delivered.Vaporisers:This is situated on the back bar ofthe anaesthetic machinedownstream of the flowmeter Itcontains the volatile liquidanaesthetic agent (e.g. isoflurane,sevoflurane). Gas is passed fromthe flowmeter through thevaporiser. The gas picks up“vapour” from the vaporiser todeliver to the patient. Mostvaporisers are calibrated (see 28).28Gas inGas outAgentvapourAgent liquidControl ValveGas inBrasscontainerCalibrated vaporiser: Designed to overcome flaws of simple model Gas entering vaporiser is split into two streams- Bypass channel (does not contact anaesthetic)- Chamber above liquid anaestheticBypassGas outChamberAgentvapourAgent liquidBi-metallic Strip A control valve adjusts the ratio of gas that bypasses the vapour chamber to the gas that passes throughthe chamber. The concentration of the vapour being “entrained” (picked up) by the gas can be increasedby adjusting this ratio. This valve is controlled by the large dial on the front of the vaporiser. The vaporiser is housed in a large block of brass to minimise the effect of temperature cooling. A bi-metallic strip is a secondary control point that adjusts the gas flow through the vaporiser. As the agentcools, the bimetallic strip moves, allowing a greater ratio of the gas to pass through the vapour chamber,entraining a greater concentration of volatile agent and mitigating the effect of temperature.

Clinical Skills:Anaesthetic Machine Anatomy293031Commongas outletBack bar:This is where thevaporiser(s) can beconnected to theanaesthetic machine.Some anaesthetic machineshave positions for more thanone vaporiser, on thesemachines there are safetyinterlocks to preventadministration of 2 volatileagents simultaneously.32Common gas outlet:This connects to theanaesthetic breathingcircuit to deliver thecombined product of gasesand anaesthetic agent tothe patient. It is also usedby the oxygen flush, in thecase of an emergency.33Wall outletO2 flush:This supplies O2 in an emergencydirectly from the high pressurecircuit (bypassing the flowmetersand vaporiser). This is pure O2 at35-60 L/min and does not containanaesthetic agent.On this old machine it is possibleto ‘hold’ the O2 flush - a dangerousfunction that is no longer possibleon newer machines due to the riskof causing barotrauma (injurycaused by ste anaesthetic gases andvolatile agents are subject to theControl of Substances Hazardousto Health and the Health andSafety at Work Act.“Scavenging” describes theremoval of environmentalcontaminants to ensure thatexposure limits are not exceeded(Isoflurane 50 ppm, N2O 50 ppm)There are 2 types of scavenging:1. Active2. Passive1. Active Scavenging Waste gases are drawnoutside of the building via afan and vent system. An air break is necessary toprevent negative pressurebeing applied to the patientbreathing system. On this machine the top of thescavenger would attach to thebreathing circuit, the bottomwould connect to the walloutlet.2. Passive Scavenging No fan Exhaled gas propelled by patient’sexpiratory effort into tubing:i. Waste gas carried via tubing tooutside of building (N.B. createshigh resistance making it moredifficult for patient to exhale).ii. Or waste gas absorbed in canisterof activated charcoal (N.B. N2O isNOT absorbed by this method). The canister should be weighedregularly to monitor lifespan andreplaced when it reaches aparticular weight.

Resetting the station:Anaesthetic Machine Anatomy1.2.3.Ensure all the name and function labels havebeen removed from the machineReturn the labels to their containersReplace the lid on the anaesthetic machineStation ready for the next person:Please inform a member of staff if equipment is damaged orabout to run out.

I wish I’d known:Anaesthetic Machine Anatomy It is essential that you know how an anaesthetic machineworks – if something goes wrong during a generalanaesthetic, you won’t have much time to figure it out!Different machines will have slight differences, make surethat you are familiar with the machine you are using,before starting the anaesthetic.

Anaesthetic Machine Anatomy O 2 flow-meter N 2 O flow-meter Link 22. Clinical Skills: 27 28 Vaporisers: This is situated on the back bar of the anaesthetic machine downstream of the flowmeter It contains the volatile liquid anaesthetic agent (e.g. isoflurane, sevoflurane). Gas is passed from the flowmeter through the vaporiser. The gas picks up vapour from the vaporiser to deliver to the .

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