Anaesthetic Machine Anatomy
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Anaesthetic Machine Anatomy Year Group: BVSc3 + Document Number: CSL_A00 Equipment list: Anaesthetic Machine Anatomy Equipment for this station: • Anaesthetic machine • Name labels • Function labels Considerations for this station: • Do not attempt to attach cylinders or connect the oxygen pipeline, this machine is for reference only and is NOT a working machine. • The first time you try to complete this task it may be worth refreshing your memory of the anaesthetic machine by reading the section of this booklet marked ‘Answers’. Anyone working in the Clinical Skills Lab must read the ‘CSL_I01 Induction’ and agree 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 Anatomy 1 2 3 Using the name labels On the bottom of the name On some of the function provided, name each part of label, place a function label labels there are additional the anaesthetic machine (match the circular tabs). questions. (match/stick the white square Place the correct answers in velcro tab to the yellow the space provided (match square tab). the semi-circular tabs). 4 5 You will need to lift the lid Once you have placed all of to find all of the the labels, use the components! information on the following pages of this booklet to check your answers. Here are some online resources and tutorials that you may find useful: 1. http://mhra.gov.uk/learningcentre/AnaestheticMachines/player.html 2. https://www.youtube.com/watch?v=1LY0eAzrIrE ANSWERS: Anaesthetic Machine Anatomy ANSWERS The following pages contain the answers i.e. the name and function of each part of an anaesthetic machine Clinical Skills: Anaesthetic Machine Anatomy Schematic Diagram of an Anaesthetic Machine Pipeline Pressure regulator oxygen (O2) O2 flush Pressure gauge O2 failure alarm Check valve and reservoir Common Oxygen gas outlet (O2) Flowmeter Vaporiser N2O cut-off Nitrous oxide (N2O) Pipeline nitrous 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 shown above. Ensure you know the functions of each of the components named in the diagram. Clinical Skills: Anaesthetic Machine Anatomy 1 2 3 Gas source: Cylinders attach via a yoke. The yoke contains a Bodok • Cylinders The yoke: seal. The Bodok seal consists (not included on this • Supports the cylinder of a non-combustible machine - do NOT attach) • Provides a gas-tight seal neoprene washer with a (Bodok seal) copper ring. • Allows unidirectional flow It ensures a gas-tight seal from the cylinder to the between the yoke and the machine gas cylinder. • Prevents the cylinder being attached to the wrong inlet (pin index system) 4 5 6 The yoke also prevents a Yoke pin positions for an cylinder being attached to oxygen cylinder. the wrong inlet via the Pin Index Safety System. Example pins on gas The yoke for each gas type cylinders: has 2 protruding pins that • Oxygen (O ) has a pin index match 2 holes on the 2 of 2 & 5 respective gas cylinders. • Nitrous oxide (N O) has a The placement of the pins 2 pin index of 3 & 5 (and holes) vary for each gas, with a potential 6 pin positions, shown above. Clinical Skills: Anaesthetic Machine Anatomy 7 8 9 Schrader sockets Gas source: Some practices use a Flexible pipelines connect • Pipeline pipeline system. the terminal outlet to the (do NOT attach the oxygen Piped gas is drawn from a anaesthetic machine. pipeline included on this central source and fed into a machine to the wall outlet) labelled and colour-coded pipeline distribution network which terminates in self-closing Schrader sockets at the wall. 10 11 12 Flexible pipelines have three 2. Flexible hosepipe 3. Non-Interchangeable components: Modern hoses are colour Screw Thread (NIST) 1. Schrader probe coded for each gas: This comprises of a nut and probe with a unique profile This prevents misconnection • Oxygen – white for each type of gas. to the wrong gas service. • Nitrous oxide – blue It includes a one-way valve to Each gas probe has a • Medical air – black & white ensure unidirectional flow. protruding index collar with a unique diameter - this only When a pipeline is used, it is fits the Schrader socket for good practice to have reserve the same gas type. cylinders available as a back- up. Clinical Skills: Anaesthetic Machine Anatomy 13 14 Spring Pressure regulator: Diaphragm The pressure regulator: • Gas from cylinders is at Reduces the cylinder pressure to a suitable very high pressure supply pressure (>10,000 kPa) Valve • Compensates as the This pressure needs to be cylinder content decreases reduced to a safe level This ensures a safe delivery that will not damage the Inlet from Outlet to of gas at a manageable anaesthetic machine cylinder machine pressure, whilst smoothing (approximately 400 kPa) HIGH LOW any fluctuations of pressure PRESSURE PRESSURE from the gas supply. 15 16 17 Pressure gauges: Oxygen (O2) is stored as a gas in On this machine the pressure The pressure gauges the cylinder. The pressure is gauges can be identified for proportional to the volume of gas indicate the pressure of both the cylinders and the in the cylinder. As the cylinder pipeline supply. gas in kPa. empties, the pressure gauge If using cylinders, use the drops in a linear fashion. pressure gauge to Nitrous oxide (N2O) is both liquid determine when the and gas in the cylinder. As N2O is cylinder is nearly empty used, liquid vapourises into the (low pressure on gauge) gaseous form and the pressure remains constant. Once the liquid and needs changing. is used up, the pressure falls quickly. As soon as the pressure gauge decreases, be aware that the cylinder is nearly empty. Clinical Skills: Anaesthetic Machine Anatomy Inlet 18 19 Alarm Valve Reservoir Outlet Check valve: O2 failure alarm: The check valve is a one way An alarm sounds when the valve that prevents backflow pressure in the oxygen of gas to the atmosphere or supply falls below 200 kPa. between cylinders on one In this machine there is a machine. reservoir of air used to supply the whistle alarm. O2 20 O2 N2O input N2O input N2O output N O output Nitrous oxide cut off: 2 The flow of N2O is dependent on oxygen pressure. When the O2 pressure falls past a certain threshold, the nitrous oxide supply is cut off. This threshold is between 130 kPa to 70 kPa, depending on the machine. This prevents the administration of a hypoxic gas mixture. Clinical Skills: Anaesthetic Machine Anatomy 21 22 23 Flowmeter: 1. Flow control valves 2. A tapered tube Flowmeters measure the • Reduce gas pressure from • Gas enters the tube when flow rate of a gas passing 420 kPa to just above the valve is open. through them. They consist atmospheric pressure 3. A bobbin or ball of: (1 atm or 100 kPa). • The bobbin floats within 1. A flow control valve • Allow fine adjustment of the tube as the gas flow 2. A tapered transparent gas flow through the passes around it. tube flowmeters by manual • The higher the flow, the 3. A lightweight rotating adjustment. higher the bobbin rises. bobbin or ball 24 25 26 N2O flow- O2 flow- meter meter Link Gas flow rate: Read the gas flow rate from: Some flowmeters have a built in To adjust the gas flow rate of • The TOP of the bobbin hypoxic guard: The O2 and N2O control valves are linked a particular gas, rotate the (not the dot) mechanically. Either valve can be respective flow control • The MIDDLE of the ball (if adjusted independently but the valve. a spherical ball is used in link maintains a minimal ratio of Take care when adjusting place of a bobbin) O2 : N2O. these valves, the mechanism If you turned on the N2O alone, is delicate and can be broken the O2 flowmeter is also by using too much force or operated so that 100% N2O is closing the valve too firmly. not delivered. If you turn the O2 off, the N2O is also turned off. In this way O2 can never be administered at less than 20-25% Clinical Skills: Anaesthetic Machine Anatomy 27 Occasionally old anaesthetic machines have an uncalibrated vaporiser. These are simple and inexpensive but have been replaced by calibrated vaporisers as the vapour produced varies depending on temperature, gas flow rate and back pressure from a ventilator. Gas enters the chamber, picks up vapour and then exits the vaporiser. It is difficult to control the concentration of agent that is delivered. As the agent vaporises it will cool. Vaporisers: The saturated vapour pressure will fall and so less agent is delivered. This is situated on the back bar of the anaesthetic machine Gas in Gas out downstream of the flowmeter It contains the volatile liquid anaesthetic agent (e.g. isoflurane, Agent sevoflurane). Gas is passed from vapour the flowmeter through the Agent liquid vaporiser. The gas picks up “vapour” from the vaporiser to deliver to the patient. Most vaporisers are calibrated (see 28). 28 Control Valve Gas in Bypass Gas out Brass Chamber container Agent vapour Calibrated vaporiser: Agent liquid • Designed to overcome flaws of simple model • Gas entering vaporiser is split into two streams - Bypass channel (does not contact anaesthetic) Bi-metallic Strip - Chamber above liquid anaesthetic • A control valve adjusts the ratio of gas that bypasses the vapour chamber to the gas that passes through the chamber. The concentration of the vapour being “entrained” (picked up) by the gas can be increased by adjusting this ratio.