1887

The anaesthetic machine and vaporizers

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Abstract

Accurate and continuous delivery of gas and vapour mixtures of desired compositions is made possible by the use of an anaesthetic machine or vaporizer. Several manufacturers produce anaesthetic machines for human or veterinary use and, although the equipment is varied, the basic design remains the same and a working knowledge of the basic components will enable familiarity with newer designs. This chapter describes gas supplies, the anaesthetic machine and vaporizers.

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Figures

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4.1 Three wall rail-mounted anaesthetic machines in a preparation room.
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4.2 A wall rail-mounted machine with twin positions for vaporizers on the back bar.
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4.3 (a) A modern anaesthetic machine with integrated ventilator and multiparameter monitor. (b) An MRI-compatible anaesthetic machine.
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4.4 A size E oxygen cylinder with protective plastic wrapping around the valve block and plastic label showing the contents and other information. The colour-coded plastic discs between the valve block and cylinder neck show when cylinder testing is next due.
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4.6 British Oxygen Company (BOC) chart showing the new cylinder colours for commonly used medical gases. (Courtesy of BOC Healthcare)
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4.7 Storage of new and used size E cylinders.
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4.8 Warning signs on the door to a medical gas cylinder store.
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4.9 Pin indexing on the valve blocks of (a) a size E oxygen cylinder and (b) a size E nitrous oxide cylinder.
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4.10 Pin-indexed yokes for (a) a size E oxygen cylinder and (b) a size E medical air cylinder.
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4.11 Chart showing cylinder types, valve types and pin-indexed valves. (Courtesy of BOC Healthcare)
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4.12 A Bodok seal.
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4.13 (a) An oxygen cylinder manifold. (b) Pipeline attached to the valve on a size J oxygen cylinder. (c) Manifold control for the medical gas banks.
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4.14 Vacuum-insulated evaporators for liquid oxygen.
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4.15 An oxygen concentrator with an anaesthetic machine. (Courtesy of MSS International Ltd)
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4.16 Gas pipeline leaving the manifold supplying medical gases to the essential areas of a veterinary hospital.
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4.17 Self-sealing wall-mounted terminal outlets (Schrader sockets) for oxygen and medical air. Active scavenging is connected to the socket on the right-hand side.
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4.18 Area valve service units (AVSUs).
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4.19 (a) Schrader probes and hoses for the terminal outlets. From top to bottom: medical air; oxygen; nitrous oxide. (b) Non-interchangeable screw threads (NISTs) for nitrous oxide, oxygen and medical air, attached to the anaesthetic machine.
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4.20 (a) Master alarm for pipeline medical gas supply to the hospital and (b) local area alarm for medical gases.
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4.21 (a) Pressure gauges for oxygen above the cylinders on an older anaesthetic machine and (b) pressure gauges for oxygen, nitrous oxide and medical air on the front panel of a modern anaesthetic machine.
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4.22 (a) Pressure-reducing valves (A) for nitrous oxide in an older anaesthetic machine and (b) pressure regulator from a modern Datex Ohmeda Excel 210 machine. (Courtesy of GE Medical Systems Ltd)
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4.23 Piped gases are regulated at their source.
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4.24 Flowmeter with flow indicator using (a) a ball and (b) a bobbin.
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4.25 A flowmeter block. Note the larger size of the oxygen flow control. Oxygen is on the left and nitrous oxide on the right, with medical air in the middle.
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4.26 Hypoxic guard in a GE Healthcare anaesthetic machine. (a) Oxygen and nitrous oxide flowmeter controls are linked by a sprocket and chain. (b) Note the adjacent oxygen and nitrous oxide flowmeters. The photograph also shows ‘cascade’ flowmeters, which allow accurate measurement of gas flows less than 1 l/min. (Courtesy of GE Medical Systems Ltd)
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4.27 The Quantiflex MDM. Note that the oxygen flowmeter is on the right and that for nitrous oxide on the left.
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4.28 Modern microprocessor-controlled anaesthetic machines use ‘virtual flow tubes’. (Courtesy of GE Medical Systems Ltd)
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4.29 The back bar, attached to the right of the flowmeter block.
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4.30 ‘Selectatec’ station for vaporizer attachment to the back bar.
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4.31 (a) Selectatec block (compatible with TEC 3, MSS 3 and other Selectatec-compatible vaporizers. Note the O-rings placed on the male ports to ensure an airtight seal when mounted on the back bar). (b) Corresponding TEC 3 vaporizer assembly with two female ports; this assembly is only compatible with older Selectatec fittings that do not have a pin. (c) A modern Selectatec block which will only take modern vaporizers. (Note the pin, which will not allow the use of TEC 3 and MSS 3 vaporizers). (d) A modern Selectatec bar with a TEC 7 vaporizer in place. (e) Corresponding vaporizer assembly showing two female ports, accessory pin and locking recess for a TEC 7 vaporizer.
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4.32 Safety interlock. An extension rod protrudes from each vaporizer; the rod extends sideways from one vaporizer as it is turned on and immobilizes the equivalent rod on the adjacent vaporizer.
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4.33 Dräger mounting system. (a) When the vaporizer dial is moved to the ‘Transport’ position, the locking lever to the rear of the vaporizer fits into a groove on top of the dial and prevents spillage of liquid anaesthetic agent into the bypass channel during transport. (b) The Dräger Auto Exclusion vaporizer mounting mechanism incorporates a safety interlock preventing two vaporizers from being used simultaneously. (Courtesy of Dräger Medical UK)
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4.34 Common gas outlet and emergency oxygen flush. The latter supplies oxygen directly to the breathing system at a rate of 30–70 l/min. In modern machines, the flush does not have a locking facility (to reduce risk of barotrauma).
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4.35 Auxiliary gas sockets for oxygen and medical air.
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4.36 Pressure-relief valve.
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4.37 Visual oxygen failure alarm on a Penlon Prima anaesthetic machine.
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4.39 Internal design of the Dräger Vapor 2000 vaporizer. (Courtesy of Dräger Medical UK)
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4.40 Performance of the Penlon Sigma Delta vaporizer for sevoflurane over a range of (a) temperatures and (b) fresh gas flows. The Sigma Delta Vaporizer is produced by Penlon Ltd, UK (www.penlon.com).
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4.41 TEC 6 vaporizer for desflurane.
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4.42 Schematic diagram of the TEC 6 desflurane vaporizer. (Reproduced from with permission of the publisher)
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4.43 Dräger D ‘Vapor’ vaporizer. (Courtesy of Dräger Medical UK)
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4.44 Dräger DIVA vaporizer. (Courtesy of Dräger Medical UK)
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4.45 (a) Diagram illustrating the Aladin cassette vaporizer’s internal design. (b) Aladin cassette vaporizer in place on the anaesthetic machine. (Courtesy of GE Medical Systems Ltd)
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4.46 (a) Proximal end of keyed filler for isoflurane: the grooves on the screw top will only fit on to the collar of an isoflurane bottle. (b) Distal end of the keyed filler for isoflurane: this ‘key’ will only fit into the filling ports of an isoflurane vaporizer.
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4.47 Sealed bottles of (a) sevoflurane (Abbott Quik-Fil system) and (b) desflurane (Baxter Saf-T-Fil system) fitting into the filling ports of their specific vaporizers.
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4.48 Correct positioning for sevoflurane and isoflurane vaporizers on the back bar, based on the ratio of saturated vapour pressure (SVP)/minimum alveolar concentration (MAC).
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4.49 Komesaroff anaesthetic machine. (a) Complete unit. (b) Flowmeter on the Komesaroff machine, designed for delivering very low flows. (c) Low-resistance draw-over vaporizers for isoflurane and halothane.
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4.50 Stephens’ anaesthetic machine.

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