How to pressure check an anaesthetic machine
Abstract
Pre-anaesthetic checks, including those focusing on the anaesthetic machine, form an important part of patient safety and have become an integral part of the peri-anaesthetic checklists currently being introduced into veterinary medicine. Careful testing of the anaesthetic machine involves pressure testing the various components, allowing detection of any defective workings prior to use. Implementing a step by step guide ensures that no important stages are omitted from pressure checking and prevents patient safety from being compromised. Visual checks of the gas cylinder connections, vaporiser(s), flow meters and common gas outlet should be followed by testing of the low and high pressure systems within the anaesthetic machine and then the vaporiser and its attachment to the back bar. Any leaks detected should be identified and resolved if possible or repairs organised and alternative equipment utilised.
Patient safety is an area of veterinary medicine that is rapidly increasing in awareness amongst anaesthetists, nurses and practitioners. Anaesthetic and surgical safety checklists are gaining in popularity in veterinary medicine after their successful implementation into human medicine. An important step prior to induction of anaesthesia is to test the anaesthetic machine, ensuring it is correctly set up, functioning normally and therefore safe to use. The anaesthetic machine itself should be pressure tested at least once daily, preferably prior to first use and the breathing system selected should be leak tested prior to each and every use.
Anaesthetic machines used in veterinary medicine are found in a variety of designs and are often ex-hospital machines (Figure 1). It is important to be aware of any particular features when planning pre-use testing, as the machine set up may vary depending on the design. Anaesthetic machines may be supplied by one or more gas cylinders (e.g. oxygen, nitrous oxide, medical air) or pipelines (Figures 2a and b), and have vaporisers fixed within the machine or positioned on a selectatec bar (Figure 3a and b). It is important to be aware of where connections such as the common gas outlet (CGO) are positioned and which, if any, safety features are fitted to the machine being used. Safety features may consist of an oxygen low-pressure alarm, hypoxia alarm if nitrous oxide is used, and a gas on/off switch. Cylinder connections onto the machine will be dependent on the size of cylinder. Size E and J cylinders will have a yoke attachment (Figure 4), whereas size F cylinders will have a screw thread (bullnose) attachment (Figure 5) with the first stage regulator and pressure manometer attached.
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