EDITOR:
Recently we had an incident, which has important implications for the checking of anaesthetic machines. A pre-use check of a Dräger Cato anaesthetic machine (Dräger Medical UK Ltd, Hertfordshire, UK) revealed that on disconnecting the oxygen pipeline, the oxygen failure alarm was working. The oxygen cylinder was then opened and the pressure gauge registered that it was full. However, on opening the oxygen flow-meter (rotameter) there was no flow of oxygen. Changing the cylinder made no difference, as the pressure gauge registered full but no flow of oxygen occurred, and so an alternative machine that was fully functional was used.
Investigation of the fault in our anaesthetic workshop concluded that a one-way valve between the cylinder and anaesthetic machine was sticking. Following its replacement, the machine was fully functional. The manufacturer’s Technical Support Manager (Dräger Medical UK Ltd) was informed by letter. He replied to the effect that there had been no previous reports of this fault and that the valve design had changed.
The purpose of the one-way (check) valve is to prevent retrograde leak, and it is a feature of most, if not all, modern anaesthetic machines.
The commonly used guideline for checking anaesthetic machines is Checking Anaesthetic Equipment, 3rd edition (2004) by the Association of Anaesthetists of Great Britain and Ireland. For checking medical gas supplies this advocates a ‘tug test’ for the pipeline and a contents check of cylinders using the pressure gauge. It also recommends a weekly disconnection of the oxygen hose to check the oxygen failure alarm and the concomitant gas shut-off device.
We point out that none of these checks will detect the problem of a sticking one-way (check) valve. Clearly, having done the pipeline disconnection for the oxygen failure alarm test, one should also check that opening the oxygen cylinder and flow-meter results in the actual flow of oxygen. We suggest that this be incorporated into the next edition of Checking Anaesthetic Equipment.
