Anaesthetic management of an extremely obese woman undergoing open gastric bypass.

EDITOR: I wish to report an unexpected failure of fresh gas flow and anaesthetic machine function during routine general anaesthesia. An uneventful gynaecological procedure was in progress. The patient’s lungs were being ventilated with a ‘bag-in-bottle’ ventilator driving a circle system, using low fresh gas flows (1.0 L min 1). The anaesthetic machine being used was a DatexOhmeda Aestiva/5. A Baxter APII patient-controlled analgesia (PCA) device was placed on the right-hand side of the main anaesthetic machine shelf. Approximately 1 min after this, it was noted that the capnograph trace on the monitor was not detecting the presence of exhaled carbon dioxide. The ventilator bellows had stopped moving. The lever on the circle system was switched to manual ventilation mode but inflation of the patient’s lungs was not possible, as the reservoir bag would not fill with gas. A glance at the rotameter bobbins showed that no fresh gas was being delivered to the circuit. It was then noted that the main anaesthetic machine on/off switch (Fig. 1) at the bottom right-hand corner of the main shelf had been accidentally turned into the ‘off’ position by the PCA device pressing against the switch. The anaesthetic machine was switched on, fresh gas flow returned and the anaesthetic was completed uneventfully, with no adverse effects for the patient. It is interesting to note that no machine alarms were triggered because its power supply had been switched off. The abnormal capnograph trace was noticed before its separately powered alarm was activated. It was felt that no undue pressure was used in placing the PCA pump on the anaesthetic machine shelf. This was confirmed by using the pump to switch off other anaesthetic machines of similar design. The position of the on/off switch on the main shelf of the anaesthetic machine makes this a potentially repeatable error (Fig. 1). This was reported to, and investigated by the Medicines and Healthcare Products Regulatory Agency (MHRA). They concluded that it is an ‘obvious design requirement that inadvertent operation of the off switch should be prevented, this is written into the appropriate standards such as EN740’. Datex-Ohmeda replied that the ‘rotary design of the aestiva appears to meet this as it requires a turn rather than a switch’. The MHRA report concludes ‘unfortunately these standards [EN740] are quite general so as to limit innovation and change, which can leave them very open to interpretation’. I would therefore like to bring this occurrence to your readers’ attention and to recommend that objects are not placed near the on/off switch of this machine.