Inadvertent administration of 100% oxygen during anaesthesia.

Sir,—Modern anaesthetic machines have a device (usually referred to as "the oxygen bypass" or "emergency oxygen") which enables the anaesthetist to administer high flows of 100% oxygen. When a patient is connected to an anaesthetic machine it is possible to overlook the fact that the emergency oxygen device is in the "on" position and is delivering 100% oxygen. This occurrence is most likely if the device operates quietly and uses a "push-pull" switch. The Cape Waine Mark II anaesthetic machine and ventilator has such a mechanism. Accidents have occurred in our operating theatre on two occasions when patients had been transferred from the anaesthetic room to the operating theatre and connected to a machine. On both occasions a junior anaesthetist failed to notice for some time that the emergency oxygen device was "on" and the paralysed patients received higher concentrations of oxygen than intended. The following day, not unexpectedlyj the patients complained of awareness during anaesthesia.