Awareness during surgery--a new approach.

With modern light anaesthesia the problem of awareness during surgery has defied analysis, because no physical sign reliably signals the conscious level. A test has been developed which entails direct communication with the patient at the end of surgery, noting the earliest moment after withdrawal of nitrous oxide at which he makes the appropriate response to a verbal request, the "time to correct response" (TCR). This test showed premedication with lorazepam 4 mg/70 kg to be significantly better than morphine 10 mg for ensuring unconsciousness when the main anaesthetic agent was nitrous oxide, in two groups of patients undergoing abdominal surgery (P less than 0.01). All patients who had lorazepam were able, on request, to hold up the head a few minutes after surgery. Thus the benefits of light anaesthesia were retained whilst ensuring unconsciousness.