The cardiovascular effects of high-dose butorphanol-nitrous oxide anaesthesia before and during operation.

The cardiovascular effects of high doses of butorphanol (0.3-0.45 mg . kg-1) plus 60 per cent N2O anaesthesia were measured at unconsciousness, following tracheal intubation, and immediately before and at one and ten minutes after surgical stimulation in 17 A.S.A. class I and II patients undergoing elective gastric or gall bladder surgery. Butorphanol and N2O produced unconsciousness with only small decreases in heart rate and cardiac output but did not result in sufficient analgesia to block or treat stimulation of the cardiovascular system secondary to tracheal intubation or surgical incision, even when supplemented with additional butorphanol to high cumulative dose levels (1.0 mg . kg-1). The data suggest that even high dose butorphanol - N2O anaesthesia requires supplementation with other anaesthetics or anaesthetic adjuvants to prevent cardiovascular stimulation during general abdominal surgery.