Towards a standardized anaesthetic state using isoflurane and morphine.

In 34 patients undergoing major surgery, the inspired isoflurane concentration was adjusted by a control system designed to maintain systolic arterial pressure at a predetermined value. An empirical rule allowed additional morphine administration if the demand of the system for isoflurane was excessive. Satisfactory control of systolic arterial pressure was achieved in 31 patients and the anaesthetic state was clinically acceptable to an independent observer; no awareness was reported and the mean recovery time was 9.6 min. In these patients, control of systolic arterial pressure produced a pattern of clinical signs recognizable as general anaesthesia.