Controlled anaesthesia: a clinical evaluation of an approach using patient characteristics identified during uptake

The performance of a system to control the alveolar concentration of halothane in patients undergoing halothane and nitrous oxide or halothane anaesthesia with controlled ventilation has been evaluated. The method involved the identification and quantification of the uptake characteristics of patients from their early response to the anaesthetic and implements the vaporizer control necessary to achieve and maintain a desired alveolar halothane concentration. Initial targets are based on the concept of MAC, but modifications to the desired alveolar concentration may be effected readily by the anaesthetist at any time during the procedure if evaluation of the normal clinical signs indicates inappropriate depth of anaesthesia. The results obtained during anaesthesia for routine surgery in 80 patients demonstrated that the system was accurate, stable, robust and able to adapt for variability between patients in the uptake of halothane.