Dose requirements of propofol by infusion during nitrous oxide anaesthesia in man. I: Patients premedicated with morphine sulphate.

The study was performed to determine the ED50 and ED95 of a continuous infusion of the emulsion formulation of propofol during 67% nitrous oxide anaesthesia in 57 patients premedicated with morphine sulphate 0.15 mg kg-1. Anaesthesia was induced with propofol 2 mg kg-1, and maintained before incision with a fixed-rate infusion of propofol to supplement nitrous oxide. The response to the first surgical incision, made at least 30 min after induction of anaesthesia, was observed. The ED50 was 53.5 micrograms kg-1 min-1 and the ED95 was 112.2 micrograms kg-1 min-1. At the time of the first surgical incision, the venous whole blood concentrations of propofol at the ED50 and ED95 infusion rates (EC50 and EC95) were 1.66 micrograms ml-1 and 3.39 micrograms ml-1, respectively. The satisfactory maintenance of anaesthesia provided by nitrous oxide supplemented with propofol was associated with haemodynamic stability and rapid, uncomplicated recovery.