DOSE REQUIREMENTS OF PROPOFOL BY INFUSION DURING NITROUS OXIDE ANAESTHESIA IN MAN II: Patients Premedicated with Lorazepam

The infusion rate of propofol required to supplement 67% nitrous oxide in oxygen to maintain surgical anaesthesia was determined in 72 patients premedicated with lorazepam. Following an induction dose of propofol 2 mg kg −1 , groups of eight patients received an infusion of propofol varying from 60 to 200 μg kg −1 . Probit analysis was used to determine the ED 50 (130 μg kg minus;1 min −1 ; 95% confidence limits: 106–167 μg kg −1 min −1 ) and ED 95 (348 μg kg −1 min −1 ; 95% confidence limits: 233–1296 μg kg −1 min −1 ;) for propofol infusion. Whole blood propofol concentrations at the time of surgical incision correlated strongly with the infusion rate, giving an EC 50 value of 2.5 μg ml −1 , and an EC 95 value of 5.92 μg ml −1 . There was no significant correlation between the rate of infusion of propofol, or the total propofol dose, and the times to response to command, or to recall of birthdate.