DOSE REQUIREMENTS OF PROPOFOL BY INFUSION DURING NITROUS OXIDE ANAESTHESIA IN MAN

Abstract

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 ED₅₀ (130 μg kg^minus;1 min⁻¹; 95% confidence limits: 106–167 μg kg⁻¹ min⁻¹) and ED₉₅ (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 EC₅₀ value of 2.5 μg ml ⁻¹, and an EC₉₅ 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.