TOTAL I.V. ANAESTHESIA WITH PROPOFOL AND ALFENTANIL: DOSE REQUIREMENTS FOR PROPOFOL AND THE EFFECT OF PREMEDICATION WITH CLONIDINE^†

We determined in 51 healthy patients undergoing body surface surgery the dose requirements for propofol, as part of a total i.v. anaesthesia technique with an alfentanil infusion. After premedication with temazepam, patients received alfentanil 50 μg kg⁻¹ followed by an infusion of 50 μg kg⁻¹ h⁻¹. Patients were anaesthetized with a loading dose of propofol followed by a three-stage infusion designed to reach one of five preselected blood concentrations of propofol. The motor response to the initial surgical incision was noted and probit analysis was used to derive the ED₅₀ (2.94 mg kg⁻¹ h⁻¹; 95% confidence limits: 2.35−3.37 mg kg⁻¹ h⁻¹). and ED₉₅ (4.98 mg kg⁻¹ h⁻¹; 95% limits: 4.13−8.8 mg kg⁻¹ h⁻¹) for the final propolol infusion rate under these conditions. Whole blood concentration of propofol at the time of the incision was related linearly to the infusion rate and the EC₅₀ and EC₉₅ (probit analysis) were derived as 1.44 (95% confidence limits 0.62−1.87) and 4.05 (95% confidence limits 2.78−30.5) μg ml⁻¹, respectively. Postoperative recovery was rapid, uncomplicated and uneventful. In a subgroup of eight patients, the addition of clonidine 0.6mg to the premedication significantly decreased the requirement for propofol (P <0.05) during surgery, but resulted in prolonged recovery times.