[The course of blood concentrations of propofol administered at a constant rate, combined with fentanyl].

The blood concentration of propofol was studied in 14 ASA 1 informed patients, who were to undergo orthopaedic or plastic surgery lasting at least 90 min. Anaesthesia was induced with a 2 mg.kg-1 bolus of propofol together with 0.86 microgram.kg-1 fentanyl. This was followed by a constant rate infusion of propofol and fentanyl, 5 mg.kg-1.h-1 and 3 micrograms.kg-1.h-1 respectively. The mean duration of propofol infusion was 153 +/- 63 min, with extremes of 90 and 315 min. Propofol concentration was measured using gas phase chromatography on total arterial blood; the lower limit of detection was 0.05 mg.l-1. During the infusion, blood concentrations were found between 2 and 4 mg.l-1. It was 2.25 mg.l-1 at the fifth min; this was 80% of the concentration found at the 120th min. There was in fact no statistically significant difference between the values found at the 90th, 120th and 150th min. On stopping the infusion, the concentrations fell rapidly during the first 5 min, and then more slowly. By the 30th min, it had reached a value 4.5 times less than that at the end of the infusion. However, individual variations were found, which could explain delayed recovery. The calculated pharmacokinetic parameters were: elimination half-life = 41.7 +/- 20 min, clearance = 2.14 +/- 0.55 l.min-1 and equilibrium distribution volume = 43.4 +/- 15.2 l. These results are discussed. It is therefore possible to give propofol continuously at a constant rate without having any accumulative effect.