Infusion model for fentanyl based on pharmacokinetic analysis.

The calculation of pharmacokinetic parameters after a bolus injection of fentanyl allowed an i.v. infusion scheme which guarantees analgesia for the entire duration of surgery, with the advantage of steady plasma concentration and body content. In the initial phase after bolus injection, the serum concentration decreased rapidly for about 10 min, indicating extensive transfer to the peripheral compartment. This was followed by a slower elimination phase with a half-life of about 2 h. The total volume of distribution of 80 litre exceeded the body weight only slightly. The total plasma clearance was 500ml min-1. In developing a model for total i.v. anaesthesia we considered two different consecutive infusion rates. The pharmacokinetic model proved to be valid for all patients. The plasma concentrations duration anaesthesia coincided well with the predicted steady state plasma concentrations and provided continuous analgesia during operation.