How should we administer intravenous anaesthetic drugs?

Abstract

The intravenous hypnotic agents thiopentone, methohexitone and propofol can be administered to maintain adequate anaesthesia as an alternative to volatile anaesthetic agents. The intravenous agent must be accurately administered to maintain the appropriate target concentration to ensure rapid recovery. It is important to scale drug dosage by patient LBM rather than TBW, to allow for variations in body build. A variety of delivery techniques may be used to maintain the target concentration. The use of intermittent bolus doses of an hypnotic agent is prone to widely fluctuating blood levels. A bolus dose followed by a fixed rate infusion is suitable only for the delivery of propofol. A variable infusion rate based on the prediction of a pharmacokinetic model for the drug can be delivered by a computer-assisted infusion pump or can be approximated as a series of constant rate infusions delivered by a standard infusion pump. However, pharmacokinetic models derived from a single dose of the drug have major deficiencies which limit their ability to accurately predict dosage requirements. We have developed an empirical error correcting method, plasma drug efflux, to derive infusion profiles for maintaining a constant arterial concentration of any drug. Infusion profiles have been developed for propofol, thiopentone and methohexitone which can accurately maintain the desired target concentration. These infusion profiles can be delivered by the advanced syringe pump we have developed or by a standard infusion pump with reference to a time versus rate table. Clinical practice has shown that these infusion profiles are simple to use and reliable.