• Johan Raeder and Siv Cathrine Høymork.
• Anestesiavdelingen, Oslo universitetssykehus, Ullevål og Institutt for sykehusmedisin Det medisinske fakultet Universitetet i Oslo, Norway. johan.rader@medisin.uio.no
• Tidsskr. Nor. Laegeforen. 2010 Mar 25;130(6):628-32.

BackgroundAnaesthetic pharmacology is characterized by use of drugs in high doses for a short period of time. Knowledge of pharmacokinetics is important for precise control of drug effects (onset, maintenance and offset).Material And MethodsThe paper is based on own research, experience from clinical practice, teaching, and up-to-date knowledge of the available literature.ResultsTraditional pharmacokinetic terms; such as volume of distribution, clearance and elimination half-life are useful within anaesthesiology, but two other important concepts should be considered: time to effect onset (keO) and context sensitive elimination half-life. keO is dependent upon distribution of drug from plasma to site of effect and the speed of cellular effect activation. The context sensitive elimination half-life upon discontinuation of a drug depends on how long the drug has been administered, and is shorter than terminal elimination half-life for anaesthetic drugs when used shorter than 12 - 24 hrs. With short-term use of drugs there is a profound initial drug distribution into tissues in addition to elimination. With prolonged use there is more drug deposited in the tissues, lower diffusion gradient and prolonged context sensitive elimination half-time. Computerized infusion pumps (Target Control Infusion, TCI) enable dosing of opioids or propofol to a preset concentration, either in plasma or at the site of effect.InterpretationKnowledge of pharmacologic principles and modeling from studies on volunteers and patients form the basis for good clinical monitoring of anaesthetic drug effects.

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