[Modern concepts in pharmacokinetics of intravenous anesthetics]

From a pharmacological perspective, anesthesia is concerned with controlling the time course of drug effect. Mathematical models are commonly used to relate the administered drug dose to the measured drug concentration (a pharmacokinetic model) and to relate the measured drug concentrations to the measured drug effects (a pharmacodynamic model). With such models, the time course of the drug effect for different drug regimens can be predicted. Although the conventional pharmacokinetic parameters such as the volume of distribution, clearance, distribution and elimination half-lives can be used to accurately describe the time course of the plasma concentration, the plasma is usually not the site of drug effect. An understanding of the "effect compartment concept" and the "time of the peak effect site concentration," together with the concepts of" context sensitive"half-time and "relevant decrement time,' contribute substantially to the anesthetist's understanding of the principles governing the onset and offset of drug effect. As part of a computer-controlled infusion system, the pharmacokinetic model facilitates optimized and rational dosing. These systems, also called target-controlled infusion systems (TCI), calculate the infusion rates for rapidly achieving and then maintaining a target concentration.