The role of pharmacokinetics in anaesthesia: application to intravenous infusions

Pharmacokinetic concepts describe the relationship between drug dose and resulting plasma concentration. A drug's pharmacokinetic profile can be described by distribution and elimination half-lives, initial volume of distribution, steady-state distribution volume, and metabolic and distributional clearance. After initiating a fixed rate of drug infusion, four to five terminal elimination half-lives are required to reach a steady state of constant plasma concentration. If a loading dose is given, a steady state can be achieved more rapidly. The most rapid method of achieving a constant plasma concentration involves using a variable rate of drug infusion that adjusts for the metabolic clearance and distribution of the drug. Computer-driven infusion pumps can be used to rapidly achieve, then maintain, constant plasma concentrations of a drug.