Target-controlled infusion systems - Role in anaesthesia and analgesia

Drug delivery by target-controlled infusion (TCI) allows automatic adjustme nts of the infusion rate of a drug to maintain a desired target concentrati on. Since drug effect is more closely related to blood concentration than t o infusion rate, drug delivery via TCI is capable of creating stable blood concentrations of intravenous anaesthetics and analgesics. In this article the concept and history of TCI are described. The rational administration of TCI requires an appropriate pharmacokinetic data set and knowledge of the concentration-effect relationship; therefore, general phar macokinetic and pharmacodynamic aspects of intravenous anaesthetics and ana lgesics are also addressed. Intraoperative investigations have demonstrated that TCI drug delivery allows rapid titration to a desired effect. The use of TCI for postoperative analgesia is still experimental, but TCI can, in part, overcome the disadvantages associated with continuous infusions and p atient-controlled analgesia regimens in the postoperative period. Although TCI is capable of creating stable blood concentrations, when the t arget concentration is changed the resulting effect correlates better with a theoretical effect site concentration. The efficacy of TCI systems that c an perform effect-site steering are still to be explored.