Pharmacokinetics of Analgesics, Sedatives and Anesthetic Agents during Cardiopulmonary Bypass

Abstract

CBP is accompanied by profound physiologic changes that may alter pharmacokinetics of many drugs. Drug distribution can be affected by changes in blood flow, hemodilution, and a decrease in protein binding. A reduction in drug elimination is secondary to impairment of hepatic and renal clearance resulting from decreased perfusion and hypothermia. While no single anesthetic technique has been shown to be superior for cardiac surgery, the choice of agent is more often based on cardiovascular side effects than on the need for anesthesia and analgesia. All 'too often the changes in pharmacokinetic behaviour of drugs imposed by CPB are ignored. These changes become clinically apparent in the postoperative period with patients remaining obtunded and requiring ventilatory support for a protracted period of time, some would argue, unnecessarily. A rational choice for cardiac anesthesia cannot be made without knowledge of the characteristics of the CPB system being used for a given case. Alterations in type of priming fluid or in the use of normC!thermic compared with hypothermic bypass, for example, may result in profound alterations in the behaviour of individual agents. With increasing pressure for cost-effectiveness and efficient utilization of critical care beds it becomes more necessary to understand the way in which CPB affects the behaviour of drugs, in particular that many agents have prolonged half-lives and thus a hangover effect in the postoperative