[Pharmacokinetic basis of constant-flow administration of drugs during long-lasting anesthesia]

The criteria for intravenous administration of anesthetics or their adjunctives in continuous and constant flow remain imprecise and incompletely understood. Drugs with a very short half-life are usually preferred, without this being a restrictive notion. The theoretical bases for the kinetics of constant flow intravenous infusion are well known but not the practical carrying out, and the practitioner remains confronted with various fundamental questions. Indeed, the quantity administered must take in account it's elimination, but what happens in cases of destructive metabolism, above all when the metabolites are toxic? On the other hand, can the kinetics observed for a given dose be extrapolated to any dose that is administered? Using real examples during constant-flow anestesia, we reconsider a simple calculation method based on the total clearance for a given substance and providing the theoretical constant-concentration level. This study shows how complex the kinetics of constant-flow administration area. All these techniques should be preceded before human application, by serious research on adequate experimental models.