Abstract

Most anaesthetists using target-controlled infusion systems will have observed that the calculated effect-site concentration at loss of consciousness is usually higher than the concentration at emergence. Inertia is the ability of biological systems to keep a functional state at rest or in activity and is an active process of resistance to change in state. Hysteresis is a phenomenon whereby the value of a physical property lags behind changes in the effect that is causing it and this is also seen in anaesthesia pharmacology. Recently, a phenomenon called neuronal inertia has been proposed when trying to explain the resistance observed to changes in consciousness induced by general anaesthesia, independent of drug kinetics. This review discusses the existence of this phenomenon and the conceptual and practical impact it may have on induction and recovery from general anaesthesia.