Linear thinking does not reflect the newer 21st-century anesthesia concepts. A narrative review.

The brain constitutes a good example of a chaotic, nonlinear biological system where large neuronal networks operate chaotically with random connectivity. This critical state is significantly affected by the anesthetic loss of consciousness induced by drugs whose pharmacological behavior has been classically based on linear kinetics and dynamics. Recent developments in pharmacology and brain monitoring during anesthesia suggest a different view that we tried to explore in this article. The concepts of effect-site for hypnotic drugs modeling a maximum effect, electroencephalographic dynamics during induction, maintenance, and recovery from anesthesia are discussed, integrated into this alternative view, and how it may be applied in daily clinical practice.

Neural inertia and differences between loss of and recovery from consciousness during total intravenous anaesthesia: a narrative review.

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.