The implications of circadian rhythms for anaesthesia

Although anaesthetists often regard humans as essentially homeostatic, our physiology and behaviour are in fact characterised by robust, predictable 24-h oscillations generated by the circadian clock (Fig. 1).1 These rhythms influence nearly every major biological system and, consequently, produce substantial time-of-day variation in both the pharmacokinetics and pharmacodynamics of many drugs.2 Despite long-standing recognition that circadian biology has important implications for anaesthesia, its relevance is frequently underappreciated in clinical settings.