The Neurobiology of Anesthetic Emergence

Abstract

Achieving a smooth and rapid emergence from general anesthesia is of particular importance for neurosurgical patients and is a clinical goal for neuroanesthesiologists. Recent data suggest that the process of emergence is not simply the mirror image of induction, but rather controlled by distinct neural circuits. In this narrative review, we discuss (1) hysteresis, (2) the concept of neural inertia, (3) the asymmetry between the neurobiology of induction and emergence, and (4) recent attempts at actively inducing emergence.

Mechanisms of hysteresis in human brain networks during transitions of consciousness and unconsciousness: Theoretical principles and empirical evidence

“…Traditionally, it has been assumed that the induction of and emergence from general anesthesia are mirror images of one another. However, the asymmetric anesthetic concentrations associated with induction and emergence have long been recognized and explained by pharmacokinetics[ 13 – 17 ]. Recently, it has become clear that the neural circuits mediating loss of consciousness do not entirely overlap with the neural circuits mediating recovery of consciousness.…”

“…Neural inertia suggests that hysteresis is not a pharmacokinetic attribute, but a fundamental neurobiological process that stabilizes states of consciousness and creates resistance to rapid and potentially catastrophic transitions[ 8 ]. Accumulating evidence indicates that the relevant sites mediating the induction of and emergence from anesthesia are distributed globally rather than localized in the brain[ 13 ]. If hysteresis is a large-scale network phenomenon in the brain then, like many other biological and physical systems, the state transitions may be governed by the same network mechanism, which is referred to as ‘explosive synchronization.’…”

Complexity measures of the electroencephalograph capture loss and recovery of consciousness in patients anesthetized with propofol

“…Additionally, monitoring anesthetic depth is becoming increasingly important, since lighter planes of anesthesia speed recovery times, decrease operative costs (Dexter, Macario, Manberg, & Lubarsky, 1999) and reduce morbidity, including the potential for post-operative delirium and cognitive dysfunction in vulnerable populations of surgical patients (B.A. Fritz, Maybrier, & Avidan, 2018;Bradley A. Fritz et al, 2016;Kertai et al, 2011;Petsiti et al, 2015;Tarnal, Vlisides, & Mashour, 2015); though see also (Kalkman, Peelen, Moons, Group, & Group, 2011;Wildes et al, 2019) for limitations. However, lighter planes of anesthesia impart a greater risk of intraoperative recall in patients (Avidan et al, 2013;G.…”

“…These delta rhythms are gradually replaced by burst suppression patterns as patients transition to deeper surgical planes of anesthesia (Pilge, Jordan, Kreuzer, Kochs, & Schneider, 2014). Interestingly, recovery of consciousness is associated with much less delta activity and higher amounts of low amplitude, fast activity on awakening, indicating a hysteresis of brain states for loss and recovery from anesthesia (Chander et al, 2014;Stanski, Hudson, Homer, Saidman, & Meathe, 1984), also termed 'neural inertia' which may reflect differential activation of neural networks during these states (Friedman et al, 2010;Tarnal et al, 2015). Emergence from general anesthesia also does not typically follow a stereotyped pattern, but rather a more heterogenous spectral pattern during the establishment of conscious awareness and responsivity (Chander et al, 2014).…”

Emergence from anesthesia: a winding way back

“…However, the matter seems to be more complex. Indeed, emergence from anaesthesia is not simply the reverse process of induction as it is subjected to the control of different neural pathways [7] while, probably, several EEG patterns characterize the recovery of consciousness from DoA status [8].…”