Duration and pattern of emergence from anesthesia is poorly investigated and understood. Traditionally, it has been assumed that the induction of and emergence from general anesthesia are mirror images of one another. The asymmetry—or “hysteresis”—of anesthetic concentrations required for induction vs. emergence has long been recognized but has been attributed to pharmacokinetic characteristics. Emerging evidence suggests that this asymmetry may reflect a distinct neurobiology of the two processes and that the neural circuits mediating induction do not entirely overlap with the neural circuits mediating emergence [2] .

The recovery from anesthesia does not occur all at once, but rather it appears to occur in a bottom-up manner.  Anatomically, there is activation of a core network involving subcortical and limbic regions (like hippocampus) initially upon emergence and later they become functionally coupled with parts of frontal and inferior parietal cortices. Physiologically, when emerging from deep anesthesia there will first be signs of autonomic arousal, followed by a slow return of brainstem reflexes, eventually leading to reflexive or uncoordinated movements that occur somewhat before subjects can willfully respond to simple commands. Thus, emergence of a conscious state, precedes the full recovery of neocortical processing required for establishing contact with the surroundings. Arousal (spoken command) induced brain activations during emergence from anesthesia are mostly localized in deep, phylogenetically old brain structures (limbic cortex or mesial temporal structures) than in neocortex [3].

The potential association between hippocampal volume and the time and pattern of emergence from anesthesia remains unclear [4,5]. A retrospective analysis of cohort data suggests that surgery may be associated with a decrease in brain volume (volume of limbic system) [6]. Also it is well known that subcortical and hippocampus form the core network during arousal after general anaesthesia [3]. However, no studies suggesting potential link between preoperative hippocampal volume and post anaesthesia recovery characteristics have been analyzed. 

            Apart from anatomical structures even functional components namely patient education, working and leisure activities are known to contribute to patient emergence characters [7]. These components determine the preexisting functional reserve of brain and its resistance to surgical or anesthetics stress. Hence, we would like to study the correlation of pre-operative MRI guided hippocampal volume and functional reserve with time and pattern of emergence after general anesthesia in elective neuro surgical procedures.

Hypothesis

Our hypothesis is that there will be correlation between the preoperative hippocampal volume and the time to emergence from general anaesthesia in neurosurgical patients.