Current controversies in intraoperative awareness: II

The sine qua non of general anesthesia is loss of consciousness. To the anesthesiologist, the failure of a patient to respond to a meaningful verbal command, such as “Open your eyes,” has been proposed as a satisfactory indication of loss of consciousness that avoids any complex philosophical discussions about the exact nature of consciousness itself. In reality, however, loss of responsiveness does not guarantee unconsciousness. A person may be able to respond but may choose not to or may be conscious but physically unable to respond. A germane example related to anesthesia is a patient who has received a muscle relaxant with an insufficient dose of a hypnotic agent, such as an inhalational anesthetic gas. This person could be described as an inverse zombie: a person who appears unconscious but who is actually awake and conscious (see chapter by LaRock, this volume). The loss of consciousness associated with general anesthesia is sometimes compared with sleep. The main phenotypic difference between sleep and general anesthesia is that a sensory stimulus may disrupt sleep and result in rapid and reliable restoration of consciousness; general anesthesia is a relatively stable state of unconsciousness that is not presently amenable to immediate reversal. This distinction from sleep is crucial since the goal of general anesthesia is to maintain unconsciousness in the face of the varied and often noxious stimuli of surgical procedures. There are several other goals of anesthesia that may conflict with the objective of assuring unconsciousness.