Intraoperative Awareness (a.k.a. Anesthesia awareness) occurs as a complication during general anesthesia, where the intended state of complete unconsciousness is not maintained throughout the whole procedure.
“The incidence of this anesthesia complication is variable and seems to affect 0.2% to 0.4% of patients according to the surgical setting carried out. This variation reflects the surgical setting as well as the physiological state of the patient. Thus, the incidence is 0.2% in general surgery, about 0.4% during caesarean section, between 1 and 2% during cardiac surgery and between 10% and 40% for anesthesia of the traumatized.”
“The causes of intraoperative awareness are as yet unknown, and the problem may be multifactorial. At least 4 broad categories of causes are plausible. First, unexpected patient-specific variability in dose requirements of anesthetic drugs may be a result of altered expression or function of target receptors. Second, patients may be unable to tolerate a sufficient dose of anesthetic because of low physiologic reserves related to factors such as poor cardiac function or severe hypovolemia. Third, physiologic characteristics that would indicate the need for a dose change may be masked by factors such as use of β-adrenergic receptor blockers or presence of a pacemaker. Fourth, intended drug delivery systems may be compromised by events such as equipment malfunction or misuse.”
Source: Awareness during anesthesia Beverley A. Orser, C. David Mazer and Andrew J. Baker, CMAJ January 15, 2008 178 (2) 185-188.
Also see :General Anaesthetics