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Purpose of Review: Initial studies suggested that the use of processed electroencephalogram technology could significantly decrease the incidence of unintended intraoperative awareness events during general anesthesia. Subsequent work has cast doubts on these findings. This review will examine the current state of awareness monitoring., Recent Findings: Recently published randomized controlled trials examining the use of the bispectral index during general anesthesia have not been able to show superiority over other forms of monitoring depth of anesthesia, such as end-tidal anesthetic-agent concentration. Additionally, there is current interest in utilizing the unprocessed electroencephalogram to ascertain depth of anesthesia and recent studies have demonstrated its use in preventing postoperative delirium., Summary: Although awareness monitors such as the bispectral index monitor may have benefit in patients in whom volatile anesthetic agents must be minimized - such as in hemodynamically unstable patients, or patients undergoing total intravenous anesthesia - these monitors do not appear to be useful for all patients.

Background: Patient memories of the operating room (OR) may serve as the informational basis for assessing satisfaction with individual anesthesiologists. Furthermore, the provision of clinically important information may assume that perioperative memories are retained. Studies assessing the extent of perioperative amnesia and factors associated with perioperative amnesia are sparse. Therefore, we assessed patient amnesia of the OR and of the preoperative holding area in hospitals where midazolam is typically administered in the preoperative holding area and evaluated whether midazolam dose administered in the preoperative holding area and patient age were associated with amnesia of the OR before induction of anesthesia., Methods: This was a retrospective study among 7750 adult patients who had general anesthesia and participated in the B-Unaware and Bispectral Index or Anesthetic Gas to Reduce Explicit Recall (BAG-RECALL) clinical trials. The last location the patient remembered before induction of anesthesia and the first location they remembered after induction of anesthesia were determined through a modified Brice questionnaire administered over the phone 30 days postoperatively. Regarding the preoperative period, patients were excluded if their last memory was unclear with respect to location before induction of anesthesia or if they were recruited at Winnipeg, where midazolam was typically first administered in the OR. Midazolam dose (mg/kg) administered in the preoperative holding area was divided into quartiles. Poisson regression models were used to calculate age- and multivariable-adjusted odds ratios (95% confidence intervals [CIs]) for the association between midazolam dose and amnesia of the OR before induction of anesthesia., Results: Of the 5339 patients included, 59.5% (95% CI, 58.2–60.9) of patients had amnesia of the OR before induction of anesthesia. In addition, 44.1% (95% CI, 42.8–45.7) last remembered the preoperative holding area, and 15.4% (95% CI, 14.4–16.4) only had preoperative memories before the holding area. The percentages of patients with amnesia of the OR before induction of anesthesia differed according to age groups: 50.7% (95% CI, 47.7%–53.7%) in patients aged 18 to 47 years versus 70.0% (95% CI, 67.0%–72.9%) in patients aged 73 to 99 years. Patients in the highest midazolam quartile had an adjusted prevalence ratio of 1.31 (95% CI, 1.22–1.42) for amnesia of the OR compared with those who did not receive midazolam., Conclusions: In hospitals where patients typically receive midazolam in the preoperative holding area, the majority of patients do not remember the OR, and a clinically relevant number of patients does not remember the preoperative holding area. If additional studies produce results indicating that a substantial proportion of patients has amnesia of the anesthesiologist, these findings would argue against the validity of assessing patient satisfaction with individual anesthesiologists providing exclusively OR care in such hospitals. Furthermore, if additional studies yield findings suggesting patient amnesia of the preoperative holding area, these results would suggest reconsideration of providing clinically important information only in the preoperative holding area. Older age and midazolam-induced anterograde amnesia are probably associated with impaired perioperative memories.

Background: Intraoperative awareness with explicit recall occurs in approximately 1-2 cases per 1000. Given the rarity of the event, a better understanding of awareness and its sequelae will likely require the compilation of data from numerous studies. As such, a standard description and expression of awareness events would be of value., Methods: We developed a novel classification instrument for intraoperative awareness events: Class 0: no awareness; Class 1: isolated auditory perceptions; Class 2: tactile perceptions (e.g., surgical manipulation or endotracheal tube); Class 3: pain; Class 4: paralysis (e.g., feeling one cannot move, speak, or breathe); and Class 5: paralysis and pain. An additional designation of "D" for distress was also included for patient reports of fear, anxiety, suffocation, sense of doom, sense of impending death, or other explicit descriptions. We reviewed 15 studies of the incidence of awareness that provided specific information about awareness reports. Five anesthesiologists at three institutions who developed the categories independently classified the events. An additional 20 individuals (attending anesthesiologists, anesthesiology residents, nurse anesthetists, medical students, and ancillary staff) not involved in the development of the categories also independently classified the events. Fleiss's kappa statistic was used to evaluate inter-observer agreement., Results: One hundred fifty-one cases of intraoperative awareness in adults were identified as valid for analysis. The overall kappa value was 0.851 (0.847-0.856, 95% confidence interval) for the basic Classes 1-5. Including additional designations of emotional distress, the overall kappa value was 0.779 (0.776-0.783, 95% confidence interval)., Conclusion: We report a novel classification instrument for intraoperative awareness events that has excellent inter-observer agreement and that may facilitate the study of intraoperative awareness.