We have reviewed randomized controlled trials to assess the effectiveness and safety of anaesthetics which omitted nitrous oxide (N2O) to prevent postoperative nausea and vomiting (PONV). Early and late PONV (6 and 48 h after operation, respectively), and adverse effects were evaluated using the numbers-needed-to-treat (NNT) method. In 24 reports with information on 2478 patients, the mean incidence of early and late vomiting with N2O (control) was 17% and 30%, respectively. Omitting N2O significantly reduced vomiting compared with a N2O regimen; the combined NNT to prevent both early and late vomiting with a N2O-free regimen was about 13 (95% confidence intervals (CI) 9, 30). The magnitude of the effect depended on the incidence of vomiting in controls. In studies with a baseline risk higher than the mean of all reports, the NNT to prevent both early and late vomiting with a N2O-free anaesthetic was 5 (95% CI 4, 10). When the baseline risk was lower than the mean, omitting N2O did not improve outcome. Omitting N2O had no effect on complete control of emesis or nausea. The NNT for intraoperative awareness with a N2O-free anaesthetic was 46 compared with anaesthetics where N2O was used. This clinically important risk of major harm reduces the usefulness of omitting N2O to prevent postoperative emesis.

<h4>Background</h4>Awareness during anesthesia is uncommon. The number of cases that are found in one single study are insufficient to identify and estimate the risks, causal factors and sequelae. One method of studying a large number of cases is to analyze reports of cases of awareness that have been published in scientific journals.<h4>Methods</h4>We conducted an electronic search of the literature in the National Library of Medicine's PubMed database for case reports on "Awareness" and "Anesthesia" for the time period between 1950 through August, 2005. We also manually searched references cited in these reports and in other articles on awareness. We used two surgical control groups for comparative purposes. The first group in a study by Sebel et al. consisted of patients who did not experience awareness. The second group, from the 1996 data from the National Survey of Ambulatory Surgery included patients who received general anesthesia. We also used data from the National Center for Health Statistics to compare weight and Body Mass Index.<h4>Results</h4>We compared the data of 271 cases of awareness with 19,504 patients who did not suffer it. Aware patients were more likely to be females (P < 0.05), younger (P < 0.001) and to have cardiac and obstetrics operations (P < 0.0001). Only 35% reported the awareness episode during the stay in the recovery room. They received fewer anesthetic drugs (P < 0.0001), and were more likely to exhibit episodes of tachycardia and hypertension during surgery (P < 0.0001). A much larger percentage of these patients (52%, P < 0.0001) voiced postoperative complaints related to awareness. Inability to move and feelings such as helplessness, sensation of weakness, and hearing noises and voices were related to the persistence of complaints such as sleep disturbances and fear about future anesthetics (P < 0.041-0.0003). Twenty-two percent of the patients suffered late psychological symptoms.<h4>Conclusions</h4>Our review suggested light anesthesia and a history of awareness as risk factors. Obesity and avoidance of nitrous oxide use did not seem to increase the risk. Light anesthesia was the most common cause. Our findings suggest preventive procedures that may lead to a decrease in the incidence of awareness.

Summary Unintended accidental awareness during general anaesthesia represents failure of successful anaesthesia, and so has been the subject of numerous studies during the past decades. As return to consciousness is both difficult to describe and identify, the reported incidence rates vary widely. Similarly, a wide range of techniques have been employed to identify cases of accidental awareness. Studies which have used the isolated forearm technique to identify responsiveness to command during intended anaesthesia have shown remarkably high incidences of awareness. For example, the Cons CIOUS ‐1 study showed an incidence of responsiveness around the time of laryngoscopy of 1:25. On the other hand, the 5th Royal College of Anaesthetists National Audit Project, which reported the largest ever cohort of patients who had experienced accidental awareness, used a system to identify patients who spontaneously self‐reported accidental awareness. In this latter study, the incidence of accidental awareness was 1:19,600. In the recently published SNAP ‐1 observational study, in which structured postoperative interviews were performed, the incidence was 1:800. In almost all reported cases of intra‐operative responsiveness, there was no subsequent explicit recall of intra‐operative events. To date, there is no evidence that this occurrence has any psychological consequences. Among patients who experience accidental awareness and can later remember details of their experience, the consequences are better known. In particular, when awareness occurs in a patient who has been given neuromuscular blocking agents, it may result in serious sequelae such as symptoms of post‐traumatic stress disorder and a permanent aversion to surgery and anaesthesia, and is feared by patients and anaesthetists. In this article, the published literature on the incidence, consequences and management of accidental awareness under general anaesthesia with subsequent recall will be reviewed.

epted: 2 December 2020 20 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights rese Permissions, please email: permissions@elsevier.com Accidental awareness during general anaesthesia (AAGA) is a rare but severe complication of anaesthetic care. Despite advances in physiological monitoring and an improved understanding of the neural mechanisms underlying anaesthesia, the incidence of AAGA has remained steady for several decades. At present, there is a disparity between reports of AAGA from patients (1e2 in 1000 general anaesthetics) and from anaesthesia care providers (1 out of 15,000 general anaesthetics). The 5th National Audit Project (NAP5) of the Royal College of Anaesthetists, the largest patient-centred report on AAGA to date, examined more than 400 individual experiences of AAGA and found considerable variation in the incidence of AAGA across anaesthetic techniques. The long-term health-related consequences of AAGA can be devastating. We note that 43% (15/35) of patients with history of definite or possible AAGA in threemajor AAGA trials including the B-Unaware (Anaesthesia Awareness and the Bispectral Index) trial, the BAG-RECALL (BIS or Anaesthesia Gas to Reduce Explicit Recall) trial, and the MACS (Michigan

Effect of flunitrazepam (Rohypnol) on awareness during anaesthesia for caesarean section. The incidence of awareness was compared in three groups of patients undergoing elective or emergency Caesarean section, using pethidine alone or pethidine plus flunitrazepam (Rohypnol), as adjuvants to nitrous oxide: oxygen, muscle relaxant technique of general anaesthesia. The use of 0.03 mg/kg body weight of flunitrazepam was associated with a low incidence (4%) of awareness, cardiovascular stability, postoperative sedation and anterograde amnesia. The reduced incidence of awareness is probably due to increased depth of anaesthesia and anterograde amnesic effect produced by the drug. Published in African journal of medicine and medical sciences (1988)

Effect of diazepam on awareness during caesarean section under general anaesthesia. The use of diazepam for premedication before elective caesarean section increased the incidence of unpleasant recall postoperatively, compared with atropine in a previous study. This finding suggests that diazepam is unsuitable for this type of anaesthesia. Published in British medical journal (1969)

English) or anaesthesia (British English) is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary Anesthesia (American English) or anaesthesia (British English) is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prevention of pain), paralysis (muscle relaxation), amnesia (loss of memory), and unconsciousness. An individual under the effects of anesthetic drugs is referred Anesthesia (American English) or anaesthesia (British English) is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prevention of pain), paralysis (muscle relaxation), amnesia (loss of memory), and unconsciousness. An individual under the effects of anesthetic drugs is referred to as being anesthetized. Anesthesia enables the painless performance of procedures that would otherwise require physical restraint in a non-anesthetized individual, or would otherwise be technically unfeasible. Three broad categories of anesthesia exist:

dose than for medically induced coma protocols, it is effectively impossible for the condemned to wake up. Anesthesia awareness occurs when general anesthesia Lethal injection is the practice of injecting one or more drugs into a person (typically a barbiturate, paralytic, and potassium chloride) for the express purpose of causing death. The main application for this procedure is capital punishment, but the term may also be applied in a broader sense to include euthanasia and other forms of suicide. The drugs cause the person to become unconscious, stop T…