Awareness during anesthesia: risk factors, causes and sequelae: a review of reported cases in the literature.

BACKGROUND: 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.

METHODS: 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.

RESULTS: 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.

CONCLUSIONS: 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.