BIS Monitoring on Intraoperative Awareness： A Meta-analysis

Intraoperative awareness is a very serious complication of general anesthesia. Several studies have evaluated the potential association between bispectral index （BIS） and intraoperative awareness, however, the results obtained were controversial. Therefore, we performed a metaanalysis to further assess the association between the BIS monitoring and the incidence of intraoperative awareness. A comprehensive search was conducted to identify all eligible studies from the online literature databases published prior to Feb. 2017. A total of five studies with 17 432 cases and 16 749 controls were included. An odds ratio （OR） and a 95% confidence interval （CI） were calculated to examine the strength of the association. The results showed that in the overall analysis, the association between the BIS monitoring and the incidence of intraoperative awareness was not significant （OR=0.58, 95% CI= 0.22-1.58, P=0.29）. A stratified analysis by comparing different anesthesia methods revealed that BIS monitoring group showed a lower incidence of intraoperative awareness in patients with intravenous anesthesia when compared with non-BIS monitoring group （OR=0.20, 95% CI=0.08-0.49, P=-0.0004）, whereas there was no statistically significant difference in the incidence of intraoperative awareness between BIS and non-BIS monitoring groups in patients with inhalation anesthesia （OR=1. 13, 95% CI=0.56- 2.26, P=-0.73）. In conclusion, our meta-analysis showed that BIS monitoring had no appreciable advantage in the reduction of the intraoperative awareness incidence in inhalation anesthesia, while showed a remarkable superiority in intravenous anesthesia.

Awareness during emergence from anesthesia: Features and future research directions

The anesthesia awareness with recall(AAWR) phenomenon represents a complication of general anesthesia consisting of memorization of intraoperative events reported by the patient immediately after the end of surgery or at a variable distance from it. Approximately 20% of AAWR cases occur during emergence from anesthesia. Clinically, these unexpected experiences are often associated with distress especially due to a sense of paralysis. Indeed, although AAWR at the emergence has multiple causes, in the majority of cases the complication develops when the anesthesia plan is too early lightened at the end of anesthesia and there is a lack of use, or misuse, of neuromuscular monitoring with improper management of the neuromuscular block. Because the distress caused by the sense of paralysis represents an important predictor for the development of severe psychological complications, the knowledge of the phenomenon, and the possible strategies for its prophylaxis are aspects of considerable importance. Nevertheless, a limited percentage of episodes of AAWR cannot be prevented. This paradox holds also during the emergence phase of anesthesia which represents a very complex neurophysiological process with many aspects yet to be clarified.