Monitoring depth of anaesthesia in a randomized trial decreases the rate of postoperative delirium but not postoperative cognitive dysfunction

Postoperative delirium in elderly patients is a frequent complication and associated with poor outcome. The aim of this parallel group study was to determine whether monitoring depth of anaesthesia influences the incidence of postoperative delirium. Patients who were planned for surgery in general anaesthesia expected to last at least 60 min and who were older than 60 yr were included between March 2009 and May 2010. A total of 1277 patients of a consecutive sample were randomized (n638 open, n639 blinded) and the data of 1155 patients were analysed (n575 open, n580 blinded). In one group, the anaesthesiologists were allowed to use the bispectral index (BIS) data to guide anaesthesia, while in the other group, BIS monitoring was blinded. Cognitive function was evaluated at baseline, 1 week, and 3 months after operation. Delirium incidence was lower in patients guided with BIS. Postoperative delirium was detected in 95 patients (16.7) in the intervention group compared with 124 patients (21.4) in the control group (P0.036). In a multivariate analysis, the percentage of episodes of deep anaesthesia (BIS values 20) were independently predictive for postoperative delirium (P0.006; odds ratio 1.027). BIS monitoring did not alter the incidence of postoperative cognitive dysfunction (7th day P0.062; 90th day P0.372). Intraoperative neuromonitoring is associated with a lower incidence of delirium, possibly by reducing extreme low BIS values. Therefore, in high-risk surgical patients, this may give the anaesthesiologist a possibility to influence one precipitating factor in the complex genesis of delirium. ISRCTN Register: 36437985. .