• Miklos D Kertai, Ben J A Palanca, Nirvik Pal, Beth A Burnside, Lini Zhang, Furqaan Sadiq, Kevin J Finkel, Michael S Avidan, and B-Unaware Study Group.
• Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri, USA. miklos.kertai@duke.edu
• Anesthesiology. 2011 Mar 1;114(3):545-56.

BackgroundPostoperative mortality has been associated with cumulative anesthetic duration below an arbitrary processed electroencephalographic threshold (bispectral index [BIS] <45). This substudy of the B-Unaware Trial tested whether cumulative duration of BIS values lower than 45, cumulative anesthetic dose, comorbidities, or intraoperative events were independently associated with postoperative mortality.MethodsThe authors studied 1,473 patients (mean ± SD age, 57.9 ± 14.4 yr; 749 men) who underwent noncardiac surgery at Barnes-Jewish Hospital in St. Louis, Missouri. Multivariable Cox regression analysis was used to determine whether perioperative factors were independently associated with all-cause mortality.ResultsA total of 358 patients (24.3%) died during a follow-up of 3.2 ± 1.1 yr. There were statistically significant associations among various perioperative risk factors, including malignancy and intermediate-term mortality. BIS-monitored patients did not have lower mortality than unmonitored patients (24.9 vs. 23.7%; difference = 1.2%, 95% CI, -3.3 to 5.6%). Cumulative duration of BIS values less than 45 was not associated with mortality (multivariable hazard ratio, 1.03; 95% CI, 0.93-1.14). Increasing mean and cumulative end-tidal anesthetic concentrations were not associated with mortality. The multivariable Cox regression model showed a good discriminative ability (c-index = 0.795).ConclusionsThis study found no evidence that either cumulative BIS values below a threshold of 40 or 45 or cumulative inhalational anesthetic dose is injurious to patients. These results do not support the hypothesis that limiting depth of anesthesia either by titration to a specific BIS threshold or by limiting end-tidal volatile agent concentrations will decrease postoperative mortality.

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