Purpose: The purpose of this paper is to review the current evidence relating anesthetic depth to long-term survival after surgery.
Source: Using PubMed as the principal source, this review included published studies in all languages comparing mortality in patients with low- and high-processed electro-encephalo-graphic index values.
Principal findings: All published studies used the bispectral index (BIS) monitor to measure anesthetic depth. The majority of the published observational studies were post hoc analyses of studies undertaken for other purposes. Most of these studies report a statistically significant association between deep general anesthesia (i.e., BIS values < 45) and death. Some studies also suggest an association between deep general anesthesia and myocardial infarction or postoperative cognitive decline. The combination of low BIS values and low delivered anesthetic concentrations (thus defining increased anesthetic sensitivity) may identify patients at particularly high risk. One of the three available randomized controlled trials reports worse outcomes in the BIS = 50 group compared with the BIS > 80 group, and two report no difference in mortality between the BIS = 35 and BIS = 50-55 groups.
Conclusions: The available evidence on anesthetic depth and long-term survival is inconclusive. Randomized controlled trials with carefully controlled arterial blood pressure are required.