Abstract:

Recently postoperative mortality has been associated with cumulative anesthetic duration of low bispectral index (BIS). It was suggested that cumulative deep hypnotic time (cumulative duration of low BIS) was an independent predictor of 1 year mortality after major noncardiac surgery in 2005. Reports confirmed that the mortality-hypnosis association was all derived from secondary analyses of data collected prospectively for other purposes, which were to evaluate the effect of BIS monitoring on the incidence of intraoperative awareness. In these substudies, it was found that cumulative time at BIS less than 45 was associated with an increased risk of death for up to 2 year after surgery. It was also found that the absence of low BIS values was associated with improved survival and reduced morbidity (myocardial infarction and stroke). The substudy of the B-Unaware Trial added the evidence confirming the association between cumulative duration of low BIS and postoperative mortality. In this investigation, 17.8% of patients died in the first 3 year after cardiac surgery, with the risk of death increased by 29% for every cumulative hour for which the BIS was less than 45 during surgery. These three studies along with another report on the ICU patients who experienced burst suppression had a significantly higher 6-month mortality rate compared with patients who did not have burst suppression when sedated (59% vs 33%). Recognizing that the hypnosis-mortality association exists warrants further studies on the association.

Key words: depth of anesthesia, long-term mortality, bispectral index