The bispectral index (BIS, Aspect Medical Systems, Inc. Newton, MA) is becoming the gold standard for assessing depth of anesthesia in adult patients. Indeed, BIS values are highly correlated with the concentration of hypnotic drugs such as propofol or sevoflurane (1–8). The BIS is derived from a large database of EEG traces obtained in adult patients under various conditions of anesthesia (9)....