Bispectral Index (BIS) monitor is a noninvasive neurophysiological monitoring device that been introduced since late 1990's. By applying a sensor to the forehead, the BIS obtained electroencephalograms(EEG) and electromyograms(EMG) which were transformed into simplified scaled numbers through 0-100. It has been applied in the real time monitor of anesthesia depth during operation or recovery, monitor of sleep in critical illness patients and gastrointestinal endoscopy sedation.