The EEG Bispectral Index/sup TM/ (BIS/sup TM/): development and utility

Bispectral analysis of the electroencephalogram (EEG) quantifies the first-order, nonlinear phase and power coupling among sinusoidal components comprising the EEG. Previous work has demonstrated that EEG bispectrum correlate with changes in consciousness level (i.e., hypnotic state). The Bispectral Index (BIS), derived substantially from bispectral EEG descriptors, was created as a new clinical tool to monitor the hypnotic state of patients during sedation and anesthesia. BIS is a univariate EEG descriptor scaled from 100 (awake) to 0 (no cortical activity.) Subjects maintained with BIS values below 70 have a very low probability of explicit recall, while subjects maintained with BIS values below 60 have a very low probability of responding to verbal command (i.e., being conscious.) Compared with standard practice, anesthetic procedures titrated using BIS required less hypnotic agent, cost less, and provided faster patient recoveries.