Bispectral analysis of the electroencephalogram: a review of its development and use in anesthesia

Objective To evaluate the different methodologies used to monitor anesthetic depth and to review the principles and potential applications of bispectral index (BIS) monitoring in veterinary anesthesia. Databases used Medline (1966 to present); Pubmed (mid-1960s to present); personal files. Conclusions Current anesthetic monitoring techniques rely on indirect measures of corticocerebral arousal after a noxious stimulus. Some anesthetics and pre-anesthetics suppress responses that are used to gauge adequate hypnosis and analgesia. The BIS is a direct measure of corticocerebral activation and is inversely related to the degree of hypnosis. Dynamic changes in the BIS after a noxious stimulus may signify early nociceptive activation of the cerebral cortex and may be a useful marker of inadequate analgesia. However, application of this technique during the use of various drug combinations (i.e. clinical anesthesia) will require further research and understanding.