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.