What is BIS?

The BIS monitor is a processed EEG device manufactured by Aspect Medical Corporation.  Using a proprietary multiple regression algorithm it generates a dimensionless value that ranges from 0 to 100.  According to the manufacturer this index correlates to some of the components of the general anesthesia state including level of consciousness and probability of recollection when anesthetic agents that act though increasing chloride conductance into GABAa neurons are used.  They claim that a value between 40 – 60 represents a level of cortical brain inhibition compatible with adequate hypnotic levels of general anesthesia (although not predicting lack of movement or adequate analgesia).  They also claim that the probability of a patient being aware and having recall with BIS values in this range is extremely low (see Aspect Medical’s Web site for a discussion of their claims, http://www.aspectmedical.com/ ).  There are other brands of processed EEG devices being sold or under development for use in this manner.  However the largest published experience has been with the Aspect Medical device.

David S. Smith, M.D., Ph.D.