Until recently, anesthesiologist lacked the ability to monitor the effects of anesthetics on the brain in terms of “depth” or “adequacy”of anesthesia. Because it is believed that general anesthetics block consciousness by depressing the central nervous system, and electrical activity of the cerebral cortex can be measured using the electroencephalogram (EEG), it is expected that some component of the EEG should relate to adequacy of anesthesia. The first and only technology approved by the U.S. Food and Drug Administration for marketing as an EEG-based monitor for anesthetic effect is the bispectral analysis derivative known as the Bispectral Index Scale (BIS).