As a result, several neurophysiologic monitors have been introduced in an attempt to provide a measure of the anesthetic state. With the introduction of newer anesthetic compounds and the use of multiple drugs to provide the anesthetic state, these clinical signs no longer provide a reliable guide to determine the depth of anesthesia. The first attempts at evaluating depth of anesthesia used clinical signs such as those described by Snow and subsequently by Guedel. Measuring the depth of general anesthesia has been an enigma ever since drugs were introduced that can render patients unconscious. The prediction probability was also calculated. The relation among BIS, measured drug concentration, responsiveness score, and presence or absence of recall was determined by linear and logistic regression for both the individual drugs and, when appropriate, for the pooled results.

The BIS (version 2.5) score was recorded in real-time and the BIS (version 3.0) was subsequently derived off-line from the recorded raw EEG data.

An OAAS score of 2 or less was considered unconscious. At each pseudo-steady-state drug concentration, a BIS score was recorded, the participant was shown either a picture or given a word to recall, an arterial blood sample was obtained for subsequent analysis of drug concentration, and the participant was evaluated for level of sedation as determined by the responsiveness portion of the observer's assessment of the alertness/ sedation scale (OAAS). A frontal montage was used for continuous recording of the EEG. Each volunteer was administered a dose-ranging sequence of one of the study drugs to achieve predetermined target concentrations. Volunteers were given either isoflurane, propofol, midazolam, or alfentanil. Seventy-two consenting volunteers were studied at four institutions.

Endnote for mac emory