Low Bispectral Index Values in Awake Volunteers Receiving a Combination of Propofol and Midazolam

THE Bispectral Index (BIS) is increasingly used to monitor the level of (un)consciousness during surgical anesthesia and conscious sedation. Generally, an intraoperative BIS of 40-60 is considered sufficient to maintain adequate hypnosis for surgery. 2,3 Recently, a new version of the BIS® monitor has been introduced: the BIS-XP® (Aspect Medical Systems, Newton, MA). The BIS-XP® is said to exhibit improved resistance to artifacts from electrocautery devices and to detect and filter interference from electromyo graphic activity and other conditions commonly encountered during monitored anesthesia care sedation that may cause artifacts.# We report three cases in which volunteers receiving combinations of propofol and midazolam as part of a pharmacokinetic-dynamic interaction study remained responsive to verbal command, although the BIS-XP® values were at, or just above, 40. A Web enhancement is provided with an MPEG1 digital video file displaying the responsiveness of one of the volunteers in relation to the BIS-XP® values.