Changes of Bispectral Index and Auditory Evoked Potential Index during General Anesthesia with Propofol, Midazolam and Ketamine

Abstract

BACKGROUND: The Bispectral Index (BIS) and the Auditory Evoked Potential (AEP) have been suggested to reflect the level of sedation or hypnosis for intravenous and inhalational anesthetics. The Auditory Evoked Potential Index (AEPindex) has been shown to be reliable in indicating potential awareness during propofol anesthesia. This study was designed to determine the effects of three different anesthetic techniques on the AEPindex and BIS. The three techniques used were midazolam/Remifentanil, ketamine/Remifentanil, and propofol/Remifentanil. All agents were delivered using target controlled infusion (TCI). METHODS: We studied 39 patients scheduled for elective cardiac surgery. Patients were allocated randomly to receive either midazolam/remifentanil (n = 15), ketamine/remifentanil (n = 9) or propofol/remifentanil (n = 15) administered by TCI. AEPindex and BIS were monitored continuously and blood concentrations of propofol, midazolam and ketamine were measured every 5 minutes during anesthesia until the start of surgery. RESULTS: AEPindex and BIS had high values in the awake state, which declined following anesthetic induction. Values of AEPindex were comparable between all the three anesthetic techniques, whereas BIS was significantly higher during anesthesia with midazolam or ketamine than during propofol anesthesia. CONCLUSIONS: AEPindex was a reliable monitor of the depth of general anesthesia irrespective of the anesthetic used. BIS showed marked variability during anesthesia produced by midazolam/remifentanil and ketamine/remifentanil, and would not be suitable for measuring depth of anesthesia with these techniques. [By kind permission, KoreaMed, Korean Association of Medical Journal Editors.]