title: Bispectral Index (BIS) may not predict awareness reaction to intubation in surgical patients.
abstract: Bispectral Index (BIS) has been marketed as a measure of the hypnotic component of anesthesia and is recommended as a guide for the administration of hypnotic drugs during anesthesia. BIS values between 40 and 60 are recommended for surgery under general anesthesia. This study investigates whether a BIS baseline between 50 and 60 prevents awareness reaction to endotracheal intubation. After approval by the university's Ethics Committee, 20 consenting patients were enrolled in the study. Midazolam (0.1 mg/kg PO) was given 30 minutes before induction. Anesthesia was induced with alfentanil (10 mcg/kg, followed by 2 mcg/kg(-1) x min(-1)) and propofol infusion was adjusted to a BIS target level between 50 and 60. Propofol infusion rate was maintained constant for 5 minutes with constant BIS. Prior to intubation, patients were tested in one-minute intervals for awareness using Tunstall's isolated forearm technique. Three minutes after endotracheal intubation, the study period ended and surgery was performed. After intubation, 8 of 20 patients showed an awareness reaction, squeezing the investigator's hand in response to a command. No patient had recall. Comparison of patients with and without awareness reaction revealed no differences in BIS before or after intubation. This study shows that a BIS value between 50 and 60 prior to intubation is inadequate to prevent an awareness reaction to endotracheal intubation during propofol/alfentanil anesthesia. Because BIS cannot differentiate between patients with and without awareness reaction, its value as a monitor for awareness and a measurement of the hypnotic component of anesthesia must be questioned.
authors.affiliation: Department of Anesthesiology, Technische Universität München, Munich, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Schneider
authors.forename: Klaus
authors.initials: K
authors.lastname: Wagner
authors.forename: Wolfram
authors.initials: W
authors.lastname: Reeker
authors.forename: Frank
authors.initials: F
authors.lastname: Hänel
authors.forename: Christian
authors.initials: C
authors.lastname: Werner
authors.forename: Eberhard
authors.initials: E
authors.lastname: Kochs
mesh_terms: D000328:Adult; D000768:Anesthesia, General; D001364:Awareness; D001794:Blood Pressure; D004569:Electroencephalography / Q000187:drug effects; D005260:Female; D006339:Heart Rate; D006801:Humans; D007442:Intubation, Intratracheal; D008297:Male; D008875:Middle Aged; D015742:Propofol
chemical_list: D015742:Propofol