Anesthesia awareness and the bispectral index.
BACKGROUND
Awareness during anesthesia is a serious complication with potential long-term psychological consequences. Use of the bispectral index (BIS), developed from a processed electroencephalogram, has been reported to decrease the incidence of anesthesia awareness when the BIS value is maintained below 60. In this trial, we sought to determine whether a BIS-based protocol is better than a protocol based on a measurement of end-tidal anesthetic gas (ETAG) for decreasing anesthesia awareness in patients at high risk for this complication.


METHODS
We randomly assigned 2000 patients to BIS-guided anesthesia (target BIS range, 40 to 60) or ETAG-guided anesthesia (target ETAG range, 0.7 to 1.3 minimum alveolar concentration [MAC]). Postoperatively, patients were assessed for anesthesia awareness at three intervals (0 to 24 hours, 24 to 72 hours, and 30 days after extubation).


RESULTS
We assessed 967 and 974 patients from the BIS and ETAG groups, respectively. Two cases of definite anesthesia awareness occurred in each group (absolute difference, 0%; 95% confidence interval [CI], -0.56 to 0.57%). The BIS value was greater than 60 in one case of definite anesthesia awareness, and the ETAG concentrations were less than 0.7 MAC in three cases. For all patients, the mean (+/-SD) time-averaged ETAG concentration was 0.81+/-0.25 MAC in the BIS group and 0.82+/-0.23 MAC in the ETAG group (P=0.10; 95% CI for the difference between the BIS and ETAG groups, -0.04 to 0.01 MAC).


CONCLUSIONS
We did not reproduce the results of previous studies that reported a lower incidence of anesthesia awareness with BIS monitoring, and the use of the BIS protocol was not associated with reduced administration of volatile anesthetic gases. Anesthesia awareness occurred even when BIS values and ETAG concentrations were within the target ranges. Our findings do not support routine BIS monitoring as part of standard practice. (ClinicalTrials.gov number, NCT00281489 [ClinicalTrials.gov].).
Avidan
Michael S
MS
Department of Anesthesiology, Washington University School of Medicine, St. Louis, MO 63110, USA. avidanm@wustl.edu
Zhang
Lini
L
Burnside
Beth A
BA
Finkel
Kevin J
KJ
Searleman
Adam C
AC
Selvidge
Jacqueline A
JA
Saager
Leif
L
Turner
Michelle S
MS
Rao
Srikar
S
Bottros
Michael
M
Hantler
Charles
C
Jacobsohn
Eric
E
Evers
Alex S
AS
D000328:Adult; D000368:Aged; D000465:Algorithms; D000768:Anesthesia, General; D018681:Anesthetics, General / Q000008:administration & dosage / Q000032:analysis; D001364:Awareness; D001944:Breath Tests; D004569:Electroencephalography / Q000379:methods*; D005260:Female; D006801:Humans; D007432:Intraoperative Period; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D011446:Prospective Studies; D012306:Risk; D012815:Signal Processing, Computer-Assisted; D011795:Surveys and Questionnaires
D018681:Anesthetics, General