Authors' objectives:

This study aims to review the effectiveness and cost-effectiveness of the bispectral index (BIS) monitor, a commercial device to assess the depth of anesthesia.

Authors' results and conclusions: The results show BIS monitoring does not completely prevent intraoperative awareness. Although BIS monitoring may reduce the incidence of intraoperative awareness generally for patients undergoing anesthesia, it has limited value for individual patients for the following reasons: - It is a relatively good indicator of the state of being alert, but its algorithm is inaccurate for predicting an unconscious state. It has low sensitivity for the detection of the state of being asleep, and it may show values higher than 60 in those already asleep. - In the Bi-Aware trial, patients were kept close to the lower threshold index value. In another large trial (non-RCT with historical cohort), patients were kept below the recommended values for general anesthesia. These two studies found a lower incidence of intraoperative awareness. However, in clinical practice, the incidence of intraoperative awareness might not decrease if patients are kept close to the upper threshold values. This could become problematic for high-risk patients in whom light anesthesia is preferable. - The BIS monitor is insensitive to specific anesthetic agents. - The BIS monitor interferes with medical devices that are typically used in the operating room. This interference contaminates EEG data and reduces the performance of the monitor. - The Medical Advisory Secretariat did not find any study that recommended relying only on BIS monitoring to manage anesthetized patients.

Authors' recommendations: In both of the large studies that demonstrated a lower incidence of intraoperative awareness (i.e., the Bi-Aware RCT and European prospective study), the anesthesia was deep during maintenance (a mean BIS score of 44.5 [SD, 6.8]in the Bi-Aware trial, and a mean BIS score of 38 [SD, 8]in the European study). In clinical practice, a patient's hemodynamic status has such a substantial impact on the administration of drugs that anesthesiologists concentrate more on hemodynamics than the depth of anesthesia. Deep anesthesia can cause hemodynamic disturbances, including low blood pressure and cardiac output. It should be noted that in the Bi-Aware trial, marked hypotension was significantly higher in the BIS group. Several limitations of the BIS monitor decrease its usefulness to guide anesthesia. A consciousness monitor must have enough sensitivity to indicate reliably when a patient is awake or asleep. As shown in the studies discussed in this review, the sensitivity of BIS monitors is not adequate to detect the state of being asleep. This weakness could jeopardize a patient if BIS-guided anesthesia leads to the administration of extra doses of anesthetic agents. Another limitation is that it gives different results when different anesthetic agents are used. The primary reason for using a depth-of-anesthesia monitor must be to improve patient care; that is, the benefits of monitoring should outweigh the risks. According to one estimate, however, 861 patients would need to be monitored to avoid one incidence of recall. Considering the low sensitivity of BIS monitoring to detect the state of being asleep, several patients would be at risk of receiving unnecessary hypnotic medications to save one from intraoperative awareness. Prevention of awareness should remain a clinical decision for anesthesiologists to make based on their experience with intraoperative awareness in their practices. Adherence to the practice guidelines will reduce the risk of intraoperative awareness.

Authors' methods: Systematic review

Project Status: Completed

Year Published: 2004

URL for published report: http://www.health.gov.on.ca/english/providers/program/mas/tech/reviews/pdf/rev_bis_060104.pdf

URL for additional information: http://www.hqontario.ca/evidence/publications-and-ohtac-recommendations/ohtas-reports-and-ohtac-recommendations/bispectral-index-monitor

English language abstract: An English language summary is available

Publication Type: Not Assigned

Country: Canada

Organisation Name: Medical Advisory Secretariat

Contact Address: Medical Advisory Secretariat, 20 Dundas Street West, 10th Floor, Toronto, ON M5G 2N6 CANADA. Tel: 416-314-1092l; Fax: 416-325-2364;

Contact Name: MASinfo.moh@ontario.ca

Contact Email: MASinfo.moh@ontario.ca

Copyright: Medical Advisory Secretariat, Ontario Ministry of Health and Long-Term Care