BIS monitoring significantly reduces the risk of awareness under general anesthesia in high-risk adult surgical patients.

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• P S Myles, K Leslie, J McNeil, A Forbes, and M T V Chan.
• Department of Anaesthesia and Pain Management, Alfred Hospital, Melbourne, Australia. p.myles@alfred.org.au
• Lancet. 2004 May 29;363(9423):1757-63.

BackgroundAwareness is an uncommon complication of anaesthesia, affecting 0.1-0.2% of all surgical patients. Bispectral index (BIS) monitoring measures the depth of anaesthesia and facilitates anaesthetic titration. In this trial we determined whether BIS-guided anaesthesia reduced the incidence of awareness during surgery in adults.MethodsWe did a prospective, randomised, double-blind, multicentre trial. Adult patients at high risk of awareness were randomly allocated to BIS-guided anaesthesia or routine care. Patients were assessed by a blinded observer for awareness at 2-6 h, 24-36 h, and 30 days after surgery. An independent committee, blinded to group identity, assessed every report of awareness. The primary outcome measure was confirmed awareness under anaesthesia at any time.FindingsOf 2463 eligible and consenting patients, 1225 were assigned to the BIS group and 1238 to the routine care group. There were two reports of awareness in the BIS-guided group and 11 reports in the routine care group (p=0.022). BIS-guided anaesthesia reduced the risk of awareness by 82% (95% CI 17-98%).InterpretationBIS-guided anaesthesia reduces the risk of awareness in at-risk adult surgical patients undergoing relaxant general anaesthesia. With a cost of routine BIS monitoring at US16 dollars per use in Australia and a number needed to treat of 138, the cost of preventing one case of awareness in high-risk patients is about 2200 dollars.

This article appears in the collections: Post-operative awareness monitoring & prevention and Landmark articles in Anesthesia.

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