Bispectral index monitoring to prevent awareness during anaesthesia

Bispectral index monitoring to prevent awareness during anaesthesia


B-aware trial

2463 non-cardiac surgery patients at risk of awareness under anaesthesia randomised to bispectral index (BIS) monitoring resulted in the reduction in the incidence of awareness compared with routine care. This led to widespread use of this monitoring technology in patients undergoing high risk surgery.

Principal investigator

Professor Paul Myles (Alfred Health and Monash University).


2463 Patients were enrolled between September 2000 and December 2002.

Participating countries

Australia, New Zealand, United Kingdom, Hong Kong and Thailand.

Published abstract

Awareness 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.

We 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. incidence of awareness during surgery in adults.

Of 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%). incidence of awareness during surgery in adults.

BIS-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.


The B-Aware trial was funded by project grants from the Australian and New Zealand College of Anaesthetists, the Alfred Hospital Research Trust, Royal Hobart Hospital Research Foundation (S Swallow), and the Centre for Encouragement of Philanthropy in Australia.

Primary results publication

Myles PS, Leslie K, McNeil J, Forbes A, Chan MT. Bispectral index monitoring to prevent awareness during anaesthesia: the B-Aware randomised controlled trial. Lancet. 2004 May 29;363(9423):1757-63.

Pubmed link

The full abstract can be viewed on Pubmed.

Last updated 12:23 18.11.2022