Bispectral index (BIS) monitoring measures the depth of anaesthesia by analysis of brain EEG patterns and produces a score between 0 (deep anaesthesia) and 100 (awake). Scores of 40-60 are suitable for surgical anaesthesia; however, BIS has not previously been assessed in a randomised trial to guide the delivery of anaesthesia in order to reduce awareness during surgery.
Paul Myles from Alfred Hospital, Victoria, Australia, and colleagues randomly allocated around 2500 patients known to be at risk of awareness during surgery to receive either BIS-guided anaesthesia or standard care. Reported awareness was documented independently a few hours, one day, and one month after surgery.
BIS-guided anaesthesia reduced the incidence of awareness during surgery by over 80%; there were only two reported cases of awareness with BIS-guided anaesthesia compared with 11 reports among patients given standard care.
Professor Myles comments: "We have shown that use of BIS monitoring can reduce the incidence of awareness under general anaesthesia in patients at risk, suggesting that greater use of BIS monitoring is warranted in patients at increased risk of awareness undergoing relaxant general anaesthesia".
In an accompanying Commentary (p 1747) Claes Lennmarken from University Hospital, Linkoping, Sweden, concludes: "Myles and colleagues' study is a great leap forward, and hopefully it will also inspire those who have denied the potential of the neuromonitoring technologies to join in the efforts to ensure the sometimes missing component in what was started in 1846-general anaesthesia."
Lancet 2004; 363: 1747, 1757-63
Contact: Professor Paul S Myles, Department of Anaesthesia & Pain Management, Alfred Hospital, PO Box 315, Prahran, Victoria 3181, Australia;
T) 61-3-9276-2000;
F) 61-39-276-2813;
E) p.myles@alfred.org.au
Journal
The Lancet