Assessing the depth-of-hypnosis

BACKGROUND: There has been a breakthrough in the understanding of anaesthetic drug effects during the last two decades, and new monitors aimed at quantifying such effects have been developed. MATERIAL AND METHODS: This review is based on publications from the last 15 years, oral presentations, and rewritten parts of the author's PhD thesis. RESULTS: General anaesthesia can be regarded as a combination of hypnosis (sleep), analgesia and muscle relaxation. Modern anaesthetic drugs aim at each of these effects separately. Pharmacological variation makes it impossible to find one dose suitable for all, so tools for measuring drug effects in the individual patient are warranted. Monitors for measuring depth-of-hypnosis and partly analgesic effect are commercially available. Among these, BIS (bispectral index), based on EEG, is by far the best documented. BIS is proven useful for preventing undesired awareness and overdosing, but there are major limitations. Use of such technology in clinical practice is under constant debate. INTERPRETATION: Even though the BIS technology is promising and used widely, no health authorities have so far recommended that such monitors should be compulsory during general anaesthesia, but rather that it should be considered on an individual basis. So far, it seems like this is a sensible approach in Norway as well.

Tidsskr Nor Laegeforen. 2010 Mar 25;130(6):633-7. Høymork SC. Anestesi- og intensivavdelingen, Vestre Viken, Sykehuset Asker og Baerum 1309 Rud, Norway. s.c.hoymork@medisin.uio.no