Deep anaesthesia and poor outcomes: the jury is still out

The ideal anaesthetic depth is where the risk of operative recall or awareness is as low as possible, regardless of what is happening surgically, and where blood pressure and heart rate are kept optimal for the individual patient. Advances in technology have resulted in the development of a number of methods for monitoring the depth of anaesthesia, including the bispectral index (BIS):1 a numerical scale based on electrical activity in the brain, where complex electroencephalogram signals are converted to a single number using algorithms. In the patients in whom the BIS target was achieved (the per-protocol group), survival between the two BIS groups was not different; however, the numbers of patients to whom this applied was much lower than the sample size calculation.