The Influence of Anaesthetic Depth on Patient Outcome after Major Surgery

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Approximately 450,000 people undergo surgery for various reasons in New Zealand. Most of these people are given general anaesthesia for their procedure. We use a range of monitoring to assess vital signs and other safety factors. One of the monitoring systems we use is the Bi-spectral Index (BIS), which uses electroencephalogram (EEG) waves to determine the depth (how deeply anaesthetised) patients are during their procedure. These monitoring systems are widely available nationally and internationally, however, the optimal depth at which anaesthetics should be given is unknown. Recent observational studies have shown a 20% increase in mortality in patients undergoing major surgery who receive relatively deep anaesthesia. We plan to perform a large scale randomized trial investigating the difference between two clinically standard depth ranges, which are commonly referred to “light” and “deep” anaesthesia, to definitively answer the question of whether anaesthetic depth alters surgical outcome. In particular we will look at death rate at one year and also whether there are differences in other complications of surgery and anaesthesia, including wound infection, cardiovascular and neurological complications, pain and awareness