Delirium and cognitive decline after surgery: a randomised controlled trial of anaesthetic management to improve postoperative mental health outcome.

Previous clinical trials and animal experiments have suggested that long-lasting exposure to general anaesthetics may lead to postoperative mental disturbance. Intraoperative monitoring of processed electroencephalogram (EEG), such as the bispectral index (BIS), has been shown to facilitate titration of anaesthetic drug delivery.1,2 The BIS monitor analyses raw EEG signals and displays a dimensionless number, ranging from 0 (isoelectric EEG) to 100 (fully awake), to indicate the depth of anaesthesia. By aiming at a BIS value between 40 and 60 during anaesthesia, the doses of hypnotic agents administered can be reduced by 11% to 27%.3,4 However, it is unclear whether a lower dose of anaesthetics with BIS monitoring will minimise anaesthetic side effects, leading to an improvement of cognitive function after surgery. We have recently published study to evaluate the impact of BISguided anaesthesia on postoperative mental health in elderly patients undergoing major surgery.5 The Cognitive Dysfunction after Anesthesia (CODA) Trial recruited 921 patients aged ≥65 years having general anaesthesia for major colorectal surgery. Patients were randomised to receive either BIS-guided anaesthesia (n=462) or routine care (n=459), in which anaesthetic drug administration was titrated according to clinical judgement. All patients were interviewed before surgery and at 30 days and 3 months after surgery for objective neuropsychology assessments. A cognitive failure questionnaire was used to measure subjective change in perception, memory, and motor function. Patients were monitored daily after surgery until discharge to detect complications and occurrence of delirium using the Confusion Assessment Method criteria. Anaesthesia guided by BIS reduced anaesthetic drug dosage as indicated by a reduced volatile Hong Kong Med J 2014;20(Suppl 7):S28-9 HHSRF project number: 04060271 MTV Chan *, T Gin