The results from this updated review indicate that BIS could be useful in guiding the anaesthetic dose to avoid the risk of intraoperative recall in surgical patients with high risk of awareness. Furthermore, anaesthesia guided by BIS could improve anaesthetic delivery and recovery from anaesthesia.
General anaesthesia requires multiple agent administration to achieve unconsciousness (hypnotics), muscle relaxation, analgesia and haemodynamic control. Many anaesthesiologists rely on clinical signs alone to guide anaesthetic management. Bispectral index (BIS) is a scale derived from the measurement of cerebral electrical activity in anaesthetized patients so that the level of anaesthesia and drug delivery can be optimized. We systematically reviewed 31 randomized controlled studies to find out whether BIS can reduce the risk of intraoperative recall and reduce anaesthetic use and recovery times in adult surgical patients. The risk of intraoperative recall awareness was determined in selected patients who were at potentially high risk of awareness. Two studies (2493 patients) that used clinical signs as a guide to anaesthetic administration in the control group demonstrated a significant reduction in the risk of awareness with BIS monitoring. Two studies (1981 patients) compared BIS monitoring with end tidal anaesthetic gas monitoring as a guide to management of anaesthesia and this did not demonstrate any difference. No intraoperative recall awareness was reported in the trials in surgical patients with low risk of awareness. There was an overall reduction in volatile anaesthetic dose and the dose of propofol. Recovery from anaesthesia was quicker and post-anaesthesia recovery care unit stay was shorter. The limitations of some of the clinical trials on BIS are discussed.