The results from this updated review indicate that BIS can be useful in guiding the anaesthetic dose to avoid the risk of intraoperative awareness in surgical patients at high risk for awareness. Furthermore, anaesthesia guided by BIS improves 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. 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 optimised. We systematically reviewed 36 randomized controlled studies to find out whether BIS could reduce the risk of intraoperative awareness and reduce anaesthetic use and recovery times in adult surgical patients. The risk of intraoperative awareness was determined in selected patients who were at potentially high risk for awareness. Four studies (7761 patients) that used clinical signs as a guide to anaesthetic administration in standard practice, as the control group, demonstrated a significant reduction in the risk of awareness with BIS monitoring. Four studies (26,530 patients) compared BIS monitoring with end tidal anaesthetic gas (ETAG) monitoring as a guide to management of anaesthesia and they did not demonstrate any difference in terms of intraoperative awareness. There was an overall reduction in volatile anaesthetic dose and the dose of propofol in the BIS group. Recovery from anaesthesia was quicker and postanaesthesia recovery care unit stay was shorter. The limitations of some of the clinical trials on BIS are discussed.