BACKGROUND: It is important that the level of general anaesthesia (GA) is appropriate for the individual patient undergoing surgery. If anaesthesia is deeper than required to keep a patient unconscious, there might be increased risk of anaesthetic-related morbidity, such as postoperative nausea, vomiting and cognitive dysfunction. This may also prolong recovery times, potentially increasing health-care costs. If anaesthesia is too light, patients may not be fully unconscious and could be at risk of intraoperative awareness.
OBJECTIVE: The objective of this report is to assess the clinical effectiveness and cost-effectiveness of Bispectral Index (BIS), E-Entropy and Narcotrend technologies, each compared with standard clinical monitoring, to monitor the depth of anaesthesia in surgical patients undergoing GA.
DATA SOURCES: A search strategy was developed and run on a number of bibliographic electronic databases including MEDLINE, EMBASE, The Cochrane Library and the Health Technology Assessment (HTA) database. For the systematic review of patient outcomes, databases were searched from the beginning of 2009 to November 2011 for studies of BIS (and then updated in February 2012), and from 1995 to November 2011 (and then updated in February 2012) for studies of E-Entropy and Narcotrend. For the systematic review of cost-effectiveness, searches were from database inception to November 2011 (an update search was performed in February 2012).
REVIEW METHODS: The systematic review of patient outcomes followed standard methodology for evidence synthesis. A decision-analytic model was developed to assess the cost-effectiveness of depth of anaesthesia monitoring compared with standard clinical observation. A simple decision tree was developed, which accounted for patients' risk of experiencing short-term anaesthetic-related complications in addition to risk of experiencing intraoperative awareness.
RESULTS: Twenty-two randomised controlled trials comparing BIS, E-Entropy and Narcotrend with standard clinical monitoring were included in the systematic review of patient outcomes, alongside evidence from a recent Cochrane review. Six trials of patients classified with risk factors for intraoperative awareness were combined in a fixed-effect meta-analysis. The overall pooled Peto's odds ratio was 0.45 (95% confidence interval 0.25 to 0.81) in favour of BIS. However, there was statistically significant heterogeneity. The base-case cost per quality-adjusted life-year (QALY) for BIS compared with standard clinical monitoring ranged from £22,339 to £44,198 depending on patient subgroups (type of GA received; level of risk for awareness). For E-Entropy, base-case estimates ranged from £14,421 to £31,430. For Narcotrend, estimates varied from a cost per QALY of £8033 to Narcotrend dominating standard clinical monitoring.
LIMITATIONS: The analysis was limited by lack of clinical effectiveness data, particularly for E-Entropy and Narcotrend.
CONCLUSIONS: The available evidence on the impact of the technologies on reducing the likelihood of intraoperative awareness is limited. However, there were reductions in general anaesthetic consumption and anaesthetic recovery times. The cost-effectiveness of depth of anaesthesia monitoring appears to be highly dependent on a number of factors, including probability of awareness.
STUDY REGISTRATION: PROSPERO registration number CRD42011001834.
FUNDING: The National Institute for Health Research Health Technology Assessment programme.
