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02-10-2012 | Anaesthesiology | Article

Alarms could be key to avoiding intraoperative awareness


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medwireNews: Bispectral index (BIS) monitoring is unlikely to be better than monitoring based on anesthetic concentrations for preventing intraoperative awareness, shows a randomized trial.

The intended study size was 30,000 patients, because of the rarity of intraoperative awareness, but it was halted for futility after the interim analysis, with 21,601 patients enrolled.

Among 18,836 patients who were interviewed about intraoperative awareness, 0.12% of those in the BIS group and 0.08% of those in the anesthetic concentrations group reported definite intraoperative awareness, which was not a significant difference, the researchers report in Anesthesiology.

Definite awareness involved explicit recall of surgical events and was agreed on by three blinded experts who reviewed the interviews.

Editorialists Stavros Memtsoudis and Spencer Liu (Hospital for Special Surgery, New York, USA) praise the study for being in line with the principles of comparative effectiveness research. But they note that the findings question the value of using BIS monitoring, which is more expensive than standard care.

However, the findings do suggest a strategy for reducing intraoperative awareness. In a post-hoc analysis, George Mashour (University of Michigan Medical School, Ann Arbor, USA) and colleagues divided patients into three groups based on whether they actually received the intended intervention.

They found that the rate of intraoperative awareness was 0.12% in patients who received monitoring based on anesthetic concentrations, 0.05% in those who received BIS monitoring, and 0.15% in those who did not receive an intervention. The corresponding rates of probable or definite awareness were 0.20%, 0.08%, and 0.38%; by this measure, patients who received no intervention were significantly more likely to experience awareness than those who received BIS monitoring.

Mashour et al suggest that the difference in favor of BIS monitoring may be because the system generated about twice as many alarms as did the protocol based on anesthetic concentrations.

In their editorial, Memtsoudis and Liu say: "These alert systems are not widely in place at this time but are increasingly of clinical interest and viability."

They add: "A critical feature of automated monitoring alerts is careful selection of alarm values to enhance vigilance without creating alarm fatigue, and further work may be needed to refine these values for BIS and [minimum alveolar concentration] monitoring."

medwireNews ( is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2012

By Eleanor McDermid, Senior medwireNews Reporter

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