Prevention of Intraoperative Awareness with Explicit Recall in an Unselected Surgical Population

Abstract

Background Intraoperative awareness with explicit recall occurs in approximately 0.15% of all surgical cases. Efficacy trials based on the Bispectral Index™ (BIS) monitor and anesthetic concentrations have focused on high-risk patients, but there are no effectiveness data applicable to an unselected surgical population. Methods We conducted a randomized controlled trial of unselected surgical patients at three hospitals of a tertiary academic medical center. Surgical cases were randomized to alerting algorithms based on either BIS values or anesthetic concentrations. The primary outcome was the incidence of definite intraoperative awareness; prespecified secondary outcomes included postanesthetic recovery variables. Results The study was terminated due to futility. At interim analysis the incidence of definite awareness was 0.12% (11/9376) (95% CI 0.07 to 0.21%) in the anesthetic concentration group and 0.08% (8/9460) (95% CI 0.04 to 0.16%) in the BIS group (p = 0.48). There was no significant difference between the two groups in terms of meeting criteria for recovery room discharge or incidence of nausea and vomiting. By post hoc secondary analysis, the BIS protocol was associated with a 4.7-fold reduction in definite or possible awareness events compared to a cohort receiving no intervention (p = 0.001; 95% CI 1.7 to 13.1). Conclusion This negative trial could not detect a difference in the incidence of definite awareness or recovery variables between monitoring protocols based on either BIS values or anesthetic concentration. By post hoc analysis, a protocol based on BIS monitoring reduced the incidence of definite or possible intraoperative awareness compared to routine care.

The incidence of intra‐operative awareness in the UK: under the rate or under the radar?

“…Based on cases of awareness that became known to anaesthetists during 2011, the survey suggests that the current incidence of AWR in the UK is about 1 in 15 000. This is much lower than the 1 to 2 per 1000 incidence that has been found in several prospective studies that have assessed AWR [2][3][4]. This is not the first time the field of anaesthesia has been confronted with an investigation reporting an incidence of AWR one order of magnitude lower than that found in prospective studies.…”

“…It has been demonstrated that patients are unlikely to report spontaneously an AWR event to an anaesthetist [16], perhaps because of the brief interaction and limited relationship. Based on data from a single hospital complex in the US, a retrospective audit of spontaneous patient reports revealed a six-fold lower incidence of AWR [17] than a study in which patients were questioned directly [4]. Any study that relies on spontaneous patient reports of AWR rather than proactive questioning of all patients is likely to underestimate considerably the incidence of AWR.…”

“…In studies conducted outside of the UK, AWR has been estimated to affect 1 to 2 per thousand surgical patients [2][3][4]. If this incidence is extrapolated to the UK, it would suggest that thousands of surgical patients a year could be experiencing this complication.…”

“…Evidence has accumulated over the past few years that might be helpful in framing clinical decision pathways [23]. Practitioners should be encouraged to set alerts for a threshold low ETAC when using a volatile-based anaesthetic, as this practice probably decreases AWR [4,12,24]. If neuromuscular blocking drugs are deemed necessary, deliberation should be given to using a volatile-based technique, as TIVA is associated with a higher incidence of AWR [12][13][14].…”

“…Indeed, a 2009 Cochrane review [4] on outreach and EWS found only two reliable randomised controlled trials worldwide. One showed an improvement for in-hospital mortality but the other reported no statistical change at all.…”