Prevention of intraoperative awareness with explicit recall in an unselected surgical population: a randomized comparative effectiveness trial

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 (Covidien, Boulder, CO) 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 because of futility. At interim analysis the incidence of definite awareness was 0.12% (11/9,376) (95% CI: 0.07-0.21%) in the anesthetic concentration group and 0.08% (8/9,460) (95% CI: 0.04-0.16%) 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 with a cohort receiving no intervention (P = 0.001; 95% CI: 1.7-13.1).

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 with routine care.

Figures

Figure 1

Flow diagram of recruitment and follow-up interviews. BIS=Bispectral Index

Figure 2

Primary outcome of definite awareness in modified intention-to-treat groups, defined as those recruited, randomized to Bispectral Index (BIS)- or anesthetic concentration-guided care, and interviewed at one month for intraoperative awareness. Note that the BIS randomization group includes patients that did not have BIS values generated.

Figure 3

Secondary outcomes of definite or possible awareness in post hoc groups.