Increased risk of intraoperative awareness in patients with a history of awareness

Background: Patients with a history of intraoperative awareness with explicit recall (AWR) are hypothesized to be at higher risk for AWR than the general surgical population. In this study, the authors assessed whether patients with a history of AWR (1) are actually at higher risk for AWR; (2) receive different anesthetic management; and (3) are relatively resistant to the hypnotic actions of volatile anesthetics. Methods: Patients with a history of AWR and matched controls from three randomized clinical trials investigating prevention of AWR were compared for relative risk of AWR. Anesthetic management was compared with the use of the Hotelling's T2 statistic. A linear mixed model, including previously identified covariates, assessed the effects of a history of AWR on the relationship between end-Tidal anesthetic concentration and bispectral index. Results: The incidence of AWR was 1.7% (4 of 241) in patients with a history of AWR and 0.3% (4 of 1,205) in control patients (relative risk = 5.0; 95% CI, 1.3-19.9). Anesthetic management did not differ between cohorts, but there was a significant effect of a history of AWR on the end-Tidal anesthetic concentration versus bispectral index relationship. Conclusions: Surgical patients with a history of AWR are five times more likely to experience AWR than similar patients without a history of AWR. Further consideration should be given to modifying perioperative care and postoperative evaluation of patients with a history of AWR.