Intraoperative awareness risk, anesthetic sensitivity, and anesthetic management for patients with natural red hair: a matched cohort study Translated title: Le risque d’éveil peropératoire, la sensibilité aux anesthésiques et la gestion anesthésique chez les patients naturellement roux: une étude de cohorte appariée

Propensity-score matching is increasingly being used to estimate the effects of treatments using observational data. In many-to-one (M:1) matching on the propensity score, M untreated subjects are matched to each treated subject using the propensity score. The authors used Monte Carlo simulations to examine the effect of the choice of M on the statistical performance of matched estimators. They considered matching 1–5 untreated subjects to each treated subject using both nearest-neighbor matching and caliper matching in 96 different scenarios. Increasing the number of untreated subjects matched to each treated subject tended to increase the bias in the estimated treatment effect; conversely, increasing the number of untreated subjects matched to each treated subject decreased the sampling variability of the estimated treatment effect. Using nearest-neighbor matching, the mean squared error of the estimated treatment effect was minimized in 67.7% of the scenarios when 1:1 matching was used. Using nearest-neighbor matching or caliper matching, the mean squared error was minimized in approximately 84% of the scenarios when, at most, 2 untreated subjects were matched to each treated subject. The authors recommend that, in most settings, researchers match either 1 or 2 untreated subjects to each treated subject when using propensity-score matching.

Unintended intraoperative awareness, which occurs when general anesthesia is not achieved or maintained, affects up to 1% of patients at high risk for this complication. We tested the hypothesis that a protocol incorporating the electroencephalogram-derived bispectral index (BIS) is superior to a protocol incorporating standard monitoring of end-tidal anesthetic-agent concentration (ETAC) for the prevention of awareness. We conducted a prospective, randomized, evaluator-blinded trial at three medical centers. We randomly assigned 6041 patients at high risk for awareness to BIS-guided anesthesia (with an audible alert if the BIS value was 60, on a scale of 0 to 100, with 0 indicating the suppression of detectable brain electrical activity and 100 indicating the awake state) or ETAC-guided anesthesia (with an audible alert if the ETAC was 1.3 minimum alveolar concentration). In addition to audible alerts, the protocols included structured education and checklists. Superiority of the BIS protocol was assessed with the use of a one-sided Fisher's exact test. A total of 7 of 2861 patients (0.24%) in the BIS group, as compared with 2 of 2852 (0.07%) in the ETAC group, who were interviewed postoperatively had definite intraoperative awareness (a difference of 0.17 percentage points; 95% confidence interval [CI], -0.03 to 0.38; P=0.98). Thus, the superiority of the BIS protocol was not demonstrated. A total of 19 cases of definite or possible intraoperative awareness (0.66%) occurred in the BIS group, as compared with 8 (0.28%) in the ETAC group (a difference of 0.38 percentage points; 95% CI, 0.03 to 0.74; P=0.99), with the superiority of the BIS protocol again not demonstrated. There was no difference between the groups with respect to the amount of anesthesia administered or the rate of major postoperative adverse outcomes. The superiority of the BIS protocol was not established; contrary to expectations, fewer patients in the ETAC group than in the BIS group experienced awareness. (Funded by the Foundation for Anesthesia Education and Research and others; BAG-RECALL ClinicalTrials.gov number, NCT00682825.).