Duration Versus Magnitude of BIS-Measured EEG Suppression and Postoperative Recovery Patterns: A Prospective Observational Study

Background: This study aimed to determine whether the duration or the magnitude of intraoperative BIS suppression has a greater impact on postoperative recovery. Methods: In this observational study, 141 patients were monitored for BIS values, suppression ratio (SR), maximum suppression ratio (SRmax), and total suppression time (SRT) during the perioperative period. Recovery phenotypes were assessed using the Richmond Agitation-Sedation Scale (RASS). Statistical analyses evaluated the relationship between BIS suppression parameters (SR, SRmax, SRT) and postoperative sedation or emergence agitation. Optimal thresholds for clinically significant suppression were determined. Results: Patients classified into the sedation group according to RASS scores exhibited significantly higher intraoperative SRmax values (p: 0.038) and prolonged SRT (p: 0.001) compared to the agitated group. An SRT ≥ 7.5 min predicted sedated recovery with 86.7% sensitivity and 39.4% specificity (AUC = 0.651, 95% CI: 0.561–0.742, p: 0.002). Similarly, an SRmax ≥ 19.5 was associated with sedated recovery (85.3% sensitivity, 53.0% specificity; AUC = 0.683, 95% CI: 0.592–0.775, p: 0.001). No significant association was found between BIS suppression and emergence agitation. Conclusions: Prolonged intraoperative BIS suppression and higher SRmax values are comparably predictive of postoperative sedation but not agitation. Monitoring these parameters may aid in anticipating recovery patterns.