Cumulative cerebral desaturation burden during cardiopulmonary bypass predicts postoperative S100B elevation in pediatric cardiac surgery: a prospective cohort study

Background Pediatric cardiac surgery with cardiopulmonary bypass (CPB) carries a high risk of perioperative brain injury, while the optimal threshold of cerebral regional oxygen saturation (C-rSO₂) for early risk identification remains unclear. This study aimed to investigate the association between cumulative cerebral desaturation burden during CPB and perioperative serum S100B levels in children undergoing congenital heart surgery, and to evaluate the consistency of this association across four relative desaturation thresholds via sensitivity analysis. Methods In this prospective cohort study, intraoperative C-rSO₂ was continuously monitored, and the area under the curve (AUC) for C-rSO₂ below baseline (5%, 10%, 15%, 20% below individual baseline) during CPB was calculated. Serum S100B was measured at anesthesia induction (T0, baseline), end of surgery (T1), and first postoperative day (T2). Multiple linear regression models adjusted for confounders were compared, and receiver operating characteristic (ROC) curve analysis was performed to explore the optimal cutoff value. Results A total of 118 children were finally included. After adjusting for confounders, the association between cumulative desaturation burden and S100B elevation was consistent across all tested thresholds, with the ≥5% threshold being the most sensitive predictor at both T1 (B = 0.22, 95%CI 0.19–0.25, P < 0.001) and T2 (B = 0.15, 95%CI 0.12–0.18, P < 0.001), with the best model performance (adjusted R 2 : 0.80 at T1, 0.79 at T2). ROC analysis showed an AUROC of 0.87 (95%CI: 0.78–0.97) for predicting elevated peak S100B, with an optimal cutoff of 217.1%·min (sensitivity 86.2%, specificity 84.3%). A significant dose-response relationship was observed, and both markers were elevated in children with postoperative seizures. Conclusion Cumulative C-rSO₂ desaturation burden ≥5% during CPB is a robust independent predictor of early postoperative S100B elevation.