Persistent Cardiac Surgery-Associated Acute Kidney Injury Identifies a High-Risk Phenotype after Pediatric Congenital Heart Surgery

Abstract Background Cardiac surgery-associated acute kidney injury (CS-AKI) is heterogeneous, and persistence may define a clinically important postoperative phenotype. We examined early CS-AKI phenotypes, their perioperative associations and clinical outcomes, and exploratory discrimination of persistent CS-AKI. Methods This retrospective single-center cohort included 219 eligible patients from 288 consecutively screened children aged ≤ 18 years who underwent congenital heart surgery in 2023–2024. Early CS-AKI was classified as transient CS-AKI if it had resolved by postoperative day 3 and as persistent CS-AKI if it remained present on postoperative day 3 or if therapeutic renal replacement therapy precluded valid creatinine-based assessment. The primary CatBoost model used preoperative, intraoperative, and first-24-hour postoperative variables while excluding postoperative creatinine and was evaluated using nested cross-validation. Results Early CS-AKI occurred in 69 patients (31.5%): 40 had transient CS-AKI and 29 had persistent CS-AKI. Short-term in-hospital mortality was 0.7%, 5.0%, and 44.8% in the no early CS-AKI, transient CS-AKI, and persistent CS-AKI groups, respectively. In the multivariable model, persistent CS-AKI remained associated with younger age, Society of Thoracic Surgeons-European Association for Cardio-Thoracic Surgery (STAT) category 4–5 procedures, a vasoactive-inotropic score (VIS) > 15, and POD0 fluid accumulation. The primary exploratory model achieved a cross-validated area under the receiver operating characteristic curve of 0.85 (95% confidence interval, 0.77–0.93), with a calibration slope of 0.87 and a Brier score of 0.073. Conclusions Persistent CS-AKI, rather than transient, identified a high-risk postoperative phenotype associated with substantially worse short-term outcomes than transient CS-AKI. Routine perioperative variables showed promising exploratory discrimination of persistence after the first postoperative day, but prospective multicenter external validation is required before clinical use.