This study aimed to investigate whether prebypass endogenous melatonin concentrations are associated with perioperative oxidative DNA injury, indexed by urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG), and to explore their relationship with postoperative N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels in children undergoing cardiac surgery with cardiopulmonary bypass (CPB).

A prospective, observational study.

A single-center study conducted in a tertiary care hospital.

Eighty pediatric patients (neonates to 18 years) undergoing corrective cardiac surgery with CPB.

No experimental intervention was performed; blood and urine samples were collected perioperatively for biochemical analysis.

Serum prebypass and postbypass melatonin levels were measured by enzyme-linked immunosorbent assay; urinary 8-OHdG and NT-proBNP were quantified immediately and 24 hours postoperatively. Postbypass melatonin concentrations correlated positively with age (r = 0.288, p = 0.010) and negatively with surgical duration (r = −0.230, p = 0.040). Higher prebypass melatonin levels tended to be associated with lower postoperative urinary 8-OHdG (r = −0.300, p = 0.007). Postoperative 8-OHdG showed strong linear correlations with NT-proBNP both immediately and 24 hours after surgery (r = 0.516, p < 0.001; r = 0.451, p < 0.001). In multivariable analysis, 8-OHdG remained an independent predictor of NT-proBNP, whereas melatonin did not.

Oxidative DNA injury is strongly associated with postoperative myocardial stress in pediatric patients undergoing CPB. Prebypass melatonin status showed an exploratory, nonindependent relationship with perioperative oxidative stress, while oxidative stress markers were robustly linked to NT-proBNP. These findings delineate a redox-cardiac stress axis in pediatric CPB and support further investigation into the role of endogenous antioxidant capacity in perioperative cardiac stress.