To identify risk factors associated with inadequate heparin response in pediatric congenital heart surgery requiring cardiopulmonary bypass and to develop age-specific predictive scoring systems.

Retrospective cohort study.

Tertiary medical center.

Pediatric patients (age <18 years) undergoing congenital heart surgery on cardiopulmonary bypass between December 2022 and May 2024.

None.

Inadequate heparin response was defined as an activated clotting time of <400 seconds following our institutional standard weight-based heparin bolus dose (300 units/kg in neonates; 350 units/kg in non-neonatal patients). Separate risk scores were developed for neonates and non-neonates. Among 1,746 surgical procedures, inadequate heparin response was observed in 220 (12.6%). In the non-neonatal cohort, the incidence was 10.4% (n = 159) and was associated with surgical urgency, higher platelet count (≥380 K/µL), and higher absolute neutrophil count (≥4.6 K/µL). In the neonatal cohort, inadequate heparin response occurred in 61 (28.8%) of cases and was associated with lower hematocrit (<43%), lower absolute neutrophil count (<8.6 K/µL), and higher fibrinogen level (≥185 mg/dL). The non-neonatal risk score demonstrated fair discrimination (area under the curve 0.775), while the neonatal risk score demonstrated good discrimination (area under the curve 0.827).

Inadequate heparin response is common in pediatric cardiac surgery. Factors associated with inadequate heparin response were identified in both neonatal and non-neonatal pediatric cohorts, enabling the development of age-specific risk scores based on routine laboratory values and thus facilitating early risk stratification and tailored anticoagulation strategies. These findings may be a surrogate of underlying coagulation pathology; further investigation is needed to delineate the fundamental pathophysiology.