To evaluate the relationship between cardiopulmonary bypass (CPB) duration, change in thoracic fluid content (ΔTFC) measured using electrical cardiometry, and postoperative oxygenation in infants undergoing ventricular septal defect (VSD) closure.

Prospective observational study.

Single tertiary academic cardiac center.

Thirty infants (1–12 months) undergoing elective VSD closure with CPB.

Thoracic fluid content was measured using an electrical cardiometry (ICON monitor) before CPB and after separation from CPB. Arterial blood gases and ventilatory parameters were recorded at corresponding time points.

CPB duration was positively correlated with ΔTFC (r = 0.50, p = 0.0045) and negatively correlated with a change in PaO₂/F_IO₂ ratio (ΔP/F; r = –0.60, p = 0.0005) and dynamic compliance (r = –0.48, p = 0.007). Receiver operating characteristic analysis demonstrated excellent discrimination for postoperative oxygenation impairment (P/F <300) for both ΔTFC (area under the curve [AUC] = 0.91) and CPB duration (AUC 0.92). The optimal thresholds obtained were ΔTFC ≥13 kΩ^–1 and CPB ≥84 minutes. In the multivariate linear regression adjusted for IL-6, prime volume/kg, transfusion/kg, and conventional ultrafiltration, ΔTFC independently predicted the postoperative P/F ratio (β = –5.68; p = 0.013), whereas CPB duration was not independently associated.

Prolonged CPB is associated with greater thoracic fluid accumulation and impaired oxygenation in infants undergoing VSD closure. However, the relationship between CPB duration, ΔTFC, and pulmonary dysfunction appeared multifactorial and was influenced by perioperative inflammatory and fluid-related variables. Perioperative ΔTFC monitoring may provide a useful noninvasive adjunct for assessing postoperative pulmonary status after pediatric cardiac surgery.