659: Inhaled Epoprostenol for Refractory Hypoxemia in an Adult Fontan Patient With Hlhs: A Case Report

Introduction: Hypoplastic left heart syndrome (HLHS) is a rare congenital cardiac defect in which systemic circulation is dependent on right ventricular output. The Fontan procedure creates a pathway for blood to circulate directly into the lung, which ultimately results in persistent shunt physiology. The complex hemodynamic physiology that arises is especially challenging in critically ill patients, where adequate oxygenation is of utmost importance. Inhaled pulmonary vasodilators such as epoprostenol (EPO) can selectively reduce pulmonary vascular resistance (PVR), improve ventilation-perfusion matching, and optimize systemic oxygen delivery. Description: 32-year-old male with HLHS status post-Fontan presented with progressive dyspnea following a week of nausea and vomiting. He transitioned from an oxymizer to high-flow nasal cannula (40 L/min, FiO2 1.0), then to BiPAP (12/5, FiO2 1.0), but remained hypoxic. ABG on BiPAP showed PaO2 50 mmHg. He was intubated for worsening respiratory failure, but oxygenation declined with PEEP of 8 cm H2O (PaO2 54 mmHg on FiO2 0.8, SpO2 92.5%), likely due to impaired pulmonary blood flow from elevated intrathoracic pressure. Inhaled epoprostenol was initiated, resulting in marked improvement in oxygenation. The patient was weaned to HFNC with epoprostenol, then transitioned as low as HFNC 30L/.45 FIO2 and transferred to a congenital heart center for further management. Discussion: In Fontan patients, positive pressure ventilation can worsen oxygenation by impeding passive pulmonary blood flow and increasing right-to-left shunting. Inhaled epoprostenol improves V/Q matching by reducing PVR and enhancing pulmonary flow without systemic vasodilation. This case demonstrates the utility of epoprostenol as a rescue strategy for refractory hypoxemia in adults with complex congenital heart disease. Recognition of unique physiologic interactions in this population is crucial for individualized management in the ICU.