C63-35 When the Fontan Fails: Evaluation and Management of Acute Hypoxemia in an Adult With Single Ventricle Physiology

Abstract Background Hypoplastic left heart syndrome (HLHS) is a rare congenital condition characterized by severe underdevelopment of left-sided cardiac structures. Staged palliative surgeries ending with the Fontan procedure allows for survival into adulthood by creating a total cavo-pulmonary circulation. This circulation allows for systemic venous return that bypasses the heart and flows passively into the pulmonary arteries. However, the resulting physiology predisposes patients to chronic hypoxemia and multisystem complications, including Fontan-associated liver disease (FALD) and right ventricular dysfunction. Acute decompensation in these patients presents unique diagnostic and management challenges. Case Presentation A 29-year-old male with HLHS status post extracardiac Fontan complicated by cirrhosis, polycythemia, and chronic hypoxemia, presented with acute worsening of oxygen saturation from baseline 85-90% to the low 70s. Initial evaluation revealed tachycardia, elevated hematocrit (58.5%), mildly elevated troponin, NT-proBNP of 480 pg/mL, and hypoxemia (PaO2 41 mmHg on 100% FiO2). CT imaging showed volume overload with ascites and small bilateral pleural effusions. Echocardiography demonstrated a severely dilated right ventricle with moderate systolic dysfunction and a positive bubble study for both intra- and extracardiac shunting. CTA ruled out pulmonary embolism. Management and Outcome The patient was initiated on noninvasive positive pressure ventilation with partial improvement in oxygenation. Empiric antibiotics were discontinued when infection was excluded. Careful intravenous diuresis with furosemide 40 mg twice daily was initiated to reduce central venous congestion, with close monitoring to avoid preload depletion. Due to persistent hypoxemia and evidence of right ventricular failure, milrinone infusion was started for inotropic support and to enhance forward flow. Over five days, oxygenation improved to baseline levels, and milrinone and diuretics were successfully weaned. Partial guideline-directed medical therapy with sacubitril-valsartan and eplerenone was initiated prior to discharge. Discussion and Conclusion In adult patients with Fontan circulation, acute on chronic hypoxemia often reflects a combination of shunting physiology, ventricular dysfunction, and venous congestion. Evaluation should include echocardiography with bubble study, cross-sectional imaging, and laboratory markers of congestion and hepatic function. Management requires balancing preload and afterload while optimizing systemic output. In this case, targeted diuresis and short-term inotropic therapy effectively restored hemodynamic stability and oxygenation. Awareness of Fontan physiology and its multisystem implications is essential for prompt recognition and management of decompensation in this growing adult population. This abstract is funded by: None