(1137) Unraveling the Mystery: A Case Report on an Occult Cause of Hypoxemia

Introduction: Hypoxemia is a common ICU presentation, often due to identifiable causes like pneumonia, pulmonary edema or COPD exacerbation. However, some cases defy immediate diagnosis. We present a unique case of a patient who developed pulmonary embolism (PE) leading to elevated right ventricular (RV) pressures and the reopening of a previously silent patent foramen ovale (PFO). PFO is a common congenital cardiac anomaly, often asymptomatic, but can become significant under certain hemodynamic stresses. This report recounts the systematic identification of a rare cause of hypoxemia.

Description: A 70-year-old female with hypertension, hyperlipidemia, hypothyroidism, breast cancer, and renal cell carcinoma presented with chronic dizziness, dyspnea, and low oxygen saturation (85-89%). Four months prior, she was diagnosed with a PE and started on Apixaban. Despite treatment, her hypoxemia worsened, requiring high-flow nasal cannula oxygen. She experienced dizziness when standing, improving when lying flat, and dyspnea on exertion. Initial CT imaging showed a chronic thrombus in the right lower lobe and stable PE without RV dilation. Her lung parenchyma was clear, with no evidence of alveolar disease or pulmonary edema. She had no COPD exacerbation or elevated CO2 levels. Clinically non-toxic, she still required high oxygen levels. On ABG with 100% FiO2, her PaO2 was 54, and saturation was 89%. A shunt was considered, and a TTE showed TAPSE 1.0 and RV S' 7.1 but a non-diagnostic bubble study. A TEE revealed a large PFO (6.4mm) with a significant right-to-left shunt. She was referred for PFO closure and discharged on room air few days after procedure.

Discussion: This case highlights the importance of a broad differential for atypical hypoxemia and dyspnea. While initial considerations may include common conditions like pneumonia or PE, negative routine studies should prompt exploration of less common causes such as shunts or arteriovenous malformations. Here, a PFO significantly influenced oxygenation dynamics, exacerbated by elevated RV pressures from subacute PE, causing a right-to-left shunt and severe hypoxemia. Timely recognition and intervention are crucial. Treatment typically involves anticoagulation for PE and potential PFO closure.