B64-11 Up Side Down: Unexpected Benefit of Proning in a Patient With Saddle PE

Abstract Acute respiratory distress syndrome (ARDS) is a leading cause of hypoxemic respiratory failure, and prone positioning (PP) improves oxygenation and provides lung protection. PP can also reduce right ventricular (RV) afterload by enhancing pulmonary recruitment and mitigating hypoxic pulmonary vasoconstriction. Its benefit in RV dysfunction due to pulmonary embolism (PE) remains unclear. We present a patient with a saddle PE whose oxygenation improved following PP. A 23-year-old woman with schizophrenia and intellectual disability was admitted after being found unresponsive in the bathroom, covered in vomitus, following a possible seizure or a syncopal event. She developed cardiac arrest, likely secondary to aspiration, and was admitted to the medical ICU post-resuscitation. On examination, she was sedated, intubated, tachycardic, and had clear bilateral breath sounds. Arterial blood gas showed pH 7.22, PCO2 81 mmHg, PO2 48 mmHg, and lactate 4.4 mmol/L. Chest X-ray revealed no infiltrates, with a P/F ratio of 185 mmHg. Despite FiO2 100% on APV-CMV mode, SpO2 remained 60-70%. Prone positioning, inhaled nitric oxide (20 ppm), paralysis, and sedation were initiated. Echocardiogram demonstrated RV strain. After 24 hours of pronation, FiO2 requirement improved to 50%, with resolution of respiratory acidosis. CT pulmonary angiogram subsequently revealed a saddle PE. The patient was anticoagulated, weaned off vasopressors, and follow-up echocardiogram showed normalization of RV function. Prone positioning (PP) is a well-established intervention for moderate to severe ARDS, shown in the PROSEVA trial to reduce mortality and improve hemodynamics, with fewer cardiac arrest events and more cardiovascular failure-free days. No pulmonary embolism-specific guidelines exist for PP, but case reports have described improved oxygenation and right ventricular (RV) function in patients with PE, suggesting potential benefits beyond ARDS.Proposed mechanisms include enhanced ventilation-perfusion (V/Q) matching, reduced RV afterload without high PEEP, decreased hypercapnia from more uniform ventilation, and lower driving pressures via recruitment of dependent lung regions.In our case, the patient initially treated for presumed ARDS did not meet Berlin criteria and was later found to have a saddle PE. Following PP, oxygenation improved markedly, consistent with prior PE-related observations.Although evidence is limited, PP may serve as a supportive bridge for refractory hypoxemia in PE, particularly when RV strain or severe V/Q mismatch contributes to respiratory failure. Further studies are needed to clarify its physiologic and clinical role. This abstract is funded by: N/A