Worsening hypoxemia in the face of increasing PEEP: A case of large pulmonary embolism in the setting of intracardiac shunt

Objective: Rare co-existance of disease or pathology Background: Patent foramen ovale (PFO) are common, normally resulting in a lefttoright shunt or no net shunting. Pulmonary embolism (PE) can cause sustained increased pulmonary vascular resistance (PVR) and right atrial pressure. Increasing positive end-expiratory pressure (PEEP) improves oxygenation at the expense of increasing intrathoracic pressures (ITP). Airway pressure release ventilation (APRV) decreases shunt fraction, improves ventilation/ perfusion (V/Q) matching, increases cardiac output, and decreases right atrial pressure by facilitating low airway pressure. Case Report: A 40-year-old man presented with dyspnea and hemoptysis. Oxygen saturation (SaO₂) 80% on room air with Aa gradient of 633 mmHg. Post-intubation SaO₂ dropped to 71% on assist control, FiO2 100%, and PEEP of 5 cmH₂0. Successive PEEP dropped SaO₂ to 60-70% and blood pressure plummeted. APRV was initaiated with improvement in SaO₂ to 95% and improvement in blood pressure. Hemiparesis developed and CT head showed infarction. CT pulmonary angiogram found a large pulmonary embolism. Transthoracic echocardiogram detected right-to left intracardiac shunt, with large PFO. Conclusions: There should be suspicion for a PFO when severe hypoxemia paradoxically worsens in response to increasing airway pressures. Concomitant venous and arterial thromboemboli should prompt evaluation for intracardiac shunt. Patients with PFO and hypoxemia should be evaluated for causes of sustained right-toleft pressure gradient, such as PE. Management should aim to decrease PVR and optimize V/Q matching by treating the inciting incident (e.g., thrombolytics in PE) and by minimizing ITP. APRV can minimize PVR and maximize V/Q ratios and should be considered in treating patients similar to the one whose case is presented here.