The Paradox of Support: Mechanical Ventilation-Induced Hypoxemia Through a Patent Foramen Ovale.

Patent foramen ovale (PFO) is common and usually harmless, but can cause significant positional and refractory hypoxemia in situations when there is a significant right-to-left shunt across it, and this phenomenon often goes unnoticed, especially in patients on ventilators, in whom it can be fatal. Platypnea-orthodeoxia syndrome (POS) is a condition characterized by positional dyspnea (platypnea) and hypoxemia (orthodeoxia), usually associated with right-to-left interatrial shunting across a PFO or an atrial septal defect (ASD). The positional variation is believed to be due to interatrial stretch, facilitating right-to-left shunt across PFO. We report a 79-year-old woman with longstanding dyspnea, obstructive sleep apnea, and a remote history of pulmonary embolism on chronic anticoagulation who was admitted with worsening hypoxia that did not improve with bronchodilators, steroids, or oxygen therapy. Her workup, including chest computed tomography (CT) angiography, was unremarkable. Clinically, she continued to worsen, leading to severe respiratory failure requiring intubation with high oxygen and positive end-expiratory pressure (PEEP) requirements. Cardiac workup revealed a large PFO with right-to-left shunting, and its subsequent closure with an Amplatzer device led to rapid improvement in oxygen levels and prompt extubation. PFO should be considered in anyone with positional dyspnea and hypoxemia or persistent refractory hypoxemia despite being on adequate ventilatory support. Early closure can be highly effective in selected patients.