When hypoxemia does not respond to oxygen therapy: a case of platypnea-orthodeoxia syndrome.

Platypnea-orthodeoxia syndrome (POS) is a rare clinical entity characterized by the onset of dyspnea and hypoxemia that normally manifests in the upright position, improving with recumbency. POS is generally caused by both anatomical and functional defects that lead to a right-to-left shunt. Herein, we present an illustrative case of POS in an elderly patient admitted for severe hypoxemia, in which a massive right-to-left shunt through a patent foramen ovale facilitated by an anatomic disturbance was found. Percutaneous closure of the defect was performed, thus correcting the POS.