[Platypnea-orthodeoxia syndrome]

Platypnea-orthodeoxia syndrome (POS) is a rare clinical syndrome characterized by dyspnea (platypnea) and arterial desaturation (orthodeoxia) upon changing from a lying to a standing or sitting position. The underlying physiopathological mechanisms involved are complex. Hypoxemia is attributed to the mixing of deoxygenated venous blood with arterial blood through a shunt, which can be intracardiac, or extracardiac. Patent foramen ovale is the main cause of intracardiac shunting. The transthoracic bubble contrast echocardiogram with intravenous agited saline is the most important test in the diagnosis process. Management is specific to the underlying etiology.