Platypnea-orthodeoxia syndrome (POS) is a rare condition involving positional dyspnea (platypnea) and arterial desaturation (orthodeoxia). Orthodeoxia refers to a situation where arterial oxygen tension drops in the upright position by more than 5% or 4 mmHg. POS is characterized by breathlessness that is alleviated when lying down and aggravated when sitting or standing. The pathophysiology and etiologies of orthodeoxia and platypnea are still not fully understood, but they seem to involve both a functional and an anatomical component.

In general, causes can be divided into extracardiac and intracardiac shunting. One or more of the following conditions can cause intracardiac shunting: patent foramen ovale (PFO), atrial septal defect (ASD), atrial septal aneurysm with septal fenestration, partial anomalous pulmonary venous connection, transposition of the great vessels, and unroofed coronary sinus. The most common cause of intracardiac shunting is a PFO. Ventilation-perfusion mismatch, pulmonary shunting, or a combination of these may all be considered extracardiac shunting.

This presentation will review the common presenting problems of POS, their key diagnostic features, approach to the underlying pathophysiology, how frequent is this condition misdiagnosed and how to sustain an appropriate diagnostic skill related to this condition, all of which correlated to the recent literature. The presentation will also show a case report witnessed by the presenter and how to avoid possible delays in the diagnosis.