Diagnostic Clues to Platypnoea Orthodexia Syndrome.

Platypnoea orthodeoxia syndrome is a rare cause of positional dyspnoea, characterised by breathlessness and arterial desaturation in the upright position that improves with lying flat. This phenomenon is typically due to a right to left shunt, most commonly cardiac, that allows deoxygenated blood to bypass the pulmonary circulation, therefore reducing oxygen saturation in the systemic circulation. This shunt is accentuated by postural changes, worsening hypoxaemia when the patient sits or stands, and ameliorated by recumbency, which alters intracardiac pressures and improves oxygenation. Despite its clinical significance, platypnoea orthodeoxia syndrome remains underdiagnosed. We are presenting two patients with platypnoea orthodeoxia syndrome. Both patients were found to have significant positional hypoxaemia in the upright position that was found to be improving on recumbency, both of whom were subsequently diagnosed with a patent foramen ovale with right to left flow, in addition to aortic dilatation as the underlying cause. They both underwent a series of investigations to confirm orthodeoxia, which is the term referring to dropping of oxygen saturation in an upright position, as well as to rule out other causes of desaturation. They both went on to have minimally invasive closure of the patent foramen ovale later in the course of their management with the resolution of symptoms and improvement in oxygen saturation.