Platypnea-Orthodeoxia syndrome, a rare case of unexplained hypoxemia

Abstract

Platypnea-Orthodeoxia syndrome (POS) is a condition of hypoxemia at rest in upright position that resolves on lying down. A 71-year-old OSAS patient, with a previous unexplained temporary amnesia, experienced resting hypoxemia and mild exertional dyspnea, despite normal supine saturation and oximetry during CPAP treatment. Whilst blood gas analysis showed respiratory failure and at transthoracic echocardiogram atrial septal aneurysm without evidence of shunt was detected. Respiratory function tests, chest angio-CT and perfusive-ventilatory lung scan, cardiac stress test and myocardial stress tomography resulted normal. Based on clinical suspected of right-to-left cardiac shunt, transcranial ultrasound with microbubble (TCD) and transesophageal echocardiogram test indicated a diagnosis of Patent foramen ovale (PFO). The patient underwent to percutaneous closure of the defect. Arterial saturation and TCD with patient in a sitting and supine position while using CPAP was performed. Saturation remained above 90% and blood flow from right to the left atrium was slightly reduced. POS may have various etiology, the most common intracardiac forms are due to PFO. However POS is rare and most people with an isolated PFO do not have a real shunt. A number of patients exhibits a juxtaposition of the septum primum and secundum without fusion, potentially leading in adulthood to dynamic right-left shunt, which decreases from orthostasis to the supine position. POS should always be considered in a case of not justified respiratory failure and it is essential to evaluate the patient in orthostatic and supine position to discover an underlying difficult to diagnose pathology.