Abstract Introduction Platypnea-orthodeoxia syndrome (POS) is a rare clinical condition characterized by positional dyspnea and desaturation in the upright position. The most common cause is an intracardiac shunt, in combination with an anatomical or functional factor. Recognition of this syndrome is crucial, as extensive workup can be avoided with suspicion and appropriate testing. Here we present the case of a 74-year-old woman with unexplained hypoxemia. Case A 74-year-old woman with an ascending aortic aneurysm was admitted for an elective total arch repair and subsequent CABG. The surgery was aborted due to significant intraoperative bleeding; she returned to the cardiothoracic ICU. Over the next five days, she experienced persistent hypoxemia requiring high flow nasal cannula. Vital signs and laboratory studies remained within normal limits, except for low oxygen saturation. Thorough evaluation via CTICU team, including echocardiogram, bilateral arterial blood gases, and chest CT angiogram were largely unremarkable. When seen by pulmonology, her physical exam revealed clear breath sounds with non-labored breathing despite the significant oxygen requirement of 15L. Upon further investigation, she was found to desaturate more upon sitting up than lying flat. Repeat echocardiogram obtained in the upright position revealed patent foramen ovale with right to left shunting. She underwent percutaneous closure of the PFO with resolution of hypoxemia. Discussion Platypnea-orthodeoxia syndrome is defined by dyspnea and desaturation that worsen in the upright position, with improvement when supine. Its etiologies are categorized as intracardiac, extracardiac, and miscellaneous, with intracardiac being most common. In the intracardiac case, the right to left shunting occurs through a shunt defect, such as a PFO, accompanied by a secondary functional/structural abnormality. This patient was found to have PFO in the setting of a known ascending aortic aneurysm. While the exact mechanism is unclear, it is thought that the change in position (standing upright) causes redirection of blood flow given the alteration of the anatomy allowing for increased mixture of oxygenated and deoxygenated blood. Diagnosis includes a high degree of suspicion, and typically echocardiogram with bubble study is the first diagnostic test (though as in this case, echocardiogram may need to be performed in the upright position). Treatment then includes correction of the cardiac anomaly. This case highlights the importance of maintaining a high index of suspicion for POS in patients with unexplained hypoxemia. Early recognition is essential, as identifying and confirming the diagnosis can lead to targeted management, including closure of the underlying defect. This abstract is funded by: none
Gipson et al. (Fri,) studied this question.