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An Unusual Cause of Hypoxia in an 87-year old Female

Pishoy Gouda, Faisal Al-Qoofi, Nanette Alvarez, Ben J Wilson

November 16, 2019

An 87 year-old female presented to hospital with syncope.  Her medical history is significant for aortic regurgitation, hypothyroidism and a small pulmonary arteriovenous malformation (AVM) that was diagnosed four years earlier.  While seated upright, her level of consciousness acutely deteriorated with oxygen saturation dropping from 91% on 3L of oxygen to 50%. The patient was placed supine and high flow oxygen was administered.  Oxygen saturation subsequently recovered to 99%.

The physical examination finding of hypoxemia in the upright position with resolution when supine is known as playtpnea-orthodeoxia syndrome (POS).  It occurs as a result of right to left heart shunting of deoxygenated blood that is dependent on body position. In this patient, transesophageal echocardiography confirmed a patent foramen ovale (PFO). Saline contrast study demonstrated significant right to left shunting in the upright position, which diminished dramatically in the supine position (Figure 1). The patient underwent percutaneous closure of the PFO using a 30mm Gore-Helex device. Post-operative echocardiography demonstrated a well-seated device without residual shunting. The patient was asymptomatic at discharge with no demonstrable positional hypoxemia.

Figure 1 – Transesophageal Echocardiogram Bubble Study Demonstrating Positional Shunt Though Patent Foramen Ovale

Panel A – Supine: No interatrial shunting.

Panel B – 45 degrees: moderate right to left shunt.

Panel C – Sitting: severe shunt.

Panel D – Post-device closure: flow within the inter-atrial device without interatrial shunting.

Abbreviations: RA – right atrium; LA – left atrium; AV – aortic valve; IAS Interatrial septum


What is the most common precipitant cause of POS in adult patients with a PFO?

  1. Post-pneumonectomy

  2. Ascending aortic dilation

  3. COPD

  4. Tetralogy of Fallot

  5. Obstructive sleep apnea


a) Post-pneumonectomy


In the case series by Shah et al., all 52 patients with POS had a PFO (1). While 20% of the population may have a PFO, POS is reported in only 3% of such patients (2). Therefore, it is believed that the development of POS requires a precipitating condition in addition to an anatomical variation.  The precipitating etiologies in this case series were post-pneumonectomy or lung transplant (n=10), ascending aortic pathology (n=8), COPD (n=2), Tetralogy of Fallot (n=2) and obstructive sleep apnea (n=3). A significant portion of patients (n=20) did not have any clear predisposing etiology or condition.

In cardiac etiologies of POS, the anatomical defect is most commonly a PFO or an atrial septal defect. The functional defects can be grouped in those that cause abnormal blood flow through the interatrial communications (ascending aortic aneurysm, atrial septal aneurysm, aortic valve replacement, anomalous venous return) or transient reversal of left-to-right pressure gradients due to an increase in right atrial pressure (chronic obstructive pulmonary disease (COPD), pneumonectomy, pulmonary hypertension, pulmonary embolism) (1, 3)(2). In non-cardiac etiologies, the anatomical defect permitting right-to-left shunting are pulmonary AVMs and severe ventilation-perfusion mismatching. The functional defect in these cases can be any cause that worsens mismatching or preferentially increases blood flow through the pulmonary AVM.  Such conditions include hepatopulmonary syndrome, chronic liver disease, COPD and acute respiratory distress syndrome (1, 3). POS should be considered in any patient with hypoxia out of proportion to their known pulmonary disease.


1. Shah AH, Osten M, Leventhal A, Bach Y, Yoo D, Mansour D, et al. Percutaneous intervention to treat platypnea–orthodeoxia syndrome: the Toronto experience. JACC: Cardiovascular Interventions. 2016;9(18):1928-38.

2. Mojadidi MK, Gevorgyan R, Noureddin N, Tobis JM. The effect of patent foramen ovale closure in patients with platypnea‐orthodeoxia syndrome. Catheterization and Cardiovascular Interventions. 2015;86(4):701-7.

3. Knapper JT, Schultz J, Das G, Sperling LS. Cardiac Platypnea‐Orthodeoxia Syndrome: An Often Unrecognized Malady. Clinical cardiology. 2014;37(10):645-9.


Pishoy Gouda is a second-year internal medicine resident at the University of Calgary. He graduated from medical school (National University of Ireland, Galway) in 2015 and completed his MSc in Clinical Trials (London School of Hygiene and Tropical Medicine) in 2017.

Faisal al-Qoofi is an interventional cardiologist at the University of Calgary. He was born in Saudi Arabia and attended Medical School in King Saud University in Riyadh. Faisal joined the Internal Medicine Program at McMaster University, Hamilton Ontario in 2001. Faisal headed west to the University of Calgary where began the Cardiology Training Program in January 2004.

Nanette Alavarez attended medical school in Kingston, Ontario, graduating in 1981. She then did an internship in New Zealand returning to complete her Internal Medicine specialty in Montreal, Quebec and subsequently Toronto, Ontario. She completed her Cardiology sub-specialty training in Toronto. She joined the staff of the Calgary General Hospital and the University of Calgary in 1989. She is an Associate Professor in the Department of Cardiac Sciences. She is the Director of the Adult Congenital Heart Disease Clinic at the University of Calgary and Director of Echocardiography at the Peter Lougheed Centre.

Ben Wilson is a general internist at the Peter Lougheed Centre (PLC) in Calgary, Alberta.  He is a passionate clinical educator.  Ben is actively involved in the University of Calgary Internal Medicine Residency Program and is the Medical Teaching Unit Director at the PLC.  He strives to bring medicine back to the bedside and away from the screenside.  His clinical interests are critical care and diagnostic dilemmas.