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 Table of Contents  
Year : 2019  |  Volume : 8  |  Issue : 2  |  Page : 130-133

Acute onset of refractory hypoxemia: A rare hemodynamic cause of dyspnea

Department of Medicine, Medical High Dependency Unit, Ospedale Niguarda Ca' Granda, Milano, MI, Italy

Date of Submission25-Jan-2019
Date of Decision20-Apr-2019
Date of Acceptance04-May-2019
Date of Web Publication1-Jul-2019

Correspondence Address:
Dr. Tommaso Valobra
Ospedale Niguarda Ca' Granda, Piazza dell'Ospedale Maggiore, 3, 20162 Milano, MI
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijrc.ijrc_2_19

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Platypnea-orthodeoxia syndrome (POS) is a rare condition of positional dyspnea with hypoxemia that can pose a diagnostic challenge to clinicians. We report two cases of POS with different pathophysiologic triggers and similar clinical features. In our report, both patients manifested a severe hypoxemia with low response to increase of fractional inspired oxygen, unremarkable physical examination of the lungs, and no radiological findings of the pulmonary embolism. In both cases, an interatrial communication was found in association with a right-to-left interatrial shunting. Recognition of POS is crucial because symptoms can be quickly relieved by recumbency, unlike other types of hypoxemia. This simple solution may prevent the use of sedative therapy, invasive ventilatory support, and vasopressor agents, which could even exacerbate the right-to-left extrapulmonary shunt and worsen clinical conditions.

Keywords: Dyspnea, echocardiogram, forame ovale, hypoxemia

How to cite this article:
Valobra T, Ceratti U, Cernuschi A. Acute onset of refractory hypoxemia: A rare hemodynamic cause of dyspnea. Indian J Respir Care 2019;8:130-3

How to cite this URL:
Valobra T, Ceratti U, Cernuschi A. Acute onset of refractory hypoxemia: A rare hemodynamic cause of dyspnea. Indian J Respir Care [serial online] 2019 [cited 2022 Aug 18];8:130-3. Available from: http://www.ijrc.in/text.asp?2019/8/2/130/261895

  Introduction Top

Refractory hypoxemia is a critical state that requires immediate action and represents a diagnostic challenge for clinicians. We present two different cases with hypoxia which was unresponsive to supplement oxygen, but quickly relieved by recumbency. This condition is better known as platypnea-orthodeoxia syndrome (POS).

Platypnea is defined as dyspnea and orthodeoxia as arterial oxygen desaturation, induced or accentuated by upright posture and improved with supine positioning. The pathogenesis requires an anatomical substrate for a shunt, most commonly at the atrial level, and an anatomical or functional trigger to reverse the blood flow across it.[1] For this reason, it represents a very confusing and misleading condition, especially when the patient's medical history is not available, or no congenital cardiovascular defects are known.

In our report, both patients manifested a severe hypoxemia with low response to increase of fractional inspired oxygen, and an interatrial communication was found in association with a right-to-left interatrial shunting, most likely caused by extracardiac functional aberrations.

  Case Reports Top

Case A

A 60-year-old female was admitted to the emergency department (ED) with acute dyspnea following a paracentesis in the Oncology Day Hospital. She was diagnosed to have signet-ring cell carcinoma of the stomach, previously treated by surgery and chemotherapy, and was recently found to have peritoneal carcinomatosis with ascites. She was receiving a second-line chemotherapy treatment.

On arrival in our ED, the patient was afebrile but presented with tachycardia at 95 beats/min, blood pressure of 90/60 mmHg, respiratory rate of 26 breaths/min and oxygen saturation of 80% on room air, and 82% with a 10 L/min oxygen flow. Arterial blood gas showed severe hypoxemia with hypocapnia (PaO2/FIO2 ratio <200, PCO25 mmHg). She denied having chest pain and electrocardiography showed sinus tachycardia with no features suggestive of myocardial ischemia. Clinical examination revealed hepatomegaly, mild abdominal tenderness elicited by deep palpation on the right upper quadrant, and decreased breath sounds and dullness over the right lower thorax. Elevation of the right hemidiaphragm was noted on the chest radiography [Figure 1]a.
Figure 1: A chest radiography shows an elevation of the right hemidiaphragm (a), and a bedside transthoracic echocardiography demonstrated an ab-estrinseco compression of the right atrium (b), In the other patient, the transthoracic echocardiogram confirmed a note atrial septal aneurysm with patent foramen ovale (c)

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A focused cardiovascular ultrasound revealed a preserved ejection fraction, no valvular heart disease, but an extrinsic compression of the right atrial roof due to peritoneal carcinomatosis [Figure 1]b and subsequent elevation of the right hemidiaphragm [Figure 2]a. Fluid replacement and oxygen therapy through a nonrebreather mask were prescribed, but the gas exchange did not improve significantly. Computerized tomography (CT) pulmonary angiogram was obtained to rule out pulmonary embolism. The examination did not detect lung perfusion abnormalities. However, it was noted that, during the CT scan, while he was lying in a supine position to undertake the scan, oxygen saturation levels improved to normal levels with supplemental oxygen. A contrast echocardiogram, performed in both the supine and sitting positions, revealed a large right-to-left interatrial shunt which worsened in the sitting position. She was therefore transferred to the oncology ward to evaluate the indication for a new cycle of chemotherapy with the aim to reduce the abdominal mass.
Figure 2: Computerized tomography scan demonstrated an ab-estrinseco compression of the right atrial roof due to peritoneal carcinomatosis and subsequent elevation of the right hemidiaphragm (a), A microbubble contrast-enhanced echocardiogram showed bubbles within the right to the left atrium (b) and endovascular closure of the atrial septal defect was successfully performed (c)

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Case B

An 87-year-old female was recovering from deep-vein thrombosis and pulmonary embolism in the general medicine unit where anticoagulant therapy had been administered and physical rehabilitation was performed. On admission, a moderately enlarged and elongated ascending aorta was identified by CT. Her medical history was only significant for hypertension and kyphoscoliosis. Her general conditions were gradually improving when, suddenly, she showed acute dyspnea and oxygen desaturation. The patient showed mild tachycardia, with a heart rate of 90 beats/min, and hypoxia, with an oxygen saturation of 84% on room air. The patient denied shortness of breath or chest pain.

Physical examination was unremarkable except for signs of mild dehydration, and laboratory tests suggested an uncomplicated infection of the urinary tract. Oxygen saturation, tachycardia, and tachypnea did not improve with the administration of supplementary oxygen in the supine position. Arterial blood gas analysis confirmed hypoxemia with respiratory alkalosis. Physical examination of the respiratory and cardiac systems, chest radiography, and electrocardiography showed normal findings. A CT pulmonary angiogram did not reveal any evidence of pulmonary embolism. Her left and right ventricular ejection fractions were both within the normal limits, and there were no indirect signs of elevated pulmonary artery pressure [Figure 1]c. A bubble study followed, and transthoracic echocardiography then revealed an intracardiac right-to-left shunt caused by an aneurysmal interatrial septum with patent foramen ovale (PFO). However, when she was placed supine, her clinical condition improved dramatically. To clarify the etiology of POS, a right heart catheterization was done which revealed normal pulmonary arterial pressure. On the same occasion, endovascular closure of the atrial septal defect was done [Figure 2]c. Her cyanosis and oxygen saturation obtained through transcutaneous oximetry, improved while she was lying in the supine position. The patient experienced an uneventful recovery and cessation of orthodeoxia.

  Discussion Top

Both patients manifested a severe hypoxemia with low response to increase of fractional inspired oxygen, unremarkable physical examination of the lungs, and no radiological findings of the pulmonary embolism. Moreover, oxygen saturation improved slightly with the Trendelenburg position. The diagnosis was POS, a positional dyspnea with hypoxemia paradoxically exacerbated in the upright position.

Pathophysiological issues

Three primary mechanisms have been postulated for this rare syndrome: intracardiac shunting, anatomic pulmonary vascular shunting, and ventilation-perfusion mismatching.[2] In most cases, right-to-left atrial shunting is caused by a PFO, rarely by an atrial septal defect or an atrial septal aneurysm with septal fenestration.[3]

Most PFOs are not expected to cause sufficient right-to-left shunting to elicit hypoxemia due to higher left atrial pressure and greater compliance of the right atrium and ventricle.[4] Shunt across the interatrial communication has been suggested in the presence of an elevated right atrial pressure, as in chronic obstructive pulmonary disease, pulmonary hypertension, pulmonary embolism, constrictive pericarditis, pericardial effusion, or pneumonectomy.[1] However, many patients with platypnea are found to have normal pulmonary artery pressure.[5] Another possible mechanism to explain shunting in the absence of elevated right heart pressure is called “flow phenomenon:” the preferential flow of the blood, exacerbated by the upright position, is directed from the inferior vena cava toward the foramen ovale, as seen during intrauterine life.[6]

Certain cardiac or pulmonary functional aberrations can preferentially direct the blood flow through the interatrial defect worsening the shunt in the absence of a pressure gradient.[1] These functional aberrations can be classified in intrinsic cardiac anatomical pathologies, such as ascending aorta elongation [7],[8] and in extracardiac intrathoracic pathologies, such as severe kyphosis [9] or hemidiaphragm paralysis.[10]

Clinical picture

The first patient had a PFO, and the trigger was represented by an extrinsic compression of the right atrial roof due to peritoneal carcinomatosis and subsequent elevation of the right hemidiaphragm [Figure 2]a. Although an elevated hemidiaphragm with atelectasis of the lower lobe can potentially cause a variable hypoxemia, in the presence of severe impairment in arterial oxygenation that does not improve with high-flow oxygen supplementation, a POS should be suspected.[11] In the presence of an elevated right hemidiaphragm or after pneumonectomy, the inferior vena cava becomes more directly aligned with the foramen ovale due to horizontal positioning of the interatrial septum.[12]

In the second patient, the transthoracic echocardiogram confirmed a known atrial septal aneurysm as well as PFO. A microbubble contrast-enhanced echocardiogram showed the movement of bubbles from the right to the left atrium, mostly in an upright position, confirming the presence of an intracardiac shunt [Figure 2]b. A right heart catheterization measured normal pressure waves in the cardiac chambers and allowed, at the same time, to perform a successful endovascular closure of the atrial septal defect [Figure 2]c. Our hypothesis is that multiple factors may have contributed to cause POS, including kyphoscoliosis, ascending aorta elongation, and hypovolemia. The phenomenon of worsening of the shunt as a consequence of dehydration has been previously described.[4],[6],[13],[14] Interatrial shunting in the upright position is thought to be possibly related to decreased compliance of the right ventricle on standing.[6] Reduction of intravascular volume, as in our patient, can reduce right ventricular compliance, further exacerbating the shunt.[3]

Diagnostic assessment

The first assessment should be the evaluation of a possible association between dyspnea and upright posture.[15] For this reason, pulse oximetry and blood gas analysis should be performed both in recumbency and upright positions. The finding of orthostatic desaturation can direct the diagnosis toward an atrial septum discontinuity.[16] Echocardiography with Doppler mode and conjunct contrast-enhanced echocardiography are paramount to establish the diagnosis. Both examinations should ideally be performed in the lying and upright positions. These investigations may allow one to identify, localize, and semiquantitate the shunt at the atrial level because of the passage of microbubbles from the right chambers to the left within three cardiac cycles.[17]

Other modalities for assessing intracardiac defects include right heart catheterization, Doppler transesophageal echocardiogram in the sitting position,[18] ventilation-perfusion scan, and transcranial Doppler study. However, these tests should typically be employed only in the setting of an inconclusive echocardiographic study.[19]


Treatment of platypnea-orthodeoxia should always be directed at the underlying source of vascular shunting.[20] Percutaneous transcatheter closure remains the treatment of choice for PFO presenting with POS.[21] Closure of the interatrial shunt results in a good prognosis, with symptoms often resolving quickly,[22] as seen in the patient described in our report.

  Conclusion Top

Before making a diagnosis of POS, it is important to exclude other causes of hypoxemia. In most cases, right-to-left atrial shunting is caused by a PFO associated with a functional aberration. POS represents a very confusing and misleading condition, but its recognition is crucial because symptoms can quickly relieve by recumbency preventing the use of sedative therapy, invasive ventilatory support, and vasopressor agents, which could even exacerbate the right-to-left extrapulmonary shunt.[23]

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.


We gratefully thank Dr. Chiara Piagnani for performing language editing and proofreading.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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Ducey S, Cooper J. Hypovolemia resulting in Platypnea-orthodeoxia syndrome. J Emerg Med 2016;50:482-4.  Back to cited text no. 3
Salazar C, Majano RA. Acute hypoxic and refractory respiratory failure induced by an underlying PFO: An unusual case of Platypnea orthodeoxia and transient complication after transcatheter closure. Case Rep Crit Care 2017;2017:4397163.  Back to cited text no. 4
Blanche C, Noble S, Roffi M, Testuz A, Müller H, Meyer P, et al. Platypnea-ORTHODEOXIA syndrome in the elderly treated by percutaneous patent foramen ovale closure: A case series and literature review. Eur J Intern Med 2013;24:813-7.  Back to cited text no. 5
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Teupe CH, Groenefeld GC. Platypnea-orthodeoxia due to osteoporosis and severe kyphosis: A rare cause for dyspnea and hypoxemia. Heart Int 2011;6:e13.  Back to cited text no. 9
Sakagianni K, Evrenoglou D, Mytas D, Vavuranakis M. Platypnea-orthodeoxia syndrome related to right hemidiaphragmatic elevation and a 'stretched' patent foramen ovale. BMJ Case Rep 2012;2012. pii: bcr-2012-007735.  Back to cited text no. 10
Fabris T, Buja P, Cucchini U, D'Amico G, Cazzuffi R, Balestro E. Right-to-left interatrial shunt secondary to right hemidiaphragmatic paralysis: An unusual scenario for urgent percutaneous closure of patent foramen ovale. Heart Lung Circ 2015;24:e56-9.  Back to cited text no. 11
Zanchetta M, Rigatelli G, Ho SY. A mystery featuring right-to-left shunting despite normal intracardiac pressure. Chest 2005;128:998-1002.  Back to cited text no. 12
Wranne B, Tolagen K. Platypnoea after pneumonectomy caused by a combination of intracardiac right-to-left shunt and hypovolaemia. Relief of symptoms on restitution of blood volume. Scand J Thorac Cardiovasc Surg 1978;12:129-31.  Back to cited text no. 13
Hirai N, Fukunaga T, Kawano H, Honda O, Sakamoto T, Yoshimura M, et al. Platypnea – orthodeoxia syndrome with atrial septal defect. Circ J 2003;67:172-5.  Back to cited text no. 14
De Vecchis R, Baldi C, Ariano C. Platypnea-orthodeoxia syndrome: Multiple pathophysiological interpretations of a clinical picture primarily consisting of orthostatic dyspnea. J Clin Med 2016;5. pii: E85.  Back to cited text no. 15
Rodrigues P, Palma P, Sousa-Pereira L. Platypnea-orthodeoxia syndrome in review: Defining a new disease?. Cardiology 2012;123:15-23.  Back to cited text no. 16
Akin E, Krüger U, Braun P, Stroh E, Janicke I, Rezwanian R, et al. The platypnea-orthodeoxia Syndrome. Eur Rev Med Pharmacol Sci 2014;18:2599-604.  Back to cited text no. 17
Nakahira A, Matsumura Y, Tatsumi H, Sasaki Y, Hirai H, Hanatani A, et al. Platypnea-orthodeoxia diagnosed by sitting transesophageal echocardiography. Ann Thorac Surg 2010;89:1284-6.  Back to cited text no. 18
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  [Figure 1], [Figure 2]


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