Platypnoea-orthodeoxia syndrome

Last revised by Rohit Sharma on 6 Aug 2022

Platypnoea-orthodeoxia syndrome refers to the concomitant occurrence of dyspnea and hypoxemia, respectively, which are precipitated by assuming an upright position and alleviated by assuming a recumbent position 4.

As the name of the syndrome suggests, the hallmark clinical feature is platypnoea - dyspnea when upright that improves in a supine position. Patients may also have clinical features attributable to the underlying etiology of the syndrome, for example, clinical features of a congenital heart defect.

Confirmed clinically by the dynamic change of arterial oxygenation with a positional change from supine/recumbent to seated/upright, quantified as follows:

  • decrease in arterial PaO2 by 4 mmHg or more
  • decrease in arterial oxygen saturation by 5% or more

Gold standard diagnosis is achieved by cardiac catheterization.

Requires the presence of right-to-left shunting, which is most commonly related to a cardiac etiology i.e. an intracardiac shunt. Extracardiac etiologies have also been described.

The right-to-left shunting may be exacerbated by hemodynamic perturbations, such as right heart failure and pulmonary hypertension, or anatomic factors predisposing preferential flow of blood toward (and across) the interatrial septum 2.

Echocardiography may be utilized with agitated saline as a contrast medium ('bubble study') to demonstrate the presence of right-to-left shunting.

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