Platypnoea-orthodeoxia syndrome refers to the concomitant occurrence of dyspnoea and hypoxaemia, respectively, which are precipitated by assuming an upright position and alleviated by assuming a recumbent position 4.
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Clinical presentation
As the name of the syndrome suggests, the hallmark clinical feature is platypnoea - dyspnoea when upright that improves in a supine position. Patients may also have clinical features attributable to the underlying aetiology of the syndrome, for example, clinical features of a congenital heart defect.
Diagnosis
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 catheterisation.
Pathology
Aetiology
Requires the presence of right-to-left shunting, which is most commonly related to a cardiac aetiology i.e. an intracardiac shunt. Extracardiac aetiologies have also been described.
- intracardiac shunting
-
patent foramen ovale (PFO) 1
- most common association
- atrial septal defect (ASD)
- atrial septal aneurysm
- partial anomalous pulmonary venous return
- iatrogenic
- transposition of the great vessels
-
patent foramen ovale (PFO) 1
The right-to-left shunting may be exacerbated by haemodynamic perturbations, such as right heart failure and pulmonary hypertension, or anatomic factors predisposing preferential flow of blood toward (and across) the interatrial septum 2.
- extracardiac shunting
- intrapulmonary shunt
- pulmonary arteriovenous malformations (AVM)
- hepatopulmonary syndrome 3
- acute respiratory distress syndrome
- pneumonia
- ventilation-perfusion mismatch
- chronic obstructive pulmonary disease (COPD)
- pulmonary embolism
- intrapulmonary shunt
Radiographic features
Ultrasound
Echocardiography may be utilised with agitated saline as a contrast medium ('bubble study') to demonstrate the presence of right-to-left shunting.
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