What is orthodeoxya?

Orthodeoxia: Definition and Clinical Significance

Orthodeoxia is a clinical phenomenon characterized by worsening hypoxemia (decreased oxygen saturation) when a patient assumes an upright position, with improvement when lying down. 1

Pathophysiology

• Orthodeoxia is commonly associated with platypnea (worsening dyspnea in upright position), forming the platypnea-orthodeoxia syndrome (POS) 1
• The physiological basis involves positional changes that exacerbate right-to-left shunting, bypassing normal pulmonary gas exchange 1
• Most commonly occurs due to:
  • Intracardiac shunts (through patent foramen ovale, atrial septal defects) 1, 2
  • Intrapulmonary shunts (pulmonary arteriovenous malformations) 1
  • Ventilation-perfusion mismatch (in certain pulmonary conditions) 3

Clinical Presentation

• Patients experience decreased oxygen saturation when sitting or standing upright 1
• Oxygen levels improve when the patient assumes a recumbent position 2
• Often accompanied by positional dyspnea (platypnea) 3
• May present with symptoms of hypoxemia including lightheadedness, dizziness, and fatigue 1

Common Causes

Intracardiac Causes

• Patent foramen ovale (PFO) 1, 4
• Atrial septal defects (ASD) 1, 2
• These defects allow right-to-left shunting when upright position changes cardiac anatomy 5

Pulmonary Causes

• Pulmonary arteriovenous malformations (PAVMs) 1
• Hepatopulmonary syndrome in patients with liver disease 1
• Severe COVID-19 pneumonia (recently reported) 6
• Other pulmonary conditions: pneumonectomy, recurrent pulmonary emboli, chronic lung disease 4

Diagnosis

• Measure arterial blood gases or oxygen saturation in both supine and upright positions - a drop of at least 5% in saturation or 4 mmHg in PaO2 when upright is diagnostic 6, 4
• Echocardiography (transthoracic and transesophageal) with contrast in both supine and upright positions to detect intracardiac shunts 5
• CT angiography to identify pulmonary arteriovenous malformations 1
• Diagnostic criteria include:
  • Orthostatic desaturation
  • Evidence of anatomic shunt
  • Absence of pulmonary hypertension in many cases 4

Treatment

• Treatment depends on the underlying cause:
  • For intracardiac shunts: Percutaneous or surgical closure of the defect (PFO or ASD) 2, 5
  • For pulmonary arteriovenous malformations: Endovascular occlusion of feeding arteries 1
  • For hepatopulmonary syndrome: Liver transplantation may be considered 1

Clinical Pearls

• Orthodeoxia is often overlooked in clinical practice and requires a high index of suspicion 3
• It should be considered in patients with unexplained hypoxemia that worsens with upright positioning 1
• Closure of intracardiac shunts can be curative in appropriate cases 1, 2
• The condition is distinct from orthostatic hypotension, which involves blood pressure changes rather than oxygen saturation 7
• In patients with PAVMs, 65-83% of lesions are located in the lower lobes, explaining the gravitational effect on shunting when upright 1

Common Pitfalls

• Failure to measure oxygen saturation in both supine and upright positions can lead to missed diagnosis 4
• Not considering orthodeoxia in patients with unexplained positional dyspnea 3
• Overlooking the possibility of multiple coexisting mechanisms of shunting (as seen in post-COVID cases) 6