Hypoxia and normal chest x-ray (CXR)

DDx

Asthma
Pulmonary embolism
Early pneumonia
Early interstitial lung disease
Early pneumocystis pneumonia (PCP)
Shunt, eg, atrial or ventricular septal defect, arteriovenous malformation, atelectasis
Pulmonary hypertension
Chronic alveolar hypoventilation

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