A patient with diffuse bilateral infiltrates and severe hypoxemia most likely has which syndrome?

• A. Acute respiratory distress syndrome
• B. Pulmonary edema from left heart failure
• C. Pneumonia
• D. Acute interstitial pneumonitis

Answer: (D)

Diffuse bilateral infiltrates with severe hypoxemia point to a noncardiogenic diffuse lung injury, most classically acute respiratory distress syndrome. In ARDS, an insult such as sepsis, trauma, or aspiration damages the alveolar-capillary membrane, allowing protein-rich fluid to flood the alveoli. This fills air spaces, reduces lung compliance, and creates a large shunt with mismatched ventilation and perfusion. Oxygenation drops dramatically and is often refractory to high levels of supplemental oxygen.

On the chest radiograph you see widespread, bilateral interstitial and alveolar opacities rather than a single lobar consolidation. This pattern helps distinguish ARDS from cardiogenic pulmonary edema from left-heart failure, which typically shows signs of volume overload and heart enlargement. Pneumonia can cause infiltrates as well, but it is usually focal rather than the diffuse, widespread pattern seen with ARDS. Acute interstitial pneumonitis can produce diffuse markings, but the combination of acute onset, diffuse bilateral infiltrates, and severe hypoxemia most strongly points to ARDS.