USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What is characteristic of Acute Respiratory Distress Syndrome (ARDS)?

1. Bronchospasm

2. Increased lung compliance

3. Normal pulmonary infiltrates

4. Decreased oxygenation with bilateral pulmonary infiltrates

The correct answer is: Decreased oxygenation with bilateral pulmonary infiltrates

Acute Respiratory Distress Syndrome (ARDS) is characterized by decreased oxygenation in the setting of bilateral pulmonary infiltrates. This condition typically arises from various triggers such as infections, trauma, or acute inflammation that lead to increased permeability of the alveolar-capillary membrane. This increased permeability results in pulmonary edema, which subsequently impairs gas exchange and leads to hypoxemia. The presence of bilateral pulmonary infiltrates on imaging demonstrates the widespread involvement of lung parenchyma, aligning with the pathophysiological changes observed in ARDS. The hypoxemia is often disproportionate to the degree of lung compliance which can be decreased rather than increased, contrary to what is seen in conditions like asthma where bronchospasm and increased airway resistance might occur. In ARDS, the lungs become stiff and less compliant due to the accumulation of fluid and the inflammatory process, further emphasizing the importance of recognizing the specific characteristics that define this syndrome.