The nurse's assessment of the client includes rapid, shallow respirations, respiratory acidosis, and inspiratory crackles. Which additional assessment finding would confirm a diagnosis of acute respiratory distress syndrome (ARDS)?

A. Asymmetrical chest expansion: Unequal chest expansion may indicate localized lung pathology such as pneumothorax or atelectasis, but ARDS typically causes diffuse alveolar damage affecting both lungs, leading to symmetric restrictions rather than asymmetry. B. Pink, frothy sputum: Pink, frothy sputum is characteristic of pulmonary edema from left-sided heart failure (cardiogenic pulmonary edema). ARDS is non-cardiogenic, resulting from increased alveolar-capillary permeability rather than hydrostatic pressure, frothy sputum is not a hallmark finding. C. Hypoxemia unresponsive to oxygen: ARDS is defined by severe hypoxemia due to alveolar flooding, decreased lung compliance, and impaired gas exchange. Supplemental oxygen often fails to correct the hypoxemia because shunting occurs from non-ventilated alveoli. This refractory hypoxemia is a defining criterion for ARDS and confirms the diagnosis. D. Circumoral cyanosis: Cyanosis reflects significant hypoxemia but is a late, nonspecific sign. While it indicates low oxygen saturation, it does not confirm the pathophysiologic mechanisms of ARDS, which include diffuse alveolar damage and oxygen-refractory hypoxemia.