On day 3 of admission for severe acute pancreatitis after hemodynamic stability, a patient develops tachypnea and hypoxia with bilateral infiltrates. ABG shows respiratory alkalosis. What is the most likely diagnosis?

• A. Pulmonary edema
• B. ARDS
• C. Pneumonia
• D. Pulmonary embolism

Answer: (B)

Inflammation-driven lung injury from a severe pancreatitis episode can cause noncardiogenic pulmonary edema, known as ARDS. This typically develops within a few days of the insult, and day 3 fits that window. The lungs become inflamed and capillary permeability increases, leading to diffuse, bilateral infiltrates and hypoxemia that aren’t explained by heart failure or fluid overload. The ABG showing respiratory alkalosis reflects the patient’s rapid breathing trying to compensate for low oxygen—hyperventilation is a common early finding in ARDS. This pattern distinguishes it from cardiogenic pulmonary edema, which would usually show signs of volume overload or heart failure with a different radiographic pattern, and from pneumonia, which tends to produce focal rather than diffuse bilateral infiltrates. Pulmonary embolism can cause hypoxemia, but it doesn’t typically produce bilateral infiltrates on imaging in this context. So the presentation points most toward ARDS.