During resuscitation after an MVA, a patient has pulmonary infiltrates and low oxygen saturation; administration of a bolus of normal saline leads to worsening of oxygen saturation. What is the most likely diagnosis?

• A. Pulmonary contusion
• B. ARDS
• C. Pneumothorax
• D. Pulmonary edema

Answer: (A)

In blunt chest trauma, damage to the lung tissue causes alveolar hemorrhage and capillary leak, producing patchy infiltrates on imaging and significant hypoxemia. This injury disrupts the alveolar–capillary barrier, so when you give fluids, the already leaky vessels allow more fluid into the airspaces. The resulting increase in local edema and blood in the alveoli worsens gas exchange, making oxygen saturation fall further.

This pattern—trauma with patchy infiltrates and a rapid drop in oxygenation after a fluid bolus—fits pulmonary contusion best. Other possibilities are less likely in this context: a pneumothorax would typically show focal lung collapse and exam findings like decreased breath sounds; ARDS can occur after trauma but usually presents with diffuse, bilateral infiltrates and often evolves over hours to days; true pulmonary edema from volume overload tends to be more diffuse and not tied specifically to a focal contusion pattern after blunt trauma.

So the most likely diagnosis is pulmonary contusion.