A 19-year-old man sustains severe lower-extremity trauma, including a femur fracture and a crush injury to his foot. He requires vascular reconstruction of the popliteal aery. On the day after surgery, he becomes dyspneic and hypoxemic and requires intubation and mechanical ventilation. Which of the following is the most likely etiology of his decompensation?

Fat embolism syndrome is a relatively uncommon complication of long-bone fractures and is characterized by acute respiratory failure, altered mental status, and petechiae. Unfounately, there are no reliable diagnostic tests, and management is suppoive only. Pulmonary edema is unlikely in an otherwise healthy 19-year-old male without chest trauma or evidence of a cardiac contusion. Aspiration is unlikely in an awake patient with normal mental status. Pneumonias typically present with fever and/or leukocytosis, productive cough, and a new infiltrate on chest x-ray. Atelectasis in and of itself is not a cause for respiratory failure.