Review Question - QID 212651

A 33-year-old woman presents to the emergency department after a motor vehicle collision. She was the front seat unrestrained driver in a head on collision at 25 miles per hour. Her temperature is 99°F (37.2°C), blood pressure is 129/66 mmHg, pulse is 127/min, respirations are 16/min, and oxygen saturation is 99% on room air. The primary and secondary survey are performed and are only notable for bruising along her chest wall bilaterally. An initial pelvic radiograph, an electrocardiogram (ECG) are performed and are unremarkable. A chest radiograph is performed and is notable for a sternal fracture and several rib fractures. The patient is given morphine and her heart rate subsequently improves to 80/min. The patient is observed in the emergency department over the next 6 hours and her laboratory values and a repeat ECG return within normal limits. The patient suddenly complains of shortness of breath. Her temperature is 99.5°F (37.5°C), blood pressure is 127/68 mmHg, pulse is 120/min, respirations are 28/min, and oxygen saturation is 91% on room air. A repeat chest radiograph is performed as seen in Figure A. Which of the following is the most likely diagnosis?