A 52-year-old man comes to the emergency department due to increasing shortness of breath. He had sustained trauma to the chest after falling from the stairs in the morning. He does not have a significant past or medical history. He smokes 1-2 cigarettes per day. He has no history of alcohol or use of illicit drugs. Temperature is 37.1 C (98.6 F), blood pressure is 100/60 mm of Hg, pulse 98/min, and respirations are 27/min. His oxygen saturation is 95%. Neck veins are slightly distended. Local examination reveals ecchymoses over his left chest. There are decreased breath sounds on the left side. No murmurs are heard. A chest x-ray is shown in the exhibit.