Review Question - QID 214819

A 33-year-old man with a past medical history of intravenous drug use presents to the emergency department acutely obtunded. He was found passed out in an alley and was not responsive when police tried to wake him. The patient’s medical history is unknown. His temperature is 97.5°F (36.4°C), blood pressure is 102/63 mmHg, pulse is 92/min, respirations are 7/min, and oxygen saturation is 88% on room air. Physical exam reveals an obtunded man with pinpoint pupils. The patient is given multiple doses of naloxone and placed on a non-rebreather; however, his oxygen saturation fails to improve. The patient is subsequently intubated and admitted to the intensive care unit (ICU). A chest radiograph at the time of intubation shows that the tube is in good position with clear lung fields. On day 2 in the ICU, a chest radiograph is performed as seen in Figure A. An ultrasound at the base of the lung shows normal lung sliding. Which of the following is the most likely diagnosis?