Review Question - QID 212417

A 55-year-old man presents to the emergency department after he was found unconscious at a playground. The patient is homeless, has a history of polysubstance abuse, and smells of alcohol. His temperature is 101°F (38.3°C), blood pressure is 107/58 mmHg, pulse is 120/min, respirations are 27/min, and oxygen saturation is 89% on room air. Physical exam is notable for a unkempt man who answers questions inappropriately. A chest radiograph is performed as seen in Figure A. The patient begins to vomit and is promptly suctioned and intubated. The patient is transferred to the intensive care unit, and his positive end-expiratory pressure is optimized to maximize lung compliance. The fraction of inspired oxygen and positive end-expiratory pressure is steadily increased to maintain the patient’s oxygen saturation. The patient suddenly decompensates with his oxygen saturation dropping from 93% to 82%. Which of the following is the most likely etiology of this patient’s acute decompensation?