A 64-year-old man presents to the emergency department after a witnessed syncopal episode at home. His wife reports that he suddenly became short of breath and collapsed while walking to the bathroom. He underwent a right total knee arthroplasty 10 days ago and has been recovering well until today. He denies any chest pain prior to the event but reports a sensation of “suffocating” air hunger. His past medical history includes hypertension and hyperlipidemia. His current medications include lisinopril, atorvastatin, and aspirin. He has no known drug allergies. He is a former smoker with a 20 pack-year history.

He appears diaphoretic, anxious, and in acute respiratory distress. His blood pressure is 78/50 mmHg with a weak, thready pulse of 125 bpm. He is tachypneic at 32 breaths per minute, and his oxygen saturation is 86% on room air. He is afebrile.