Prerenal acute kidney injury Quiz: Ace Your Exams

A 69-year-old man is brought to the emergency department by his daughter with a 2-day history of fever, productive cough, and worsening shortness of breath. The patient has a history of prostate cancer that is currently being treated with chemotherapy and radiation. The patient is able to void freely. Temperature is 38.9°C (102°F), blood pressure is 85/50 mmHg, pulse is 115 beats/min, respiratory rate is 28 breaths/min, and oxygen saturation is 88% on room air. Physical examination reveals respiratory distress, use of accessory muscles. The skin of the upper and lower extremities appears flush and warm to palpation. Cardiac exam is unremarkable. Pulmonary exam reveals rhonchi at the right lower lung base. Chest X-ray demonstrates a right lower lobe consolidation. Laboratory studies reveal a serum creatinine of 3.5 mg/dL (baseline 1.2 mg/dL) and a blood urea nitrogen (BUN) of 44 mg/dL. Urinalysis is unremarkable. Lactate is 5 mmol/L, and blood cultures/sputum cultures are pending. The patient is started on broad-spectrum antibiotics. Which of the following is the most likely cause of this patient's elevated BUN and serum creatinine?