Approach to postoperative acute kidney injury Quiz: Ace Your Exams

A 58-year-old man is seen on the medical floor on post-op day 4 after emergent aortic valve repair for acute infective endocarditis complicated by aortic regurgitation. He tolerated the surgery well and it was uncomplicated. His urine output has decreased to 15 mL/hour. He received iodinated contrast dye for a preoperative CT scan performed on the same day as the surgery. He has a history of gastroesophageal reflux and hypertension for which he takes omeprazole, metoprolol, and lisinopril. He is started on intravenous (IV) furosemide and a combination of IV vancomycin and gentamicin. Temperature is 37.5°C (99.5°F), heart rate is 86/min, blood pressure is 140/85 mm Hg, respiratory rate is 19/min, and oxygen saturation is 97% on room air. Physical examination is notable for bilateral lower extremity edema; and a tender, healing surgical site without signs of infection. Laboratory evaluation reveals a rise in serum creatinine to 3.4 mg/dL from a baseline of 1.2 mg/dL, and a blood urea nitrogen (BUN) of 30 mg/dL. Urinalysis shows muddy brown granular casts. Which of the following is the most likely cause of this patient’s acute kidney injury?