A 65-year-old hospitalized man is evaluated for decreased urine output and increased serum creatinine. The patient was admitted for 3-vessel coronary artery disease and underwent coronary artery bypass grafting surgery yesterday. Other medical conditions include type 2 diabetes mellitus and hypertension. He received a dose of intravenous vancomycin prior to the surgery for prophylaxis of surgical infection. The patient has also been receiving 100 mL/hour of intravenous normal saline for the past 24 hours. He is afebrile. Blood pressure is 130/80 mm Hg and pulse is 80/min. Examination shows bibasilar crackles. The abdomen is soft. Urine output over the past 6 hours is 100 mL. Laboratory results are as follows: Urine sediment microscopy is shown in the exhibit.

Which of the following is the most likely cause of this patient's current condition?

Question

A 65-year-old hospitalized man is evaluated for decreased urine output and increased serum creatinine. The patient was admitted for 3-vessel coronary artery disease and underwent coronary artery bypass grafting surgery yesterday. Other medical conditions include type 2 diabetes mellitus and hypertension. He received a dose of intravenous vancomycin prior to the surgery for prophylaxis of surgical infection. The patient has also been receiving 100 mL/hour of intravenous normal saline for the past 24 hours. He is afebrile. Blood pressure is 130/80 mm Hg and pulse is 80/min. Examination shows bibasilar crackles. The abdomen is soft. Urine output over the past 6 hours is 100 mL. Laboratory results are as follows:

Urine sediment microscopy is shown in the exhibit.

Which of the following is the most likely cause of this patient's current condition?

Quizplus · Accepted Answer

11ec160b_3a26_df67_9249_9b1c844aa708_MD0001_00 This patient with acute kidney injury has muddy brown casts on urine microscopy; in the setting of recent major surgery this presentation suggests acute tubular necrosis (ATN) due to intraoperative renal ischemia. Surgeries complicated by significant blood loss or those requiring the use of cardiopulmonary bypass (eg, coronary artery bypass grafting) or aortic clamping can cause renal hypoperfusion. The risk is increased in the elderly and those with a history of chronic kidney disease, diabetes, or congestive heart failure. ATN is characterized by the presence of muddy brown granular casts composed of sloughed renal tubular epithelial cells. Patients have increased serum creatinine, blood urea nitrogen/ creatinine ratio <20:1 (indicating intrinsic renal pathology), and oliguria (low urine output). Histologically, flattened tubular epithelial cells with cellular necrosis and loss of the brush border are seen. (Choice A) Crystalline-induced kidney injury most commonly occurs from acyclovir or sulfonamide (eg, sulfadiazine) usage. Urinalysis demonstrates needle or rosette-shaped crystals. Vancomycin is not associated with crystal formation. (Choice B) Vancomycin can cause ATN, but this typically occurs after a prolonged course (days). It is highly unlikely that a single dose would cause ATN. (Choice C) Glomerulonephritis can cause acute kidney injury, but hematuria and red blood cell casts are expected on urinalysis. In addition, patients are typically hypertensive. (Choice D) Acute interstitial nephritis can occur after exposure to new drugs, particularly antibiotics and diuretics. However, white blood cells and white cell casts are expected on urinalysis, and patients often have fever and rash. (Choice F) Prerenal azotemia occurs from less significant renal hypoperfusion without renal ischemia (eg, dehydration). Urinalysis reveals hyaline casts (reflecting concentrated urine) and the blood urea nitrogen/creatinine ratio is elevated (>20:1). Educational objective: Surgeries complicated by significant blood loss or those requiring the use of cardiopulmonary bypass or clamping of the aorta can cause sustained renal hypoperfusion and result in acute tubular necrosis (ATN). ATN presents with oliguria, increased serum creatinine, and blood urea nitrogen/creatinine ratio <20:1. Urinalysis is characterized by muddy brown granular casts composed of sloughed renal tubular epithelial cells.

A 65-Year-Old Hospitalized Man Is Evaluated for Decreased Urine Output