Question

A 72 year old female with abdominal pain and unstable vital signs is found on angiography to have a ruptured abdominal aortic aneurysm. Past medical history includes hypertension, diabetes, and chronic renal insufficiency with baseline creatinine of 1.2 mg/dL. The patient is rushed to surgery and her aorta is successfully repaired in an eight hour operation where the patient receives five units of packed red blood cells and several liters of intravenous fluid. On the day following the operation, laboratory analysis reveals plasma creatinine of 2.1 mg/dL and BUN of 46 mg/dL. The fractional excretion of sodium (FeNa) is calculated to be 0.53%, and microscopic urinalysis shows occasional hyaline casts, but no RBCs, WBCs, or cellular or granular casts. Which of the following is the most likely explanation for this patient's abnormal laboratory values?

A. Cytotoxic effects of iodinated contrast material
B. Reduced blood flow to the kidneys
C. Ischemic necrosis of renal tubule cells
D. Obstruction of the distal urinary outflow system
E. Interstitial inflammation caused by drug hypersensitivity

Answer 1

The most likely cause of the patient's abnormal laboratory values post-aortic surgery is Reduced blood flow to the kidneys, which can lead to acute renal failure.

Step-by-step explanation:

The most likely explanation for the abnormal laboratory values of a 72-year-old female with a postoperative rise in plasma creatinine and blood urea nitrogen (BUN) after surgery for a ruptured abdominal aortic aneurysm is B. Reduced blood flow to the kidneys. The patient's history of hypertension, diabetes, and chronic renal insufficiency, along with the stress of a major surgery, receiving a high volume of intravenous fluids and blood transfusions, contribute to a condition called acute renal failure (ARF). The relatively low fractional excretion of sodium (FeNa) and the absence of red blood cells (RBCs), white blood cells (WBCs), or cellular or granular casts on microscopic urinalysis suggest that the kidneys' ability to filter blood is compromised due to reduced perfusion rather than direct tubular damage or urinary outflow obstruction.