This patient is presenting with congestive heart failure that has been treated and pre-renal azotemia. The most likely cause is diuresis with furosemide.
Furosemide is a common treatment for acute exacerbations of CHF. When patients are diuresed with diuretics such as furosemide, they can become dehydrated and experience electrolyte abnormalities. This dehydration leads to decreased perfusion of the kidney and can result in a pre-renal azotemia. Pre-renal azotemia will present with an elevated BUN and Cr with a BUN:Cr ratio > 20 as in this patient. Treatment for pre-renal azotemia is administration of fluids/decreasing diuresis; however, in a CHF patient this should be done carefully so as to not induce a volume overload state.
Figure A demonstrates an EKG that has a normal rate, rhythm, and is without ST elevation. Figure B demonstrates a chest radiograph with an increased cardiac width and pulmonary edema suggesting a diagnosis of CHF.
Answer 2: Intrarenal kidney injury typically occurs when there is an offending toxic agent or hypoperfusion that leads to damage of the kidney. Patients will have a BUN:Cr ratio around 10:1 from loss of dilute, un-concentrated urine. Acute diuresis is more likely to lead to a pre-renal azotemia.
Answer 3: Urinary tract obstruction reflects a diagnosis of post-renal azotemia. This can occur secondary to a stone, stricture, tumor, or benign prostatic hypertrophy. The BUN:Cr ratio will typically be > 15:1. Given the patient's history of appropriately treated CHF, pre-renal azotemia caused by furosemide is a more likely diagnosis.
Answer 4: Chronic kidney disease (CKD) presents with hypertension, hyperkalemia, hypocalcemia (from low 1,25-dihydroxyvitamin D), and an elevated BUN and Cr. This patient has no history of CKD, and his symptoms started after a properly treated CHF flare.
Answer 5: Cholesterol emboli could result after an interventional cardiac procedure and would present with livedo reticularis (lacy erythematous rash), peripheral ischemia (blue toes), eosinophilia, and decreased kidney function. This patient did not have a myocardial infarction given his normal EKG, thus a cardiac procedure was not performed.
Pre-renal azotemia can occur in any volume depleted state such as excessive diuretic use, and will demonstrate laboratory abnormalities such as an elevated BUN and Cr with a BUN:Cr ratio > 20.