A 55-year-old man develops AKI after cardiac surgery (creatinine rises from 0.9 to 3.2 mg/dL). Urine microscopy reveals muddy-brown granular casts and tubular epithelial cell casts. FENa is 3.2%. The MOST appropriate management is:
- A IV furosemide to maintain urine output >1 mL/kg/h
- B IV N-acetylcysteine for renal protection
- C Urgent haemodialysis
- D Supportive care — optimise haemodynamics, avoid nephrotoxins, and monitor ✓
Explanation
Muddy-brown granular casts and tubular epithelial cell casts are diagnostic of acute tubular necrosis (ATN). FENa >2% confirms intrinsic renal (tubular) injury, not prerenal cause. Management of ATN is supportive: ensure adequate intravascular volume, optimise cardiac output, avoid further nephrotoxins (NSAIDs, aminoglycosides, contrast), and carefully monitor electrolytes/fluid balance. Furosemide does not prevent or treat ATN and may worsen outcomes if given without adequate volume status correction. Urgent dialysis is reserved for life-threatening indications (severe hyperkalemia, acidosis, fluid overload). N-acetylcysteine is for contrast-induced AKI prevention.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.