Acute Kidney Injury and Critical Care Nephrology
Acute Kidney Injury and Critical Care Nephrology
This domain tests KDIGO staging, differentiating prerenal, intrinsic, and postrenal AKI, and managing dialysis indications in critically ill patients.
Core rules
- KDIGO AKI: rise in creatinine ≥0.3 mg/dL within 48 hours, ≥1.5× baseline within 7 days, or urine output <0.5 mL/kg/h for 6 hours.
- Prerenal AKI: bland sediment, FENa <1%, improves with volume. FENa is unreliable with diuretics, CKD, or contrast.
- Intrinsic AKI: ATN shows muddy brown casts; AIN shows WBC casts and eosinophiluria; glomerulonephritis shows RBC casts.
- Postrenal AKI: check bladder scan and renal ultrasound; relieve obstruction promptly.
- Dialysis indications: AEIOU-acidosis, electrolyte imbalance such as refractory hyperkalemia, intoxication, overload, uremia with encephalopathy or pericarditis.
- CRRT is preferred for hemodynamic instability; intermittent HD for urgent toxin removal.
Worked example
A 70-year-old with vomiting and diarrhea has creatinine 2.0 mg/dL from baseline 1.0, urine Na 10 mmol/L, FENa 0.4%, and bland sediment. This is prerenal AKI from volume depletion. Give isotonic crystalloid and stop NSAIDs; recheck creatinine and urine output.
Traps
- Relying on creatinine alone, which lags behind GFR decline.
- Using FENa in a patient on furosemide.
- Missing obstruction in unexplained AKI.
- Continuing nephrotoxins during critical illness.