Acute Kidney Injury



    Acute Interstitial Nephritis

    • Hypersensitivity reaction to medication
    • Fever, rash, eosinophilia.
    • Urine Findings:
      • Leukocyte casts
      • Eosinophils
      • Urine protein:creatine ratio < 2.5 mg/mg


    Contrast-Induced Nephropathy

    (Source: "Little ICU Book" Marino 2009)

    • Injection of iodinated radiocontrast dye causes AKI (hyperosmolar damage to the endothelium of blood vessels and oxidative injury in renal tubular cells)
      • Low osmolar contrast is through to be safer than high.
    • Definition:
      •  Definition of CIN:

        • Creatinine increase > 0.5 mg/dL (44.2 µmol/L) OR increase in creatinine of 25% from baseline at 48 hours after contrast administration
    • Predisposing conditions:
      • Diabetes
      • HTN
      • Pre-Existing Renal Disease
      • Congestive Heart Failure
      • Osmolality and Volume of contrast agent.
    • Renal injury occurs within 72 hours after dye administration
      • Most resolve in 2weeks, some need dialysis.
    • Prevention:
      • Volume Expansion (maximize renal perfusion)
        • 3mL/kg over 1 hour just prior to procedure
        • 1-1.5 mL/kg/hr during and 4-6h post-procedure (total 6mL/kg of fluid post-procedure - regardless of fluid type)
      • N-AcetylCysteine (NAC)
        • Very controversial (studies are inconsistent)
        • Some societies recommend it (KDIGO, uptodate), and some do not (ACC/AHA)
          • Rationale: Low cost, low toxicity, potential benefit.
        • One of the largest trials: ACT Trial (2308 pts) did not show benefit (but has critisisms)
        • If using, suggested 1200mg po NAC bid a day prior to procedure and a day post procedure
        • (IV not advised due to possible anaphylactoid reactions and lack of evidence)

    Acute Interstitial Nephritis

    (Source: "Little ICU Book" Marino 2009)

    • Inflammatory condition of renal interstitium --> can progress to renal failure.
    • Causes:
      • Drugs (most common)
        • Typically occur 7-10days after exposure to drug
          • Antibiotics (particularly penicillins) are biggest offenders.
          • Antibiotics CNS Drugs Diuretics














            NSAIDs Others






            ACE inhibitors

            Iodinated Dyes


    • Diagnosis
      • Often Difficult (Onset of renal failure can be months post-exposure)
      • Hypersensitivity Syndrome
        • Typical Triad: fever, rash, eosinophilia - not reliable (only 10% have this!!)
      • Eosinophils or Leukocyte Casts in Urine
        • Urine eosinophils was the classic test done by Hansel staining.
        • However: poor sensitivity, poor specificity, disproven as a useful test.
      • Renal biopsy (gold standard)
        • If clear story, may not need renal biopsy, unless does not respond to stopping offending agent.
    • Treatment:
      • Discontinue offending drugs
      • Prednisone 0.5-1 mg/kg daily for 1-4w can speed up recovery (controversial, usually not done unless failure to respond to discontinuation of offending agent)
      • Resolution can take months.

    Rhabdomyolysis / Myoglobinuria

    • AKI in 1/3 of patients with rhabdomyolysis (typically requires CK > 10,000 to cause AKI)
      • Often also need profound dehydration (not just myoglobin/CK). 
    • Myoglobin released from injured muscle cells --> damages renal tubular epithelial cells (after filtering through glomerulus)
      • Concomitant hypovolemia, acidosis, hypophosphatemia
    • Causes:
      • Drugs (ALL statins)
      • Infection
      • Excessive Exertion
      • Prolonged Immobilization
    • Diagnosis:
      • Myoglobin in urine (using dip stick - orthotoluidine dipstick Hemastix) that normally detects blood in urine.
        • If positive --> can centrifuge urine to separate RBCs and supernatant passed through micropore filter (removes hemoglobin)  --> then test again --> if positive = myoglobin present.
    • Labs:
      • Hypocalcemia, Hyperphosphatemia, Hyperuricemia, Metabolic Acidosis
      • CK elevation > 5,000-10,000
    • Management:
      • Correct hypovolemia (most effective!)
      • Alkalinizing urine with Na HCO3 (useful in animal studies, but usually not necessary)
      • 30% require dialysis, but permanent renal failure is rare​
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