Acute kidney injury

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Background

  • Majority of cases of community-acquired ARF is secondary to volume depletion although consideration of pre-renal, post renal, and renal causes are important.

RIFLE Classification

  • Risk - Serum creatinine increased 1.5x baseline
  • Injury - Serum creatinine increased 2.0x baseline
  • Failure - Serum creatinine increased 3.0x baseline OR creatinine >4 and acute increase >0.5
  • Loss - Complete loss of kidney function for >4wk
  • ESRD - Need for renal replacement therapy for >3mo

Chronic Kidney Disease Stages

  • Useful if patient's baseline creatinine is unknown
    • Stage 1: Kidney damage (e.g. proteinuria) and normal GFR; GFR >90
    • Stage 2: Kidney damage (e.g. proteinuria) and mild decrease in GFR; GFR 60-89
    • Stage 3: Moderate decrease in GFR; GFR >30-59
    • Stage 4: Severe decrease in GFR; GFR 15-29
    • Stage 5: Kidney failure (dialysis or kidney transplant needed); GFR <15

Risk Factors

Clinical Features

Etiologies

Differential Diagnosis of Acute Kidney Injury.png

Prerenal

Intrinsic

Postrenal

Evaluation

  • Prerenal
    • BUN/creatinine ratio > 20
    • FeNa <1% ((urine sodium/plasma sodium) / (urine creatinine / serum creatinine))
      • < 2% for neonates
    • Urine osm >500
    • Urine sodium < 20 mEq/L
    • Specific gravity > 1.020
    • Fractional excretion of urea < 35%
    • Microscopic analysis
      • Hyaline casts
  • Instrinsic
    • FeNa >1%
      • > 2.5% for neonates
    • Urine Osm <350
    • Urine sodium > 40 mEq/L
    • Specific gravity < 1.020
    • Fractional excretion of urea > 50%
    • Microscopic analysis
      • Acute glomerulonephritis: RBCs, casts
      • Acute tubular necrosis: protein, tubular epithelial cells
  • Postrenal
    • FeNa >1%
    • Urine Osm <350

Work-up

  • Urine
  • Prostate exam
  • Urinalysis, urine sodium, urine creatinine, urine urea
  • ECG (hyperkalemia)
  • Chronic renal failure features
    • Anemia, thrombocytopenia
    • Iron studies with low Fe, low TIBC, low iron saturation, normal ferritin
    • Secondary rise in PTH, high phos, low calcium

Imaging

  • CXR
    • Evidence of volume overload, pneumonia
  • US: renal/bladder
    • Test of choice in setting of acute renal failure
    • Bladder size (post-void)
    • Hydronephrosis
    • IVC collapsibility (prerenal)
  • CT
    • Useful to determine cause of post renal failure (identification of abdominal masses etc.)
    • Should generally not be used with IV contrast due to potential risk for CIN
    • Indicated if hydronephrosis found on ultrasound in order to define the location of obstruction

Management

Treat underlying cause

  • Prerenal: IVF (or pRBCs if bleeding)
  • Intrinsic: Depends on cause
  • Obstruction:
    • Note: Postobstructive diuresis can result in significant volume loss and death
      • Typically occurs when obstruction has been prolonged / has resulted in renal failure
      • Admit patients with persistent diuresis of >250 mL/h for >2hr
    • Foley Catheter, consider Coude Catheter
    • Suprapubic (if Coude fails)

Dialysis

  • Indicated for:
    • A: Acidosis (severe)
    • E: Electrolyte abnormality (e.g. uncontrolled hyperkalemia)
    • I: Ingestions (lithium, ASA, methanol, ethylene glycol, theophylline)
    • O: Overload (volume) with persistent hypoxia
    • U: Uremic pericarditis/encephalopathy/bleeding dyscrasia
    • Also:
      • Na <115 or >165 mEq/L
      • creatinine > 10
      • BUN >100
  • See Dialysis catheter placement
  • See Austere peritoneal dialysis

Phlebotomy to Treat Pulmonary Edema

  • Possible last ditch effort to tide patient over to formal dialysis if hours away
  • If traditional pulmonary edema treatments are not working for SCAPE patient, one may attempt to remove 200-300 cc of blood as a bridge to dialysis[1]
  • If Hb too low, may consider temporary venous tourniquets on each leg proximally q30 min to reduce preload volume to the heart, alternating legs

Disposition

  • Admit

See Also

External Links

References

  1. Eiser AR et al. Phlebotomy for pulmonary edema in dialysis patients. Clin Nephrol. 1997 Jan;47(1):47-9.