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

  • Acute renal failure itself has few symptoms until severe uremia develops:
  • Patients more likely to present with symptoms related to underlying cause:
    • Prerenal
      • Thirst, orthostatic light-headedness, decreasing urine output
    • Intrinsic
    • Postrenal
      • Alternating oliguria and polyuria is pathognomonic of obstruction
      • Anuria

Etiologies

Differential Diagnosis of Acute Kidney Injury.png

Prerenal

Intrinsic

Postrenal

  • Infants and children
    • Urethra and bladder outlet
      • Anatomic malformations
        • Urethral atresia
        • Meatal stenosis
        • Anterior and posterior urethral valves
    • Ureter
      • Anatomic malformations
        • Vesicoureteral reflux (female preponderance)
        • Ureterovesical junction obstruction
        • Ureterocele
        • Retroperitoneal tumor
  • All ages
    • Various locations in GU tract
      • Trauma
      • Blood clot
    • Urethra and bladder outlet
      • Phimosis or urethral stricture (male preponderance)
      • Neurogenic bladder
        • Diabetes mellitus, spinal cord disease, multiple sclerosis, Parkinson's
        • Pharmacologic: anticholinergics, a-adrenergic antagonists, opioids
  • Adults
    • Urethra and bladder outlet
      • BPH
      • Cancer of prostate, bladder, cervix, or colon
      • Obstructed catheters
    • Ureter

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
    • 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 hydronephrois found on ultrasound in order to define the location of obstruction

Management

Treat underlying cause

  • Prerenal: IVF
  • 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

Disposition

  • Admit

See Also

External Links

References