Acute kidney injury

Background

• Majority of cases of community-acquired ARF is secondary to volume depletion

RIFLE Classification

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

Chronic Kidney Disease Stages

• Useful if pt'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 decr 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

1. Atherosclerosis
2. Chronic hypertension
3. Chronic kidney disease
4. NSAIDs
5. ACEI/ARB
6. Sepsis
7. Hypercalcemia
8. Hepatorenal syndrome
9. Radiocontrast agents

Etiology

Prerenal

1. Hypovolemia
   1. GI: decreased intake, vomiting and diarrhea
   2. Pharmacologic: diuretics
   3. Third spacing
      1. Pancreatitis
   4. Skin losses: fever, burns
   5. Miscellaneous
      1. Hypoaldosteronism
      2. Salt-losing nephropathy
      3. Postobstructive diuresis
2. Hypotension
   1. Septic vasodilation
   2. Hemorrhage
   3. Decreased cardiac output
      1. Ischemia/infarction
      2. Valvulopathy
   4. Pharmacologic
      1. B-blockers
      2. CCBs
      3. Antihypertensive medications
   5. High-output failure
      1. Thyrotoxicosis
      2. AV fistula
3. Renal artery and small-vessel disease
   1. Embolism: thrombotic, septic, cholesterol
   2. Thrombosis: atherosclerosis, vasculitis, sickle cell disease
   3. Dissection
   4. Pharmacologic
      1. NSAIDs
      2. ACEI/ARB
         1. Observed shortly after initiation of therapy
   5. Microvascular thrombosis
      1. Preeclampsia
      2. HUS
      3. DIC
      4. vasculitis
      5. SCD
   6. Hypercalcemia

Intrinsic

1. Tubular diseases
   1. Ischemic acute tubular necrosis
      1. Caused by more advanced disease due to the prerenal causes
2. Nephrotoxins
   1. Aminoglycosides, radiocontrast, amphotericin, heme pigments (rhabdo, hemolysis)
   2. Obstruction
      1. Uric acid, calcium oxalate, myeloma, amyloid
      2. Pharmacologic: sulfonamide, triamterene, acyclovir, indinavir
3. Interstitial diseases
   1. Acute interstitial nephritis: typically a drug reaction (NSAIDs, abx, phenytoin)
   2. Infection: bilateral pyelonephritis, Legionnaire disease, hantavirus
   3. Infiltrative disease: sarcoidosis, lymphoma
   4. Autoimmune diseases: SLE
4. Glomerular diseases
   1. Rapidly progressive glomerulonephritis
      1. Goodpasture, Wegener granulomatosis, HSP, SLE, membranoproliferative GN
   2. Postinfectious glomerulonephritis
5. Small-vessel diseases
   1. Microvascular thrombosis
      1. Preeclampsia, HUS, DIC, TTP, vasculitis (PAN, SCD, atheroembolism)
   2. Malignant hypertension
   3. Scleroderma
   4. Renal vein thrombosis

1. 1. FeNa <>1%
   2. FeUN >50%

Postrenal

• Loss of renal function occurs over course of 10-14d in setting of complete obstruction
  • Risk of permanent renal failure increases significantly if complicated by UTI

Etiology

1. Infants and children
   1. Urethra and bladder outlet
      1. Anatomic malformations
         1. Urethral atresia
         2. Meatal stenosis
         3. Anterior and posterior urethral valves
   2. Ureter
      1. Anatomic malformations
         1. Vesicoureteral reflux (female preponderance)
         2. Ureterovesical junction obstruction
         3. Ureterocele
         4. Retroperitoneal tumor
2. All ages
   1. Various locations in GU tract
      1. Trauma
      2. Blood clot
   2. Urethra and bladder outlet
      1. Phimosis or urethral stricture (male preponderance)
      2. Neurogenic bladder
         1. DM, spinal cord disease, multiple sclerosis, Parkinson's
         2. Pharmacologic: anticholinergics, a-adrenergic antagonists, opiates
3. Adults
   1. Urethra and bladder outlet
      1. BPH
      2. Cancer of prostate, bladder, cervix, or colon
      3. Obstructed catheters
   2. Ureter
      1. Calculi, uric acid crystals
      2. Papillary necrosis
         1. SCD, DM, pyelonephritis
      3. Tumor: Ureter, uterus, prostate, bladder, colon, rectum; retroperitoneal lymphoma
      4. Retroperitoneal fibrosis: idiopathic, tuberculosis, sarcoidosis, propranolol
      5. Stricture: TB, radiation, schistosomiasis, NSAIDs
      6. Miscellaneous
         1. Aortic aneurysm
         2. Pregnant uterus
         3. IBD
         4. Trauma

Clinical Features

• Acute renal failure itself has few symptoms until severe uremia develops:
  • N/V, drowsiness, fatigue, confusion, coma
• Pts more likely to present w/ symptoms related to underlying cause:
  • Prerenal
    • Thirst, orthostatic light-headedness, decreasing urine output
  • Intrinsic
    • Flank pain, hematuria
      • Nephrolithiasis
      • Papillary necrosis
      • Crystal-induced nephropathy
    • Myalgias, seizures, recreational intoxication
      • Pigment-induced ARF (rhabdo)
    • Darkening urine and edema (esp w/ preceding pharyngitis or cutaneous infection)
      • Acute glomerulonephritis
    • Fever, arthralgia, rash
      • Acute interstitial nephritis
    • Cough, dyspnea, hemoptysis
      • Goodpasture, Wegener granulomatosis
  • Postrenal
    • Alternating oliguria and polyuria is pathognomonic of obstruction
    • Anuria

Diagnosis

1. Prerenal
   1. BUN/Cr ratio > 20
   2. FeNa <1% ((urine sodium/plasma sodium) / (urine creatinine / serum creatinine))
   3. Urine osm >500
   4. Microscopic analysis
      1. Hyaline casts
2. Instrinsic
   1. FeNa >1%
   2. Urine Osm <350
   3. Microscopic analysis
      1. Acute glomerulonephritis: RBCs, casts
      2. Acute tubular necrosis: protein, tubular epithelial cells
3. Postrenal
   1. FeNa >1%
   2. Urine Osm <350

Work-up

1. Urine
   1. UA, urine sodium, urine creatinine, urine urea
2. ECG (hyperkalemia)
3. Imaging
   1. CXR
      1. Evidence of volume overload, PNA
   2. US
      1. Test of choice in setting of acute renal failure
         1. Bladder size (post-void)
         2. Hydronephrosis
         3. IVC collapsibility (prerenal)
   3. CT
      1. Indicated if hydronephrois found on US in order to define the location of obstruction

Treatment

1. Treat underlying cause
2. IVF (prerenal)
3. Obstruction
   1. Note: Postobstructive diuresis can result in significant volume loss and death
      1. Typically occurs when obstruction has been prolonged / has resulted in renal failure
      2. Admit pts w/ persistent diuresis of >250 mL/h for >2hr
   2. Foley
   3. Suprapubic (if foley fails)
4. Dialysis
   1. Indicated for:
      1. A: Acidosis (severe)
      2. E: Electrolyte abnormality (e.g. uncontrolled hyperkalemia)
      3. I: Intoxicants (Lithium, ASA, methanol, ethylene glycol, theophylline)
      4. O: Overload (volume) w/ persistent hypoxia
      5. U: Uremic pericarditis/encephalopathy/bleeding dyscrasia
      6. Also:
         1. Na <115 or >165 mEq/L
         2. BUN >100

Disposition

Admit

See Also

Hyperkalemia

Source

Tintinalli