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

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

1. Prerenal (70%)

Excessive vomiting, diarrhea, urination, hemorrhage, fever, or sweating can reduce circulating volume enough to precipitate ARF. Causes of endothelial leak and third spacing, such as sepsis, pancreatitis, burns, and hepatic failure, can also result in prerenal disease. Progression of heart failure from any cause or overdiuresis of the patient with compensated congestive heart failure can result in ARF. Decreased fluid intake from physical or cognitive disability can result in hypovolemia sufficient to cause ARF, with vague mental status change as the presenting symptom.

1. 1. BUN/Cr ratio > 20
   2. FeNa <1%
   3. FeUN <35%
2. Instrinsic (20%)

The most common cause of intrinsic renal failure is ischemic ARF. Traditionally known as acute tubular necrosis and now called acute kidney injury, it occurs when renal perfusion is decreased so much that the kidney parenchyma suffers ischemic injury. Individuals with chronic hypertension develop altered renal autoregulation, which establishes conditions under which renal ischemia can occur in spite of systemic blood pressures that would be normal for most patients. This condition is called normotensive ischemic ARF

• • • Often be anticipated because of symptoms of their precipitating cause
      • Cardiac arrest
      • Severe sepsis
      • , or other cause of systemic hypotension or microvascular ischemia

1. 1. FeNa <>1%
   2. FeUN >50%
2. Postrenal (10%)

failure should be suspected in patients with appropriate risk factors, including men with known prostatic disease or advanced age and patients with indwelling bladder catheters. 

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

Work-up

1. UA
2. Urine sodium, creatinine, urea (for those on diuretics)
3. Foley

Disposition

Admit

See Also

Hyperkalemia

Source

Tintinalli