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Key Features

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Essentials of Diagnosis
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  • Sudden inability to excrete urine of sufficient quantity or composition to maintain body fluid homeostasis

  • Explanations include quickly reversible problems such as dehydration or urinary tract obstruction, as well as new-onset renal disease (eg, acute glomerulonephritis), drug-related toxic nephropathies, or renal ischemia

  • Renal ischemia is suspected when significant hemodynamic instability or other circumstances result in decreased renal perfusion

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General Considerations
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  • Classifying acute kidney injury as prerenal, renal, and postrenal is helpful in determining whether an immediately reversible cause is present

  • Prerenal causes

    • Compromised renal perfusion is most common cause of acute decreased renal function in children

    • Usually secondary to true intravascular volume depletion or a decrease in effective circulating volume, as may be seen in cardiac failure, cirrhosis, or nephrotic syndrome

  • Renal causes

    • Include acute glomerulonephritides, hemolytic-uremic syndrome, acute interstitial nephritis, and nephrotoxic injury

    • Diagnosis of acute tubular necrosis is reserved for those cases in which renal ischemic insult is believed to be the likely cause; should be considered when

      • Correction of prerenal or postrenal problems does not improve renal function

      • There is no evidence of de novo renal disease

  • Postrenal causes

    • Usually found in newborns with urologic anatomic abnormalities

    • Accompanied by varying degrees of kidney disease

    • Possibility of acute urinary tract obstruction in acute kidney injury, especially in the setting of anuria of acute onset, should be considered

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Clinical Findings

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  • Oliguria with subsequent variable rise in serum creatinine and BUN is hallmark of acute kidney injury

  • Entities that can be quickly addressed and corrected, for example, intravascular volume depletion or urinary tract obstruction, should be considered first

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Diagnosis

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  • Urine osmolality and sodium concentration should be interpreted in light of the child's age-related capacity for these parameters (eg, newborns have limited urinary concentrating capacity and excrete more sodium than older children)

  • Urine osmolality

    • Prerenal failure: > 500

    • Acute tubular necrosis: < 350

  • Urine-specific gravity

    • Prerenal failure: > 1.020

    • Acute tubular necrosis: ~ 1.010

  • Urine sodium

    • Prerenal failure: < 20 mEq/L

    • Acute tubular necrosis: > 40 mEq/L

  • Fractional excretion of sodium

    • Prerenal failure: < 1%

    • Acute tubular necrosis: > 3%

  • Ratio of urine creatinine to plasma creatinine

    • Prerenal failure: > 40:1

    • Acute tubular necrosis: < 20:1

  • Ratio of blood urea nitrogen (BUN) to plasma creatinine

    • Prerenal failure: > 20:1

    • Acute tubular necrosis: < 10–15

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Treatment

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Nonpharmacologic
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  • Prerenal and postrenal factors should be excluded and rectified

  • Normal circulating volume should be maintained and normal blood pressure and cardiac performance established with appropriate fluid or vasopressor support

  • Placement of a Foley bladder catheter can aid in timely measurement of output

  • Measurement of central venous pressure may be indicated

  • Routine assessment of weight is helpful to assess fluid balance

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Pharmacologic
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  • Furosemide (1–5 mg/kg, per dose, intravenously, maximum of 200 mg every 6 hours)

    • Effective dose depends on the amount of functional compromise

      • If < 50% function, initiate attempt at diuresis with maximum dose

      • If a response ...

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