Kidney Injury, Acute

Key Features

Essentials of Diagnosis

• 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

General Considerations

• 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

Clinical Findings

• 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

Diagnosis

• 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

Treatment

Nonpharmacologic

• 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

Pharmacologic

• Furosemide (1–5 mg/kg, per dose, intravenously, maximum ...