Nephrology

Acute Kidney Injury (Acute Renal Failure, Acute Renal Injury) in Neonates

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Oliguric: Anuria or oliguria (<0.5 mL/kg/h in children; <1 mL/kg/h in infants) with an associated increase in serum creatinine
Non-oliguric: Increased serum creatinine with normal or increased urine output (usually seen with nephrotoxic medications)

It should be understood that the following classifications of etiology are somewhat artificial because there can be a great deal of overlap (eg, sepsis can cause both prerenal and intrinsic renal disease; obstructive uropathy, if severe enough, can also cause intrinsic renal disease).

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Prerenal	Intrinsic Renal	Postrenal
Reduced intravascular volume Hemorrhage Dehydration CHD Polycythemia Indomethacin use Adrenergic drugs Birth asphyxia Sepsis	ATN Congenital abnormalities Renal agenesis Renal dysplasia Polycystic disease Thromboembolic disease Nephrotoxins Medications Radiographic contrast Maternal ACE inhibitor or indomethacin use	Urethral obstruction (eg, posterior urethral valves) Ureterocele Ureteropelvic obstruction Ureterovesicular obstruction Extrinsic compression of ureters Neurogenic bladder Megacystis or megaureter syndrome

Perform history to elicit predisposing factors listed above and physical exam to palpate for abdominal masses and other congenital urogenital abnormalities.
Bladder catheterization to confirm inadequate urine output and r/o obstruction.
If prerenal failure is suspected on the basis of history or physical exam and there is no evidence of heart failure or volume overload, a fluid challenge of 10–20 mL/kg of normal saline can be administered over 30–60 min. Lack of response suggests intrinsic renal or postrenal failure.
Laboratory studies
- Serum electrolytes, BUN, creatinine
- CBC, platelet count
- Urinalysis with microscopic analysis
- Urinary sodium and creatinine with simultaneous serum sodium and creatinine to calculate FENa (these studies are not valid if diuretic is used)