Section 25. Disorders of the Kidney and Urinary Tract >
Part 2. Abnormalities of the Kidney and Urinary Tract >
Chapter 468. Kidney or Urinary Tract DisordersJohn W. Foreman
Topics Discussed: oliguria; renal disease; urologic diseases; urology and nephrology.
Sections: Enuresis, References.
Excerpt:"Oliguria denotes very low urine flow, and anuria means
virtually no urine flow. Oliguria is common in children and is usually
related to volume contraction rather than to a renal abnormality.
Oliguria is defined as a urine flow rate less than 0.5 ml/kg
per hour in children or less than 1 ml/kg
per hour in infants. Eight percent of healthy newborns do not void
in the first 24 hours of life, but 98% do so by 48 hours.10 The
average urine output in the first 2 days of life is 20 ml/day
and rises to 200 ml by the end of the second week of life. Most
children with oliguria do not have renal disease, but the low urine
flow is a renal response to dehydration from other nonrenal sources
of volume and electrolyte loss such as diarrhea or sweat (especially
in cystic fibrosis) and increased insensible losses. A careful history
and physical examination can usually identify the presence of dehydration
as the cause for the oliguria. Laboratory clues include an elevated blood
urea nitrogen compared to serum creatinine and concentrated urine.
With severe dehydration, there may also be a small amount of blood
and protein in the urine along with granular, but not cellular,
casts. With the development of renal parenchymal injury from dehydration
and hypotension (acute tubular necrosis), the kidney often loses
the ability to concentrate and retain sodium, so the urine specific gravity
is fixed at 1.010 to 1.012, the urine/serum creatinine
ratio is less than 10, and the fraction excretion of sodium is greater..."
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