Pediatric emergency medicine trisk 2856 2856
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due to isolated water deficit is termed dehydration. If both salt and water
deficits are present, this condition is termed hypovolemia.
Diarrhea is a common cause of hypernatremia in the acute care setting.
Although the degree of sodium deficit may vary, generally children who
present for care have true hypovolemia. Breastfed infants may be at
increased risk of hypernatremia due to inadequate intake. Hypernatremia
due to salt excess is rare but it can occur with the improper mixing of infant
formulas or iatrogenic administration of a salt load. The latter can result
after sodium bicarbonate infusion during cardiopulmonary resuscitation or
during therapy of refractory metabolic acidosis. Hypernatremia secondary
to nearly pure water loss may develop if replacement of insensible water
loss from the skin and respiratory tract is inadequate. Central diabetes
insipidus is due to insufficient release of ADH from the hypothalamus, and
nephrogenic diabetes insipidus is due to a renal resistance to the effect of
ADH. Most children affected with these disorders have normal thirst and
free access to water and are able to maintain acceptable water balance.
However, infants who do not have free access to water and children with
intercurrent illness precluding adequate intake of free water are at risk for
the development of hypernatremic dehydration.
The cause of hypernatremia is usually evident from the presenting
history. Feeding history in breastfed infants may reveal inadequate intake.
In formula-fed infants, an accurate account of formula preparation should
be pursued to evaluate for inappropriate mixing, which would result in
increased renal osmotic load. Inquiries of urine volume should also be
made, as the production of significant urine in a child who presents with
apparent hypernatremic dehydration suggests diabetes insipidus. The
physical examination should assess weight, perfusion, and mental status.
During hypernatremic hypovolemia, water moves from the intracellular to
the extracellular space. Given the relative preservation of the extracellular
volume, the objective signs of volume depletion may develop later in the
patient’s course of illness than with other types of dehydration. Laboratory
studies should include serum electrolytes, serum osmolality, BUN, and
renal serum creatinine. If the underlying diagnosis remains in question,
urine studies may be informative. Urine osmolality should be compared to
serum osmolality and would be elevated if renal concentrating mechanisms
are intact. If the urine osmolality is inappropriately low when compared to
