Pediatric emergency medicine trisk 2853 2853
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Appropriate evaluation to determine the cause of hyponatremia begins
with a thorough physical examination in order to estimate volume status.
History may reveal obvious sources of sodium loss or raise the concern for
water intoxication. Laboratory tests should include serum electrolytes,
osmolality, and assessment of renal function. Concomitant urine studies
should include osmolality, urine sodium, and urinalysis. In children with
hyponatremia and concentrated urine, the urine sodium may distinguish
between states of decreased effective circulating volume (urine sodium <25
mEq/L) and euvolemic hyponatremia, such as the SIADH (urine sodium
>40 mEq/L).
Clinical manifestations. The symptoms of hyponatremia are primarily
neurologic and due to the development of cerebral edema. The symptoms
mirror the severity of cerebral edema, which in turn is related to the degree
of hyponatremia and the acuity of the process. The mechanisms of cellular
adaptation include movement of intracellular electrolytes to the
extracellular space, which can occur within minutes. Over hours to days,
organic solutes move to the extracellular space. Given the ability for
cerebral adaptation, the degree of cerebral edema and neurologic symptoms
are less severe in chronic hyponatremia. Early neurologic symptoms
include nausea and malaise, and may be seen when the serum sodium
concentration falls below 125 mEq/L. With progressive derangement of
cerebral cell volume, symptoms of headache, altered mental status, lethargy,
ataxia, and psychosis may ensue. Signs of severe cerebral edema include
seizures, coma, and respiratory depression.
