Pediatric emergency medicine trisk 1896 1896
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Most patients with SIADH are asymptomatic until the plasma [Na+ ] falls to less than 125
mEq/L. Associated with the low serum sodium, children may be weak, have altered mental
status, or have seizures. Patients may have mild signs of hypervolemia.
Triage
Assess mental status and neurologic examination, treat for precipitating conditions.
Initial Assessment/H&P
Symptoms associated with hyponatremia range from anorexia, headache, nausea, vomiting,
irritability, disorientation, and weakness to seizures and coma, leading potentially to death.
Absence of edema and dehydration are usual and significant clinical findings.
Management/Diagnostic Testing
Laboratory investigations for diagnostic purposes must include concomitant serum and urine
samples ( Table 89.9 ).
Hyponatremia, hypoosmolality (serum), and low blood urea nitrogen will be present. In
contrast, the urinary osmolality and [Na+ ] are inappropriately elevated for the hypotonicity of
the serum. Due to the euvolemic or hypervolemic state, aldosterone is suppressed and urine
potassium will be low. Radioimmunoassay for ADH is available and has been helpful in
defining this syndrome; however, the results of this test are unlikely to be available on an
emergency basis.
The underlying cause of the syndrome should be investigated according to the physician’s
clinical judgment. Severe hyperlipidemia may falsely lower laboratory measurement of [Na+ ],
leading to a factitious hyponatremia. Hyperglycemia and hypoproteinemia, however, lead to
true hyponatremia. Renal salt wasting secondary to adrenal insufficiency should be
accompanied by hyperkalemia and dehydration. Cerebral salt wasting may have laboratory
parameters similar to SIADH but is characterized by hypovolemia and a high urine output as
long as renal perfusion remains intact. The urine osmolality in water intoxication states is
usually low compared with that found in SIADH.
Severely Symptomatic Children
Patients with a persistent seizure attributable to severe hyponatremia and those who are
severely lethargic or comatose need urgent treatment with hypertonic (3%) saline by infusing
small amounts of 3% saline in the range of 3 mL/kg every 10 to 20 minutes until symptoms
remit. One milliliter per kilogram of 3% saline should raise the serum [Na+ ] by
approximately 1 mEq/L. Since the administration of 3% is high-risk therapy, it should only
be given in the quantity needed to extinguish the adverse clinical finding (e.g., altered mental
status, seizure). A single dose of furosemide (1 mg/kg) also can be administered
intravenously. Close monitoring of fluid balance, plasma and urinary sodium, potassium, and
osmolality is essential.
Seizures should be treated concomitantly with a standard emergency anticonvulsant protocol
(see Chapters 72 Seizures and 97 Neurologic Emergencies ). Of note, phenytoin (Dilantin®)
or fosphenytoin (Cerebyx®) intravenously (5 to 10 mg/kg) inhibits ADH release and may be
helpful in the patient with seizures secondary to CNS causes of SIADH.
