Syndrome of inappropriate antidiuretic hormone secretion (SIADH).

SIADH consists of hyponatremia and hyposmolality, continued urinary loss of sodium, excretion of an inappropriately concentrated urine, and absence of dehydration, usually in the presence of normal renal and adrenal function. The retention of excess water caused by the inappropriate secretion of antidiuretic hormone is central to the development of the syndrome. In pediatrics, SIADH is most commonly seen in patients with meningitis or postoperatively. Fluid restriction is vital in such patients to prevent the development of symptomatic SIADH. Fluid restriction alone will also result in the correction of serum electrolyte composition in patients with SIADH. Hypertonic saline should be used only in severely symptomatic patients.