Syndromes of excess antidiuretic hormone release.

Hyponatremia, particularly that due to the syndrome of inappropriate antidiuretic hormone secretion (SIADH), is common in patients seen in the critical care setting. Because of aging-associated changes in the hormonal and renal systems involved in regulation of water and sodium balance, older persons are at higher risk than the young. The high prevalence of disease states and drug use in the elderly can affect water and sodium conservation and further contribute to the risk of hyponatremia in this population. The approach to management is dependent both on the severity of hyponatremia-related symptoms and the rapidity with which hyponatremia has developed. Careful monitoring of serum sodium during treatment is essential to produce prompt resolution of symptoms while avoiding the development of central pontine myelinolysis. Several therapeutic modalities are available for the longterm management of chronic hyponatremia.