Causes and management of hyponatremia

To review clinical information on the incidence and causes of hyponatremia (defined as a serum sodium level <130 mEq/L), the most common electrolyte abnormality seen in general hospital patients, and to discuss the diagnosis and treatment of hyponatremia in relation to these factors.

Primary sources and review articles were identified via MEDLINE (1981-July 2003) for entries on hyponatremia. We limited the search to specific topics including incidence, risk factors, diagnosis, treatment, and clinical disorders and medications associated with hypotonic hyponatremia.

All of the articles identified were evaluated, and relevant and representative information was included in this review.

Hyponatremia can result from several disease states, injury, surgery, physical exercise, or the administration of certain drugs (e.g., antidepressants, antiepileptics) and is associated with advanced age. Drug-induced hyponatremia is often asymptomatic and usually resolves following water restriction and monitoring of medication. Symptoms of hyponatremia are primarily neurologic; the principal danger of hyponatremia relates to effects on central nervous system function due to changes in brain size.

Although hyponatremia can be a serious condition, appropriate measures for the management of at-risk and affected patients will lead to full recovery in most cases.