Syndrome of Inappropriate Secretion of Antidiuretic Hormone and Hyponatremia

Knowledge Gaps

Hyponatremia is a common electrolyte disturbance in hospitalized children that is often related to increased action of antidiuretic hormone; practitioners should be familiar with clinical characteristics of children at risk for syndrome of inappropriate secretion of antidiuretic hormone (SIADH), as well as approach to diagnosis. By knowing how to identify children with SIADH or those at risk for developing hyponatremia, modifications can be made in the prescription of intravenous fluid to avoid the development of hyponatremia or to treat hyponatremia.

Objectives

After completing this article, readers should be able to:

1. Review the mechanisms that control water excretion and maintain normal plasma osmolality.

2. Describe the major causes of hyponatremia in children.

3. Apply clinical tests to identify children with hyponatremia to determine the underlying condition.

4. Identify children at risk for syndrome of inappropriate secretion of antidiuretic hormone (SIADH) and modify fluid management to avoid development of hyponatremia.

5. Describe the approach to treatment of hyponatremia and, in particular, hyponatremia secondary to SIADH.

The discussion of the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) begins with review of the causes of hyponatremia, since SIADH is a major cause of hyponatremia and hyponatremia is usually the abnormal finding that leads to its diagnosis. SIADH is defined as the presence of hypo-osmolality when urine is inappropriately concentrated (osmolality is inappropriately high) and there is no evidence of renal salt wasting or hypovolemia in an individual with normal renal, adrenal, thyroid, cardiac, and liver functions (Table 1). (1) It is reversible with water restriction. In SIADH, antidiuretic hormone (ADH) activity is considered “inappropriate,” since there is no identifiable osmotic or hemodynamic stimulus for its action. Factors that control plasma osmolality …