Hyponatremia in Children
Robert C. Kelsch MD1
William J. Oliver MD1
1 Professor of Pediatrics, University of Michigan Medical Center, Ann Arbor
Hyponatremia is usually recognized following an electrolyte screen since it is not symptomatic, except in its severest degrees. The pathophysiologic implications of hyponatremia and its therapy are quite varied. The purpose of this review is to present a diagnostic plan which in most instances will resolve the therapeutic dilemma. This approach is a minor modification of that developed by Schrier and Berl1 for evaluating hyposmolar states.
GENERAL PRINCIPLES
The occurrence of hyponatremia indicates a failure of those receptor and effector mechanisms designed to assure that the quantity of water in the body will closely relate to the amount of solute in the major bodywater spaces. The principal sensors are designed to recognize osmolar changes, not changes in sodium concentration. Nevertheless, measurement of serum sodium concentration is the most readily available tool for estimation of disturbances in osmolality. Fanestil2 has recorded 14 formulae designed to estimate osmolality from serum sodium concentration or sodium, glucose, and urea concentrations. The simplest of these formulae, osmolality = 2 x Na+ + 10, is satisfactory in the vast majority of clinical circumstances occurring in pediatrics. Diabetes mellitus is the only relatively common state that requires the use of alternate formulations to correct for hyperglycemia. The contribution to serum osmolality by glucose can be approximated by adding to the above formula 1 mOsm for each 18 mg/100 ml of blood glucose above the level of 100 mg/100 ml.
