Sodium is the dominant cation in the ECF and is necessary for the maintenance of intra vascular volume. Hypernatremia is defined as a serum sodium concentration of > 145 meq/l. The 2 mechanisms to protect against developing hypernatremia are the ability to produce concentrated urine by the action of ADH and a powerful thirst response.
The basic mechanisms of hypernatremia are water deficit (decreased intake or increased excretion) and solute excess. Hypernatremia is usually associated with hypovolemia. This can occur in conditions which cause combined water and solute loss ( water loss in excess to sodium loss) or free water loss. Combined loss can be: extra-renal- gastrointestinal, burns and renal- osmotic diuretics, chronic kidney disease, post-obstructive diuresis. Free water loss is seen in central/ nephrogenic diabetes insipidus and can also be seen in conditions with increased…show more content… Children present with irritability and agitation, which can progress to lethargy, somnolence and coma. The skin can feel doughy or velvety due to intracellular water loss. It is important to remember that the degree of dehydration can be underestimated in children with hypernatremia due to shift of water from intracellular space to the extravascular space. Complications include subarachanoid or subdural hemorrhage due to rupture of bridging veins and dural sinus thrombosis. Hypernatremia is associated with a mortality rate as high as 15-20%.
The etiology of hypernatremia is usually evident based on the history and physical exam. Urine volume, concentrating ability and osmolality can help differentiate renal and extra-renal causes. In diabetes insipidus, the urine is inappropriately dilute with normal urine volume and urine osmolality less than the serum osmolality. In extra renal causes, the body tries to conserve fluids with appropriately low urine volume, high specific gravity and urine osmolality > serum
