Abstract
Hypernatremic dehydration (HD) is dehydration associated with an elevated serum sodium concentration that is generally defined as a level of 150 mEq/L or higher. Hypernatremia is seen in a variety of clinical states in infancy, but this article is concerned with its occurrence in the clinical setting of diarrheal dehydration in otherwise healthy infants. Such a focus is a practical one, as this is the setting for well over 90% of the cases of HD in infants younger than 2 years of age. Diabetes insipidus, renal disease, mental deficiency, and a number of other conditions may predispose to HD, but although they may help elucidate pathophysiologic findings, they are relatively unimportant contributors to the overall incidence of the disorder. CLINICAL FEATURES The clinical importance of HD stems from its noticeable distinction from nonhypernatremic dehydration (NHD) as a clinical problem. Almost all clinical reports comment on its relatively high mortality (Table