Dehydration versus volume depletion

Abstract

To the Editor: In his recent Nephrology Forum, Dr. Friedman1 makes a number of interesting and cogent observations regarding enteral and parenteral fluid and electrolyte therapy in infants and children. However, I believe discussions of fluid and electrolyte disorders, and their treatments, become much clearer and more easily understood when terms such as "hydration," "dehydration," "volume depletion," and "volume expansion" are used in a more exacting and restricted fashion. As Menge et al2 describe in their article, "hydration" is best used to define the ratio between total body solute and total body water, and is usually reflected by the sodium concentration. In the absence of internal water translocations such as those produced by hyperglycemia, hyponatremia indicates that body water is increased in relation to solute and overhydration exists, while hypernatremia indicates a relative deficit of water, or excess of sodium, and indicates dehydration. In contradistinction, volume depletion defines contraction of the ECF and vascular spaces as may result from blood loss or the loss of salt and volume due to diarrhea, and is appropriately treated by the infusion of volume expanding solutions such as saline or blood.