Dehydration and Rehydration

Body fluid balance is controlled by both physiological and behavioral actions. However, when there is lack of fluid availability, exposure to extreme environments, or illness, inability to maintain fluid balance can seriously jeopardize health and the ability to perform. This chapter presents an overview of topics surrounding hydration, dehydration, and rehydration. The terms euhydration, hypohydration, and hyperhydration will be used. Euhydration defines a normal, narrow fluctuation in body water content, whereas the terms hypohydration and hyperhydration define, respectively, a general deficit hypohydration and surfeit hyperhydration in body water content beyond normal. The term dehydration specifically defines the condition of hypertonic hypovolemia brought about by the net loss of hypotonic body fluids. Isotonic or hypotonic hypovolemia, manifest by large losses of solute and water, is defined simply as hypovolemia. Table 70-1 lists the two principal forms of body water deficit and the physiology and particular circumstances associated with each form of deficit.