Troubles de l’hydratation cellulaire et extracellulaire

Abstract

In the organism, water balance control is aimed at normalizing cellular hydration and sodium balance control at normalizing extracellular volume. Hydration disorders are caused by a disorder in sodium and/or water balance. Water balance control is based on the regulation of body fluid tonicity while the control of sodium balance is based on the regulation of effective arterial volume. Disorders of water balance act on cellular hydration; primary disorders induce a change in tonicity and secondary disorders are induced by a change in tonicity. Primary water balance disorders induce a proportional change in tonicity and natremia and do not affect extracellular and effective arterial volumes in a clinically perceptible manner, and thus induce only a disturbance of cellular hydration. Disorders of sodium balance act on extracellular volume; primary sodium balance disorders induce a change in effective arterial volume and secondary disorders are induced by a change in the effective arterial volume. A sodium balance disorder may be due to an isotonic sodium load or loss; in this case there are no changes in tonicity and natremia and thus no change in cellular hydration. However, sodium balance disorders are often complex and induce a variation in both cellular and extracellular hydration. Physical examination of the patient allows assessing the extracellular volume and the severity of the sodium balance disorder. Natremia that reflects tonicity allows assessing cellular hydration and determining the type of water balance disorder. In the case of natremia disturbance, the estimation of both the tonicity and the extracellular volume allows the determination of the type of water and/or sodium balance disorder which is necessary to prescribe the adequate therapy.