Invest Med: February 1997 / Vol 20, issue 1/Effective water clearance and tonicity balance: the excretion of water revisited

The effect of potassium excretion on body tonicity

Fig. 7: Tonicity balance. A particular amount of water is needed to absorb sodium and potassium intakes without a change in body tonicity. Total intakes are usually hypotonic. Total water intake can be thought of as isotonic sodium plus isotonic potassium plus electrolyte-free water (EFW). The EWC represents the difference between the total urinary water excreted and the water required for the isotonic excretion of sodium and potassium. At physiological equilibrium, EWC represents the excretion of the electrolyte-free water intake. Insensible losses (cutaneous and pulmonary) are assumed to be equal to metabolic water and the water content in food.[32]

[ Return to text ]