How does water restriction affect hyponatremia?

Updated: Aug 16, 2019
  • Author: Christie P Thomas, MBBS, FRCP, FASN, FAHA; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Water excretion is normal in these patients, and water restriction corrects the hyponatremia. In a patient on a normal diet and an average solute (protein and salts) intake, a substantial amount of water must be imbibed for hyponatremia to develop. Consider an individual who has 700 mOsm (primarily consisting of urea, Na+, potassium, and chloride) to excrete per day. Ordinarily, these individuals can vary their urine osmolality between 50 and 1400 mOsm/L and thus can excrete the osmotic load in a minimum of 500 mL and a maximum of 14 L. As long as their fluid intake is between these extremes, they adjust urine osmolality to excrete the load. To become hyponatremic, such an individual must drink more than 14 L a day.

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