A clinical approach to common electrolyte problems. 1. Hyponatremia.

The clinical approach to hyponatremia described in this paper involves identification of the hyponatremia as iso-osmolar (factitious), hyperosmolar (mediated by osmotically induced flux of water from cells) or hypo-osmolar. Hypo-osmolar hyponatremia results from decreased renal excretion of dilute urine. This may be caused by renal failure through decreased delivery of filtrate to or function of the ascending limb of the loop of Henle, where dilute urine is made, or through increased water reabsorption in the collecting duct, either independent of antidiuretic hormone or related to a physiologic, drug-induced or pathologic increase in the bioactivity of antidiuretic hormone. The treatment of hyponatremia must be individualized.