ABSTRACT
Hyponatremia is a frequent medical problem and can produce serious neurological manifestations and death. Salt-losing nephritis is another cause of hypovolemic hyponatremia. The physiological response to an increase in water intake is a decrease in plasma Na+ and osmolality which suppresses antidiuretic hormone (ADH) secretion and thirst, leading to the formation of a dilute urine and excretion of the excess water. The most common clinical setting leading to such abnormalities is a decrease in plasma volume, i.e., dehydration, hemorrhage. A variant of this group is the hyponatremia of the postoperative patients in which seemingly inappropriate ADH secretion may persist for several days. A more common factor in the generation of hyponatremia is the loss of Na+ via the kidney or the gastrointestinal tract. The principal extracellular osmol is Na+ and the principal intracellular osmol is potassium. The common denominator of all these edematous states associated with hypervolemic hyponatremia is the presence of low urinary Na+, usually less than 20 mEq/l.
