Symptomatic hyponatremia in rats: effect of treatment on mortality and brain lesions.

Hyponatremia was induced in rats over 3 days with dextrose in water and vasopressin. Eighty-five percent of the rats survived for 5 mo after spontaneous correction of mild hyponatremia. However, spontaneous correction of symptomatic hyponatremia (serum sodium less than 120 meq/l) resulted in 32% survival. Rapid correction of symptomatic hyponatremia by hypertonic saline with an absolute change in serum sodium of greater than 14 and less than 25 meq/l in the first 24 h allowed 100% of the rats to survive for 5 mo without brain lesions. On the other hand, correction of symptomatic hyponatremia with an absolute change in serum sodium of greater than 25 meq/l in the first 24 h resulted in 12% survival and development of brain lesions. We conclude that rapid correction of symptomatic hyponatremia improves survival and is safe if the absolute change in serum sodium is between 14 and 25 meq/l in the first 24 h. Increased mortality and brain lesions are associated with an absolute change in serum sodium of greater than 25 meq/l in the first 24 h.