Frequency of hyponatremia and nonosmolar vasopressin release in the acquired immunodeficiency syndrome.

The frequency and pathophysiology of hyponatremia were studied in the acquired immunodeficiency syndrome. Of 71 hospitalized patients surveyed retrospectively, hyponatremia was observed in 37 (52%). Of 48 patients studied prospectively, 27 (56%) were hyponatremic. In 16 hyponatremic patients, volume status; serum and urine osmolalities; renal, adrenal, and thyroid function; and plasma vasopressin levels were assessed. Urine osmolalities were inappropriately elevated (mean, 377 mmol/kg of water) relative to serum osmolalities (mean, 268 mmol/kg of water). Four patients had moderate renal insufficiency. Plasma vasopressin levels were elevated in 15 patients, with the highest levels seen in patients who died (median, 7.08 pmol/L). Hyponatremia of multiple etiologies occurred in a majority of inpatients with the acquired immunodeficiency syndrome, often following the administration of hypotonic fluids, and was associated with a 30% (8/27) short-term mortality.