June 1st 2003ABSTRACT: To identify the cause of hyponatremia, determine the patient's volume status and measure urinary sodium and osmolality; also ask about diuretic use. Hypovolemic hyponatremia is associated with vomiting, diarrhea, laxative abuse, renal disease, nasogastric suction, salt-wasting nephropathy, Addison disease, solute diuresis, and diuretic use. Euvolemic hyponatremia with a normal urinary sodium level can result from glucocorticoid deficiency, hypothyroidism, certain drugs, and the syndrome of inappropriate antidiuretic hormone secretion. Euvolemic hyponatremia with low urinary osmolality can be caused by psychogenic polydipsia, "tea and toast" syndrome, or beer potomania. Hypervolemic hyponatremia is associated with congestive heart failure, nephrotic syndrome, and cirrhosis. To reduce the risk of serious neurologic sequelae, avoid both undertreatment and overtreatment of hyponatremia. In chronic hyponatremia, total correction should not exceed 8 to 12 mEq/L/24 h (a maximum correction rate of 0.5 mEq/L/h). In acute hyponatremia, rates of correction up to approximately 1 mEq/L/h are acceptable. Avoid overcorrection of serum sodium concentration (ie, to a level higher than 140 to 145 mEq/L).
