Management of severe hyponatremia: rapid or slow correction?

Case reports and the literature on the treatment of severe hyponatremia were reviewed. It appeared that the conflicting opinions with respect to the rate of correction of severe hyponatremia could be reduced to not differentiating between acute and chronic hyponatremia, to using different criteria for this distinction, and to differences in treatment strategy. After reviewing the available data in the literature, it is suggested that hyponatremia should be classified as acute whenever the rate of decrease of serum sodium exceeds 0.5 mmol/L/hour. If it is unknown at which rate the hyponatremia has developed, it can be assumed to be acute if within a short period of time (two to three days), large quantities of fluid are ingested orally or administered parenterally, especially hypotonic fluids in the presence of impaired water excretion. In other cases, chronic hyponatremia is probable. It is concluded that acute hyponatremia should be treated without delay and rapidly at a rate of at least 1 mmol/L/hour, to prevent severe neurologic damage or death. With respect to chronic hyponatremia, it appeared that severe neurologic complications almost exclusively occurred in patients who were treated with hypertonic or isotonic saline without the addition of furosemide or an osmotic diuretic agent, resulting in a (rapid) correction rate of 0.5 mmol/L/hour or more. In contrast, patients with severe chronic hyponatremia treated with furosemide and isotonic or hypertonic saline almost uniformly did well after rapid correction. Uneventful recovery is also the rule when severe chronic hyponatremia is corrected slowly, at a rate less than 0.5 mmol/L/hour. On pathophysiologic grounds, and bearing in mind that slow correction was used in the majority of reported patients in the literature with severe chronic hyponatremia who recovered without neurologic complications, this treatment modality is preferable. Whenever the available data do not permit a differentiation between acute or chronic hyponatremia, rapid correction has to be pursued by means of administration of hypertonic or isotonic saline together with furosemide.