Hyponatremia in critical care patients: frequency, outcome, characteristics, and treatment with the vasopressin V2-receptor antagonist tolvaptan

Hyponatremia is a common problem in critical care patients and is associated with increased duration of hospital stay and increased morbidity and mortality. The prevalence of hyponatremia in the intensive care unit (ICU) has been reported to be as high as 30% to 40%. Recent studies have found hyponatremia at ICU admission in up to 14% of patients in unselected groups; patients with hyponatremia were at elevated risk of mortality vs normonatremic patients. Most cases in the ICU are euvolemic or hypervolemic hyponatremia, with the syndrome of inappropriate secretion of antidiuretic hormone being a predominant cause. The oral selective vasopressin V2-receptor antagonist tolvaptan is effective in treating euvolemic and hypervolemic hyponatremia and may be useful in the management of hyponatremic critical care patients. Tolvaptan treatment increases serum sodium via aquaresis-ie, increased electrolyte-free water excretion-and thus presents an advantage in patients with syndrome of inappropriate secretion of antidiuretic hormone or other euvolemic states or hypervolemic hyponatremia. This article provides a review of hyponatremia and of the potential use of tolvaptan in critical care settings. Case reports provide examples of tolvaptan use in correcting severe hyponatremia and associated abnormal mental status and in resolving hyponatremia prior to surgery.