Dysnatremias in the intensive care unit.

Dysnatremias (hypo- and hypernatremia) are common in patients admitted to the intensive care unit (ICU) with a prevalence approaching 20-30% in some studies. Recent data reveals that both hypo- and hypernatremia present on admission to or developing in the ICU are independent risk factors for poor prognosis. The origin of hypernatremia in the ICU is often iatrogenic and due to inadequate free water replacement of ongoing water losses. The pathogenesis of hyponatremia in the ICU is more complicated but often is related to the combination of dysregulated arginine vasopressin production and concomitant inappropriate hypotonic fluid administration. Both the dysnatremia itself and the treatment of the electrolyte disturbance can be associated with morbidity and mortality making careful monitoring for and treatment of sodium disorders an imperative in the critically ill patient. Formulae have been devised to guide the therapy of severe hypo- and hypernatremia, but these formulae regard the patient as a closed system and do not take into account ongoing fluid losses that can be highly variable. Thus, a cornerstone of proper therapy is serial measurements of serum and urine electrolytes. The appropriate use of hypertonic (3%) saline in the treatment of hyponatremic encephalopathy has also shown to be very effective and the use of this therapy is reviewed here. Vasopressin receptor antagonists have also been shown to be effective at increasing serum sodium levels in patients with either euvolemic or hypervolemic hyponatremia and represent another therapeutic option. Recent data demonstrates that proper correction of hyponatremia is associated with improved short- and long-term outcomes.