Hyponatraemia

Hyponatraemia is the most frequent electrolyte disorder in hospitalised patients and represents an important clinical and social problem. Hyponatraemia, particularly when acute and severe, can be a life-threatening condition and it has been associated with an increased risk of death. However, recent evidence showed that also mild and chronic hyponatraemia can negatively affect the health status, by causing for instance gait disturbances, attention deficits, falls and fracture occurrence, and bone loss. Many pathological conditions may be associated with hyponatraemia. Hyponatraemia may be distinguished into hypertonic, isotonic or hypotonic forms, based on osmolality measurement. Attention should be always dedicated to the assessment of fluid volume, which is of pivotal importance in the diagnostic work-up, together with laboratory data. A correct diagnosis is mandatory, in order to initiate the appropriate treatment. Isotonic or hypertonic saline solutions are used in hypovolaemic and normovolaemic/hypervolaemic hyponatraemia, respectively. Fluid restriction is generally used in asymptomatic normovolaemic/hypervolaemic hyponatraemia, although its efficacy is rather poor. Vasopressin receptor antagonists, also known as vaptans, represent a new treatment option for the correction of hyponatraemia. Vaptans prevent free water reabsorption and increase urine volume by blocking the binding of vasopressin to V2 receptors expressed in renal collecting duct cells. Therefore, they should not be used in hypovolaemic hyponatraemia. Vaptans have been shown to effectively correct serum sodium in normovolaemic and hypervolemic hyponatraemia. Whereas in the U.S. tolvaptan and conivaptan have been approved for the treatment of both normovolaemic and hypervolemic hyponatraemia, in Europe only tolvaptan has been approved in 2009 for the treatment of adult patients with hyponatraemia secondary to the syndrome of inappropriate ADH secretion.