Autoren

Abstract

: Hyponatraemia is the most frequent electrolyte disorder in hospitalised patients and represents an important clinical and social prob- lem. Hyponatraemia, particularly when acute and severe, can be a life-threatening condition and has been associated with an increased risk of death. However, recent evidence shows that also mild and chronic hyponatraemia can negatively affect health status by causing for in- stance gait disturbances, attention deficits, falls and fracture occurrence as well as bone loss. Many pathological conditions may be associated with hyponatraemia. It may be divided into hyper- tonic, isotonic, or hypotonic forms, based on osmolality measurement. Attention should always be 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 appro- priate treatment. Isotonic or hypertonic saline solutions are used in hypovolaemic and normo- volaemic/hypervolaemic hyponatraemia, respec-tively. Fluid restriction is generally used in asymp- tomatic normovolaemic/hypervolaemic hyponatraemia although its efficacy is rather poor. Vaso- pressin receptor antagonists, also known as vaptans, represent a new treatment option for the correction of hyponatraemia. Vaptans pre-vent free-water re-absorption and increase urine volume by blocking the binding of vasopressin to V 2 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 hypervolaemic hyponatraemia. While tolvaptan and conivaptan have been approved in the US for the treatment of both normovolaemic and hypervolaemic hyponatrae- mia, in Europe only tolvaptan was approved in 2009 for the treatment of adult patients with hy- ponatraemia secondary to the syndrome of inappropriate ADH secretion.