The use of an algorithm to aid diagnosis and treatment of patients with hyponatraemia secondary to SIADH
Joseph Verbalis1 & Ewout Hoorn2
Hyponatraemia is the most common electrolyte disorder encountered in clinical practice, occurring in 15% to 30% of both acutely and chronically hospitalised patients. Hyponatraemia is important clinically because: 1) acute severe hyponatraemia can cause substantial morbidity and mortality; 2) mortality is higher in hyponatraemic patients with a wide range of underlying diseases; 3) overly rapid correction of chronic hyponatraemia can cause osmotic demyelination; 4) even mild asymptomatic hyponatraemia can be accompanied by neurocognitive disturbances, gait instability, and increased falls; 5) chronic hyponatraemia causes bone loss in animals and is associated with a greater risk of osteoporosis in humans. Optimal treatment strategies have not been well defined, in part because of marked differences in symptomatology and clinical outcomes based on the acuteness or chronicity of hyponatraemia. As a result, hyponatraemia is frequently mismanaged, and incorrect management has been associated with increased mortality. Tolvaptan, a selective vasopressin V2 receptor antagonist that reliably reduces urine osmolality, increases electrolyte-free water excretion (aquaresis), and safely raises the serum sodium concentration, was approved by the EMEA for the treatment of hyponatraemia caused by the syndrome of inappropriate antidiuretic hormone secretion (SIADH) in 2009. A critical review of the clinical data related to correction of hyponatraemia using various therapeutic modalities has prompted the development of an algorithm for selecting the appropriate therapy for hyponatraemia patients based primarily on the presenting symptoms rather than on the level of serum sodium. Application of this algorithm to clinical practice should aid physicians both with making a correct diagnosis of SIADH, and with selecting the most appropriate initial treatment for hyponatraemia caused by SIADH. Future studies will enable assessment of the effects of using the algorithm to improve clinical outcomes across a variety of different disease states by virtue of reducing morbidity and mortality associated with hyponatraemia in patients with SIADH.