Diagnosis and management of hyponatraemia in the older patient.

Hyponatraemia (serum sodium concentration below 135 mmol/L) is the most common electrolyte disturbance and occurs commonly in older people. The causes can be complex to diagnose and treat and many published guidelines do not focus on the issues in an older patient group. Here, we are principally concerned with diagnosis and management of euvolaemic and hypervolaemic hyponatraemia in hospitalised patients over 70 years old. We also aim to increase awareness of hyponatraemia in residential aged care facilities and the community. Hyponatraemia can have many causes; in older people, chronic hyponatraemia can often be the result of medications used to treat chronic disease, particularly thiazide or thiazide-like drugs (such as indapamide) or drugs acting on the central nervous system. Where a reversible trigger (such as drug-induced hyponatraemia) can be identified, hyponatraemia may be treated relatively simply. Chronic hyponatraemia due to an irreversible cause will require ongoing treatment. Fluid restriction can be an effective therapy in dilutional hyponatraemia, although poor compliance and the burdensome nature of the restrictions are important considerations. Tolvaptan is an oral vasopressin receptor antagonist that can increase serum sodium concentrations by increasing electrolyte-free water excretion. Tolvaptan use is supported by clinical trial evidence in patients with hypervolaemic or euvolaemic hyponatraemia below 125 mmol/L. Clinical trial evidence also supports its use after a trial of fluid restriction in patients with symptomatic hyponatraemia above 125 mmol/L. The use of tolvaptan is affected by regulatory restriction of chronic therapy due to safety concern and the non-subsidised cost of treatment.