The patient’s volume status should be first assessed and then the diagnosis made (Table 2). Diagnosing the cause of the hyponatraemia is the cornerstone of therapy. Most oedematous patients have heart failure and there is often confusion as to the role of diuretics in the treatment of heart failure and their contribution to hyponatraemia. Most patients with heart failure have an excess of salt and water and diuretics are indicated. When serum sodium falls to dangerous levels (below 125 mmol/ L), it is useful to restrict water intake to less than one litre
per day. Diuretics should be ceased and reinstated when the serum sodium begins to climb, while maintaining water restriction.