Prevalence, risk factors and prognosis of hypernatraemia during hospitalisation in internal medicine

Hypernatraemia in hospitalised patients is less common and less studied than hyponatraemia, although it also seems to be associated with a poor prognosis. The present study evaluates its prevalence, risk factors and prognosis in an internal medicine department.

Full hospital stays over 28 months in a 36-bed internal medicine department were analysed retrospectively. Patients with at least one plasma sodium ≥ 150 mmol/l were compared first with all other patients and then individually with sex- and age-matched normonatraemic controls.

Plasma sodium ≥ 150 mmol÷l was observed during 49÷1945 hospitalisations (2.6%); it was acquired during hospitalisation in 30 cases (61%). Hypernatraemic patients were significantly older with no gender difference. They were comparable with their matched normonatraemic controls regarding the Charlson comorbidity index, although individual comorbidities varied. They were bedridden in 45% vs 15% for controls (p = 0.001). Nearly one-third of hypernatraemic patients had an increased extracellular fluid volume. Hypernatraemia was associated with higher in-hospital mortality (43% vs 2%, p < 0.001) and longer hospitalisation (median 21 vs 10 days, p = 0.004).

Hypernatraemia is more likely to occur in older and dependent patients and is associated with poor prognosis. Unlike classical teaching, it is often associated with increased extracellular fluid volume, even outside intensive care units.