Aims of the study: Profound hyponatremia (<125 mmol/l) is frequent in the emergency department. Its incidence appears to increase during hot weather. Our objectives were to investigate seasonal variations in the incidence of profound hyponatraemia and identify its risk factors.
Methods: The incidence of profound hyponatremia among patients admitted to the emergency department of a university hospital was compared between summer and winter periods over two successive years. Risk factors for profound hyponatraemia were analysed in a case-control retrospective study. Each adult patient admitted during the study periods with a blood sodium level <125 mmol/l was matched with two patients who had normal blood sodium concentrations.
Results: Of 28 734 analysed patients, 264 cases of profound hyponatraemia (0.92%) were identified. The incidence of profound hyponatraemia was higher in summer than in winter (1.29% vs 0.54%; odds ratio [OR] 2.39, 95% confidence interval [CI] 1.83-3.12). In a multivariate analysis, age (OR 1.02, 95% CI 1.01-1.03), psychiatric disorders (OR 2.69, 95% CI 1.86-3.89), and use of thiazide diuretics (OR 7.79, 95% CI 4.73-12.85) or potassium-sparing diuretics (OR 4.69, 95% CI 2.31-9.52) were associated with increased risk. Mortality was higher in cases than in controls (11.7% vs 6.9%, OR 1.75, 95% CI 1.05-2.92).
Conclusions: The incidence of profound hyponatraemia was higher during the summer than the winter and was associated with excess risk of overall mortality. The use of thiazide and potassium-sparing diuretics was associated with the highest risk of hyponatraemia.