Epidemiology and characteristics of hyponatremia in the emergency department

Background: Hyponatremia is the most common electrolyte abnormality and it is associated with increased morbidity and mortality. The aim of the study was to investigate the underlying causes and management of hyponatremia in an unselected population presenting with hyponatremia to the emergency department.

Methods: A descriptive, retrospective hospital record study was performed. A database search was conducted for all patients presenting to the emergency departments in Lund and Malmo and patients with a P-Na-value<135mmol/L were identified. Patients were divided into four groups based on the severity of hyponatremia (Group 1: P-Na<120mM, Group 2: Na 120-124mM, Group 3: Na 125-129mM, Group 4: Na 130-134mM) and 100 patients from each group were included. Groups 2-4 were matched to Group 1 for age, gender and month for ER visit.

Results: The prevalence of hyponatremia (P-Na<135mmol/L) was 3% in the entire emergency population. A single underlying cause was identified in 45% of patients in Group 1. The leading aetiologies were thiazide diuretics (17%), SIADH (17%) and other diuretics (14%). The likelihood of being on thiazide diuretics increased with hyponatremia severity (p<0.0001) and patients in Group 1 were 3.6 times (CI95%:1.9-6.8) more likely to be on thiazide diuretics compared to Group 4. The in-hospital mortality ranged between 2 and 7% between the groups (NS). One patient developed osmotic demyelinisation syndrome but survived. Only 31% of patients in Group 1 were evaluated with a basic laboratory investigation.

Conclusions: Thiazide diuretics and SIADH were dominating underlying causes of hyponatremia, however, the frequency of adequate diagnostic testing was low. The majority of patients were treated with sodium chloride infusion.