Hyponatremia in the emergency department

Hyponatremia is a clinical manifestation of a wide variety of diseases, some of which have high mortality rates. To assess the prevalence, cause, and prognosis of hyponatremia encountered in the emergency department, we conducted a prospective study at a major hospital in southern Taiwan. We included all adult internal medicine patients treated in the emergency department during a 2-month period. Hyponatremia was defined as a serum sodium level below 134 mEq/L, and cases patients were followed till being discharged. Among the 3,784 patients included, 166 case patients were identified. Most (65%) case patients were hypovolemic, and the overall mortality rate was 17.9%. The mortality rate increased as the sodium level decreased, but was not related to gender, age, cause, or serum potassium level. When 21 hyperglycemic patients whose serum sodium levels went beyond 134 mEq/L after the adjustment for blood sugar levels were excluded, the prevalence of true hyponatremia was 3.83%. The most common underlying diseases were those of the gastrointestinal system. It is concluded that hyponatremia is a common condition encountered in the emergency department. The mortality is correlated with the serum sodium level, and adjustment of the level is required in hyperglycemic patients to make a correct diagnosis. Unlike the cases in some other clinical settings, almost all cases of hyponatremia encountered in the emergency department were not iatrogenic and had recognizable underlying diseases. Therefore, more effort is generally required to identify the cause of hyponatremia cases in the emergency department.