Is the sodium level per se related to mortality in hospitalized patients with severe hyponatremia?

Introduction: Severe hyponatremia is a serious medical condition that is associated with morbidity and mortality. Controversy still exists regarding the prevalence, cause and mortality of hyponatremia. Patients and methods: Of the hyponatremic patients, we studied 116 severe hyponatremic patients. Severe hyponatremia was defined as a serum sodium concentration equal to or less than 120 mmol/l at least twice. Results: The mean age of the patients was 67.3 ± 14.9 years. The mean sodium level at the time of diagnosis was 114.9 ± 5.2 mmol/l. Normal extracelluar fluid volume (ECFV) was reported in 44 patients (37.9%). 24 (20.7%) of 44 patients were diagnosed with the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Excess ECFV and depleted ECFV were reported in 37 (31.9%) and 18 patients (15.5%), respectively. In 17 patients (14.7%), the exact causes could not be determined due to incomplete laboratory studies. On the univariate analysis, age (p = 0.030), the Charlson's risk index (p = 0.000) and the correction rate (p = 0.000) were associated with the 1-year survival. The time of onset (p = 0.051) and the initial serum sodium level (p = 0.986) were not associated with the 1-year survival. On the multivariate analysis, the Charlson's risk index (p = 0.003) and the correction rate (p = 0.033) were independently associated with 1-year survival. Conclusion: This study showed that the sodium level per se is not related to mortality, but a higher Charlson's risk index and a slow rate of correcting the sodium are related with mortality. For improving the survival of patients with severe hyponatremia, we should pay more attention to correct the underlying comorbidity.