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

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.

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.

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.

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.