Increased mortality risk associated with serum sodium variations and borderline hypo- and hypernatremia in hospitalized adults

Abstract

Background This study aimed to evaluate short-term and long-term mortalities in a cohort of unselected hospitalized patients with serum sodium concentration ([Na+]) variations within and outside of reference range. Methods All adult patients admitted to the Mayo Clinic, Rochester, MN, USA from January 2011 to December 2013 (n = 147358) were retrospectively screened. Unique patients admitted during the study period were examined. The main exposure was serum [Na+] variation. Outcome measures were hospital and 1-year all-cause mortalities. Results A total of 60944 patients, mean age 63 ± 17 years, were studied. On admission, 17% (n = 10066) and 1.4% (n = 852) had hypo- and hypernatremia, respectively. During the hospital stay, 11044 and 4128 developed hypo- and hypernatremia, respectively, accounting for 52.3 and 82.9% of the total hypo- and hypernatremic patients. Serum [Na+] variations of ≥6 mEq/L occurred in 40.6% (n = 24 740) of the 60 944 patients and were significantly associated with hospital and 1-year mortalities after adjusting potential confounders (including demographics, comorbidities, estimated glomerular filtration rate, admission serum [Na+], number of [Na+] measurements and length of hospital stay). Adjusted odds ratios for hospital and 1-year mortalities increased with increasing [Na+] variations in a dose-dependent manner, from 1.47 to 5.48 (all 95% confidence intervals >1.0). Moreover, in fully adjusted models, [Na+] variations (≥6 mEq/L) within the reference range (135–145 mEq/L) or borderline hypo- or hypernatremia (133–137 and 143–147 mEq/L, respectively) compared with 138–142 mEq/L were associated with increased hospital and 1-year mortalities. Conclusion In hospitalized adults, [Na+] fluctuation (≥6 mEq/L) irrespective of admission [Na+] and borderline hypo- or hypernatremia are independent predictors of progressively increasing short- and long-term mortality burdens.

The prognostic importance of serum sodium levels at hospital discharge and one‐year mortality among hospitalized patients

“…We tested the difference in clinical characteristics among discharge sodium groups using ANOVA for continuous variables and the Chi-square test for categorical variables. We categorized discharge serum sodium into five groups; ≤132, 133-137, 138-142, 143-147, and ≥148 mEq/L, as previously described in literature, [14][15][16] What's known?…”

“…The association between dysnatremia and increased short and long-term mortality was previously reported by several investigators. 5,9,14,15,17 Both decrease and increase in discharge serum sodium from the optimal range were associated with increased 1-year mortality, as shown in the U-shape mortality curve. We observed that any degree of deviation of discharge serum sodium from the optimal range was associated with increased 1-year mortality, even if the deviation was minimal.…”

“…We selected discharge serum sodium of 138-142 mEq/L as the reference group for outcome comparison because this range is associated with the most favorable survival in the literature. [14][15][16] We measured patient survival from hospital discharge and followed until death or one year after hospital discharge. Patients who were lost to follow-up or whose vital status was not known were censored at the date of their last inpatient/outpatient follow-up visit.…”

“…The previous studies consistently reported the impact of mild dysnatremia on mortality. 5,15 Therefore, targeting serum sodium to the optimal range before hospital discharge may potentially lead to more favorable long-term survival.…”

“…[5][6][7][8]14 These studies observed the U-shape relationship between serum sodium levels and mortality and suggested that the optimal range of serum sodium was 138-142 mEq/L. 10,12,[14][15][16] Most of the previous studies focused on the impact of admission serum sodium, which is the serum sodium level before interventions during hospitalization. The knowledge of the associations of discharge serum sodium, which is the serum sodium level after being modified by therapeutic interventions in hospital and considered safe for discharge by treating physicians, with clinical outcomes has been limited.…”