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.

Keywords: borderline hypo- or hypernatremia; hypernatremia; hyponatremia; serum sodium ([Na+]) variation; short-term and long-term mortalities.

FIGURE 1

Adjusted OR (95% CI) for hospital mortalities of the entire cohort of patients (n = 60 944) with serum [Na⁺] variations from 2 to ≥12 mEq/L. Adjusted for age; sex; race; principal diagnosis; CCI score; history of coronary artery disease, congestive heart failure, peripheral vascular disease, stroke, diabetes mellitus, chronic obstructive pulmonary disease and cirrhosis; eGFR; admission serum [Na⁺]; number of serum [Na⁺] measurements and length of hospital stay. x-axis: OR (95% CI) y-axis: Δ[Na⁺] (mEq/L) = peak serum [Na⁺] – nadir serum [Na⁺]