Serum Sodium Levels Predict Mortality in Elderly Acute Kidney Injury Patients: A Retrospective Observational Study

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PURPOSE: We examined the relationship between different levels of serum sodium and mortality among elderly patients with acute kidney injury (AKI). METHODS: We retrospectively enrolled elderly patients from Chinese PLA General Hospital from 2007, to 2018. All-cause mortality was examined according to eight predefined sodium levels: <130.0 mmol/L, 130.0-134.9 mmol/L, 135.0-137.9 mmol/L, 138.0-141.9 mmol/L, 142.0-144.9 mmol/L, 145.0-147.9 mmol/L, 148.0-151.9 mmol/L, and ≥152.0 mmol/L. We estimated the risk of all-cause mortality using a multivariable adjusted Cox analysis, with a normal sodium level of 135.0-137.9 mmol/L as a reference. RESULTS: In total, 744 patients were suitable for the final evaluation. After 90 days, the mortality rates in the eight strata were 36.1, 27.8, 19.6, 24.4, 30.7, 48.6, 52.8, and 57.7%, respectively. In the multivariable adjusted analysis, patients with sodium levels <130.0 mmol/L (HR: 2.247; 95% CI: 1.117-4.521), from 142.0 to 144.9 mmol/L (HR: 1.964; 95% CI: 1.100-3.508), from 145.0 to 147.9 mmol/L (HR: 2.942; 95% CI: 1.693-5.114), from 148.0 to 151.9 mmol/L (HR: 3.455; 95% CI: 2.009-5.944), and ≥152.0 mmol/L (HR: 3.587; 95% CI: 2.151-5.983) had an increased risk of all-cause mortality. After 1 year, the mortality rates in the eight strata were 58.3, 47.8, 33.7, 38.9, 45.5, 64.3, 69.4, and 78.4%, respectively. Patients with sodium levels <130.0 mmol/L (HR: 1.944; 95% CI: 1.125-3.360), from 142.0 to 144.9 mmol/L (HR: 1.681; 95% CI: 1.062-2.660), from 145.0 to 147.9 mmol/L (HR: 2.631; 95% CI: 1.683-4.112), from 148.0 to 151.9 mmol/L (HR: 2.411; 95% CI: 1.552-3.744), and ≥152.0 mmol/L (HR: 3.037; 95% CI: 2.021-4.563) had an increased risk of all-cause mortality. CONCLUSION: Sodium levels outside the interval of 130.0-141.9 mmol/L were associated with increased risks of 90-day mortality and 1-year mortality in elderly AKI patients.