Joint Association of Low Nadir Serum Sodium and Potassium with Worse Outcomes after Ischemic Stroke

Abstract

Background. Potassium and sodium are inextricably linked to the maintenance of cell potential and electrolyte homeostasis. Few studies have examined their joint relationship with outcomes after stroke. The objective of this study is to ascertain whether combined low nadir serum sodium and potassium levels are correlated with an unfavorable outcome in ischemic stroke. Methods. Retrospective cohort study of 2,920 consecutive patients with first-ever ischemic stroke. Serum sodium and potassium levels were measured at 10 consecutive time points over 10 days poststroke. The Youden Index was performed to identify patients with low nadir sodium (<140 mmol/L) and potassium (<3.65 mmol/L) levels, defined as a NaK score of 2. Multivariable logistic regression and Cox proportional hazard analysis were used to evaluate the independent relationship of sodium and potassium levels with clinical outcomes at three months. Results. A total of 2,920 patients with ischemic stroke were analyzed (mean age $62.14\pm 14.13$ years; 60.19% male), of whom 740 (25.3%) with both low nadir sodium and potassium levels had a quintuple 3-month case fatality compared to other patients (10.6% vs. 2.1%). Multivariable analyses identified $\text{NaK}=2$ as an independent predictor of 3-month death (adjusted odds ratio (OR) 2.23; 95% confidence interval (CI) 1.17-4.53; $p=0.019$) and an unfavorable shift in the distribution of scores on the modified Rankin scale (adjusted OR 1.51, 95% CI 1.12-2.04; $p=0.007$). Conclusions. Low sodium and potassium levels are common after ischemic stroke and are independent predictors of subsequent death.