Mild hyponatremia is associated with functional and cognitive decline in chronic hemodialysis patients.

BACKGROUND: A high incidence and adverse outcomes of cognitive impairment in dialysis patients have recently become recognized. Classical risk factors, uremia, anemia, metabolic disturbances, and hemodynamic instability during dialysis accelerate vascular cognitive impairment. AIMS: To evaluate laboratory factors that influence cognitive function in consecutive chronic hemodialysis (CHD) patients over a 2-year period.
METHODS: Between June 2010 and June 2011 we conducted a prospective, single-center trial that evaluated cognitive function in adult chronic hemodialysis (HD) patients. A battery of cognitive function tests was used: modified mini mental state (3MS), trailmaking tests A (trails A) and B (trails B). The 15-item geriatric depression scale (GDS) and the activities of daily living (ADL) test were used, respectively, for assessing symptoms of depression and global functional status. All tests were performed twice at yearly intervals in consecutive HD patients. Global cognitive impairment was defined as a 3MS < 80 and impaired executive function as a Trails A performance time > 75 seconds and Trails B > 180 seconds.
RESULTS: 56 chronic HD patients aged 65.00 ± 17.8 years were studied; 57% of them were males. 86% suffered from hypertension (HTN), 40% were diabetics and ~ 1/3 had ischemic heart disease, congestive heart failure (CHF), and dyslipidemia. Average plasma calcium, phosphorus, and PTH were within the recommended range. No features suggestive of malnutrition, severe anemia, inflammation, or inadequate dialysis were detected. 14 patients (24%) had mild chronic hyponatremia (Na ranges 131 - 135 meq/L). Significant disturbances in global cognitive and executive function were detected in the study patients. In 2010, 50% had 3MS < 80, 71% and 91% had severely impaired trails A and B tests (respectively), 54% had symptoms of depression and 50% suffered from impaired ADL. Retesting of the survivors in 2011 revealed increased prevalence of cognitive and functional declines along with worsening depression scoring. Univariate analysis demonstrated significant correlation between cognitive decline and age, female gender, education, poor executive and functional status, inadequate dialysis dose (Kt/V < 1.2, p = 0.023), high plasma phosphorus levels (p > 6 mg/dL, p = 0.034), and hyponatremia (Na < 135 mEq/L, p = 0.001). Multivariate stepwise logistic regression analysis revealed statistically significant associations between hyponatremia and impaired ADL (p = 0.043) and impaired ADL and mortality (p = 0.002).
CONCLUSIONS: A high prevalence of global cognitive and executive impairment was detected in our hemodialysis cohort. We found an association between mild chronic hyponatremia and impaired functional status. Whether treatments aimed at modifying hyponatremia could mitigate functional decline or mortality remains to be elucidated.