Acute variation in cognitive function in hemodialysis patients: A cohort study with repeated measures

Background: Although cognitive function in hemodialysis patients is believed to be best 24 hours after the dialysis session, the extent of variation during the dialysis cycle is unknown. Study Design: Cohort study with repeated measures. Setting & Participants: Hemodialysis centers; patients aged 55 years or older. Predictor: Time of assessment related to the dialysis session. Time 1 (T1) occurred approximately 1 hour before the dialysis session; T2, 1 hour into the session; T3, 1 hour after; and T4, the next day. Outcomes: Measures of cognitive function using a 45-minute cognitive battery. An average composite score was calculated to measure global cognitive function, equal to the average of subjects' standardized scores on all tests given at each test time. Times were classified as best and worst according to composite scores. Measurements: Testing was conducted on average over 2 dialysis sessions to avoid test fatigue. The cognitive battery included tests of verbal fluency, immediate and delayed verbal and visual memory, and executive function, administered at 4 times. Results: In the 28 subjects who completed testing at 3 or 4 testing times, mean age was 66.7 +/- 9.5 years and mean dialysis vintage was 44.7 +/- 33.3 months. Using a general linear model for correlated data, the composite score was significantly lower (poorer) during dialysis (T2) than shortly before the session (T1) or on the next day (T4; P < 0.001 for both). Limitations: Relatively small sample size, testing delays, results may not be generalizable. Conclusion: Global cognitive function varies significantly during the dialysis cycle, being worst during dialysis and best shortly before the session or on the day after. Clinician visits may be most effective at these times. Am J Kidney Dis 50:270-278. (c) 2007 by the National Kidney Foundation, Inc.