Effect of a single dialysis session on cognitive function in CKD5D patients: a prospective clinical study

Cognitive function declines in parallel to the decrease in glomerular filtration rate, best epitomized by the markedly reduced cerebral performance in patients undergoing maintenance haemodialysis [chronic kidney disease stage 5 dialysis (CKD5D)]. Aside from structural permanent damage, there seems to be a reversible part of low cognitive performance. The potential effect of a single dialysis session on cognitive function remains still elusive. The aim of the study was to assess cognitive function using a widespread test battery and avoiding excluding effects of circadian variations.

Twenty-eight medically stable CKD5D patients (age: 54.9 ± 13.2 years, dialysis vintage: 46.2 ± 51.0 month) at two tertiary care centres with outpatient dialysis units were enrolled. Cognitive testing was always performed twice within 24 h, 1 h prior to haemodialysis (T1pre-dialysis) as well as 19 h after the end of dialysis (T2post-dialysis) including assessment of memory, attention and concentration, executive functioning, word fluency and psychomotor speed by using a well-validated neuropsychological test battery. Patients were randomized into two groups. One group was examined before (T1pre-dialysis) and after (T2post-dialysis) Dialysis Session 1. The other group was first examined the day after Dialysis Session 1 (T2post-dialysis) and then before Dialysis Session 2 (T1pre-dialysis) in order to exclude potential learning effects. Twenty age-matched subjects with normal excretory renal function were used for comparison.

Neuropsychological testing found that the CKD5D performed significantly worse on measures of alertness, attention, working memory, logical and visual memory, word fluency and executive functions compared with non-CKD subjects. No differences in short-term memory, selective attention, as well as problem-solving and planning were found between CKD5D patients and non-CKD subjects. A single haemodialysis session led to a significant improvement in logical (Rivermead Behaviour Memory Test story: P < 0.001) and visual memories [Rey-Osterrieth Complex Figure Test (RCFT) memory quotient: P < 0.001], psychomotor speed [Trail Making Test (TMT) B: P = 0.020], activity planning (executive functions) (RCFT copy/points deduction: P < 0.001) and concentration (TMT A: P < 0.001).

Our data demonstrate improvements in memory functions, executive functions and psychomotor abilities after a single dialysis session, pointing to a reversible component of low cognitive performance in CKD5D.