Gibt es einen Unterschied der kognitiven Leistungsfähigkeit bei Patienten mit terminaler Niereninsuffizienz während der Dialyse im Vergleich zum dialysefreien Tag?

Cognitive impairment in chronic kidney disease (CKD), especially in End-Stage- Renal-Disease (ESRD), has been recognized with a prevalence up to 87 %, but is still undiagnosed. The cause is still unknown but several studies have shown that haemodialysis itself, different co morbidities like cerebrovascular diseases and diabetes mellitus as well as uremia can cause cognitive impairment. Patients with cognitive impairment, especially haemodialysis patients, might not be able to follow their strong medication plans and might need special daily care. As it is still undiagnosed patients should be tested regularly. Several studies investigated cognitive impairment in patients receiving haemodialysis during different time points of the dialysis cycle. To investigate whether the point of testing in the dialysis cycle has an effect on cognitive performance we tested patients on two occasions during the dialysis cycle and once on the dialysisfree- day. In this study 31 patients were recruited in three dialysis centers in the region of central Hessen. 26 patients completed a series of three measurements during a period of 6 weeks. Cognitive impairment was tested with a neuropsychological test battery for repeated measurements named RBANS (Repeatable Battery for the Assessment of Neuropsychological Status). Once they were tested if they are depressed with a screening instrument named geriatric depression scale. Furthermore several co morbidities and blood levels were gathered to analyze if they had an influence on cognitive performance. The sequence of testing was randomized. Our studies revealed that there was no significant difference in the total scale score comparing the three different points of testing with each other (first two hours (T1) vs. last two hours (T2) vs. dialysis free day, (T3)). The best cognitive performance was achieved during the first two hours on dialysis with 81.1 points. Furthermore our results showed that patients were significantly better in language at the point of testing T1 (p <0.001) and T2 (p <0.001) compared with T3. Because of repeated measurements a learning effect has been excluded. At the third time of testing, regardless which time point of testing, patients showed deficits in long term memory. Comparing these three different time points of testing (T1 vs. T2 vs. T3) our results showed no significant difference in cognitive performance. This result differs from earlier studies. The reason for that might be found in different study designs. In this study we randomized the sequence, had just one medical student for all testings to avoid variations and used a neuropsychological test battery for repeated measurements. As this study has a small sample size these results should be verified with a greater sample size. Furthermore should be looked at the age and co morbidities as these have an influence on cognitive performance. For diagnostic and therapy it is relevant that the physician-patientconsultation proceeds when a patient is able to follow. Some studies recommended that haemodialysis patients should be tested on the dialysis free day. As a haemodialysis patient is in a dialysis center three times a week it is difficult to include another visit in their daily life. As our results showed no difference in cognitive performance on the dialysis free day in comparison to being on dialysis it is possible to test whenever it is the best for the patient. Young and mobile patients should be tested on the dialysis free day as the occasion is more comfortable and older and immobile patients can be tested during the dialysis cycle. In general it is important to test patients regularly as cognitive impairment is still undiagnosed and of relevance for the therapy.