Cerebral haemodynamics in patients with chronic renal failure: effects of haemodialysis

Background. We measured middle cerebral artery (MCA) flow velocity (FV), dynamic pressure autoregulation, and carbon dioxide reactivity (CRCO2) in patients with chronic renal failure before and after haemodialysis using transcranial Doppler ultrasonography. Methods. Twelve patients on long-term haemodialysis were recruited. MCA FV was measured continuously. The transient hyperaemic response test was used to assess cerebral autoregulation, and per cent change in FV per kPa change in end-tidal carbon dioxide was calculated to assess CRCO2. All measurements were recorded before and after haemodialysis. Results. MCA FV (mean [sd]) decreased from 57 (10) cm s(-1) before to 46 (13) cm s(-1) after haemodialysis (P<0.01). The transient hyperaemic response ratio (THRR) was (mean [sd]) 1.29 (0.13) before haemodialysis and did not change significantly following haemodialysis (1.36 [0.10]). CRCO2 was 21.7 (8.3)% kPa(-1) before haemodialysis and remained unchanged afterwards (20.9 [3.8]% kPa(-1)). Values in normal subjects for MCA FV, THRR and CRCO2 are 56 (12) cm s(-1), 1.26 (0.13) and 22 (6)% kPa(-1), respectively. Conclusions. MCA FV decreases significantly after haemodialysis. Dynamic pressure autoregulation and CRCO2 remain normal in patients with chronic renal failure, and are not altered significantly by haemodialysis.