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 (CRCO(2)) 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 CRCO(2). 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]). CRCO(2) 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 CRCO(2) 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 CRCO(2) remain normal in patients with chronic renal failure, and are not altered significantly by haemodialysis.

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