Cerebral Perfusion and Oxygenation During Haemodialysis: A Systematic Review

Background: Adults on maintenance haemodialysis carry a high burden of cognitive impairment, white-matter injury and stroke, part of which may be delivered by the treatment itself. We examined how cerebral perfusion and oxygenation change across a session, and whether the literature can support a summary. Methods: Six sources were searched up to 3 August 2026 for in vivo measurements of cerebral perfusion or oxygenation in adults on maintenance haemodialysis (protocol preregistered retrospectively). Risk of bias was rated across eight prespecified domains and certainty with GRADE. Pooling was admissible only within one technique family and across comparable measurement intervals; no analysis met that standard, so studies are synthesised narratively. Results: Of 1934 records screened, 126 reports of 116 studies were included; 77 reports from 76 cohorts yielded extractable data (32 oximetry, 27 transcranial Doppler, 20 perfusion imaging). Velocity fell in all five Doppler studies reporting paired within-session middle cerebral artery values, by 8.3% to 23.3% of the pre-dialysis value and by 16.0% to 23.3% in the three reporting a raw dispersion (49 participants). Perfusion imaging in two cohorts agreed in direction; certainty was very low. A randomised trial measuring grey-matter perfusion found no intradialytic change. Of 32 oximetry studies, 4 reported a within-session change with dispersion under 4 incompatible definitions. Only 3 of 77 measured both arterial pressure and carbon dioxide. Conclusions: Cerebral blood flow velocity falls during haemodialysis, but this should not be equated with a fall in tissue perfusion, and the oximetry literature cannot be synthesised as it stands. We propose a minimum reporting standard.