Cerebral autoregulation in cardiopulmonary bypass surgery: a systematic review

Cardiopulmonary bypass surgery is associated with a high incidence of neurological complications, including stroke, delirium and cognitive impairment. The development of strategies to reduce the incidence of such neurological events has been hampered by the lack of a clear understanding of their pathophysiology. Cerebral autoregulation (CA), which describes the ability of the brain to maintain a stable cerebral blood flow over a wide range of cerebral perfusion pressures despite changes in blood pressure, is known to be impaired in various neurological disorders. Therefore, we aimed to systematically review studies reporting indices of CA in cardiopulmonary bypass surgery. Databases such as MEDLINE, Web of Science, Cochrane Database of Systematic Reviews and EMBASE were searched for relevant articles. Titles, abstracts and full texts of articles were scrutinized according to predefined selection criteria. Two independent reviewers undertook the methodological quality screening and data extraction of the included studies. Twenty of 2566 identified studies were relevant. Studies showed marked heterogeneity and weaknesses in key methodological criteria (e.g. population size and discussion of limitations). All but 3 of the 20 studies described impairments of CA with cardiac surgery. Eleven studies investigated clinical outcomes, and 9 of these found a significant relationship between these and impaired CA. There is a general agreement that cardiac surgery is associated with changes in CA and that clinical outcomes appear to be significantly related to impaired CA. Further studies are now needed to determine prognostic significance and to inform future therapeutic strategies.