Preservation of static and dynamic cerebral autoregulation after mild hypothermic cardiopulmonary bypass

Background. Dysfunction of cerebral autoregulation might contributeto neurological morbidity after cardiac surgery. In this study,our aim was to assess the preservation of cerebral autoregulationafter cardiac surgery involving cardiopulmonary bypass (CPB). Methods. Dynamic and static components of cerebral autoregulationwere evaluated in 12 patients undergoing coronary artery bypassgraft surgery, anaesthetized with midazolam, fentanyl, and propofol,and using mild hypothermic CPB (31–33°C). Arterialpressure (ABP), central venous pressure (CVP), and blood flowvelocity in the middle cerebral artery (CBFV) were recorded.The cerebral perfusion pressure (CPP) was calculated as a differencebetween mean ABP and CVP. Rapid decrease of CPP was caused bya sudden change of patients' position from Trendelenburg toreverse Trendelenburg. Cerebral vascular resistance (CVR) wascalculated by dividing CPP by CBFV. Index of static cerebralautoregulation (CAstat) was calculated as the change of CVRrelated to change of CPP during the manoeuvre. Dynamic rateof autoregulation (RoRdyn) was determined as the change in CVRper second during the first 4 s immediately after a decreasein CPP, related to the change of CPP. Measurements were obtainedafter induction of anaesthesia, and 15, 30, and 45 min aftertermination of CPB. Results. No significant changes were found in CAstat or RoRdynafter CPB. Significant changes in CVR could be explained byconcomitant changes in body temperature and haematocrit. Conclusion. Autoregulation of cerebral blood flow remains preservedafter mild hypothermic CPB.