Cerebral blood flow autoregulation is preserved after hypothermic circulatory arrest

Background Patients undergoing aortic operations with hypothermic circulatory arrest (HCA) may require prolonged rewarming, a maneuver associated with impaired cerebral blood flow (CBF) autoregulation. The purpose of this study was to determine the effects of HCA on CBF autoregulation with a validated method based on near-infrared spectroscopy. Methods Regional cerebral oxygen saturation (rSco₂) was monitored in 25 patients undergoing aortic reconstructive operations. HCA was used in 13 patients. Autoregulation was measured continuously during the operation by calculating the linear correlation coefficient between low-frequency changes in rSco₂ and mean arterial pressure (MAP), generating the variable cerebral oximetry index (COx). When CBF autoregulation is functional, COx is near 0, because CBF and MAP are not correlated, but approaches 1 when autoregulation is impaired (ie, CBF is pressure passive). On the basis of prior studies, impaired autoregulation was defined as COx exceeding 0.3. Results COx did not differ between HCA and non-HCA groups before cardiopulmonary bypass or during the cooling phase of the operation, although the lower limit of autoregulation tended to be lower in patients before HCA (p = 0.053). During patient rewarming, COx was lower in the HCA group (p = 0.045), and abnormal COx was less frequent (31% vs 75%, p = 0.047) compared with the non-HCA group. Conclusions During aortic reconstructive operations, CBF autoregulation is preserved during the cooling phase of the procedure in patients undergoing HCA. Perfusion maneuvers associated with HCA may be protective against impaired autoregulation during rewarming compared with the non-HCA group.