[Progress on perioperative monitoring of cerebral blood flow autoregulation]

Cerebral blood flow autoregulation is physiologically protective mechanism to maintain the stability of cerebral blood flow. Once autoregulation is impaired, the cerebral blood flow fluctuates with blood pressure, leading to the risk of brain ischemia or cerebral hyperemia. Multiple research results indicate that cerebral blood flow can be monitored indirectly and continuously with transcranial Doppler, near infrared spectroscopy or ICP. The correlation coefficient calculated by the surrogate for cerebral blood flow and blood pressure is used to judge cerebral blood flow autoregulation. When the correlation coefficient is close to 1, cerebral blood flow will be passively fluctuated by blood pressure, indicating autoregulation is impaired. When the coefficient is less than 0, cerebral blood flow will not be changed with blood pressure, indicating autoregulaiton is intact. The status of autoregualtion is closely associated with mortality or poor neurological outcomes in patients with cardiac surgery underwent cardiopulmonary bypass, liver transplantation patients or patients with deep trendelenburg position for long time or beach chair position. Continuous monitoring of cerebral blood flow autoregulation can identify the lower or the upper limit of autoregulation, and provide information to individualize the perioperative management of blood pressure.