Cerebral hemodynamics during sustained intraoperative hypotension

Area of Science:

• Neuroscience
• Physiology
• Anesthesiology

Background:

• Cerebral autoregulation (CA) normally maintains stable cerebral blood flow (CBF) above a mean arterial blood pressure (BPmean) of 60-65 mmHg.
• CBF decreases with mean arterial blood pressure below the lower limit of CA (LLCA).
• Limited data exist on CA function during sustained hypotension, as it is typically avoided in clinical practice.

Purpose of the Study:

• To analyze cerebral autoregulation (CA) during sustained, deep intraoperative hypotension.
• To determine the lower limit of cerebral autoregulation (LLCA) in patients.
• To assess the continuous CA function using the mean flow index (Mx a) during and after hypotension.

Main Methods:

• Continuous monitoring of arterial blood pressure and middle cerebral artery blood flow velocity (MCAVmean) in 23 patients.
• Determination of patient-specific LLCA and quantification of continuous CA (Mx a-CA).
• Mx a was calculated at baseline, during 1 hour of hypotension, and after blood pressure restoration.

Main Results:

• The LLCA was found to be 56 (47-74) mmHg.
• Continuous CA (Mx a) was significantly disturbed during hypotension (0.61 [0.48-0.78]) compared to baseline (0.21 [0.14-0.32]) and improved post-hypotension.
• Mx a-CA remained disturbed throughout the 1-hour hypotension period but recovered after blood pressure normalization.

Conclusions:

• Cerebral autoregulation is impaired during sustained intraoperative hypotension.
• The observed disturbances in CA are completely reversible, indicating no ischemic hyperemia.
• These findings suggest that the brain adapts to sustained hypotension without long-term consequences.