Cerebral perfusion during nonpulsatile cardiopulmonary bypass

Area of Science:

• Neurology
• Cardiovascular Surgery
• Medical Imaging

Background:

• Transcranial Doppler (TCD) offers a noninvasive method to assess cerebral circulation.
• Previous studies confirm MCA flow velocity changes reflect overall cerebral blood flow.
• Cardiopulmonary bypass (CPB) significantly impacts cerebral hemodynamics.

Purpose of the Study:

• To evaluate middle cerebral artery (MCA) flow velocity during cardiopulmonary bypass (CPB) using transcranial Doppler (TCD).
• To investigate the relationship between MCA flow velocity, hemodilution, and cerebral perfusion pressure (CPP) during CPB.
• To assess the integrity of cerebral autoregulation during CPB.

Main Methods:

• Pilot study involving 11 high-risk patients undergoing CPB.
• Continuous monitoring of MCA flow velocity via TCD.
• Simultaneous recording of arterial blood pressure (BP), central venous pressure, and epidural intracranial pressure (EDP) to calculate CPP.
• Cerebral electrical activity monitored using a cerebral function monitor.

Main Results:

• MCA flow velocity increased in 10 of 11 patients during nonpulsatile CPB (80-300% of pre-CPB levels).
• Increased MCA flow velocity correlated with the degree of hemodilution.
• MCA flow velocity demonstrated a pressure-passive relationship with CPP, indicating impaired cerebral autoregulation.
• Post-CPB, MCA flow velocity decreased but remained elevated (110-210% of pre-CPB levels) for 15 minutes.

Conclusions:

• Nonpulsatile CPB leads to increased MCA flow velocity, influenced by hemodilution.
• Cerebral autoregulation is compromised during CPB, with flow becoming pressure-passive.
• MCA flow velocity remains elevated in the early post-CPB period.