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Changes in blood flow velocity in the middle cerebral artery during nonpulsatile hypothermic cardiopulmonary bypass
Insights
Transcranial Doppler ultrasonography can monitor cerebral perfusion during cardiopulmonary bypass. Relative blood flow velocity and a novel index correlate with temperature and CO2 levels, aiding clinical management.
Area of Science:
- Neuroscience
- Cardiovascular Surgery
- Medical Imaging
Background:
- Cerebral perfusion monitoring is crucial during cardiopulmonary bypass (CPB).
- Transcranial Doppler (TCD) ultrasonography offers a non-invasive method to assess cerebral blood flow velocity.
Purpose of the Study:
- To evaluate the utility of TCD for indirectly measuring cerebral perfusion during CPB.
- To assess the correlation between blood flow velocity and physiological variables.
Main Methods:
- Simultaneous measurement of middle cerebral artery blood flow velocity and physiological variables in 18 patients.
- Management of pH and PaCO2 using the alpha-stat acid-base strategy during hypothermic CPB.
- Development of a modified cerebral metabolic rate for oxygen (mCMRO2) index.
Main Results:
- Relative blood flow velocity significantly decreased during aortic cross-clamp and increased during rewarming.
- mCMRO2 showed significant correlations with nasopharyngeal temperature across different CPB phases.
- Nasopharyngeal temperature and PaCO2 were significant determinants of relative velocity during aortic cross-clamp.
Conclusions:
- Relative velocity and mCMRO2 measurements are valuable for monitoring cerebral perfusion and metabolism during hypothermic CPB.
- TCD can serve as an effective tool for real-time assessment of cerebral status in cardiac surgery patients.
Background And Purpose:
We evaluated the utility of blood flow velocity measurements by transcranial Doppler ultrasonography as a tool to indirectly measure cerebral perfusion during cardiopulmonary bypass.
Methods:
We simultaneously measured blood flow velocity in the middle cerebral artery and physiological variables in 18 patients undergoing cardiac surgery under hypothermic cardiopulmonary bypass in which pH and PaCO2 were managed with the alpha-stat acid-base strategy. We expressed blood flow velocity as a relative value of control obtained under normothermia and normocarbia before bypass. We also developed an original index, modified cerebral metabolic rate for oxygen, to estimate cerebral metabolic rate for oxygen.
Results:
Relative velocity was significantly (P < .01) reduced during stable aortic cross-clamp compared with before bypass and was significantly (P < .01) increased during rewarming compared with at aortic cross-clamp. Modified cerebral metabolic rate for oxygen significantly correlated with nasopharyngeal temperature during cooling, aortic cross-clamp, and rewarming (r = .756, P < .0001; r = .4, P < .01; r = .725, P < .0005, respectively). Calculated temperature coefficient for modified cerebral metabolic rate of oxygen was 2.7 +/- 1.4 (mean +/- SD, n = 10) during cooling. Only nasopharyngeal temperature and PaCO2 were significant determinants of relative velocity during aortic cross-clamp.
Conclusions:
We can monitor cerebral perfusion and metabolism by measurements of relative velocity and modified cerebral metabolic rate for oxygen during hypothermic cardiopulmonary bypass.