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Relationship between cardiopulmonary bypass flow rate and cerebral embolization in dogs
H Sungurtekin1, W Plöchl, D J Cook
1Department of Anesthesiology, Mayo Foundation and Mayo Clinic, Rochester, Minnesota 55905, USA.
Insights
Reducing cardiopulmonary bypass (CPB) flow during cardiac surgery can decrease cerebral embolization. Lowering CPB flow, while maintaining mean arterial pressure, increases blood flow to the brain, reducing embolic risk.
Area of Science:
- Cardiovascular Surgery
- Neurology
- Biomedical Engineering
Background:
- Cerebral embolization is a significant cause of neurological complications after cardiac surgery.
- Cardiopulmonary bypass (CPB) presents periods of heightened risk for cerebral embolic events.
- Increasing pump flow during CPB is a theoretical strategy to mitigate cerebral embolization.
Purpose of the Study:
- To investigate the relationship between CPB flow rate and cerebral embolization in a canine model.
- To determine how CPB flow affects the distribution of blood flow to the brain.
Main Methods:
- Twenty mongrel dogs were subjected to CPB under hypothermic conditions (35°C) with alpha-stat management.
- Fluorescent microspheres were used to quantify embolic load and cerebral blood flow across 12 brain regions.
- CPB flow was adjusted to maintain mean arterial pressure between 65-75 mmHg.
Main Results:
- Cerebral blood flow remained independent of CPB pump flow.
- A higher percentage of CPB flow was directed to the brain at lower pump flow rates.
- A significant inverse correlation (r = -0.708) was observed between CPB pump flow and cerebral embolization.
Conclusions:
- Cerebral embolization during CPB is directly influenced by the pump flow rate.
- Reducing CPB flow, while maintaining mean arterial pressure, redirects a greater proportion of blood flow to the brain.
- This finding suggests a potential strategy for reducing neurological morbidity during cardiac surgery.
Background:
Cerebral embolization is a primary cause of cardiac surgical neurologic morbidity. During cardiopulmonary bypass (CPB), there are well-defined periods of embolic risk. In theory, cerebral embolization might be reduced by an increase in pump flow during these periods. The purpose of this study was to determine the CPB flow-embolization relation in a canine model.
Methods:
Twenty mongrel dogs underwent CPB at 35 degrees C with alpha-stat management and a fentanyl-midazolam anesthetic. In each animal, CPB flow was adjusted to achieve a mean arterial pressure of 65-75 mmHg. During CPB, an embolic load of 1.2 x 10(5) 67 microm fluorescent microspheres was injected into the arterial inflow line. Before and after embolization, cerebral blood flow was determined using 15-microm microspheres. Tissue was taken from 12 brain regions and microspheres were recovered. The relation between pump flow and embolization/g of brain was determined.
Results:
The mean arterial pressure at embolization was 67 +/-4 mmHg, and the range of pump flow was 0.9-3.5 l x min(-1)x m(-2). Cerebral blood flow was independent of pump flow. At lower pump flow, the percentage of that flow delivered to the brain increased. There was a strong inverse relation between pump flow and cerebral embolization (r = -0.708, P < 0.000 by Spearman rank order correlation).
Conclusions:
Cerebral embolization is determined by the CPB flow. At an unchanged mean arterial pressure, as pump flow is reduced, a progressively greater proportion of that flow is delivered to the brain.