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Cardiopulmonary bypass: studies on its damaging effects
Insights
Cardiopulmonary bypass (CPB) causes inflammation and alters organ perfusion during cardiac surgery. Preventing microcirculation abnormalities and inflammatory effects is key to safer CPB procedures.
Area of Science:
- Cardiovascular Surgery
- Physiology
- Biomedical Engineering
Background:
- Cardiopulmonary bypass (CPB) is essential for cardiac surgery but induces a pathologic inflammatory state.
- CPB activates complement, coagulation, kallikrein, and fibrinolytic cascades, causing systemic inflammation.
- Significant changes in organ perfusion and metabolism occur during CPB, influenced by flow rates.
Purpose of the Study:
- To investigate the effects of CPB on microcirculation and inflammatory responses.
- To understand how perfusion flow rates impact organ perfusion during CPB.
- To identify strategies for improving the safety of CPB.
Main Methods:
- Review of existing literature on CPB-induced inflammation and microcirculatory changes.
- Analysis of experimental studies on hypothermic and normothermic CPB effects.
- Examination of ultrafiltration data regarding microvascular permeability.
Main Results:
- Hypothermic CPB (20°C) at flow rates <1.2 L/min/m² reduces microcirculatory perfusion.
- Brain oxygen consumption and resistance remain stable with reduced flow during hypothermia, increasing relative brain blood flow.
- Normothermic CPB for 2 hours increases microvascular permeability to proteins, leading to interstitial fluid accumulation.
Conclusions:
- CPB triggers a generalized inflammatory response and alters microcirculation.
- Perfusion flow rate critically affects organ perfusion, particularly microcirculation, during CPB.
- Enhancing CPB safety requires preventing microcirculatory dysfunction and mitigating inflammatory mediator effects.
Abstract:
Despite the widespread safe application of cardiopulmonary bypass (CPB) for cardiac surgery, it is inherently a pathologic state. CPB produces a generalized inflammatory reaction involving at least the complement, coagulation, kallikrein, and fibrinolytic cascades. Marked alterations in organ perfusion and metabolism occur during CPB which are further affected by the perfusion flow rate. During hypothermic CPB at 20 degrees C, there is a progressive decrease in perfusion of the microcirculation at flow rates less than 1.2 liters/min/m2. Experimental studies suggest that brain oxygen consumption and resistance remain relatively constant as flow rates are reduced during hypothermia, and the brain becomes the passive recipient of proportionally more blood flow. Recent ultrafiltration studies have demonstrated a specific increase in microvascular permeability to proteins after 2 h of normothermic CPB. This provides experimental support to the well-known clinical observation of increased interstitial fluid following CPB. The development of uniformly safe CPB depends upon prevention of the abnormalities of the microcirculation and upon neutralization of the deleterious effects of inflammatory mediators.