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The efficacy of blood cardioplegia is not due to oxygen delivery
R W Illes1, N A Silverman, I B Krukenkamp
1Department of Surgery, University of Illinois, College of Medicine, Chicago.
Insights
Red blood cells in cardioplegic solutions improve myocardial oxygen consumption after cardiac arrest. This study found that blood-based solutions, not plasma, preserve heart function post-ischemia.
Area of Science:
- Cardiology
- Cardiovascular Surgery
- Biomedical Engineering
Background:
- Cardioplegic arrest is crucial for cardiac surgery.
- Preserving myocardial oxygen consumption post-ischemia is vital for cardiac function.
- The role of red blood cells (RBCs) in cardioplegic solutions remains unclear.
Purpose of the Study:
- To evaluate the impact of hematocrit levels in cardioplegic solutions on myocardial oxygen consumption and contractility after ischemic arrest.
- To determine if plasma or RBCs are responsible for preserving myocardial function.
Main Methods:
- Twenty-seven canine hearts were instrumented with ultrasonic dimension crystals.
- Measurements of stroke work and myocardial oxygen consumption were taken during volume loading.
- Hearts underwent 2 hours of cardioplegic arrest at 10°C using solutions with varying hematocrit values (17.0%, 8.2%, 0%).
Main Results:
- Contractility, measured by the slope of stroke work versus end-diastolic volume, remained unchanged across all groups post-arrest.
- Myocardial oxygen consumption for basal metabolism significantly increased (25.5%) after arrest in the group with plasma (0% hematocrit).
- The efficacy of blood-based solutions was not attributable to plasma or oxygen-carrying capacity alone.
Conclusions:
- Plasma-containing cardioplegic solutions may impair myocardial oxygen consumption efficiency post-ischemia.
- Red blood cells, independent of oxygen-carrying capacity, appear to play a protective role in preserving myocardial metabolism.
- Further research is needed to identify the specific RBC component responsible for this protective effect.
Abstract:
Twenty-seven canine hearts instrumented with ultrasonic dimension crystals underwent simultaneous determination of stroke work and myocardial oxygen consumption during incremental volume loading on right heart bypass before and 30 minutes after 2 hours of cardioplegic arrest at 10 degrees C. Three cardioplegic solutions were used: Hematocrit values were 17.0% (group I), 8.2% (group II), and 0% (group III). In all groups the slope of the linear stroke work versus end-diastolic volume relationship, a measure of contractility, was unchanged after ischemic arrest. However, the myocardial oxygen consumption for basal metabolism was increased an average of 25.5% after arrest with plasma (group III). Since the plasma concentration in all three groups was identical, and the oxygen available to the hearts during ischemia was the same in groups II and III, the efficacy of blood-based cardioplegic solutions cannot be attributed to a plasma component or to the greater oxygen-carrying capacity of the red blood cell. Future studies should attempt to identify the salutory entity of the red cell responsible for preservation of myocardial oxygen consumption efficiency.