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Comparative study of biocompatibility between the open circuit and closed circuit in cardiopulmonary bypass
H Nishida1, S Aomi, Y Tomizawa
1Department of Cardiovascular Surgery, Heart Institute of Japan, Tokyo Women's Medical University, Japan.
Insights
The open circuit in cardiopulmonary bypass (CPB) shows lower biocompatibility due to increased protein adsorption, despite heparin coating effectiveness. Further research is needed to confirm benefits of closed CPB systems.
Area of Science:
- Biomedical Engineering
- Cardiovascular Surgery
- Materials Science
Background:
- Cardiopulmonary bypass (CPB) systems aim to improve patient outcomes during open-heart surgery.
- Theoretical benefits of centrifugal pumps and heparin coatings in CPB are not always evident.
- The air-blood interface in open-circuit CPB systems warrants further investigation.
Purpose of the Study:
- To investigate the influence of the air-blood interface in open-circuit CPB.
- To compare the significance of heparin dose and heparin coating in CPB circuits.
- To evaluate the biocompatibility of open versus closed CPB systems.
Main Methods:
- Comparison of open and closed circuit CPB systems using identical oxygenators and circuits.
- Perfusion experiments conducted for 4 hours with heparinized human blood.
- Analysis of blood samples for platelet and white blood cell counts, beta-thromboglobulin (beta-TG), and C3a levels.
- Measurement of adsorbed protein on hollow fibers and immunoblotting.
Main Results:
- Heparin-coated circuits demonstrated significantly better biocompatibility than non-coated circuits.
- Differences between open and closed circuits were minimal for blood parameters.
- Closed circuits exhibited lower C3a levels but significantly less adsorbed protein compared to open circuits.
- Open circuits showed higher fibrinogen adsorption and conversion to fibrin.
Conclusions:
- The open circuit in CPB exhibits lower biocompatibility, evidenced by increased protein adsorption.
- The air-blood interface in open circuits appears to contribute to reduced biocompatibility.
- Further studies with varied heparin concentrations and more rigorous conditions are needed to clarify the benefits of closed CPB systems.
Abstract:
The theoretical benefit of a centrifugal pump or heparin coating demonstrated through in vitro or in vivo studies is not recognizable in cardiopulmonary bypass (CPB) during chemical open heart surgery. The objective of this study was to investigate the influence of the interface of air and blood in current CPB with an open circuit system and its relative significance in relationship to the heparin dose and heparin coating. Using the same oxygenator and circuit, an open circuit and closed circuit CPB with the same priming volume were prepared for a 4 h perfusion experiment using diluted and heparinized (3.6 U/ml) fresh human blood. In these experiments, both heparin-coated and noncoated circuits were examined. Blood was sampled before and 2, 30, 60, 120, and 240 min after the start of perfusion, and the platelet and white blood cell counts and beta-thromboglobulin (beta-TG) and C3a levels were measured. The amount of adsorbed protein in the hollow fibers was also measured after retrieval. Although the results demonstrated significantly better biocompatibility of the heparin-coated circuit than the noncoated circuit, the difference between the open and closed circuits was unexpectedly small and insignificant with either the heparin-coated circuit or noncoated circuit. In contrast, the C3a level was higher in the closed circuit than the open circuit. However, the amount of adsorbed protein was markedly lower in the closed circuit (0.7 microgram/cm2) than in the open circuit (11.1 micrograms/cm2). An immunoblot of the adsorbed protein showed a higher density of fibrinogen bands and conversion to fibrin in the open circuit. We speculate that the lower blood C3a level in the open circuit suggests that C3a was taken in by the adsorbed protein. In conclusion, analysis of the adsorbed protein indicates the lower biocompatibility of the open circuit. Similar experiments with less heparin use and more severe conditions will be necessary to elucidate the essential benefit of making a CPB closed circuit.