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This study also cannot account for the complexity of clinical practices, where manual and procedural actions can introduce additional GME into the circuit. Perfusionists often operate both suckers and vents simultaneously, and the surgeon’ s manipulation of the venous and arterial lines can significantly increase GME levels. Due to these factors, the GME produced in this controlled study is likely an underestimation compared to what occurs in clinical practice. Another difference from clinical practice is that suctioned blood typically comes from the chest cavity and contains fat and other particulates. The blood suctioned in this study was from the patient reservoir and did not contain these particles.
The study used bovine blood, which can introduce variations in viscosity, coagulation factors, and platelet composition compared to human blood. We diluted the bovine blood to achieve hematocrit and viscosity levels comparable to those found during CPB in humans. Previous studies have demonstrated that bovine blood can serve as an effective substitute for human blood in GME investigations, without significantly affecting the measurement or formation of GME [ 38 ]. If bovine blood did influence GME formation, it would likely behave similarly to human blood, as bovine blood is a reliable substitute in dynamic in vitro studies. Despite these precedents, the generalizability of the findings to human physiology remains limited.
Another consideration pertains to the measurement of GME. The two most widely used GME counters, the EDAC quantifier and the Gampt BCC, have been employed in clinical and in vitro settings. However, neither is without potential error. Studies have shown that both devices may underestimate GME count at higher flow rates and overestimate it at lower flow rates [ 54 ]. Segers et al. found that the Gampt BCC tends to overestimate GME size, while the EDAC quantifier tends to overestimate GME concentration [ 55 ]. Additionally, there has been concern about whether these counters can reliably distinguish between particulate matter and true GME [ 7 ]. Despite these limitations, existing studies support the overall accuracy and clinical utility of GME counters [ 56 ].
Further limitations include the generalizability of the findings and their direct correlation to patient outcomes. Although the study used equipment and procedures commonly found in the operating room( OR), some differences in the experimental setup may have influenced GME counts. While the lab conditions were designed to replicate OR practices, the controlled lab environment may not fully replicate the dynamic and variable conditions encountered in actual clinical settings. In the OR, factors such as suction and venting are continuously adjusted, which can affect flow rates and GME transmission. Moreover, there are currently no standardized criteria for defining GME size, volume, or duration of exposure that correlate with adverse patient outcomes. As such, any attempt to infer such correlations to neurocognitive outcomes should be approached with caution [ 54 ].
Nevertheless, despite concerns regarding generalizability and direct correlation to patient outcomes, there is widespread agreement that minimizing GME within the CPB circuit is beneficial. Therefore, measures to reduce the introduction of GME should be prioritized to improve patient safety and outcomes.
Conclusion
This study provides a unique investigation into the measurement and identification of gas microemboli( GME) transmission. While GME counters have been used in both in vitro studies and clinical practice, their application for research in clinical settings remains limited due to confounds. The in vitro design of this study offers the advantage of isolating key variables, such as air introduction, pump speed, and reservoir level, enabling a controlled assessment of their effects on GME. This feature is not possible in clinical practice. Additionally, the study employs the latest version of the stateof-the-art bubble counter, the Gampt BCC300, which enhances accuracy and data collection capabilities. By evaluating commonly used reservoirs and oxygenators currently used in clinical practice, this study helps represent what occurs during CPB procedures today.
We recommend, based on this data, that the suction speed going to a cardiotomy( single or multiple suckers) be kept to a minimum effective flow rate for any reservoir level, given their interactive combined effect on GME transmission. A worst-case and hopefully infrequent scenario, sucker bypass, where suction is high and the level is low, may introduce many GME to the patient. In general, however, suction speed and level should be continuously monitored during CPB and adjusted to prevent excessive GME transmission. Based on our results, it appears reasonable to maintain a suction speed of 50 RPM or lower( 0.65 L / min) to minimize GME transmission, particularly when the reservoir level is less than 500 mL.
Funding
This study was supported by the Midwestern University College of Health Sciences Faculty Intermural Grant( T. R.) and Graduate Fund( M. S.).
Conflicts of interest The authors declare no conflict of interest.
Data availability statement The data are available from the corresponding author upon request.
Author contribution statement
TR and MS contributed to data generation, analysis, and manuscript writing. EE and KD contributed to data generation. MR contributed to manuscript writing and data analysis. CB helped with experimental design, data analysis, and data presentation. HD helped with experimental design, data analysis, and review.
Ethics approval
The study does not involve animal or human subjects. The Midwestern University Office of Research and Sponsored Programs approved the biosafety protocol.
References
1. Pugsley W, Klinger L, Paschalis C, Treasure T, Harrison M, Newman S. The impact of microemboli during cardiopulmonary bypass on neuropsychological functioning. Stroke. 1994; 25( 7): 1393 – 1399. https:// doi. org / 10.1161 / 01. STR. 25.7.1393.