A Novel Mock Circuit to Test Full-Flow Extracorporeal Membrane Oxygenation

Abstract

Extracorporeal membrane oxygenation (ECMO) has become an important therapeutic approach in the COVID-19 pandemic. The development and research in this field strongly relies on animal models; however, efforts are being made to find alternatives. In this work, we present a new mock circuit for ECMO that allows measurements of the oxygen transfer rate of a membrane lung at full ECMO blood flow. The mock utilizes a large reservoir of heparinized porcine blood to measure the oxygen transfer rate of the membrane lung in a single passage. The oxygen transfer rate is calculated from blood flow, hemoglobin value, venous saturation, and post-membrane arterial oxygen pressure. Before the next measuring sequence, the blood is regenerated to a venous condition with a sweep gas of nitrogen and carbon dioxide. The presented mock was applied to investigate the effect of a recirculation loop on the oxygen transfer rate of an ECMO setup. The recirculation loop caused a significant increase in post-membrane arterial oxygen pressure (paO2). The effect was strongest for the highest recirculation flow. This was attributed to a smaller boundary layer on gas fibers due to the increased blood velocity. However, the increase in paO2 did not translate to significant increases in the oxygen transfer rate because of the minor significance of physically dissolved oxygen for gas transfer. In conclusion, our results regarding a new ECMO mock setup demonstrate that recirculation loops can improve ECMO performance, but not enough to be clinically relevant.

Comparison of Serial and Parallel Connections of Membrane Lungs against Refractory Hypoxemia in a Mock Circuit

“…Firstly, the cannula flow was 4× higher (10 L/min vs. 2.5 L/min) than in the previous experiment. Moreover, unlike in Upon first glance, the currently observed oxygen transfer rate of approximately 1000 mL/min seems unrealistically high compared to the rate of approximately 250 mL/min in our previous full-flow ECMO mock circuit [14]. However, there were multiple factors in the current experiment that led to these high transfer rates.…”

“…In this work, we present a simplification of an already existing mock circuit for ECMO [14]. The basic idea of building a single-pass model for the measurement sequence and performing the measurements discontinuously, establishing a venous environment first and then performing the measurement, was not changed.…”

“…An explanation for the better oxygenation performance of the serial arrangement can be deduced from the concept of the boundary layer [14][15][16][17][18]. The boundary layer is a stationary fluid layer on the outside of the gas fibers that oxygen molecules need to pass via diffusion.…”

“…The ECMO mock circuit described in this work is a simplification of a previously presented mock circuit for full-flow ECMO [14]. In contrast to previous ECMO mock circuits, the new design only requires the onboard sensors of two standard Cardiohelp platforms (Maquet Cardiopulmonar Gmbh, Getinge Group, Rastatt, Germany) to measure oxygen transfer.…”

A numerical study of the hemodynamic behavior and gas transport in cardiovascular systems with severe cardiac or cardiopulmonary failure supported by venoarterial extracorporeal membrane oxygenation

“…These studies provided important insights for understanding the effects of ECMO from various perspectives spanning from systemic hemodynamics to microcirculation perfusion, nevertheless, most of them were restricted by available techniques for in vivo measurements, making the findings less comprehensive or lack quantitative details on some variables of interest (e.g., flow patterns near the cannulation sites, oxygen saturations in different end-organs). Such limitations of in vivo studies may be partly overcome by in vitro or ex-vivo studies, especially those based on mock loop models ( Ki et al, 2019 ; Fu et al, 2021 ; Caspari et al, 2022 ; Rozencwajg et al, 2022 ; Sayed et al, 2022 ). This sort of studies are however limited by the high cost of fabricating models mimicking the complex vascular structure and difficulties in representing various cardiovascular properties using artificial devices.…”