A Mock Circulation Loop to Test Extracorporeal CO2 Elimination Setups

Background

Extracorporeal carbon dioxide removal (ECCO₂R) is a promising yet limited researched therapy for hypercapnic respiratory failure in acute respiratory distress syndrome and exacerbated chronic obstructive pulmonary disease. Herein, we describe a new mock circuit that enables experimental ECCO₂R research without animal models. In a second step, we use this model to investigate three experimental scenarios of ECCO₂R: (I) the influence of hemoglobin concentration on CO₂ removal. (II) a potentially portable ECCO₂R that uses air instead of oxygen, (III) a low-flow ECCO₂R that achieves effective CO₂ clearance by recirculation and acidification of the limited blood volume of a small dual lumen cannula (such as a dialysis catheter).

Results

With the presented ECCO₂R mock, CO₂ removal rates comparable to previous studies were obtained. The mock works with either fresh porcine blood or diluted expired human packed red blood cells. However, fresh porcine blood was preferred because of better handling and availability. In the second step of this work, hemoglobin concentration was identified as an important factor for CO₂ removal. In the second scenario, an air-driven ECCO₂R setup showed only a slightly lower CO₂ wash-out than the same setup with pure oxygen as sweep gas. In the last scenario, the low-flow ECCO₂R, the blood flow at the test membrane lung was successfully raised with a recirculation channel without the need to increase cannula flow. Low recirculation ratios resulted in increased efficiency, while high recirculation ratios caused slightly reduced CO₂ removal rates. Acidification of the CO₂ depleted blood in the recirculation channel caused an increase in CO₂ removal rate.

Conclusions

We demonstrate a simple and cost effective, yet powerful, “in-vitro” ECCO₂R model that can be used as an alternative to animal experiments for many research scenarios. Moreover, in our approach parameters such as hemoglobin level can be modified more easily than in animal models.