A mock circulation loop to test extracorporeal CO(2) elimination setups

BACKGROUND: Extracorporeal carbon dioxide removal (ECCO(2)R) 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 ECCO(2)R research without animal models. In a second step, we use this model to investigate three experimental scenarios of ECCO(2)R: (I) the influence of hemoglobin concentration on CO(2) removal. (II) a potentially portable ECCO(2)R that uses air instead of oxygen, (III) a low-flow ECCO(2)R that achieves effective CO(2) 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 ECCO(2)R mock, CO(2) 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 CO(2) removal. In the second scenario, an air-driven ECCO(2)R setup showed only a slightly lower CO(2) wash-out than the same setup with pure oxygen as sweep gas. In the last scenario, the low-flow ECCO(2)R, 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 CO(2) removal rates. Acidification of the CO(2) depleted blood in the recirculation channel caused an increase in CO(2) removal rate. CONCLUSIONS: We demonstrate a simple and cost effective, yet powerful, “in-vitro” ECCO(2)R 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.