Recirculation loop only slightly decrease decarboxylation performance in an in-vitro ECCO2R test setup and can be compensated by local acidification

One ambition of current ECCO2R research is to create low flow devices that only need minimal invasive cannulas but still provide effective decarboxylation. Herein, we apply an “in vitro” model that can simulate a human body connected to an ECCO2R to examine the influence of recirculation loops on CO2 clearance. A recirculation loop allows to drive ECCO2R membranes at higher flow rates than the cannulas can provide. This is possible by recirculating the blood from the cannulas more than once through the membrane. This procedure reduces the efficiency of an ECCO2R-setup but at the same time reduces the risk of membrane clotting. Methods: In our ECCO2R simulation we use two interconnected circuits filled with fresh pig blood. The main circuit is supposed to simulate the vena cava and creates a hypoxic and hypercapnic (venous) environment by applying a N2 and CO2 gas flow to a Quadrox PLS. The test circuit which contains the actual ECCO2R-system consists of a second Rotaflow and a pediatric Quadrox membrane. The decarboxylation rate of the system was determined from the sweep flow rate and the carbon dioxide content in the sweep outflow of the test membrane. Different blood flows and recirculation fractions were compared in respect to their CO2 clearance. In one experiment, the recirculated blood was acidified with HCl. Results: The recirculation loops caused statistically significant reductions in the CO2 clearance of the tested ECCO2R system. However, when the recirculated blood was acidified, CO2 was regenerated from HCO3- and the CO2 washout of the system was significantly increased even above what was achieved without recirculation.