RenOx, a novel artificial lung and kidney assist device, combines gas exchange and dialysis fibers for integrated respiratory and renal support, with dialysis fibers intended for toxin clearance and filtration. However, when kidney support is not needed, dialysis fibers could be repurposed for additional respiratory support for patients in exacerbated cases, and to compensate losses in CO₂ transfer caused by the partial replacement of gas exchange fibers by dialysis fibers. We analyzed the feasibility of extracorporeal gas transfer via dialysis membranes with fully oxygenated and decarboxylated dialysis fluid in a closed circuit, quantifying O₂ and CO₂ exchange during standardized in-vitro tests with blood. Oxygenated dialysate was pumped through a dialyzer with a similar dialysis fiber area (0.6 m²) to the RenOx (adult size). Gas transfer efficiency was evaluated at blood-to-dialysate flow ratios of 1, 3, and 6. Average CO₂ removal from 12 to 35 ml/L_blood was achieved by adjusting blood-to-dialysate flow ratio, approaching the full metabolic requirement of adult patients (40 ml/L_blood). Maximum oxygen supply was 15 ml/L_blood. Blood pH and hematocrit were within physiological range. This study proposes a simple method to enhance lung support in the RenOx, advancing research on CO₂ removal by dialysis.