High Efficiency Carbon Dioxide Removal Devices for Minimally Invasive Partial Respiratory Assistance

Acute and chronic lung injuries remain significant clinical problems, and are the third leading cause of death in the United States. Carbon dioxide removal (CO2R) devices can effectively manage acute hypercapnia in patients during treatment of acute exacerbations of chronic obstructive pulmonary disease (aeCOPD) and acute respiratory distress syndrome (ARDS) when combined with protective ventilation strategies. Widespread adaptation of CO2R systems for this purpose or early intervention have been hindered partially due to invasive placement of large diameter intravascular devices or high circuit blood flows necessary for available extracorporeal CO2R (ECCO2R) devices. We are in development of mechanical and enzymatic approaches that facilitate high efficiency CO2 removal in artificial lung devices to minimize invasiveness of treatment with no or low blood flow outside the body. The impeller percutaneous respiratory assist catheter (IPRAC) uses an array of rotating impellers in an annular bundle to generate an “active mixing” effect that enabled the highest efficiency CO2R of any reported artificial lung device. We investigated additional impeller design parameters finding gas exchange could be significantly improved by reducing impeller axial spacing. Total gas exchange in the IPRAC was improved by 10% versus previous work. The impeller system was adapted for extracorporeal use in the ultra-low-flow ECCO2R device (ULFED) with the objective of matching blood flow rates common for renal hemodialysis (250 mL/min). Effective CO2R at ultra-low-flows enables adaptation of common renal hemodialysis connection strategies with potential for use with dialysis equipment or to be spliced directly in existing dialysis circuitry. CO2 removal up to 75 mL/min (30-37% metabolic CO2 production) at hemodialysis blood flows was demonstrated in the ULFED. The effects of bundle aspect ratio and impeller length on gas exchange were evaluated. Reducing bundle diameter was found to improve CO2 removal performance, while bundle and impeller length insignificantly affected performance. Subsequent in vitro hemolysis testing showed the ULFED to be comparable to a control circuit, indicating no hemolysis related issues are anticipated in vivo. Carbonic anhydrase (CA) enzyme fiber coatings were also evaluated for CO2R enhancement. CA fibers previously demonstrating 37% improved performance with specific applications at ultra-low blood flows. Mini-ULFED prototypes were fabricated but did not significantly outperform control fibers in gas exchange testing versus active mixing alone