Evaluation of CO₂ removal rate of ECCO₂R for a renal replacement therapy platform in an experimental setting

A critical parameter of extracorporeal CO₂ removal (ECCO₂R) applications is the CO₂ removal rate (VCO₂). Low-flow venovenous extracorporeal support with large-size membrane lung remains undefined. This study aimed to evaluate the VCO₂ of a low-flow ECCO₂R with large-size membrane lung using a renal replacement therapy platform in an experimental animal model.

Twelve healthy pigs were placed under mechanical ventilation and connected to an ECCO₂R-CRRT system (surface area = 1.8 m²; OMNIset®, BBraun, Germany). Respiratory settings were reduced to induce two degrees of hypercapnia. VCO₂ was recorded under different combinations of PaCO₂ (50-69 or 70-89 mm Hg), extracorporeal blood flow (ECBF; 200 or 350 mL/min), and gas flow (4, 6, or 10 L/min).

VCO₂ increased with ECBF at all three gas flow rates. In severe hypercapnia, the increase in sweep gas flow from 4 to 10 L/min increased VCO₂ from 86.38 ± 7.08 to 96.50 ± 8.71 mL/min at an ECBF of 350 mL/min, whereas at ECBF of 200 mL/min, any increase was less effective. But in mild hypercapnia, the increase in sweep gas flow result in significantly increased VCO₂ at two ECBF. VCO₂ increased with PaCO₂ from 50-69 to 70-89 mm Hg at an ECBF of 350 mL/min, but not at ECBF of 200 mL/min. Post-membrane lung PCO₂ levels were similar for different levels of premembrane lung PCO₂ (p = 0.08), highlighting the gas exchange diffusion efficacy of the membrane lung in gas exchange diffusion. In severe hypercapnia, the reduction of PaCO₂ elevated from 11.5% to 19.6% with ECBF increase only at a high gas flow of 10 L/min (p < 0.05) and increase of gas flow significantly reduced PaCO₂ only at a high ECBF of 350 mL/min (p < 0.05).

Low-flow venovenous extracorporeal ECCO₂R-CRRT with large-size membrane lung is more efficient with the increase of ECBF, sweep gas flow rate, and the degree of hypercapnia. The influence of sweep gas flow on VCO₂ depends on the ECBF and degree of hypercapnia. Higher ECBF and gas flow should be chosen to reverse severe hypercapnia.