In this model, considerable CO 2 removal occurred only with the larger membrane lung surface of 0.8m 2 and when blood flow rates of ≥ 900 mL/min were used. The influence of sweep gas flow on the CO 2 removal capacity of ECCO 2R systems depends predominantly on blood flow rate and membrane lung surface area. The delta of normalized CO 2 elimination increased from 4 ± 2 to 26 ± 7 mL/min with blood flow rates being increased from 300 to 1800 mL/min, respectively. The membrane lung with a surface area of 0.8m 2 allowed a maximum normalized CO 2 elimination rate of 101 ± 12 mL/min with increasing influence of sweep gas flow. The increase in sweep gas flow from 2 to 8 L/min increased normalized CO 2 elimination from 35 ± 5 to 41 ± 6 with 900 mL blood flow/min, whereas with lower blood flow rates, any increase was less effective, levelling out at 4 L sweep gas flow/min. The membrane lung with a surface of 0.4m 2 allowed a maximum normalized CO 2 elimination rate of 41 ± 6 mL/min with 8 L/min sweep gas flow and 900 mL blood flow/min. Reversal of hypercapnia was only feasible when blood flow rates above 900 mL/min were used with a membrane lung surface area of at least 0.8m 2. Extracorporeal CO 2 elimination was normalized to a PaCO 2 of 45 mmHg before the membrane lung. Sweep gas was titrated under each condition from 2 to 8 L/min in steps of 2 L/min. During each experiment, the blood flow was increased stepwise from 300 to 900 mL/min, with further increases up to 1800 mL/min with the larger membrane lung in steps of 300 mL/min. Two different membrane lungs, with surface areas of 0.4 and 0.8m 2, were used in nine pigs with experimentally-induced hypercapnia.
The present porcine model study was aimed at determining the impact of varying sweep gas flow rates on CO 2 removal under different blood flow conditions and membrane lung surface areas. Blood flow rates range in clinical practice from 200 mL/min to more than 1500 mL/min, and sweep gas flow rates range from less than 1 to more than 10 L/min. Veno-venous extracorporeal carbon dioxide (CO 2) removal (vv-ECCO 2R) is increasingly being used in the setting of acute respiratory failure.
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