Extracorporeal CO2 Removal: The Minimally Invasive Approach, Theory, and Practice*

Objectives: Minimally invasive extracorporeal CO 2 removal is an accepted supportive treatment in chronic obstructive pulmonary disease patients. Conversely, the potential of such technique in treating acute respiratory distress syndrome patients remains to be investigated. The aim of this study was: 1) to quantify membrane lung CO 2 removal (V co 2ML ) under different conditions and 2) to quantify the natural lung CO 2 removal (V co 2NL ) and to what extent mechanical ventilation can be reduced while maintaining total expired CO 2 (V co 2tot = V co 2ML + V co 2NL ) and arterial P co 2 constant. Design: Experimental animal study. Setting: Department of Experimental Animal Medicine, University of Göttingen, Germany. Subjects: Eight healthy pigs (57.7 ± 5 kg). Interventions: The animals were sedated, ventilated, and connected to the artificial lung system (surface 1.8 m 2 , polymethylpentene membrane, filling volume 125 mL) through a 13F catheter. V co 2ML was measured under different combinations of inflow P co 2 (38.9 ± 3.3, 65 ± 5.7, and 89.9 ± 12.9 mm Hg), extracorporeal blood flow (100, 200, 300, and 400 mL/min), and gas flow (4, 6, and 12 L/min). At each setting, we measured V co 2ML , V co 2NL , lung mechanics, and blood gases. Measurements and Main Results: V co 2ML increased linearly with extracorporeal blood flow and inflow P co 2 but was not affected by gas flow. The outflow P co 2 was similar regardless of inflow P co 2 and extracorporeal blood flow, suggesting that V co 2ML was maximally exploited in each experimental condition. Mechanical ventilation could be reduced by up to 80–90% while maintaining a constant Pa co 2 . Conclusions: Minimally invasive extracorporeal CO 2 removal removes a relevant amount of CO 2 thus allowing mechanical ventilation to be significantly reduced depending on extracorporeal blood flow and inflow P co 2 . Extracorporeal CO 2 removal may provide the physiologic prerequisites for controlling ventilator-induced lung injury.