Extracorporeal CO₂ Removal

The Minimally Invasive Approach, Theory, and Practice*

Objectives: Minimally invasive extracorporeal CO₂ 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 CO₂ removal (VCO_2ML) under different conditions and 2) to quantify the natural lung CO₂ removal (VCO_2NL) and to what extent mechanical ventilation can be reduced while maintaining total expired CO₂ (VCO_2tot = VCO_2ML + VCO_2NL) and arterial PCO₂ 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 m², polymethylpentene membrane, filling volume 125 mL) through a 13F catheter. VCO_2ML was measured under different combinations of inflow PCO₂ (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 VCO_2ML, VCO_2NL, lung mechanics, and blood gases.

Measurements and Main Results: VCO_2ML increased linearly with extracorporeal blood flow and inflow PCO₂but was not affected by gas flow. The outflow PCO₂ was similar regardless of inflow PCO₂ and extracorporeal blood flow, suggesting that VCO_2ML was maximally exploited in each experimental condition. Mechanical ventilation could be reduced by up to 80–90% while maintaining a constant PaCO₂.

Conclusions: Minimally invasive extracorporeal CO₂ removal removes a relevant amount of CO₂ thus allowing mechanical ventilation to be significantly reduced depending on extracorporeal blood flow and inflow PCO₂. Extracorporeal CO₂ removal may provide the physiologic prerequisites for controlling ventilator-induced lung injury.