In vivo carbon dioxide clearance of a low-flow extracorporeal carbon dioxide removal circuit in patients with acute exacerbations of chronic obstructive pulmonary disease

Background: Veno-venous extracorporeal carbon dioxide removal allows clearance of CO 2 from the blood and is becoming popular to enhance protective mechanical ventilation and assist in the management of acute exacerbations of chronic obstructive pulmonary disease, including the prevention of intubation. The main factor determining CO 2 transfer across a membrane lung for any given blood flow rate and venous CO 2 content is the sweep gas flow rate. The in vivo characteristics of CO 2 clearance using ultra-low blood flow devices in patients with acute exacerbations of chronic obstructive pulmonary disease has not been previously described. Methods: Patients commenced on extracorporeal carbon dioxide removal for acute exacerbations of chronic obstructive pulmonary disease recruited to a randomized controlled trial of non-invasive ventilation versus extracorporeal carbon dioxide removal had pre- and post-membrane circuit gases measured after each increment of sweep gas flow to allow calculation of the transmembrane CO 2 clearance. This was compared with the clearance reported by the device and also corrected to inlet PCO 2 to allow characterization of the CO 2 clearance of the device at different sweep gas flow rates. Results: CO 2 clearance was calculated using both the transmembrane CO 2 whole-blood content difference and CO 2 clearance reported by the device. The two methods demonstrated a linear relationship and agreement with a bias of 14 mL/minute (SD = ±10) and an R 2 of 0.92. The membrane CO 2 clearance was non-linear with nearly two thirds of total clearance achieved with sweep gas flow below 2 L/minute (VCO 2 of 40 ± 16.7 mL/minute) and a plateau above 5 L/minute sweep gas flow (VCO 2 64 ± 1 2.4 mL/minute). Conclusion: The extracorporeal carbon dioxide removal device used in the study provides efficient clearance of CO 2 at low sweep flow rates which then plateaus. This has implications for how the device may be used in clinical practice, particularly during the weaning phase where the final discontinuation of the device may take longer than anticipated. (ClinicalTrials.gov: NCT02086084, registered 13 March 2014, https://clinicaltrials.gov/ct2/show/NCT02086084 )