In vivo carbon dioxide clearance of a low-flow extracorporeal carbon dioxide removal circuit in patients with acute exacerbations of chronic obstructive pulmonary disease. (July 2020) - Barrett, Nicholas A
Background: Veno-venous extracorporeal carbon dioxide removal allows clearance of CO2 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 CO2 transfer across a membrane lung for any given blood flow rate and venous CO2 content is the sweep gas flow rate. The in vivo characteristics of CO2 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 CO2 clearance. This was compared with the clearance reported by the device and also corrected to inlet PCO2 to allow characterization of the CO2 clearance of the device at different sweep gas flow rates. Results: CO2 clearance was calculated using both the transmembrane CO2 whole-blood content difference and CO2 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 CO2 clearance was non-linear with nearly two thirds of total clearance achieved with sweep gas flow below 2 L/minute (VCO2 of 40 ± 16.7 mL/minute) and a plateau above 5 L/minute sweep gas flow (VCO2 64 ± 1 2.4 mL/minute). Conclusion: The extracorporeal carbon dioxide removal device used in the study provides efficient clearance of CO2 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 )