Original Articles

Quantification of Carbon Dioxide Removal at Low Sweep Gas and Blood Flows

Address correspondence to: Juan de Villiers Hugo, BTech, Maastricht University Medical Center, P. Debyelaan 25, PO Box 5800, 6202 AZ Maastricht, The Netherlands. E-mail: juandevilliers.hugo@mumc.nl

Received: 10 January 2017
Accepted: 6 August 2017

Abstract

Advancement in oxygenator membrane technology has further expanded the boundaries in the clinical application of extracorporeal carbon dioxide removal (ECCO₂R). Despite the advent of modern poly-4-methyl-1-pentene (PMP) membranes, limited information exists on the performance of these membranes at low sweep gas and blood flows. Moreover, physiological relationships for CO₂ removal at these flows are less explored. Hence, CO₂ removal was quantified in an in vitro setting using a PMP membrane oxygenator. ECCO₂R was performed using a .8 m² surface pediatric oxygenator in an in vitro setting with freshly drawn single-source porcine blood. In this setting, low blood flows of either 200 or 350 mL/min were generated, with sweep gas flow rates of 100, 200, and 400 mL/min, respectively. CO₂ transfer ranged from 14.05 ± 4.35 mL/min/m² to 18.76 ± 4.26 mL/min/m² at a sweep gas to a blood flow ratio of .5:1 to 2:1 (p < .01). Decreasing this ratio i.e., increasing the blood flow (.5:1.75 and 2:1.75) resulted in a lower CO₂ transfer of 10.00 ± 4.77 mL/min/m² to 16.87 ± 5.09 mL/min/m², which was still statistically significant (p < .01). Alternatively, decreasing the sweep gas to blood flow ratio, while maintaining a constant gas flow, did not show a significant increase in CO₂ extraction (p > .05). At these test parameters, an increase in sweep gas improved the CO₂ transfer, whereas an increase in blood flow resulted in a lower CO₂ transfer. These results indicate that CO₂ removal in low-flow ECCO₂R is mainly sweep gas flow driven. Although these settings might not be applicable for clinical use, this study gives tangible information about the important factor involved in ECCO₂R.