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

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.