Sweep Gas Flowrate and C02 Exchange in Artificial Lungs

Abstract A simple analysis and graphic result are presented for characterizing the dependence of CO₂ exchange on the sweep gas (ventilating gas) flowrate in artificial lungs. The analysis requires no knowledge of the device-specific mass transfer characteristics of an artificial lung, nor does it require detailed mathematical modeling or computer simulation. Rather, it uses appropriate normalization to establish generic features of the gas flow dependency of CO₂ exchange that are applicable to all artificial lung devices. Principal results are that the transition from relatively gas flow-sensitive to gas flow-insensitive CO₂, exchange occurs at sweep gas flowrates of approximately 40–60 times the CO₂ exchange rate. Achieving a CO₂ exchange rate within 85% of maximal (for a given oxygenator and blood-side conditions) requires a sweep gas flowrate of no less than approximately 50 times the nominal CO₂ exchange rate. When the sweep gas flowrate is less than 20 times the CO₂ exchange rate, CO₂ exchange is highly gas flow dependent and less than one-half the maximal possible rate.