Determining oxygen exchange from gas-side analysis in artificial lungs

Blood flow rates and blood tension values are difficult to attain during an invivo test of an intravascular artificial lung. As a result, a gas-side oxygen measurement technique is needed This study will discuss two techniques used to make these gas-side measurements, the simple mass balance approach and the Haldane correction approach, and make suggestions on their usage. The simple oxygen mass balance approach involves measuring both oxygen flow and oxygen concentration of both the gas inlet and gas outlet to the artificial lung. On the other hand, the Haldane correction approach couples an addition mass balance of a tracer gas with the simple oxygen mass balance equations to eliminate the need for one of the oxygen gas flow measurements. Using the simple mass balance approach and single sample uncertainty analysis, the oxygen gas exchange error is quite large at ± 90%. Using the Haldane correction approach, assuming that there is no tracer gas mass transfer, the single sample error is reduced to ± 40% However, small amounts of tracer gas mass transfer can significantly diminish the accuracy of the Haldane correction approach; a tracer gas mass transfer rate equivalent to only 1.0% of the carbon dioxide transfer rate can increase the oxygen exchange error to ± 60%. Due to the inherent Haldane correction approach sensitivity to small amounts of tracer gas mass transfer, oxygen gas exchange analysis of artificial lungs should be done using blood-side analysis with ex-vivo testing.