Estimation of Blood Oxygen Saturation in the Circulation Circuit for Extracorporeal Membrane Oxygenation

Extracorporeal membrane oxygenation (ECMO) is a treatment that supports heart and lung functions with a circulation circuit external to the body. In ECMO, it is important to monitor blood oxygen saturation (SO
₂
) in the circulation tube. As a means of continuous SO
₂
measuring, a special connector is inserted into the circuit. However, this method is unsuitable for emergency treatment. Therefore, it is necessary to measure blood SO
₂
in the tube without the connector. However, this creates problems for SO
₂
estimation, due to varying blood concentration and flow velocity, hemolysis, and wall thickness of the tube. Therefore, we developed a SO
₂
estimation method that can calibrate the variation in blood concentration. The method is based on a conversion model between absorbance and SO
₂
(CAS), which varies depending on the concentration. In this method, the CAS for the SO
₂
estimation is estimated by CAS corresponding to two blood samples prepared in advance with different concentrations. The experiment for SO
₂
estimation was conducted with a spectroscope, a halogen light source, and a cut tube. We confirmed that the average error of estimated SO
₂
against the SO
₂
values measured by a gas analysis was 3.8% within a blood volume concentration range from 50 to 90%. In future work, to improve the estimation accuracy, we will improve our method by investigating other factors that may affect the accuracy.