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Abstract
Extracorporeal life support [ECLS] is the extended use of cardiopulmonary bypass [CPB] to support patients suffering from reversible cardiac and/or respiratory failure. Veno-venous ECLS [VV ECLS] is used to support patients suffering from only respiratory failure. Because the drainage and reinfusion cannulae for VV ECLS are both located in the venous circulation, a phenomenon known as recirculation occurs where oxygenated blood will be drained out again and recirculated through the ECLS circuit. This study compared a MATLAB simulation of recirculation with an experiment to characterize the relationship between ECLS drainage blood oxygen content and recirculation.
A MATLAB graphical user interface [GUI] was created which accepts user-specified values for saturation [SO2] and partial pressure of oxygen [PO2] for oxygenated and deoxygenated blood, as well as hemoglobin concentration, recirculation fraction, and the pH of the drainage blood. This model then predicts, based on conservation equations, the oxygen content and saturation of ECLS drainage blood. Two in vitro CPB circuits were also constructed, one for oxygenation and one for deoxygenation. The blood was then mixed in different proportions to simulate different levels of recirculation, and the oxygen content and saturation were measured and compared to model predictions.
The results illustrate that a linear relationship exists between recirculation fraction and ECLS drainage blood oxygen content [p is less than 0.001], and that the MATLAB model is a very accurate predictor of ECLS drainage blood oxygen content and saturation, based on comparison to experimental data. It was also determined that hemoglobin concentration and pH of the drainage blood can have a dramatic effect on the ECLS drainage blood oxygen content and saturation, respectively.