Oxygenator performance and artificial-native lung interaction
During extracorporeal membrane oxygenation (ECMO), oxygen (O2) transfer (V'O2) and carbon dioxide (CO2) removal (V’CO2) are partitioned between the native lung (NL) and the membrane lung (ML), related to the patient’s metabolic-hemodynamic pattern. The ML could be assimilated to a NL both in a physiological and a pathological way. ML O2 transfer (V’O2ML) is proportional to extracorporeal blood flow and the difference in O2 content between each ML side, while ML CO2 removal (V’CO2ML) can be calculated from ML gas flow and CO2 concentration at sweep gas outlet. Therefore, it is possible to calculate the ML gas exchange efficiency. Due to the ML aging process, pseudomembranous deposits on the ML fibers may completely impede gas exchange, causing a “shunt effect”, significantly correlated to V’O2ML decay. Clot formation around fibers determines a ventilated but not perfused compartment, with a “dead space effect”, negatively influencing V’CO2ML. Monitoring both shunt and dead space effects might be helpful to recognise ML function decline. Since ML failure is a common mechanical complication, its monitoring is critical for right ML replacement timing and it also important to understand the ECMO system performance level and for guiding the weaning procedure. ML and NL gas exchange data are usually obtained by non-continuous measurements that may fail to be timely detected in critical situations. A real-time ECMO circuit monitoring system therefore might have a significant clinical impact to improve safety, adding relevant clinical information. In our clinical practise, the integration of a real-time monitoring system with a set of standard measurements and samplings contributes to improve the safety of the procedure with a more timely and precise analysis of ECMO functioning. Moreover, an accurate analysis of NL status is fundamental in clinical setting, in order to understand the complex ECMO-patient interaction, with a multi-dimensional approach.