Oxygenator performance and artificial-native lung interaction

Abstract

During extracorporeal membrane oxygenation (ECMO), oxygen (O) transfer (V'O) and carbon dioxide (CO) removal (V'CO) 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 O transfer (V'OML) is proportional to extracorporeal blood flow and the difference in O content between each ML side, while ML CO removal (V'COML) can be calculated from ML gas flow and CO 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'OML decay. Clot formation around fibers determines a ventilated but not perfused compartment, with a "dead space effect", negatively influencing V'COML. 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.

Continuous monitoring of membrane lung carbon dioxide removal during ECMO: experimental testing of a new volumetric capnometer

“…3 Evaluation of the ML performance is of paramount importance during ECMO, not only because it might indicate a gradual or sudden functional impairment and therefore the need and timing for ML replacement due to clot formation inside the oxygenator, but may also provide information regarding both the native lung (NL) and the ML contribution to the global ventilation, hence guiding the weaning process. 4 Furthermore, as for NL, ML performance is assessed by measuring both O 2 transfer through the ML (V′O 2 ML) and CO 2 removal (V′CO 2 ML) through the oxygenator.…”

Extracorporeal Strategies in Acute Respiratory Distress Syndrome

“…where [CO 2 ] ML.e is the concentration at ML sweep gas outlet. 8 At flow rates at which ECCO 2 R operates, with a sufficiently large and efficient membrane, there is maximal CO 2 extraction with minimal sweep GF, VCO 2.ML therefore becomes dependent on ECBF. 9 Therefore, the resultant PaCO 2 of the patient will mainly be determined by sweep GF on VV-ECMO and by ECBF on ECCO 2 R.…”

How I approach membrane lung dysfunction in patients receiving ECMO

“…Activation of coagulation and fibrinolysis can precipitate systemic coagulopathy or hemolysis, while clot deposition can obstruct blood flow [ 6 , 7 ]. Additionally, moisture buildup in the gas phase and protein and cellular debris accumulation in the blood phase may contribute to shunt and dead-space physiology, respectively, impairing gas exchange [ 8 , 9 ]. These three categories—hematologic abnormalities, mechanical obstruction, and inadequate gas exchange—prompt the majority of ML exchanges.…”