Comparison of hemodynamic features and thrombosis risk of membrane oxygenators with different structures: A numerical study.

PURPOSE: The geometric structure of the membrane oxygenator can exert an impact on its hemodynamic features, which contribute to the development of thrombosis, thereby affecting the clinical efficacy of ECMO treatment. The purpose of this study is to investigate the impact of varying geometric structures on hemodynamic features and thrombosis risk of membrane oxygenators with different designs. METHODS: Five oxygenator models with different structures, including different number and location of blood inlet and outlet, as well as variations in blood flow path, were established for investigation. These models are referred to as Model 1 (Quadrox-i Adult Oxygenator), Model 2 (HLS Module Advanced 7.0 Oxygenator), Model 3 (Nautilus ECMO Oxygenator), Model 4 (OxiaACF Oxygenator) and Model 5 (New design oxygenator). The hemodynamic features of these models were numerically analyzed using the Euler method combined with computational fluid dynamics (CFD). The accumulated residence time (ART) and coagulation factor concentrations (C[i], where i represents different coagulation factors) were calculated by solving the convection diffusion equation. The resulting relationships between these factors and the development of thrombosis in the oxygenator were then investigated. RESULTS: Our results show that the geometric structure of the membrane oxygenator, including the location of the blood inlet and outlet as well as the design of the flow path, has a significant impact on the hemodynamic surroundings within the oxygenator. In comparison to Model 4, which had the inlet and outlet located in the center position, Model 1 and Model 3, which had the inlet and outlet at the edge of the blood flow field, exhibited a more uneven distribution of blood flow within the oxygenator, particularly in areas distant from the inlet and outlet, which was accompanied with lower flow velocity and higher values of ART and C[i], leading to the formation of flow dead zones and an elevated risk of thrombosis. The oxygenator of Model 5 is designed with a structure that features multiple inlets and outlets, which greatly improves the hemodynamic environment inside the oxygenator. This results in a more even distribution of blood flow within the oxygenator, reducing areas with high values of ART and C[i], and ultimately lowering the risk of thrombosis. The oxygenator of Model 3 with circular flow path section shows better hemodynamic performance compared to the oxygenator of Model 1 with square circular flow path. The overall ranking of hemodynamic performance for all five oxygenators is as follows: Model 5 > Model 4 > Model 2 > Model 3 > Model 1, indicating that Model 1 has the highest thrombosis risk while Model 5 has the lowest. CONCLUSION: The study reveals that the different structures can affect the hemodynamic characteristics inside membrane oxygenators. The design of multiple inlets and outlets can improve the hemodynamic performance and reduce the thrombosis risk in membrane oxygenators. These findings of this study can be used to guide the optimization design of membrane oxygenators for improving hemodynamic surroundings and reducing thrombosis risk.

Life span of different extracorporeal membrane systems for severe respiratory failure in the clinical practice.

Over the past decade, veno-venous extracorporeal membrane oxygenation (vvECMO) has been increasingly utilized in respiratory failure in patients. This study presents our institution´s experience focusing on the life span of ECMO systems reflecting the performance of a particular system. A retrospective review of our ECMO database identified 461 adult patients undergoing vvECMO (2010-2017). Patients that required more than one system and survived the first exchange >24 hours (n = 139) were included. Life span until the first exchange and exchange criteria were analyzed for all systems (PLS, Cardiohelp HLS-set, both Maquet Cardiopulmonary, Rastatt, Germany; Deltastream/Hilite7000LT, iLA-activve, Xenios/NovaLung, Heilbronn, Germany; ECC.O5, LivaNova, Mirandola, Italy). At our ECMO center, the frequency of a system exchange was 30%. The median (IQR) life span was 9 (6-12) days. There was no difference regarding the different systems (p = 0.145 and p = 0.108, respectively). However, the Deltastream systems were exchanged more frequently due to elective technical complications (e. g. worsened gas transfer, development of coagulation disorder, increased bleedings complications) compared to the other exchanged systems (p = 0.013). In summary, the used ECMO systems are safe and effective for acute respiratory failure. There is no evidence for the usage of a specific system. Only the increased predictability of an imminent exchange preferred the usage of a Deltastream system. However, the decision to use a particular system should not depend solely on the possible criteria for an exchange.

Soporte mecánico con membrana de oxigenación extracorpórea veno-arterial (ECMO-VA): evolución a corto y a largo plazo tras la retirada de la asistencia / Mechanical support with venoarterial extracorporeal membrane oxygenation (ECMO-VA): Short-term and long-term prognosis after a successful weaning

Objetivo: La membrana de oxigenación extracorpórea (ECMO) es un tipo de asistencia circulatoria que asocia elevada mortalidad. Sin embargo, superar la fase inicial de soporte mecánico no implica supervivencia ni a corto ni a largo plazo. Objetivo: describir las características y evolución de los pacientes con shock cardiogénico refractario (SCR) asistidos con ECMO veno-arterial (ECMO-VA) en un hospital con programa de trasplante cardíaco. Diseño: Estudio de cohortes y retrospectivo de centro único. Ámbito: UCI cardiológica de un hospital terciario. Pacientes: Un total de 46 pacientes asistidos consecutivamente con una ECMO-VA durante 6 años. Intervenciones: Análisis de la mortalidad hospitalaria tras la retirada del soporte mecánico, de la supervivencia global (SG) y de los factores asociados. Resultados: Quince pacientes (33%) fallecieron con la ECMO-VA y 31 (67%) sobrevivieron a su retirada tras un soporte de 8 días (RIC: 5-15); 14 pacientes fueron trasplantados. La mortalidad hospitalaria en estos pacientes fue del 32% (10/31) y se relacionó con: edad (p=0,001), SAPS-II (p=0,009), sangrado de cánulas (p=0,01), indicación de SCR post-IAM (p=0,001). Con una mediana de seguimiento de 27 meses (RIC: 11-49), seguían vivos el 91% de los pacientes que fueron dados de alta del hospital. La SG tras la retirada de la ECMO-VA se relacionó con el tipo de indicación (p=0,002), teniendo peor pronóstico los pacientes con SCR postinfarto. Conclusiones: En nuestra experiencia, la ECMO-VA es un tipo de asistencia mecánica que puede utilizarse en el manejo del SCR. Asocia una mortalidad precoz elevada, pero tras superar la fase hospitalaria la supervivencia de los pacientes es buena (AU)

Objective: Extracorporeal membrane oxygenation (ECMO) affords mechanical circulatory assistance associated to high mortality. However, weaning from such mechanical support may not imply improved short- or long-term survival. This study describes the characteristics and evolution of patients with refractory cardiogenic shock (RCS) subjected to venoarterial ECMO (VA-ECMO) in a hospital with a heart transplant program. Design: A single-center, retrospective cohort study was carried out. Setting: The cardiovascular ICU of a tertiary hospital. Patients: Forty-six patients consecutively subjected to VA-ECMO over 6 years. Interventions: Hospital mortality after weaning from ECMO and overall survival (OS) were analyzed. Results: Fifteen patients (33%) died with VA-ECMO and 31 (67%) were weaned after 8 days of support (IQR: 5-15). Fourteen patients under went transplantation. Hospital mortality in these patients was 32% (10/31), and was associated to age (P=.001), SAPS II score (P=.009), cannulation bleeding (P=.01) and post-acute myocardial infarction RCS (P=.001). After a median follow-up of 27 months (IQR: 11-49), 91% of the patients discharged from hospital were still alive. Overall survival after weaning from assistance was associated to the type of cardiac disease (P=.002). Patients with RCS after acute myocardial infarction had a poorer prognosis. Conclusions: In our experience, VA-ECMO can be used as mechanical assistance in the management of RCS. The technique is associated to high early mortality, though the long-term survival rate after hospital discharge is good (AU)

[Preliminary study of intravascular oxygenator in braid in vitro].

Intravenous membrane oxygenator (IVOX), an artificial lung usually located in vena caval system, can provide extra oxygen outside the lung for patients suffering from respiratory failure. However, gas exchange areas of IVOX are limited because of confined space in caval system. The increase of the diameter of IVOX may impede the return of venous blood to heart, and result in serious low blood pressure. Thus, it is important to increase the efficiency of IVOX by reducing the diffusive resistance of boundary layers. In the present study, the hollow member fiber of IVOX was weaved in braids; we tested the oxygen transfer efficiency and blood flow resistance of this IVOX in vitro. The results showed that the total transferred oxygen, the oxygen transfer rate and blood resistance increased with the increase of blood flow. The oxygen volume transferred by the IVOX and the oxygen transfer rate were (55.97 +/- 0.51) ml/min and (127.19 +/- 0.66) ml/(min x m)2 respectively at the blood flow of 5 L/min and hemoglobin of 120 g/L. They were significantly higher than those at 4 L/min and 3.5 L/min, respectively. The pressure drop also increased from (11.87 +/- 1.57) cmH2O at 3.5 L/min of blood flow to (18.53 +/- 0.99) cmH2O at 4 L/min and 19.77+/- 0.51 cmH2O at 5 L/min. However, they are safe to the patients (< 20 cmH2O). These results suggest that this braid type of IVOX can safely provide 20%-30% oxygen outside the lung for an adult patient.

Plasma leakage of oxygenators in ECMO depends on the type of oxygenator and on patient variables.

This study was conducted to identify the causes of plasma leakage of oxygenators in extra corporeal membrane oxygenation (ECMO). From 1996 through 2002, 91 oxygenators were used in 62 patients undergoing ECMO for respiratory and/or cardiac failure. Several types of oxygenators were used (Medtronic Maxima, Minima, PRF, Medos Hilite). Patient variables and variables related to the ECMO set-up were analysed for their relationship with oxygenator failure by a time related multiple regression analysis (Cox). Oxygenator failure occurred in 26% of the cases. The analysis identified the type of oxygenator (p=0.0016), younger patient age (p=0.04) and the number of oxygenators used (p=0.03) as the independent significant risk factors. The type of oxygenator used has the most overwhelming effect (significantly less leakage with the Medos Hilite). In conclusion, leakage of oxygenators is predominantly caused by the type of oxygenator used. Patient variables (younger age and the number of oxygenators used in one patient) are also significant and allude to an inflammatory process as underlying mechanism of plasma leakage.

Fiber manufacturing, membrane classification, and winding technologies associated with membrane oxygenators.

Fiber bundling refers to the process of winding hollow polypropylene fibers onto the central core of a membrane oxygenator. Identifying the various bundling techniques serves to facilitate the clinician's understanding of unique device characteristics and the subsequent manufacturing process. This technical information has been voluntarily provided by the product managers and engineers of current membrane manufacturers. Currently the industry employs four primary bundling techniques: single strand, mat configuration, tape and helical. Single strand wraps one fiber at a time, up and down a central core to create the fiber bundle. A modification of the single strand technique is the single strand multi toe, where multiple fibers are wound at a time. Mat technology wraps a large, woven sheet consisting of uniformly placed fibers and spacing filaments, around the oxygenator core. A modification is the double mat, where two sheets of fibers oriented at a specific bias to each other, are wrapped to yield a fiber bundle. Tape technology involves evenly spaced fibers, 5 to 10 fibers wide, wrapped up and down the length of the core. Helical utilizes a spacing filament that is spiraled around each individual fiber and then around the core of the device.

[Artificial "membranous lung"]. / Iskusstvennoe "membrannoe legkoe"

The paper reviews and anlyses the most widespread up-to-date designs of membranous oxygenators. On an example of some types of membraneous oxygenators and their functional characteristics basic parameters for a comparative evaluation and choice of the "membranous lung" and its effective utilization have been deduced, viz. the circulation rate, the rate of the oxygen and carbon dioxide transport (per 1 m2 of the oxygenating surface), pressure differential, primarily filled up volume and oxygen consumption. The authors underline the need for determining the efficiency of the oxygenator with reference to O2 and CO2 and standard values of unsaturated blood indices. With due regard for promising trends in the future development of artificial "membranous lungs" features that may be of use in the classification of membraneous oxygenators have been systematized.