Development and evaluation of a variable, miniaturized oxygenator for various test methods.

BACKGROUND: Extracorporeal membrane oxygenation (ECMO) became an accepted therapy for the treatment of severe acute respiratory distress syndrome and chronic obstructive pulmonary disease. However, ECMO systems are still prone to thrombus formation and decrease of gas exchange over time. Therefore, it is necessary to conduct qualified studies to identify parameters for optimization of ECMO systems, and especially the oxygenator. However, commercially marketed oxygenators are not always appropriate and available for certain research use cases. Therefore, we aimed to design an oxygenator, which is suitable for various test conditions such as blood tests, numerical simulation, and membrane studies, and can be modified in membrane area size and manufactured in laboratory. METHODS: Main design criteria are a homogeneous blood flow without stagnation zones, low pressure drop, manufacturability in the lab, size variability with one set of housing parts and cost-efficiency. Our newly designed oxygenator was tested comparatively regarding blood cell damage, gas transfer performance and pressure drop to prove the validity of the design in accordance with a commercial device. RESULTS: No statistically significant difference between the tested oxygenators was detected and our new oxygenator demonstrated sufficient hemocompatibility. Furthermore, our variable oxygenator has proven that it can be easily manufactured in the laboratory, allows to use various membrane fiber configurations and can be reopened easily and non-destructively for analysis after use, and the original geometry is available for numerical simulations. CONCLUSION: Therefore, we consider this newly developed device as a valuable tool for basic experimental and numerical research on the optimization of oxygenators.

Effects of Pulsatile Blood Flow on Oxygenator Performance.

Extracorporeal membrane oxygenation (ECMO) is mainly used for the therapy of acute respiratory distress syndrome and chronic obstructive lung disease. In the last years, the development of these systems underwent huge steps in optimization, but there are still problems with thrombus formation, clogging, and thus insufficient gas exchange. One idea of ECMO optimization is a pulsatile blood flow through the oxygenator, but this is still a controversy discussion. Analyzing available publications, it was not possible to identify a general statement about the effect of pulsatile blood flow on the gas exchange performance. The variety of parameters and circuit components have such a high influence on the outcome that a direct comparison of the studies is difficult. For this reason, we performed a structured study to evaluate the effects of pulsatile blood flow on the gas exchange performance of oxygenator. In in vitro tests according to DIN EN ISO 7199, we tested a small oxygenator (0.25 m2 exchange surface, polymethylpentene fibers, 33 mL priming volume) with constant and pulsatile blood flow in comparison. Therefore, we varied the mean blood flow from 250 to 1200 mL/min, the amplitude of 0, 20, and 50%, and the frequency of 30, 60, and 90 bpm. The results demonstrate that the gas transfer for pulsatile and constant blood flow was similar (oxygen: 36-64 mLO2 /LBlood ; carbon dioxide 35-80 mLCO2 /LBlood ) for the same mean blood flow ranges. Over all, the results and analyses showed a statistically nonsignificant difference between pulsatile and nonpulsatile flow. Consequently, we conclude that the implementation of pulsatile blood flow has only a small to no effect on the gas exchange performance in an oxygenator. As the results were obtained using an oxygenator with a coiled fiber bundle, the test must be verified for a stacked fiber oxygenator.

In Vitro and In Vivo Feasibility Study for a Portable VV-ECMO and ECCO2R System.

Extracorporeal membrane oxygenation (ECMO) is an established rescue therapy for patients with chronic respiratory failure waiting for lung transplantation (LTx). The therapy inherent immobilization may result in fatigue, consecutive deteriorated prognosis, and even lost eligibility for transplantation. We conducted a feasibility study on a novel system designed for the deployment of a portable ECMO device, enabling the physical exercise of awake patients prior to LTx. The system comprises a novel oxygenator with a directly connected blood pump, a double-lumen cannula, gas blender and supply, as well as control and energy management. In vitro experiments included tests regarding performance, efficiency, and blood damage. A reduced system was tested in vivo for feasibility using a novel large animal model. Six anesthetized pigs were first positioned in supine position, followed by a 45° angle, simulating an upright position of the patients. We monitored performance and vital parameters. All in vitro experiments showed good performance for the respective subsystems and the integrated system. The acute in vivo trials of 8 h duration confirmed the results. The novel portable ECMO-system enables adequate oxygenation and decarboxylation sufficient for, e.g., the physical exercise of designated LTx-recipients. These results are promising and suggest further preclinical studies on safety and efficacy to facilitate translation into clinical application.