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Background: Membranes based on triply periodic minimal surfaces (TPMS) have proven a superior gas transfer compared to the contemporary hollow fiber membrane (HFM) design in artificial lungs. The improved oxygen transfer is attributed to disrupting the laminar boundary layer adjacent to the membrane surface known as main limiting factor to mass transport. However, it requires experimental proof that this improvement is not at the expense of greater damage to the blood. Hence, the aim of this work is a valid statement regarding the structure‐dependent hemolytic behavior of TPMS structures compared to the current HFM design. Methods: Hemolysis tests were performed on structure samples of three different kind of TPMS‐based designs (Schwarz‐P, Schwarz‐D and Schoen's Gyroid) in direct comparison to a hollow fiber structure as reference. Results: The results of this study suggest that the difference in hemolysis between TPMS membranes compared to HFMs is small although slightly increased for the TPMS membranes. There is no significant difference between the TPMS structures and the hollow fiber design. Nevertheless, the ratio between the achieved additional oxygen transfer and the additional hemolysis favors the TPMS‐based membrane shapes. Conclusion: TPMS‐shaped membranes offer a safe way to improve gas transfer in artificial lungs. [ABSTRACT FROM AUTHOR]

The most common technical complication during ECMO is clot formation. A large clot inside a membrane oxygenator reduces effective membrane surface area and therefore gas transfer capabilities, and restricts blood flow through the device, resulting in an increased membrane oxygenator pressure drop (dpMO). The reasons for thrombotic events are manifold and highly patient specific. Thrombus formation inside the oxygenator during ECMO is usually unpredictable and remains an unsolved problem. Clot sizes and positions are well documented in literature for the Maquet Quadrox‐i Adult oxygenator based on CT data extracted from devices after patient treatment. Based on this data, the present study was designed to investigate the effects of large clots on purely technical parameters, for example, dpMO and gas transfer. Therefore, medical grade silicone was injected into the fiber bundle of the devices to replicate large clot positions and sizes. A total of six devices were tested in vitro with silicone clot volumes of 0, 30, 40, 50, 65, and 85 mL in accordance with ISO 7199. Gas transfer was measured by sampling blood pre and post device, as well as by sampling the exhaust gas at the devices' outlet at blood flow rates of 0.5, 2.5, and 5.0 L/min. Pre and post device pressure was monitored to calculate the dpMO at the different blood flow rates. The dpMO was found to be a reliable parameter to indicate a large clot only in already advanced "clotting stages." The CO2 concentration in the exhaust gas, however, was found to be sensitive to even small clot sizes and at low blood flows. Exhaust gas CO2 concentration can be monitored continuously and without any risks for the patient during ECMO therapy to provide additional information on the endurance of the oxygenator. This may help detect a clot formation and growth inside a membrane oxygenator during ECMO even if the increase in dpMO remains moderate. [ABSTRACT FROM AUTHOR]

Flow distribution is key in artificial lungs, as it directly influences gas exchange performance as well as clot forming and blood damaging potential. The current state of computational fluid dynamics (CFD) in artificial lungs can only give insight on a macroscopic level due to model simplification applied to the fiber bundle. Based on our recent work on wound fiber bundles, we applied particle image velocimetry (PIV) to the model of an artificial lung prototype intended for neonatal use to visualize flow distribution in a stacked fiber bundle configuration to (i) evaluate the feasibility of PIV for artificial lungs, (ii) validate CFD in the fiber bundle of artificial lungs, and (iii) give a suggestion how to incorporate microscopic aspects into mainly macroscopic CFD studies. To this end, we built a fully transparent model of an artificial lung prototype. To increase spatial resolution, we scaled up the model by a factor of 5.8 compared with the original size. Similitude theory was applied to ensure comparability of the flow distribution between the device of original size and the scaled-up model. We focused our flow investigation on an area (20 × 70 × 43 mm) in a corner of the model with a Stereo-PIV setup. PIV data was compared to CFD data of the original sized artificial lung. From experimental PIV data, we were able to show local flow acceleration and declaration in the fiber bundle and meandering flow around individual fibers, which is not possible using state-of-the-art macroscopic CFD simulations. Our findings are applicable to clinically used artificial lungs with a similar stacked fiber arrangement (e.g., Novalung iLa and Maquet QUADROX-I). With respect to some limitations, we found PIV to be a feasible experimental flow visualization technique to investigate blood-sided flow in the stacked fiber arrangement of artificial lungs. [ABSTRACT FROM AUTHOR]

Background: Extracorporeal carbon dioxide removal (ECCO2R) uses an extracorporeal circuit to directly remove carbon dioxide from the blood either in lieu of mechanical ventilation or in combination with it. While the potential benefits of the technology are leading to increasing use, there are very real risks associated with it. Several studies demonstrated major bleeding and clotting complications, often associated with hemolysis and poorer outcomes in patients receiving ECCO2R. A better understanding of the risks originating specifically from the rotary blood pump component of the circuit is urgently needed.Methods: High-resolution computational fluid dynamics was used to calculate the hemodynamics and hemocompatibility of three current rotary blood pumps for various pump flow rates.Results: The hydraulic efficiency dramatically decreases to 5-10% if operating at blood flow rates below 1 L/min, the pump internal flow recirculation rate increases 6-12-fold in these flow ranges, and adverse effects are increased due to multiple exposures to high shear stress. The deleterious consequences include a steep increase in hemolysis and destruction of platelets.Conclusions: The role of blood pumps in contributing to adverse effects at the lower blood flow rates used during ECCO2R is shown here to be significant. Current rotary blood pumps should be used with caution if operated at blood flow rates below 2 L/min, because of significant and high recirculation, shear stress, and hemolysis. There is a clear and urgent need to design dedicated blood pumps which are optimized for blood flow rates in the range of 0.5-1.5 L/min. [ABSTRACT FROM AUTHOR]

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2019. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2019 . Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901 . [ABSTRACT FROM AUTHOR]