Compact intra-and extracorporeal oxygenator developments

Optimization of the IntraVascular Oxygenator Catheter Using Angular Oscillation

We demonstrate a methodology which both improves oxygen transport and reduces or eliminates bubble formation in a novel hyperbaric membrane oxygenator catheter model system. Angular oscillations were introduced to a bundle of hollow fiber membranes (HFMs) supplied with hyperbaric 100% oxygen at average gauge pressures up to 0.35 barg. Oscillating bundles enabled delivery of an oxygen flux of up to 400 mL min-1 m-2 in an aqueous solution, a doubling over a previous non-oscillating setup. Similarly, the addition of angular oscillations facilitated a five-fold reduction in pressure to achieve similar oxygen flux. The increased angular speed of oscillation improved flux, while the addition of angular micro-oscillation variations resulted in flux reductions of 7-20% compared to continuous macro-oscillation only, depending on mixing conditions. However, semi-quantitative visual observation demonstrated that angular oscillations reduced or eliminated the instance of oxygen bubble formation on the HFMs. The modeled mass transfer coefficients indicated a quasi linear relationship between rotational velocity and flux, suggesting that faster oscillation speeds could further improve oxygen mass transport allowing for HFM bundles to maintain high oxygen fluxes while eliminating bubble formation. This encourages further development of our compact oxygenating catheter that could be used intravascularly.

Anti-thrombogenic Surface Coatings for Extracorporeal Membrane Oxygenation: A Narrative Review

Extracorporeal membrane oxygenation (ECMO) is used in critical care to manage patients with severe respiratory and cardiac failure. ECMO brings blood from a critically ill patient into contact with a non-endothelialized circuit which can cause clotting and bleeding simultaneously in this population. Continuous systemic anticoagulation is needed during ECMO. The membrane oxygenator, which is a critical component of the extracorporeal circuit, is prone to significant thrombus formation due to its large surface area and areas of low, turbulent, and stagnant flow. Various surface coatings, including but not limited to heparin, albumin, poly(ethylene glycol), phosphorylcholine, and poly(2-methoxyethyl acrylate), have been developed to reduce thrombus formation during ECMO. The present work provides an up-to-date overview of anti-thrombogenic surface coatings for ECMO, including both commercial coatings and those under development. The focus is placed on the coatings being developed for oxygenators. Overall, zwitterionic polymer coatings, nitric oxide (NO)-releasing coatings, and lubricant-infused coatings have attracted more attention than other coatings and showed some improvement in in vitro and in vivo anti-thrombogenic effects. However, most studies lacked standard hemocompatibility assessment and comparison studies with current clinically used coatings, either heparin coatings or nonheparin coatings. Moreover, this review identifies that further investigation on the thrombo-resistance, stability and durability of coatings under rated flow conditions and the effects of coatings on the function of oxygenators (pressure drop and gas transfer) are needed. Therefore, extensive further development is required before these new coatings can be used in the clinic.

Toward a Long-Term Artificial Lung

Only a very small portion of end-stage organ failures can be treated by transplantation because of the shortage of donor organs. Although artificial long-term organ support such as ventricular assist devices provide therapeutic options serving as a bridge-to-transplantation or destination therapy for end-stage heart failure, suitable long-term artificial lung systems are still at an early stage of development. Although a short-term use of an extracorporeal lung support is feasible today, the currently available technical solutions do not permit the long-term use of lung replacement systems in terms of an implantable artificial lung. This is currently limited by a variety of factors: biocompatibility problems lead to clot formation within the system, especially in areas with unphysiological flow conditions. In addition, proteins, cells, and fibrin are deposited on the membranes, decreasing gas exchange performance and thus, limiting long-term use. Coordinated basic and translational scientific research to solve these problems is therefore necessary to enable the long-term use and implantation of an artificial lung. Strategies for improving the biocompatibility of foreign surfaces, for new anticoagulation regimes, for optimization of gas and blood flow, and for miniaturization of these systems must be found. These strategies must be validated by in vitro and in vivo tests, which remain to be developed. In addition, the influence of long-term support on the pathophysiology must be considered. These challenges require well-connected interdisciplinary teams from the natural and material sciences, engineering, and medicine, which take the necessary steps toward the development of an artificial implantable lung.

Estimation Methods for Viscosity, Flow Rate and Pressure from Pump-Motor Assembly Parameters

Blood pumps have found applications in heart support devices, oxygenators, and dialysis systems, among others. Often, there is no room for sensors, or the sensors are simply unreliable when long-term operation is required. However, control systems rely on those hard-to-measure parameters, such as blood flow rate and pressure difference, thus their estimation takes a central role in the development process of such medical devices. The viscosity of the blood not only influences the estimation of those parameters but is often a parameter that is of great interest to both doctors and engineers. In this work, estimation methods for blood flow rate, pressure difference, and viscosity are presented using Gaussian process regression models. Different water–glycerol mixtures were used to model blood. Data was collected from a custom-built blood pump, designed for intracorporeal oxygenators in an in vitro test circuit. The estimation was performed from motor current and motor speed measurements and its accuracy was measured for: blood flow rate r² = 0.98, root mean squared error (RMSE) = 46 mL^.min⁻¹; pressure difference r² = 0.98, RMSE = 8.7 mmHg; and viscosity r² = 0.98, RMSE = 0.049 mPa^.s. The results suggest that the presented methods can be used to accurately predict blood flow rate, pressure, and viscosity online.

Effect of impeller design and spacing on gas exchange in a percutaneous respiratory assist catheter

Providing partial respiratory assistance by removing carbon dioxide (CO2 ) can improve clinical outcomes in patients suffering from acute exacerbations of chronic obstructive pulmonary disease and acute respiratory distress syndrome. An intravenous respiratory assist device with a small (25 Fr) insertion diameter eliminates the complexity and potential complications associated with external blood circuitry and can be inserted by nonspecialized surgeons. The impeller percutaneous respiratory assist catheter (IPRAC) is a highly efficient CO2 removal device for percutaneous insertion to the vena cava via the right jugular or right femoral vein that utilizes an array of impellers rotating within a hollow-fiber membrane bundle to enhance gas exchange. The objective of this study was to evaluate the effects of new impeller designs and impeller spacing on gas exchange in the IPRAC using computational fluid dynamics (CFD) and in vitro deionized water gas exchange testing. A CFD gas exchange and flow model was developed to guide a progressive impeller design process. Six impeller blade geometries were designed and tested in vitro in an IPRAC device with 2- or 10-mm axial spacing and varying numbers of blades (2-5). The maximum CO2 removal efficiency (exchange per unit surface area) achieved was 573 ± 8 mL/min/m(2) (40.1 mL/min absolute). The gas exchange rate was found to be largely independent of blade design and number of blades for the impellers tested but increased significantly (5-10%) with reduced axial spacing allowing for additional shaft impellers (23 vs. 14). CFD gas exchange predictions were within 2-13% of experimental values and accurately predicted the relative improvement with impellers at 2- versus 10-mm axial spacing. The ability of CFD simulation to accurately forecast the effects of influential design parameters suggests it can be used to identify impeller traits that profoundly affect facilitated gas exchange.

Improving oxygenator performance using computational simulation and flow field-based parameters

Current goals in the development of oxygenators are to reduce extrinsic surface contact area, thrombus formation, hemolysis, and priming volume. To achieve these goals and provide a favorable concentration gradient for the gas exchange throughout the fiber bundle, this study attempts to find an optimized inlet and outlet port geometry to guide the flow of a hexagonal-shaped oxygenator currently under development. Parameters derived from numerical flow simulations allowed an automated quantitative evaluation of geometry changes of flow distribution plates. This led to a practical assessment of the quality of the flow. The results were validated qualitatively by comparison to flow visualization results. Two parameters were investigated, the first based on the velocity distribution and the second calculated from the residence time of massless particles representing erythrocytes. Both approaches showed significant potential to improve the flow pattern in the fiber bundle, based on one of the parameters of up to 66%. Computational fluid dynamics combined with a parameterization proved to be a powerful tool to quickly improve oxygenator designs.

Development of a miniaturized heart-lung machine for neonates with congenital heart defect

Predominantly, standard adult heart lung machines are used for pediatric cardiac surgery, only with individually downsized components. Downsizing is limited, e.g., by the required gas exchange surface. To diminish complications, we developed a new miniaturized heart lung machine (MiniHLM) for neonates, with significantly reduced priming volume and blood contact surface by integration of all major system components in one single device. In particular, a rotary blood pump is centrically integrated into the oxygenator and the cardiotomy reservoir with integrated heat exchanger is directly connected. Thus, tubing is only necessary between patient and MiniHLM. A total priming volume of 102 ml could be achieved for the entire extracorporeal circuit (including arterial/venous line), in contrast to the currently smallest device on the market with 213 ml. In first animal experiments with female New Zealand rabbits, the MiniHLM guaranteed both a sufficient gas exchange and an adequate blood flow; 12 rabbits could successfully be weaned off after 1 hour of aortic clamp time. The first in vitro and in vivo tests confirm the concept of the MiniHLM. Its low priming volume and blood contact surface may significantly reduce complications during heart surgery in neonates.

Clinical outcomes and experience of 20 pediatric patients treated with extracorporeal membrane oxygenation in Fuwai Hospital

The purpose of this study was to report retrospectively the summarized clinical findings from 20 consecutive pediatric extracorporeal membrane oxygenation (ECMO) patients and to investigate the factors associated with mortality. The ECMO circuit system was completely covered using heparin-coating technique, and venoarterial ECMO was used in all patients. Heparin dosage was 4-20 U/kg/h and active clotting time was maintained between 146 and 360 seconds. ECMO was weaned off successfully in 15 patients (75%); 11 of 15 patients (73%) survived and were discharged from the hospital; 4 of 15 patients died of postoperative complications; 5 patients failed to be weaned off ECMO. The percentage of discharged patients was 55% (11 of 20) in this cohort study. Lactic acid concentration of artery blood before ECMO in survivor patients was significantly lower than in nonsurvivor patients (p = 0.009); patient weight between two groups also had statistical difference (p = 0.046). ECMO effectively treats cardiac and pulmonary failure secondary to cardiac surgeries for complicated congenital heart diseases. Early application of ECMO in patients with cardiac and respiratory failure is still the key point of success in preventing vital organs from irreversible damage.

The future of extracorporeal support

Extracorporeal therapy has expanded significantly over the past few decades from solely artificial renal replacement therapy. In patients with multiple organ dysfunction syndrome, it becomes necessary to provide multiple organ support therapy. Technological advances have opened the door to a multifaceted intervention directed at supporting the function of multiple organs through the treatment of blood. Indications for "old" therapies such as hemofiltration and adsorption have been expanded, and using these therapies in combination further enhances blood detoxification capabilities. Furthermore, new devices are constantly in development. Nanotechnology allows us to refine membrane characteristics and design innovative monitoring/biofeedback devices. Miniaturization is leading down the path of wearable/implantable devices. With the incorporation of viable cells within medical devices, these instruments become capable not only of detoxification but synthetic functions as well, bringing us closer to the holy grail of complete replacement of organ function. This article provides a brief overview of current and future direction in extracorporeal support in the critical care setting.

The Role of Extra Corporeal Membrane Oxygenation for Treatment of the Adult Respiratory Distress Syndrome: Review and Quantitative Analysis

The role of Extra corporeal membrane oxygenation (ECMO) has not been formally validated for patients with adult respiratory distress syndrome. In anticipation of publication of the conventional ventilation versus ECMO in severe adult respiratory failure (CESAR) trial, the role of ECMO in this setting was reviewed.

An electronic search for studies reporting the use of ECMO for the treatment of adult respiratory distress syndrome revealed two randomised controlled trials and three non-controlled trials. Bayesian analysis on the two randomised controlled trials produced an odds ratio mortality of 1.28 (credible interval 0.24 to 6.55) demonstrating no significant harm or benefit. Pooling was not possible for the non-controlled studies because of differing admission status and ECMO selection criteria and an inability to control for these differences in the absence of individual patient data. A large number (n=35) of case series have been published with generally more positive results. We also present a comprehensive narrative commentary on the history, current practice and future for ECMO.

ECMO, as rescue therapy for adult respiratory distress syndrome, appears to be an unvalidated rescue treatment option. Analysis and review of trial data does not support its application; however the body of reported cases suggests otherwise. Until the CESAR trial provides an authoritative answer ECMO will continue to be offered on a case by case basis.

Evaluation of fiber bundle rotation for enhancing gas exchange in a respiratory assist catheter

Supplemental oxygenation and carbon dioxide removal through an intravenous respiratory assist catheter can be used as a means of treating patients with acute respiratory failure. We are beginning development efforts toward a new respiratory assist catheter with an insertional size <25F, which can be inserted percutaneously. In this study, we evaluated fiber bundle rotation as an improved mechanism for active mixing and enhanced gas exchange in intravenous respiratory assist catheters. Using a simple test apparatus of a rotating densely packed bundle of hollow fiber membranes, water and blood gas exchange levels were evaluated at various rotation speeds in a mock vena cava. At 12,000 RPM, maximum CO2 gas exchange rates were 449 and 523 mL/min per m2, water and blood, respectively, but the rate of increase with increasing rotation rate diminished beyond 7500 RPM. These levels of gas exchange efficiency are two- to threefold greater than achieved in our previous respiratory catheters using balloon pulsation for active mixing. In preliminary hemolysis tests, which monitored plasma-free hemoglobin levels in vitro over a period of 6 hours, we established that the rotating fiber bundle per se did not cause significant blood hemolysis compared with an intra-aortic balloon pump. Accordingly, fiber bundle rotation appears to be a potential mechanism for increasing gas exchange and reducing insertional size in respiratory catheters.

Comparing Oxygen Transfer Performance Between Three Membrane Oxygenators: Effect of Temperature Changes During Cardiopulmonary Bypass

Recently, a new oxygenator (Dideco 903 [D903], Dideco, Mirandola, Italy) has been introduced to the perfusion community, and we set about testing its oxygen transfer performance and then comparing it to two other models. This evaluation was based on the comparison between oxygen transfer slope, gas phase arterial oxygen gradients, degree of blood shunting, maximum oxygen transfer, and diffusing capacity calculated for each membrane. Sixty patients were randomized into three groups of oxygenators (Dideco 703 [D703], Dideco; D903; and Quadrox, Jostra Medizintechnik AG, Hirrlingen, Germany) including 40/20 M/F of 68.6 +/- 11.3 years old, with a body weight of 71.5 +/- 12.1 kg, a body surface area (BSA) of 1.84 +/- 0.3 m(2), and a theoretical blood flow rate (index 2.4 times BSA) of 4.4 +/- 0.7 L/min. The maximum oxygen transfer (VO(2)) values were 313 mL O(2)/min (D703), 579 mL O(2)/min (D903), and 400 mL O(2)/min (Quadrox), with the D903 being the most superior (P < 0.05). Oxygen (O(2)) gradients were 320 mm Hg (D703), 235 mm Hg (D903), and 247 mm Hg (Quadrox), meaning D903 and Quadrox are more efficient versus the D703 (P < 0.05). Shunt fraction (Qs/Qt) and diffusing capacity (DmO(2)) were comparable (P = ns). Diffusing capacity values indexed to BSA (DmO(2)/m(2)) were 0.15 mL O(2)/min/mm Hg/m(2) (D703), 0.2 mL O(2)/min/mm Hg/m(2) (D903), and 0.18 mL O(2)/min/mm Hg/m(2) (Quadrox) with D903 outperforming D703 (P < 0.0005). During hypothermia (32.0 +/- 0.3 degrees C), there was a lower absolute and relative VO(2 )for all three oxygenators (P = ns). The O(2) gradients, DmO(2) and DmO(2)/m(2), were significantly lower for all oxygenators (P < 0.01). Also, Qs/Qt significantly rose for all oxygenators (P < 0.01). The oxygen transfer curve is characteristic to each oxygenator type and represents a tool to quantify oxygenator performance. Using this parameter, we demonstrated significant differences among commercially available oxygenators. However, all three oxygenators are considered to meet the oxygen needs of the patients.

Artificial lungs: current state and trends of clinical use and research and development

This article describes recent progress in the field of artificial lungs, centering on the current state and trends in clinical use and research and development. Trends in the recent clinical use in Japan can be found in shipment-number-based surveys as well as in the questionnaire surveys for clinical extracorporeal membrane oxygenation (ECMO) and percutaneous cardiopulmonary support (PCPS). It is likely that the use of artificial lungs for open-heart surgery has peaked, and this can be attributed to the rapid expansion and popularization of off-pump coronary artery bypass grafting surgery. In contrast, the increase in the number of artificial lungs used in assisted circulation cases is showing significant growth. Along with such clinical trends, research and development toward next-generation systems is active in the field of assisted circulation, focusing on emergency or long-term use of PCPS or ECMO. Approaches include enhancing the performance of conventional systems in terms of long-term durability and hemocompatibility, developing a novel device by integrating the oxygenator with the blood pump, and developing an implantable type of artificial lung such as an intravenous oxygenator. Next-generation devices not only will benefit a multitude of patients but also represent an important target with the prospect for expansion of the market for artificial lungs. In the future, further expansion of research and development in this field, as well as progress in practical and clinical applications of innovative devices, is expected.

Intravascular blood oxygenation using hollow fibers in a disk-shaped configuration: experimental evaluation of the relationship between porosity and performance

Implantation of hollow fibers for blood oxygenation within a human vessel has been investigated for the last 15 years. Unfortunately, the combination of limited space inside the venous system and disadvantageous blood flow conditions has resulted until now in limited gas exchange performance of the investigated oxygenators. We are developing a highly integrated intravascular membrane oxygenator (HIMOX) characterized by a homogeneous disk-shaped fiber configuration. The main advantages are a larger fiber surface as well as favorable cross flow through the fibers compared with earlier designs. Fiber porosity represents an important constructive parameter and leads to a trade-off when dimensioning the bundles with the aim of maximum gas exchange at small anatomical size. Low porosity results in higher fiber surface as well as blood velocity. Both effects potentially enhance the gas exchange, but the associated increase of the pressure drop leads to a deformation of the fiber bundle and to a blood shunt. This fluid-structure interaction influences the gas exchange in a complex way. We investigated the influence of porosity on the gas exchange in the proposed fiber configuration in vitro. Bundle deformation was proven by comparing experimental data with a theoretical model. Highest oxygen exchange supplied by a single bundle was achieved at an intermediate porosity of 0.575. Moreover, specific oxygen exchange per fiber surface, which is an indicator of favorable flow conditions, increased with increasing fiber porosity. We achieved up to 450 ml O2 min m, which is a promising result for intravascular membrane oxygenation.