Preclinical evaluation of a hollow fiber silicone membrane oxygenator for extracorporeal membrane oxygenator application

In Vitro Thrombogenesis Resulting from Decreased Shear Rate and Blood Coagulability

In vitro antithrombogenic testing with mock circulation is a useful type of pre-evaluation in ex vivo testing of mechanical assist devices. For effective in vitro testing, we have been developing a clear quantitative thrombogenesis model based on shear stress and blood coagulability. Bovine blood was used as the test medium. The activating clotting time (ACT) was adjusted with trisodium citrate and calcium chloride from 200 to 1,000 seconds. The blood was then applied to a rheometer and subjected to shear at 50 to 2,880 s-1. Blood coagulation time and degree of thrombogenesis were measured by the torque sensor of the rheometer. Prothrombin time (PT) and activated partial thromboplastin time (APTT) of the test blood were also measured after the application of shear. Blood coagulation time increased, and the degree of thrombogenesis decreased, with increases in shear rate to between 50 and 2,880 s-1. for test bloods with ACTs of 200 to 250 seconds. An ACT of 200 to 250 seconds is thus appropriate for in vitro antithrombogenic testing under a shear rate of 2,880 s-1. APTT was prolonged, whereas PT did not change, with increasing shear rate: that is, increasing the shear rate reduced thrombogenesis related to the intrinsic clotting pathway. An ACT of 200 to 250 seconds was suitable for in vitro antithrombogenic testing, and increasing the shear stress generated in the mechanical assist device reduced thrombogenesis via the intrinsic clotting pathway.

Performance of a MedArray silicone hollow fiber oxygenator

A silicone hollow fiber oxygenator was evaluated to characterize gas transfer and biocompatibility. The device's fiber bundle was composed of MedArray's silicone hollow fibers with a 320 microm outside diameter, a 50 microm wall thickness, a surface area of 0.45 m, and a 0.49 void fraction. An in vitro gas exchange study was performed comparing the MedArray device (n = 9) with the Medtronic 0600 oxygenator (n = 6) using Association for the Advancement of Medical Instrumentation standards and blood flow rates of 0.5-1.75 L/min, and an oxygen to blood flow ratio of two. Biocompatibility and resistance studies were performed in vivo using a swine venovenous extracorporeal membrane oxygenation model (MedArray n = 5, Medtronic n = 5). Average O(2) transfer at 1 L/min was 86 ml/min/m in the MedArray device and 101.1 ml/min/m in the Medtronic device. At 0.5 L/min the MedArray and Medtronic device average resistance was 15.5 and 148.5 mm Hg/(L/min), respectively. Both devices had similar platelet consumption and hemolysis. Results indicate that the MedArray device has lower O(2) transfer efficiency, similar biocompatibility, and lower resistance than the Medtronic 0600 oxygenator. Optimization of the MedArray fiber bundle and housing design is necessary to improve O(2) transfer efficiency while maintaining lower device resistance than the Medtronic oxygenator.

Multiple organ system extracorporeal support in critically ill children

Multiple organ system extracorporeal support effectively supports brain, heart, lung, liver, kidney, coagulation, red blood cell, and immune cell function in the sickest infants and children who have multiple organ system failure. These therapies have optimum benefit if: (1) the underlying disease is reversible; (2) the therapies are performed expertly and are monitored to prevent and minimize systemic hemolysis; and (3) the therapies are provided in a goal-directed manner. These therapies represent a significant advance in pediatric critical care medicine. This article provides a framework for this multidisciplinary team approach for implementing these therapies.

Enhanced oxygen delivery to primary hepatocytes within a hollow fiber bioreactor facilitated via hemoglobin-based oxygen carriers

The production of a fully functional bioartificial liver assist device (BLAD) would greatly enhance available treatment options for patients suffering from acute liver failure. Currently, inadequate oxygen provision to hepatocytes seeded within hollow fiber bioreactors hampers development of a viable hollow fiber-based BLAD. Experimentally, oxygen provision to primary rat hepatocytes cultured within hollow fiber bioreactors was measured, it was observed that supplementation with an oxygen carrier (bovine red blood cells at approximately 2% human hematocrit) did not significantly improve oxygenation compared to the absence of an oxygen carrier. Therefore, an oxygen transport model of an individual hollow fiber within the bioreactor was developed and simulated (up to approximately 10% human hematocrit) to more fully examine the effect of oxygen carrier supplementation on oxygenation within the bioreactor. The modeling analysis, supported via the experimental results, was utilized to predict optimal bioreactor operating conditions for the delivery of in vivo-like oxygen gradients to cultured hepatocytes in clinically relevant settings.

Durability improvement of polymer chamber of pulsatile extracorporeal life support system in terms of mechanical change

Twin Pulse Life Support, T-PLS has received the CE mark (2003) and Korea Food and Drug Administration (KFDA) approval (2004) for short-term application as an Extracorporeal Life Support system (ECLS). T-PLS's original intention was to apply for not only short-term but also long-term application such as Extracorporeal ventricular assist device (VAD). Hence, a long-term durability test was conducted. The 1-year reliability of the systems tested in this study did not meet the STS/ASAIO standard of 80% reliability with 60% confidence for a 1-year mission life. However, without the disposable units, which are only designed to operate for 6 h, the 1-year reliability exceeded the STS/ASAIO standard of 80% reliability with 60% confidence. In this study, by using the existing analysis methods and analyzing the root cause of the failure used by a numerical analysis. As eliminating or mitigating of the root cause of the failure, we improved the durability of blood chamber and evaluated the performance of the modified system via the hemolysis test.

Development of Ambulatory Arterio-Venous Carbon Dioxide Removal (AVCO2R): The Downsized Gas Exchanger Prototype for Ambulation Removes Enough CO2 with Low Blood Resistance

We are developing an ultra compact gas exchanger to allow ambulation during arterial-venous CO2 removal (AVCO2R). The ambulatory AVCO2R gas exchanger (135 ml prime volume and 1.3 M2 gas exchange surface area) is made of polymethylpentene hollow fibers. The gas exchanger was attached to sheep carotid artery (12F) and jugular vein (14F) by percutaneous cannulae for 6 hours (n = 5). Device CO2 removal was measured and calculated at a constant blood flow rate of 1 L/min coupled with varying sweep gas from 1 to 15 L/min, and at constant sweep gas flow of 2 L/min coupled with varying blood flow from 0.5 to 1.25 L/min to determine capacity of CO2 removal at Pa CO2 = 40-50 mm Hg. Blood gases, CO2 removal and hemodynamics were recorded at 0, 3, and 6 hours. CO2 removal increased with sweep gas flow rate and with increase of device blood flow. Hemodynamics remained unchanged throughout study. Gas exchanger resistance remained stable at 2.3 +/- 0.53 mm Hg/L/min. CO2 removal with 1 L/min blood flow and 2 L/min sweep gas was 110 +/- 12 then stabilized at 85 +/- 14 mL/min to 6 hours. The compact ambulatory AVCO2R gas exchanger achieves stable, near total CO2 removal for at least 6 hours with a simple arteriovenous shunt.

Development of silicone rubber hollow fiber membrane oxygenator for ECMO

Silicone rubber hollow fiber membrane produces an ideal gas exchange for long-term ECMO due to nonporous characteristics. The extracapillary type silicone rubber ECMO oxygenator having an ultrathin hollow fiber membrane was developed for pediatric application. The test modules were compared to conventional silicone coil-type ECMO modules. In vitro experiments demonstrated a higher O2 and CO2 transfer rate, lower blood flow resistance, and less hemolysis than the conventional silicone coil-type modules. This oxygenator was combined with the Gyro C1E3 centrifugal pump, and three ex vivo experiments were conducted to simulate pediatric V-A ECMO condition. Four day and 6 day experiments were conducted in cases 1 and 2, respectively. Case 3 was a long-term experiment up to 2 weeks. No plasma leakage and stable gas performances were achieved. The plasma free hemoglobin was maintained within a normal range. This compact pump-oxygenator system in conjunction with the Gyro C1E3 centrifugal pump has potential for a hybrid total ECMO system.

Long-term ex vivo bovine experiments with the Gyro C1E3 centrifugal blood pump

Centrifugal blood pumps are used widely for cardiopulmonary bypass, as ventricular assist devices, and for extracorporeal membrane oxygenation (ECMO). However, there is no centrifugal blood pump that is suitable for long-term ECMO. The authors developed the Gyro C1E3 centrifugal blood pump (Kyocera Corporation, Kyoto, Japan), which has superior antithrombogenic, antitraumatic, and hydraulic features in comparison with the conventional centrifugal blood pumps. Five ex vivo long-term durability tests of the Gyro C1E3 were performed using healthy miniature calves. The ECMO circuit was composed of a prototype hollow fiber silicone membrane oxygenator and a Gyro C1E3 pump. Venous blood was drained from the left jugular vein of a calf, passed through the oxygenator and infused into the left carotid artery using a Gyro C1E3. Ex vivo studies were performed from 7 to 15 days at a blood flow rate of 1 L/min. During this period, the Gyro C1E3 demonstrated a stable performance without exchanging the pump. Bleeding complications were the major reason for termination of each experiment. Rotational speed was maintained around 2,000 rpm. All five calves demonstrated neither abnormal signs nor abnormal blood examination data throughout the experiment. Neither clot nor thrombus formations were found during the necropsy in the cannula or pump nor were infarctions observed in any of the major organs. In conclusion, the Gyro C1E3 showed a stable and reliable performance during long-term ex vivo bovine experiments under the conditions tested.

Hemolytic characteristics of oxygenators during clinical extracorporeal membrane oxygenation

A connection was previously reported between the hemolytic characteristics associated with oxygenators and the pressure drop measurements in the blood chamber under experimental conditions simulating their use in cardiopulmonary bypass. We examined this association during extracorporeal membrane oxygenation (ECMO) conditions. Three oxygenators for ECMO or pediatric cardiopulmonary bypass (Menox EL4000, Dideco Module 4000, and Mera HPO-15H) were evaluated. Fresh blood from healthy Dexter strain calves anticoagulated with citrate phosphate dextrose adenine solution was used. The blood flow was fixed at 1 L/min, similar to that in ECMO. The Normalized Index of Hemolysis for Oxygenators (NIHO) has been modified according to the American Society of Testing and Materials standards, as was previously reported. The NIHO value was the lowest in the Menox (0.0070+/-0.0009) and increased from Menox to Dideco (0.0113+/-0.0099) to Mera (0.0164+/-0.0043); however, there were no significant differences among the oxygenators. This NIHO value has a close correlation to the pressure drop. In conclusion, this evaluation method is also applicable to comparison of the biocompatibility performance of different types of clinically available oxygenators for ECMO.

Extracorporeal membrane oxygenator compatible with centrifugal blood pumps

Coil-type silicone membrane oxygenators can only be used with roller blood pumps due to the resistance from the high blood flow. Therefore, during extracorporeal membrane oxygenation (ECMO) treatment, the combination of a roller pump and an oxygenator with a high blood flow resistance will induce severe hemolysis, which is a serious problem. A silicone rubber, hollow fiber membrane oxygenator that has a low blood flow resistance was developed and evaluated with centrifugal pumps. During in vitro tests, sufficient gas transfer was demonstrated with a blood flow less than 3 L/min. Blood flow resistance was 18 mm Hg at 1 L/min blood flow. This oxygenator module was combined with the Gyro C1E3 (Kyocera, Japan), and veno-arterial ECMO was established on a Dexter strain calf. An ex vivo experiment was performed for 3 days with stable gas performance and low blood flow resistance. The combination of this oxygenator and centrifugal pump may be advantageous to enhance biocompatibility and have less blood trauma characteristics.

Blood trauma induced by clinically accepted oxygenators

Hemolysis remains one of the most serious problems during cardiopulmonary bypass (CPB), extracorporeal membrane oxygenation (ECMO), and percutaneous cardiopulmonary support (PCPS). However, the hemolytic characteristics associated with oxygenators are not well defined. A specialized hemolysis test protocol for oxygenators was developed. A comparative study was performed following this protocol to determine the hemolytic characteristics of the clinically available oxygenators during CPB; pressure drop measurements in the blood chamber were also performed. Four oxygenators (Medtronic Affinity, Cobe Optima, Terumo Capiox SX25, and Bard Quantum) were evaluated. Fresh blood from healthy Dexter calves anticoagulated with citrate phosphate dextrose adenine solution was used. The blood flow was fixed at 5 L/min, similar to that used in CPB. The Normalized Index of Hemolysis for Oxygenators (NIHO) has been modified according to the American Society of Testing and Materials (ASTM) standards. The NIH value, which was obtained from the circuit without an oxygenator, was subtracted from the primary NIH value, obtained from the circuit with an oxygenator to eliminate the effects of a centrifugal pump or other artifacts. The NIHO value was the lowest in the Affinity (0.0116 +/- 0.0017) and increased from Affinity < Optima (0.0270 +/- 0.0038) < Capiox (0.0335 +/- 0.0028) < Quantum (0.0416 +/- 0.0015 g/100 L). The Optima and Capiox did not demonstrate a significant difference. In addition, this NIHO value has a close relationship to the pressure drop. In conclusion, this new evaluation method is suitable to compare the biocompatibility performance of different types of clinically available oxygenators for CPB usage.

Development of a new hollow fiber silicone membrane oxygenator: in vitro study

An experimental silicone hollow fiber membrane oxygenator for long-term extracorporeal membrane oxygenation (ECMO) was developed in our laboratory using an ultrathin silicone hollow fiber. However, the marginal gas transfer performances and a high-pressure drop in some cases were demonstrated in the initial models. In order to improve performance the following features were incorporated in the most recent oxygenator model: increasing the fiber length and total surface area, decreasing the packing density, and modifying the flow distributor. The aim of this study was to evaluate the gas transfer performances and biocompatibility of this newly improved model with in vitro experiments. According to the established method in our laboratory, in vitro studies were performed using fresh bovine blood. Gas transfer performance tests were performed at a blood flow rate of 0.5 to 6 L/min and a V/Q ratio (V = gas flow rate, Q = blood flow rate) of 2 and 3. Hemolysis tests were performed at a blood flow rate of 1 and 5 L/min. Blood pressure drop was also measured. At a blood flow rate of 1 L/min and V/Q = 3, the O2 and CO2 gas transfer rates were 72.45 +/- 1.24 and 39.87 +/- 2.92 ml/min, respectively. At a blood flow rate of 2 L/min and V/Q = 3, the O2 and CO2 gas transfer rates were 128.83 +/- 1.09 and 47.49 +/- 5.11 ml/min. Clearly, these data were superior to those obtained with previous models. As for the pressure drop and hemolytic performance, remarkable improvements were also demonstrated. These data indicate that this newly improved oxygenator is superior to the previous model and may be clinically acceptable for long-term ECMO application.

Gas transfer performance of a hollow fiber silicone membrane oxygenator: ex vivo study

Based on the results of in vitro studies of many experimental models, a silicone hollow fiber membrane oxygenator for pediatric cardiopulmonary bypass (CPB) and extracorporeal membrane oxygenation (ECMO) was developed using an ultrathin silicone hollow fiber with a 300 microm outer diameter and a wall thickness of 50 microm. In this study, we evaluated the gas transfer performance of this oxygenator simulating pediatric CPB and ECMO conditions. Two ex vivo studies in a pediatric CPB condition for 6 h and 5 ex vivo studies in an ECMO condition for 1 week were performed with venoarterial bypass using healthy calves. At a blood flow rate of 2 L/min and V/Q = 4 (V = gas flow rate, Q = blood flow rate) (pediatric CPB condition), the O2 and CO2 gas transfer rates were maintained at 97.44 +/- 8.88 (mean +/- SD) and 43.59 +/- 15.75 ml/min/m2, respectively. At a blood flow rate of 1 L/min and V/Q = 4 (ECMO condition), the O2 and CO2 gas transfer rates were maintained at 56.15 +/- 8.49 and 42.47 +/- 9.22 ml/min/m2, respectively. These data suggest that this preclinical silicone membrane hollow fiber oxygenator may be acceptable for both pediatric CPB and long-term ECMO use.