Clinical evaluation of the interpulse low resistance microporous membrane oxygenator

The Interpulse microporous membrane oxygenator has been used in 100 patients for cardiac surgery. This oxygenator features transverse furrows in the membrane and a back and forth motion of the blood as it flows between the membranes. This pulsing motion causes secondary flows or vortices to occur in the furrows of the membrane. These secondary flows promote mixing of the blood in the film. This oxygenator has been used in a single pump circuit for perfusions for up to 343 minutes at a flow rate up to 5.9 l/min. Oxygen saturation has always been 98% or greater. The pulser rate of the oxygenator influences oxygen transfer, and the pulser rate has been regulated between 80 and 225 pulses per minute to achieve a mean arterial PaO2 of 207 mmHg. Carbon dioxide transfer is affected by the oxygen flow through the device and has been adjusted to between 0.2 and 7 l/min to obtain a mean PaCO2 of 40 mmHg in this series. This device has proved to be safe and effective in perfusions for cardiac surgery.     

Cardiopulmonary bypass

The primary function of the cardiopulmonary bypass (CPB) machine is to provide oxygenated blood flow to the systemic circulation while providing the surgeon with a motionless, bloodless surgical field. The CPB circuit consists of a reservoir, blood pump, oxygenator, heat exchanger, arterial filter, cardioplegia delivery device and cannulae, interconnected by various sized tubing. The venous cannula directs blood away from the heart and lungs via the CBP circuit and the arterial cannula returns the oxygenated blood to the systemic circulation. A blood pump propels the blood volume forward through a membrane oxygenator and allows rapid transfusion of oxygenated blood back into the systemic circulation. The CPB flow needs to be enough to maintain an adequate cardiac output, therefore a flow of 1.8–2.2 litres/minute/m² is recommended when at normothermia, although these flows can be reduced if the temperature is less than 28°C. The mortality and neurological complications after cardiac surgery are similar using either normothermic or hypothermic CPB. Maintenance of anaesthesia on CPB is often achieved with a propofol infusion (sometimes with the addition of remifentanil), but the use of volatile anaesthetic is also possible through the CPB machine. A vaporizer can be attached to the CPB circuit and volatile anaesthetic delivered into the sweep gas passing through the oxygenator. A safety checklist before separation from bypass is essential, and it may include: optimal temperature, heart rhythm, de-airing, acid-base status, ventilation, electrolytes and patient position. If heparin was used to maintain anticoagulation, it should be reversed with protamine after the patient is stable off-CPB. Some patients require inotropic or mechanical support to facilitate ‘weaning’ from CPB.     

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.     

Oxygenator exhaust capnography as an index of arterial carbon dioxide tension during cardiopulmonary bypass using a membrane oxygenator

We have studied the relationship between the partial pressure of carbon dioxide in oxygenator exhaust gas (PECO2) and arterial carbon dioxide tension (PaCO2) during hypothermic cardiopulmonary bypass with non- pulsatile flow and a membrane oxygenator. A total of 172 paired measurements were made in 32 patients, 5 min after starting cardiopulmonary bypass and then at 15-min intervals. Additional measurements were made at 34 degrees C during rewarming. The degree of agreement between paired measurements (PaCO2 and PECO2) at each time was calculated. Mean difference (d) was 0.9 kPa (SD 0.99 kPa). Results were analysed further during stable hypothermia (n = 30, d = 1.88, SD = 0.69), rewarming at 34 degrees C (n = 22, d = 0, SD = 0.84), rewarming at normothermia (n = 48, d = 0.15, SD = 0.69) and with (n = 78, d = 0.62, SD = 0.99) or without (n = 91, d = 1.07, SD = 0.9) carbon dioxide being added to the oxygenator gas. The difference between the two measurements varied in relation to nasopharyngeal temperature if PaCO2 was not corrected for temperature (r2 = 0.343, P = < 0.001). However, if PaCO2 was corrected for temperature, the difference between PaCO2 and PECO2 was not related to temperature, and there was no relationship with either pump blood flow or oxygenator gas flow. We found that measurement of carbon dioxide partial pressure in exhaust gases from a membrane oxygenator during cardiopulmonary bypass was not a useful method for estimating PaCO2.      

The addition of a membrane oxygenator to a ventricular assist device in a patient with acute respiratory distress syndrome

A 12-year-old boy with Marfan's syndrome required a biventricular assist device (VAD) after an aortic root replacement. The patient developed acute respiratory distress syndrome and required escalating ventilator support. We hypothesized that the addition of a membrane oxygenator in series with the assist device would improve gas exchange and allow for a more lung-protective ventilator approach. A membrane oxygenator was placed in series with the right VAD resulting in a blood path of right atrium to VAD to oxygenator to pulmonary artery. Circuit function was gauged by monitoring flow and oxygenator pressures and periodic circuit inspections and oxygenator blood gases. Heparin was titrated to maintain unfractionated antifactor Xa levels of .3-.7 IU/mL and partial thromboplastin time of 60-80 seconds. The initial sweep gas supplying the oxygenator was 5 L/min at an F1O2 of 1.0, which achieved a pH > 7.40 and a PF ratio > 250. The pre- and post-oxygenator pressures were 55-60 mmHg and 45-50 mmHg, respectively, and the measured flow at the oxygenator outlet was 2.0-2.2 L/min. The patient was changed from high-frequency oscillatory ventilation to pressure-controlled synchronized intermittent ventilation with pH maintained at 7.35-7.40 and PF ratio > 250. Paralytics were discontinued and the patient's neurologic condition was deemed intact. The patient hemorrhaged after a sternal closure and required transfusions and antifibrinolytics that led to thrombus in the membrane and membrane circuitry, which were replaced without incident. The patient's respiratory status remained stable; however, his overall condition worsened as a result of additional organ dysfunction and septicemia, and he did not survive. The addition of a membrane oxygenator to a VAD is feasible and supplements gas exchange permitting the use of more lung protective ventilation.     

Description of a flow optimized oxygenator with integrated pulsatile pump

Extracorporeal membrane oxygenation (ECMO) is a well-established therapy for several lung and heart diseases in the field of neonatal and pediatric medicine (e.g., acute respiratory distress syndrome, congenital heart failure, cardiomyopathy). Current ECMO systems are typically composed of an oxygenator and a separate nonpulsatile blood pump. An oxygenator with an integrated pulsatile blood pump for small infant ECMO was developed, and this novel concept was tested regarding functionality and gas exchange rate. Pulsating silicone tubes (STs) were driven by air pressure and placed inside the cylindrical fiber bundle of an oxygenator to be used as a pump module. The findings of this study confirm that pumping blood with STs is a viable option for the future. The maximum gas exchange rate for oxygen is 48mL/min/L(blood) at a medium blood flow rate of about 300mL/min. Future design steps were identified to optimize the flow field through the fiber bundle to achieve a higher gas exchange rate. First, the packing density of the hollow-fiber bundle was lower than commercial oxygenators due to the manual manufacturing. By increasing this packing density, the gas exchange rate would increase accordingly. Second, distribution plates for a more uniform blood flow can be placed at the inlet and outlet of the oxygenator. Third, the hollow-fiber membranes can be individually placed to ensure equal distances between the surrounding hollow fibers.     

A clinical evaluation of the Terumo Capiox SX18R hollow fiber oxygenator

The Terumo Capiox SX18R is a commercially available, low prime, reverse phase, hollow fiber membrane oxygenator. The oxygenator consists of a 1.8 m2 microporous polypropylene hollow fiber bundle, a 2200 cm2 tubular stainless steel heat exchanger, and an open hard shell venous reservoir with integral cardiotomy filter. The Terumo Capiox SX18R oxygenator was evaluated to determine its clinical oxygenating performance. Blood samples were drawn from 25 patients yielding 114 data points. The following parameters were recorded: blood flow, cardiac index, gas flow, gas to blood flow ratio, and oxygen fraction. Samples were assayed for hematocrit, hemoglobin, arterial and venous blood gas values, and venous oxygen saturation. The data and assay results were used to calculate arterial, venous, and membrane gas oxygen content, oxygen transfer, shunt fraction, and oxygen diffusion capacity. The Terumo Capiox SX18R oxygenator performed adequately with sufficient oxygen transfer reserve and carbon dioxide clearance under a variety of clinical conditions for the tested population.     

膜式氧合器在胎羊体外循环中的运用

目的　为了改进胎羊体外循环技术 ,探讨膜式氧合器在胎羊体外循环中的应用。　方法　将健康怀孕山羊8只 ,采用 Dideco 90 1膜式氧合器和滚轴泵建立胎羊体外循环 ,常温 (37℃ )转流 6 0分钟 ,氧合器内充低氧混合气体 (8%O2 和 92 % N2 ) ,监测胎羊的血压、心率、血气、血清乳酸和胎盘血管阻力。　结果　胎羊体外循环中动脉氧分压 (PO2 )和二氧化碳分压 (PCO2 )维持在宫内生理水平 ,胎羊心搏有力 ,血压正常。但胎羊 p H值缓慢下降 (P<0 .0 5 ) ,血清乳酸值明显增高 (P<0 .0 1) ,胎盘血管阻力显著上升 (P<0 .0 1)。停体外循环后胎羊出现低氧、高碳酸血症和酸中毒。　结论　胎羊体外循环影响胎盘功能 ,膜式氧合器可以代替胎盘气体交换功能 ,体外循环中胎羊生理低水平 PO2 是否适合其需要值得探讨。     

Technical Indicators to Evaluate the Degree of Large Clot Formation Inside the Membrane Fiber Bundle of an Oxygenator in an In Vitro Setup

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.     

Impact of hollow-fiber membrane surface area on oxygenator performance: Dideco D903 Avant versus a prototype with larger surface area

This study compares the gas transfer capacity, the blood trauma, and the blood path resistance of the hollow-fiber membrane oxygenator Dideco D 903 with a surface area of 1.7 m2 (oxygenator 1.7) versus a prototype built on the same principles but with a surface area of 2 m2 (oxygenator 2). Six calves (mean body weight: 68.2 +/- 3.2 kg) were connected to cardiopulmonary bypass (CPB) by jugular venous and carotid arterial cannulation, with a mean flow rate of 4 l/min for 6 h. They were randomly assigned to oxygenator 1.7 (N = 3) or 2 (N = 3). After 7 days, the animals were sacrificed. A standard battery of blood samples was taken before the bypass, throughout the bypass, and 24 h, 48 h, and 7 days after the bypass. The oxygenator 2 group showed significantly better total oxygen and carbon dioxide transfer values throughout the perfusion (p < .001 for both comparison). Hemolytic parameters (lactate dehydrogenase and free plasma hemoglobin) exhibited a slight but significant increase after 5 h of bypass in the oxygenator 1.7 group. The pressure drop through the oxygenator was low in both groups (range, 43-74 mmHg). With this type of hollow-fiber membrane oxygenator, an increased surface of gas exchange from 1.7 m2 to 2 m2 improves gas transfer, with a limited impact on blood trauma and no increase of blood path resistance.     

The possibility of a veno-arterial bypass system using the Abiomed BVS 5000

Effect of Abiomed BVS 5000 (Cardiovascular Inc., Danvers, MA, U.S.A) has been reported for mechanical assist circulation in cardiogenic shock. However, this pump is generally used as a ventricular assist device, not as a device for veno-arterial bypass. Therefore, we evaluated its effectiveness through an experiment. The left anterior descending branch of pigs' heart was ligated to prepare a model of acute myocardial infarction, and after the onset of cardiogenic shock, circulation was initially supported for 30 min using the BVS 5000, followed by support for another 30 min using a Gyro pump (Gyro, Kyocera, Inc., Kyoto, Japan). Subsequently, circulation was additionally supported for 30 min using both a Gyro and an intra-aortic balloon pump (IABP) (Tokai Medical Inc., Aichi, Japan) (Gyro + IABP). Circulation was supported in each group at 30-min intervals in the reversed order of assisted circulation. Although the mean aortic pressure, pump flow, and total flow were not significantly different among the three setups, the pulse pressure was 48.2 +/- 3.3, 12.2 +/- 2.2, and 29.9 +/- 3.8 mm Hg in Abiomed, Gyro, and Gyro + IABP, respectively. Although neither coronary arterial nor myocardial blood flow showed significant differences among the three setups, the renal arterial blood flow was significantly larger in BVS 5000 compared to the other two setups. In this study, we selected an alpha-cube (Platium Cube NCVC 6000, Edwards Research Medical Inc., Salt Lake City, UT, U.S.A.), which is considered as an oxygenator that produces minimum pressure loss. Therefore, the pulsatile flow we obtained with the Abiomed was maintained even after we started using the oxygenator. The pulsatile flow had positive effects on renal circulation and peripheral circulation.     

Oxygenator with Built-in Hemoconcentrator: A New Concept

Abstract: A hemoconcentrator is an instrument essential for open heart surgery without blood transfusion. In order to simplify the extracorporeal blood circuit and to facilitate handling of cardiopulmonary bypass, we have combined a hollow fiber unit for gas exchange and that for hemofiltration into one component and developed a new membrane oxygenator with the function of a hemoconcentrator. The cylindrical device consists of a hollow fiber for hemofiltration with another fiber for gas exchange provided outside. Both of them adopt the blood outside perfusion system. Blood enters and flows through the central hole for hemofiltration and then flows into the oxygenator. By applying the flow mode to the device, blood is allowed to flow from the center of the core toward the hollow fiber around it. Therefore, even distribution of blood flow to the entire fiber is realized, and the performance of the device is improved. The oxygen transfer rate was 317 ml/min at a flow rate of 6 L/min, and the ultrafiltration rate was 7 L/h at a flow rate of 4 L/tnin with a hematocrit of 25%. The combined structure of the two units has not caused any adverse effects. In conclusion, by combining an oxygenator and a hemoconcentrator, excellent and simplified hemoconcentration is made available as the blood outside flow mode is adopted, which is one of the unique aspects of this device.     

Development of an Intravascular Pumping Oxygenator Using a New Silicone Membrane

Abstract: A new intravascular pumping oxygenator (IVPO) was developed for intravascular gas exchange and circulatory assistance in critically ill patients with respiratory and circulatory failure. The IVPO utilizes new silicone hollow fibers (diameter. 1 mm: membrane width, 50 μm) and consists of two driving tubes for the oxygenation and pumping of circulating blood. The performance characteristics of the IVPO were studied using an experimental ex vivo model. With a mean hemoglobin concentration of 10.5 ± 2.3 g/dl, total oxygen transfer was 5.6 ± 1.5 ml/min at a blood flow of 200 ml/min and 6.3 ± 2.2 ml/min at a blood flow of 250 ml/min. Total CO₂ transfer was 3.8 ± 1.4 ml/min at a blood flow of 200 ml/min and 4.2 ± 1.6 ml/min at a blood flow of 250 ml/min during IVPO pumping. This preliminary experiment demonstrated that the IVPO has the capacity to function both as a circulatory assist pump and as an intravascular hollow fiber oxygenator.     

Contemporary Oxygenator Design: Shear Stress‐Related Oxygen and Carbon Dioxide Transfer

Design of contemporary oxygenators requires better understanding of the influence of hydrodynamic patterns on gas exchange. A decrease in blood path width or an increase in intraoxygenator turbulence for instance, might increase gas transfer efficiency but it will increase shear stress as well. The aim of this clinical study was to examine the association between shear stress and oxygen and carbon dioxide transfer in different contemporary oxygenators during cardiopulmonary bypass (CPB). The effect of additional parameters related to gas transfer efficiency, that is, blood flow, gas flow, sweep gas oxygen fraction (FiO₂), hemoglobin concentration, the amount of hemoglobin pumped through the oxygenator per minute—Qhb, and shunt fraction were contemplated as well. Data from 50 adult patients who underwent elective CPB for coronary artery bypass grafting or aortic valve replacement were retrospectively analyzed. Data included five different oxygenator types with an integrated arterial filter. Relationships were determined using Pearson bivariate correlation analysis and scatterplots with LOESS curves. In the Capiox FX25, Fusion, Inspire 8F, Paragon, and Quadrox‐i groups, mean blood flows were 4.8 ± 0.9, 5.3 ± 0.7, 4.9 ± 0.7, 5.0 ± 0.6, and 5.7 ± 0.6 L/min, respectively. The mean O₂ transfer/m² membrane surface area was 44 ± 14, 51 ± 9, 60 ± 10, 63 ± 14, and 77 ± 18, respectively, whereas the mean CO₂ transfer/m² was 26 ± 14, 60 ± 22, 73 ± 29, 74 ± 19, and 96 ± 20, respectively. Associations between oxygen transfer/m² and shear stress differed per oxygenator, depending on oxygenator design and the level of shear stress (r = 0.249, r = 0.562, r = 0.402, r = 0.465, and r = 0.275 for Capiox FX25, Fusion, Inspire 8F, Paragon, and Quadrox‐i, respectively, P < 0.001 for all). Similar associations were noted between CO₂ transfer/m² and shear stress (r = 0.303, r = 0.439, r = 0.540, r = 0.392, and r = 0.538 for Capiox FX25, Fusion, Inspire 8F, Paragon, and Quadrox‐i, respectively, P < 0.001 for all). In addition, O₂ transfer/m² was strongly correlated with FiO₂ (r = 0.633, P < 0.001), blood flow (r = 0.529, P < 0.001), and Qhb (r = 0.589, P < 0.001). CO₂ transfer/m² in contrast was predominately correlated to sweep gas flow (r = 0.567, P < 0.001). The design‐dependent relationship between shear stress and gas transfer revealed that every oxygenator has an optimal range of blood flow and thus shear stress at which gas transfer is most efficient. Gas transfer is further affected by factors influencing the O₂ or CO₂ concentration gradient between the blood and the gas compartment.     

Tubular Vacuum-Powered Blood-Pumping Device with Active Valves

Abstract: We propose a new vacuum-driven blood pump having a tubular shape with active valves. This design avoids any possible problems caused by membrane breakage, thereby minimizing the risk of gas embolic events and stagnation regions. By using active valves, it is possible to ensure better flow control and minimize pressure gradients inside and outside the pump. The low cost of the pump's disposable parts enables it to be used for such applications as a ventricular assist device, a pulsatile pump device in extracorporeal circulation, a pump in hemodialysis and apheresis circuits, and a pump in extracorporeal membrane oxygenator systems.     

Washin and washout of isoflurane administered via bubble oxygenators during hypothermic cardiopulmonary bypass

Washin and washout of a volatile anesthetic given through the oxygenator during hypothermic (23.4 +/- 2.1 degrees C) cardiopulmonary bypass were studied in nine patients. The authors administered isoflurane and measured its partial pressure in arterial (Pa) and venous (Pv) blood and the gas exhausted from the oxygenator (PE) at 1, 2, 4, 8, 16, 32, and 48 min during washin. These measurements were repeated during washout, which coincided with rewarming. During washin, PE, Pa, and Pv progressively rose toward inlet gas partial pressure (PI). Equilibration of Pa with PI was 41% after 16 min, 51% after 32 min, and 57% after 48 min of washin. During washout, Pa declined to 24% of its peak after 16 min and to 13% after 32 min. Washin and washout were considerably slower in mixed venous blood. Washin of isoflurane appeared to occur more slowly during cardiopulmonary bypass than during administration via the lungs in normothermic patients, presumably because hypothermia increases tissue capacity, compensating for the effect of hemodilution that otherwise would decrease the blood/gas partition coefficient. During rewarming, washout appeared to occur as rapidly as from the lungs of normothermic patients. This may have resulted from the declining blood/gas partition coefficient (due to rewarming) and relatively limited tissue stores of isoflurane. The relationship between exhaust and arterial partial pressures was reasonably consistent; for clinical purposes, measurement of PE can be used to estimate Pa.     

Laboratory evaluation of a new membrane oxygenator with a built-in hemoconcentrator

In order to facilitate the handling of cardiopulmonary bypass (CPB) and simplify the circuit, we have developed a new membrane oxygenator with a hemofiltration function. The hollow fiber units for gas exchange and hemofiltration were combined in concentric circles in a cylindrical housing. The total priming volume was 190 ml. Because we used a silicon-coated hollow fiber membrane for gas exchange, this oxygenator was completely resistant to serum leakage. The gas exchange and hemofiltration sections both have a blood-outside flow configuration. All blood flows in a radial direction from around the central core to the surrounding hollow fiber units, first to the hemofiltration portion and then to the gas exchange section. Filtered fluid was easily collected through a stopcock mechanism. The oxygen transfer rate was 312 ml/min at a blood flow rate of 6 L/min, and the ultrafiltration rate was 3.5 L/hour at a blood flow rate of 4 L/min with 25% hematocrit and 200 mmHg transmembrane pressure in an in vitro study. The pressure drop was 62 mmHg at a blood flow rate of 4 L/min. We found no adverse effects in an in vivo study using a mongrel dog. In conclusion, this durable combined device could achieve excellent and simplified hemoconcentration by having all the blood in the unit flow through the hemofiltration portion, and may be useful not only in CPB during open heart surgery, but also in extracorporeal membrane oxygenation.     

Initial clinical experience with a more efficient hollow fiber oxygenator of unique design

The first 90 cardiac surgery cases perfused with a new hollow fiber membrane oxygenator in which the gas flows through the fibers and blood flows around the fibers are reported. The fibers are microporous polypropylene with a pore size of 0.03 microns. Membrane surface area is 2.0 M2 and priming volume is 480 ml, including heat exchanger PaO2 is controlled by FIO2 and PaCO2 by gas flow rate. Patients as large as 2.36 M2 were perfused up to 348 min using hemodilution and hypothermia. The mean PaO2 was 200 mmHg and the mean PaCO2 39.5 mmHg. Oxygen transfer was as high as 230 ml/min. This low prime device transfers large volumes of gas, an efficiency which results from a crossed arrangement of the fibers to break up laminar flow of the blood around them. The low priming volume makes it appropriate for use in all but the smallest patients.     

Initial In Vitro Evaluation of a Pediatric Vortex-Mixing Membrane Lung

Abstract: A new design for a pediatric membrane lung is described in this paper. The lung consists of eight blood compartments, each having six U-shaped blood channels, with microporous PTFE membranes supported on rigid plates in such a way that the membranes form furrowed blood channels. Two rolling diaphragm pumps are attached to the open ends of the U-shaped blood channels; these pumps are operated in antiphase. Mean flow is provided by a roller pump placed at the inlet end of the membrane lung. Pulsatile blood flow within the blood channels produces successive vortex formation and ejection, leading to good blood mixing and high efficiency in gas transport. The design of the rolling diaphragm piston pumps ensures that the blood prime volume is low (280 ml), and the grouping of the pumps at one end of the oxygenator allows the driving mechanism to be simple and compact. The relatively wide blood channels (minimum width 0.5 mm) and vortex mixing make priming the membrane lung particularly easy. The membrane area is 0.39 m². Preliminary performance testing of the pediatric membrane lung was undertaken by pumping blood around a circuit containing a roller pump, the membrane lung, and a bubble oxygenator (to adjust the blood gases at the inlet to the membrane lung). In five such experiments it was shown that the membrane lung transferred 80 ml O₂/min and 120 ml CO₂/min at a blood flow rate of 1.5 L/min.     

Development of an artificial placenta: CO2 elimination and hemodynamics as a function of arteriovenous blood flow

Background

As a first step toward the development of an artificial placenta, we investigated the relationship between blood flow rate through an arteriovenous (A-V) circuit/oxygenator and both CO₂ elimination and hemodynamic stability in a small animal model.

Methods

Male New Zealand rabbits (N = 10) with an average weight of 2.7 ± 0.2 kg were anesthetized, paralyzed, and heparinized before carotid-jugular cannulation. A tracheostomy tube, an arterial catheter, and an aortic flow probe were placed. Arteriovenous flow through a custom-made, low-resistance, 0.5 m² hollow fiber oxygenator was initiated. Oxygen sweep flow was maintained at 300 mL/min, whereas blood flow was controlled at 10 to 40 mL/(kg min). Ventilation was discontinued during each blood flow rate trial. Hemodynamic and preoxygenator and postoxygenator blood gas data were recorded 30 minutes after initiation of each flow rate. CO₂ removal was the product of the oxygen sweep gas flow rate and the sweep flow exhaust CO₂ content as determined by capnometry. Data were analyzed by analysis of variance with post hoc Dunnett's t test.

Results

CO₂ removal increased and Paco₂ decreased as a function of A-V blood flow rate. Simultaneously, systolic blood pressure did not significantly change. CO₂ removal was effective at device flows greater than 20% of cardiac output.

Conclusion

In this rabbit model, A-V blood flows at 25% to 30% of cardiac output allow full gas exchange without hemodynamic compromise. This model raises the possibility of using A-V support and an artificial placenta in newborns with respiratory failure.