The relationship between oxygenator exhaust P(CO2) and arterial P(CO2) during hypothermic cardiopulmonary bypass

During cardiopulmonary bypass the partial pressure of carbon dioxide in oxygenator arterial blood (P(a)CO2) can be estimated from the partial pressure of gas exhausting from the oxygenator (P(E)CO2). Our hypothesis is that P(E)CO2 may be used to estimate P(a)CO2 with limits of agreement within 7 mmHg above and below the bias. (This is the reported relationship between arterial and end-tidal carbon dioxide during positive pressure ventilation in supine patients.) During hypothermic (28-32 degrees C) cardiopulmonary bypass using a Terumo Capiox SX membrane oxygenator, 80 oxygenator arterial blood samples were collected from 32 patients during cooling, stable hypothermia, and rewarming as per our usual clinical care. The P(a)CO2 of oxygenator arterial blood at actual patient blood temperature was estimated by temperature correction of the oxygenator arterial blood sample measured in the laboratory at 37 degrees C. P(E)CO2 was measured by connecting a capnograph end-to-side to the oxygenator exhaust outlet. We used an alpha-stat approach to cardiopulmonary bypass management. The mean difference between P(E)CO2 and P(a)CO2 was 0.6 mmHg, with limits of agreement (+/-2 SD) between -5 to +6 mmHg. P(E)CO2 tended to underestimate P(a)CO2 at low arterial temperatures, and overestimate at high arterial temperatures. We have demonstrated that P(E)CO2 can be used to estimate P(a)CO2 during hypothermic cardiopulmonary bypass using a Terumo Capiox SX oxygenator with a degree of accuracy similar to that associated with the use of end-tidal carbon dioxide measurement during positive pressure ventilation in anaesthetized, supine patients.     

In vitro evaluation of gaseous microemboli handling of cardiopulmonary bypass circuits with and without integrated arterial line filters

The delivery of gaseous microemboli (GME) by the cardiopulmonary bypass circuit should be minimized whenever possible. Innovations in components, such as the integration of arterial line filter (ALF) and ALFs with reduced priming volumes, have provided clinicians with circuit design options. However, before adopting these components clinically, their GME handling ability should be assessed. This study aims to compare the GME handling ability of different oxygenator/ALF combinations with our currently utilized combination. Five commercially available oxygenator/ALF combinations were evaluated in vitro: Terumo Capiox SX25RX and Dideco D734 (SX/D734),Terumo Capiox RX25R and AF125 (RX/AF125), Terumo FX25R (FX), Sorin Synthesis with 102 microm reservoir filter (SYN102), and Sorin Synthesis with 40 microm reservoir filter (SYN40). GME handling was studied by introducing air into the venous return at 100 mL/min for 60 seconds under two flow/ pressure combinations: 3.5 L/min, 150 mmHg and 5 L/min, 200 mmHg. Emboli were measured at three positions in the circuit using the Emboli Detection and Classification (EDAC) Quantifier and analyzed with the General Linear Model. All circuits significantly reduced GME. The SX/D734 and SYN40 circuits were most efficient in GME removal whilst the SYN102 handled embolic load (count and volume) least efficiently (p < .001). A greater number of emboli <70 microm were observed for the SYN102, FX and RX/AF125 circuits (p < .001). An increase in embolic load occurred with higher flow/pressure in all circuits (p < .001). The venous reservoir significantly influences embolic load delivered to the oxygenator (p < .001). The majority of introduced venous air was removed; however, significant variation existed in the ability of the different circuits to handle GME. Venous reservoir design influenced the overall GME handling ability. GME removal was less efficient at higher flow and pressure, and for smaller sized emboli. The clinical significance of reducing GME requires further investigation.     

Evaluation of Membrane Oxygenators and Reservoirs in Terms of Capturing Gaseous Microemboli and Pressure Drops

An increasing amount of evidence points to cerebral embolization during cardiopulmonary bypass (CPB) as the principal etiologic factor of neurologic complications. In this study, the capability of capturing and classification of gaseous emboli and pressure drop of three different membrane oxygenators (Sorin Apex, Terumo Capiox SX25, Maquet QUADROX) were measured in a simulated adult model of CPB using a novel ultrasound detection and classification quantifier system. The circuit was primed with 1000 mL heparinized human packed red blood cells and 1000 mL lactated Ringer's solution (total volume 2000 mL, corrected hematocrit 26–28%). After the injection of 5 mL air into the venous line, an Emboli Detection and Classification Quantifier was used to simultaneously record microemboli counts at post‐pump, post‐oxygenator, and post‐arterial filter sites. Trials were conducted at normothermic (35°C) and hypothermic (25°C) conditions. Pre‐oxygenator and post‐oxygenator pressure were recorded in real time and pressure drop was calculated. Maquet QUADROX membrane oxygenator has the lowest pressure drops compared to the other two oxygenators (P < 0.001). The comparison among the three oxygenators indicated better capability of capturing gaseous emboli with the Maquet QUADROX and Terumo Capiox SX25 membrane oxygenator and more emboli may pass through the Sorin Apex membrane oxygenator. Microemboli counts uniformly increased with hypothermic perfusion (25°C). Different types of oxygenators and reservoirs have different capability of capturing gaseous emboli and transmembrane pressure drop. Based on this investigation, Maquet QUADROX membrane oxygenator has the lowest pressure drop and better capability for capturing gaseous microemboli.     

Accuracy of temperature measurement in the cardiopulmonary bypass circuit

Oxygenator arterial outlet blood temperature is routinely measured in the cardiopulmonary bypass (CPB) circuit as a surrogate for the temperature of the arterial blood delivered to sensitive organs such as the brain. The aim of this study was to evaluate the accuracy of the temperature thermistors used in the Terumo Capiox SX25 oxygenator and to compare the temperature measured at the outlet of the oxygenator using the Capiox CX*TL Luer Thermistor with temperatures measured at distal sites. Five experimental stages were performed in vitro to achieve this aim. Under our experimental conditions, the luer thermistors accurately measured the temperature as referenced by a precision thermometer. In the CPB circuit, the difference between arterial outlet and reference thermometer temperature varied with outlet temperature over-reading at low temperatures and under reading at high temperatures. There was negligible heat loss (-0.4+/-0.1degrees C) measured at 4.5 m from the arterial outlet. The Terumo Capiox CX*TL Luer Thermistor is an accurate and reliable instrument for measuring temperature when incorporated into the Capiox Oxygenator. The accuracy in the measurement of temperature using these thermistors is affected by the thermistor immersion depth. Under reading of the arterial blood temperature by approximately 0.5 degrees C should be considered at normothermic temperatures, to avoid exceeding the maximum arterial blood temperature as described by institutional protocols. The accuracy of blood temperature measurements should be considered for all oxygenator arterial outlet temperature probes.     

Non-destructive evaluation of membrane lung gas exchange performance

This paper describes a method of evaluating the gas exchange effectiveness of hollow fiber oxygenators utilizing gas on both sides of the membrane. The goal of the study was to develop an evaluation technique which was accurate, reliable, and did not harm or contaminate a new, sterile oxygenator. Three pediatric oxygenators were tested and compared: the Medtronic Minimax Plus, the Terumo Capiox 320, and the Sorin Masterflo 34 (all with rated blood flows of 2-2.5 L/min). Gas entering the "blood" side was a mixture of CO2, O2, and N2 in a mixture matching typical venous blood partial pressures. The "blood" flows used were 0.5, 1, 1.5, or 2 L/min. Gas entering the gas port had an FiO2 of 0.4 flowing at 0.5, 1, 1.5, 2, 2.5, 3, or 3.5 L/min. Fractional contents of CO2 and O2 at all inlets and outlets were determined using a gas analyzer and converted to partial pressures. Efficacy indices and gas transfer rates were calculated and compared. Of the devices studied, the Masterflo 34 had the highest gas transport rates and effectiveness followed by the Minimax-Plus and the Capiox 320. Reversing the direction of the flow through the "blood" phase of the Minimax-Plus greatly changed its gas exchange effectiveness. The techniques described in this study should allow for a more uniform and consistent evaluation of gas exchange by membrane lungs which can be made inexpensively and relatively quickly. In addition, these methods should allow manufactures to evaluate gas exchange effectiveness and transfer rates of individual units during production as well as reduce the complexity involved when evaluating newly developed oxygenators.     

Retrospective analysis comparing hollow fiber and silicone membrane oxygenators for neonates on ECMO

There is little information showing the use of microporous polypropylene hollow fiber oxygenators during extra-corporeal life support (ECLS). Recent surveys have shown increasing use of these hollow fibers amongst ECLS centers in the United States. We performed a retrospective analysis comparing the Terumo BabyRx hollow fiber oxygenator to the Medtronic 800 silicone membrane oxygenator on 14 neonatal patients on extracorporeal membrane oxygenation (ECMO). The aim of this study was to investigate the similarities and differences when comparing pressure drops, prime volumes, oxygenator endurance, and gas transfer capabilities between the two groups.     

Evaluation of Capiox RX25 and Quadrox‐i Adult Hollow Fiber Membrane Oxygenators in a Simulated Cardiopulmonary Bypass Circuit

The Capiox RX25 and Quadrox‐i Adult oxygenators are commonly used in clinical adult cardiopulmonary bypass circuits. This study was designed to test the effectiveness of two adult oxygenators in order to evaluate gaseous microemboli (GME) trapping capability and hemodynamic performance. A simulated adult CPB circuit was used and primed with Ringer's lactate and packed red blood cells (hematocrit 25%). All trials were conducted at flow rates of 2–5 L/min (1 L/min increments) with a closed and open arterial filter purge line at 35°C. The postcannula pressure was maintained at 100 mm Hg. After a 5 cc of bolus air was introduced into the venous line, an Emboli Detection and Classification system was used to detect and classify GME at the preoxygenator, postoxygenator, and precannula sites. At the same time, real‐time pressure and flow data were recorded, and hemodynamic energy was calculated using a custom‐made data acquisition system and Labview software. Our results showed that the oxygenator pressure drops of Quadrox‐i Adult oxygenator were lower than Capiox RX25 at all flow rates. The Quadrox‐i Adult oxygenator retained more hemodynamic energy across the oxygenator. Both oxygenators could trap the majority of GME, but Capiox RX25 did better than the Quadrox‐i Adult oxygenator. No GME was delivered to the pseudo patient at all flow rates in the Capiox group. The Capiox RX25 venous reservoir could capture more GME at lower flow rates, while the Quadrox‐i Adult venous reservoir performed better at higher flow rates. An open arterial filter purge line reduced GME slightly in the Capiox group, but GME increased in the Quadrox group. The Quadrox‐i Adult oxygenator is a low‐resistance, high‐compliance oxygenator. The GME handling ability of Capiox RX25 performed well under our clinical setting. Further optimized design for the venous/cardiotomy reservoir is needed.     

Novel Pulsatile Diagonal Pump for Pediatric Extracorporeal Life Support System

A novel pulsatile rotary flow pump has been used in clinical extracorporeal life support (ECLS) in Europe. The objective of this study is to evaluate the Medos Deltastream DP3 diagonal pump (Medos Medizintechnik AG, Stolberg, Germany) in a simulated pediatric ECLS system. The ECLS circuit consisted of a Medos Hilite 800LT hollow fiber membrane oxygenator (Medos Medizintechnik AG), a Medos Deltastream DP3 diagonal pump, a 10Fr Terumo TenderFlow Pediatric Arterial Cannula (Terumo Corporation, Tokyo, Japan), and an arterial/venous tubing. All trials were conducted at flow rates ranging from 200–800 mL/min (in 200 mL/min increments) under a blood temperature of 35°C using human blood (hematocrit 40%). The postcannula pressure was maintained 60 mm Hg by a Hoffman clamp. Real‐time pressure and flow data were recorded using a Labview‐based acquisition system (National Instruments, Austin, TX, USA). The results showed that the Medos Deltastream DP3 can generate effective pulsatile flow without backflow, provide higher flow rates and pressures than nonpulsatile flow, and then create surplus hemodynamic energy and more total hemodynamic energy than nonpulsatile flow. Pulsatility increased with increased speed differential values and flow rates, while the oxygenator pressure drop increased at an acceptable level. The Medos Deltastream DP3 diagonal pump can provide adequate quality of pulsatility without backflow, and generate more hemodynamic energy under pulsatile mode in a simulated pediatric ECLS system.     

Evaluation of neonatal membrane oxygenators with respect to gaseous microemboli capture and transmembrane pressure gradients

A series of studies performed at our center demonstrates that gaseous microemboli (GME) remain a challenge in cardiac surgical procedures. Evaluation of novel oxygenators must address hemodynamic parameters and microemboli capture capability. The objective of this study is to compare two neonatal membrane oxygenators, the Quadrox‐i (MAQUET Cardiopulmonary AG, Hirrlingen, Germany) and the Capiox RX05 (Terumo Corporation, Tokyo, Japan), with respect to GME capture and hemodynamic energy delivery. The experimental circuit included a Maquet HL‐20 heart‐lung machine, a Heater‐Cooler Unit HCU 30 (MAQUET Cardiopulmonary AG), a membrane oxygenator (Quadrox‐i Neonatal or Capiox RX05), and ¼‐inch tubing from the COBE Heart/Lung Perfusion Pack (COBE Cardiovascular, Inc., Arvada, CO, USA). A Capiox cardiotomy reservoir CX*CR10NX (Terumo Corporation) acted as a pseudopatient. The circuit was primed with human packed red blood cells and lactated Ringer's solution and de‐aired according to clinical priming procedure. Heparin (5000 IU) was added into the circuit. The total volume was 400 mL and hematocrit was 30%. Pump flow rate was maintained at 500 or 1000 mL/min under both pulsatile and nonpulsatile modes. All trials were conducted under 100 mm Hg of circuit pressure at normothermia (35°C). In each trial, bolus air (0.5 mL) was injected into the circuit at the prepump site over 5 s. Total emboli counts and total emboli volume were significantly reduced by the Quadrox‐i Neonatal membrane oxygenator compared to the Capiox RX05 membrane oxygenator. Classification and quantification of GME detected at the postoxygenator site at two different flow rates indicated that the Quadrox‐i Neonatal captures the majority of microemboli larger than 40 µm in diameter. The Quadrox‐i Neonatal membrane oxygenator had a higher transmembrane pressure drop at 500 mL/min, whereas it had a lower pressure drop at 1000 mL/min compared to the Capiox Baby RX05 oxygenator. Additionally, the Quadrox‐i Neonatal oxygenator preserved more pulsatile energy than the Baby RX05 oxygenator at both flow rates. Compared to the Capiox RX05 membrane oxygenator, the Quadrox‐i Neonatal membrane oxygenator has significantly improved GME handling capacity and had better hemodynamic energy preservation. Further research encompassing in vivo and clinical studies is needed to investigate the magnitude and mechanisms of these benefits.     

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.     

Initial clinical experience with a low pressire drop membrane oxygenator for cardiopulmonary bypass in adult patients

The new Travenol oxygenator is composed of 80 parallel blood pathways. Microporous membrane separates the blood and gas compartments. The membrane surface area is 3 m², with a pore size of 0.01 microns. Venous blood drains directly from the patient through the oxygenator, then through an integral heat exchanger and into a reservoir, from which a single arterial pump returns the blood to the patient. The advantage of this configuration of membrane oxygenator is simplicity of setup and operation. A disadvantage that we have observed is an apparent variation in resistance to blood flow through the oxygenator during clinical perfusion. Construction changes in a later version of the oxygenator have reduced the resistance to flow through the blood pathway.This device has been used for 20 perfusions at moderate hypothermia (mean 31.8 °C) in patients up to 2.1 m² body surface area for up to 313 minutes. Blood flow was 2.1 to 5.6 liters/min, partial arterial oxygen pressure 100 to 394 torr, partial arterial carbon dioxide pressure 19 to 57 torr (mean 37 torr) and, arterial pH 7.29 to 7.56 (mean 7.41). Oxygen transfer was as high as 230 ml/min.This integral oxygenator-heat exchanger-reservoir is operated like a bubble oxygenator, with direct venous drainage through the device and a single pump, but it uses a membrane oxygenator for gas exchange to eliminate the detrimental effects of bubbles.     

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.     

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.     

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.     

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.     

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.     

A multi-center trial with a modified design of the Sarns membrane oxygenator

A redesigned hollow fiber bundle was incorporated into an existing oxygenator that underwent clinical trials at seven cardiovascular surgery centers. Clinical investigators were asked to assess gas transfer performance under clinical conditions that could be considered challenging to any microporous membrane oxygenator, i.e., with large body weight patients, long bypass times, or normothermic bypass and surgery. Sixty-six patients, ranging in weight from 54.5 kg to 143 kg, constituted the initial evaluation population. Enhanced oxygen transfer was noted by all of the investigators. Fi0 2 requirements for patients weighing 100 kg or more never exceeded .85, despite oxygen consumption levels reaching as high as 396 mL/min. Two centers documented a 15% to 18% reduction in Fi0 2 requirements compared to their standard oxygenator.     

Development of a novel polyimide hollow-fiber oxygenator

We have developed a membrane oxygenator using a novel asymmetric polyimide hollow fiber. The hollow fibers are prepared using a dry/wet phase-inversion process. The gas transfer rates of O(2) and CO(2) through the hollow fibers are investigated in gas-gas and gas-liquid systems. The polyimide hollow fiber has an asymmetric structure characterized by the presence of macrovoids, and the outer diameter of the hollow fiber is 330 microm. It is found that the polyimide hollow-fiber oxygenator can enhance the gas transfer rates of O(2) and CO(2), and that the hollow fiber provides excellent blood compatibility in vitro and in vivo.     

血管内氧合器的研制

为了探索呼吸辅助的新方法，我们采用国产聚丙烯中空纤维，自行设计、制造模具，研制出一种血管内氧合器。该氧合器是一个小的、细长的可经单侧股静脉或颈静脉切开，置入腔静脉内的装置。氧合器有效长度４０ｃｍ，膜交换面积０．０９ｍ＾２。经负压调节通过血管内氧合器的氧流量，以防止纤维破裂造成的血管内气栓的危险。一根双腔导气管使气体经同一静脉切开部位循环，气体经内芯管流经血管内氧合器尖端，然后经中空纤维束流出。目前     

Studies on ECMO. (III)--Study on pumpless A-V ECMO

Silicon hollow fiber membrane oxygenator is considered to be useful for long term extracorporeal membrane oxygenation (ECMO) and blood usually flows inside of the fiber (inside flow type). But if it flows outside of the fiber (outside flow type), the pressure drop is supposed to be less than that of inside flow type. In this study the oxygenator of an outside flow type was used. At first, the pilot study was done to evaluate the capability of this oxygenator as an outside flow type. The pressure drop was 50 mmHg at the blood flow of 400 ml.min-1. At this blood flow and same gas flow, CO2 transfer rate was 22.3 ml.min-1. In the second study, the effects of pumpless arterio-venous ECMO (pumpless A-V ECMO) were studied in 8 dogs under mechanical hypoventilation. During ECMO, there were no significant changes in hemodynamics when the blood flow rate was 15% of cardiac output. PaO2 and PaCO2 recovered considerably. In conclusion, pumpless A-V ECMO using this membrane oxygenator of outside flow type is effective for CO2 removal and considered to be clinically useful.