Experimental study of pumpless ECMO during 24 hours using extracapillary blood flow type polypropylene membrane oxygenator

To remove carbon dioxide in acute respiratory failure, pumpless ECMO (extra-corporeal membrane oxygenation) experiment was carried out using extracapillary blood flow type membrane oxygenator, which was developed by our department and which has many advantages, compact, small priming volume and low pressure drop. The oxygenator is consisted with 17 cm in length, 200 microns in inner diameter, made of polypropylene with micropores. And it has 0.7 m2 of surface area and 60 ml of priming volume. In 14 canines, acute respiratory failure were made by hypoventilation (T.V. = 10 ml/kg, R.R. = 5 times/min). We compared with hypoventilation group (group 1, n = 5) and pumpless ECMO group (group 2, n = 9). Pumpless ECMO circuit is A-V bypass between femoral artery and femoral vein. The following results were obtained. 1. In group 1 severe hypoxia and hypercapnea were observed, and all 5 canines were dead within 4 hours. 2. In group 2 hypoxia and hypercapnea were improved by pumpless ECMO, and 4 in 9 lived for 24 hours. 3. Function in CO2 transfer with the P.H.O. is maintained in satisfactory condition for 24 hours. 4. The oxygenator seems to be available for long-term pumpless ECMO. 5. Degeneration of mitochondria in the acute respiratory failure was observed by electron microscopic examination. 6. Further examinations about the intracellular respiration and metabolism in pumpless ECMO should be needed.     

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.     

Development of a new silicone membrane oxygenator for ECMO.

Two types small and efficient ECMO oxygenators were developed utilizing the most up to date hollow fiber technology. Newly silicone hollow fibers possess sufficient mechanical strength while maintaining ultra thin walls of 50 micro meter. Two types of oxygenators were made with this fiber. The fiber length for the type 1 module is 150mm with a priming volume 194 cc (surface area 1.3 m(2)) and type 2 has a fiber length of 100 mm with a 144 cc priming volume (the surface area 0.8 m(2)). The studies were performed at 0.5, 1.0 and 2.0 L/min of blood flow and these oxygenators demonstrated. O(2) gas transfer rate of 69+/-4 ml/min/L for type 1 and 68+/-6 ml/min/L for type 2. The CO(2) gas transfer rate was 25+/-2 ml/min/L for type 1 and 32+/-2 ml/min/L for type 2. These results demonstrate type 2 oxygenator has similar gas exchange capabilities to those of Kolobows' oxygenator which has about 2.0 times larger surface area. Additionally, comparative hemolysis tests were preformed with this new oxygenator and the Kolbow. The NIH value was 0.006 (g/100 L) for the type 1 oxygenator and 0.01 (g/100 L) for the Kolbow oxygenator. These results suggested that this ECMO oxygenator had sufficient gas exchange performance in spite of being smaller and induced minimal blood damage.     

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.     

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.     

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.     

Development of a new hollow fiber silicone membrane oxygenator for ECMO: the recent progress.

Throughout the last 50 years, many improvements have been made for a more effective oxygenator. A large plate type membrane oxygenator, used by Clowes, and a coil type, used by Kolff, has evolved into the small hollow fiber oxygenator. The complex bubble oxygenator, or rotating disk oxygenator, has become a small disposable bubble oxygenator. The currently available oxygenators are extremely small, efficient, and can be used for extended periods of time. However, there are some problems with extracorporeal membrane oxygenation (ECMO). Currently in the United States, there are no clinically applicable hollow fiber ECMO oxygenators available, in spite of the extended ECMO application. Therefore, the development of a small, yet efficient, silicone hollow fiber membrane oxygenator for long-term ECMO usage was attempted. Based on the results of many experimental models, preclinical oxygenator models for long-term ECMO were developed in our laboratory using an ultra-thin silicone rubber hollow fiber membrane.     

Preclinical evaluation of a new hollow fiber silicone membrane oxygenator for pediatric cardiopulmonary bypass: ex-vivo study.

Based on the results of many experimental models, a hollow fiber silicone membrane oxygenator applicable for long-term extracorporeal membrane oxygenation (ECMO) was developed. For further high performance and antithrombogenicity, this preclinical model was modified, and a new improved oxygenator was successfully developed. In addition to ECMO application, the superior biocompatibility of silicone must be advantageous for pediatric cardiopulmonary bypass (CPB). An ex vivo short-term durability test for pediatric CPB was performed using a healthy miniature calf for six hours. 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 centrifugal pump. For six hours, the O2 and CO2 gas transfer rates were maintained around 90 and 80 ml/min at a blood flow rate of 2 L/min and V/Q=3, respectively. The plasma free hemoglobin was maintained around 5 mg/dl. These data suggest that this newly improved oxygenator has superior efficiency, less blood trauma, and may be suitable for not only long-term ECMO but also pediatric CPB usage.     

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.     

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.     

Comparison of four stainless steel heat exchangers for neonatal ECMO applications

Conventional neonatal extracorporeal membrane oxygenation (ECMO) circuits utilize a heat exchanger distal to the oxygenator to replace ambient heat loss and maintain patient normothermia. A secondary function of the ECMO heat exchanger is to act as an arterial line bubble trap to protect the patient against accidental air embolism. Using an asanguinous recirculating test circuit, we measured and compared heat transfer properties, pressure drop, air trapping capabilities, and priming characteristics of four commercially available stainless steel heat exchangers currently being used in neonatal ECMO circuits: Avecor ECMOtherm, Gish HE-3, Gish HE-4, and Electromedics D1079. Manufacturers' product specifications were also compared. The pressure drop across all four heat exchangers was less than 10 mmHg with flow rates up to 500 ml/min. The Gish HE-3 and HE-4 were the easiest to prime and de-air, while the Electromedics D1079 was the most difficult. The heat exchangers with integral bubble traps (D1079 and HE-4) have superior air trapping capabilities. The ECMOtherm provided moderate air trapping capabilities ( greater than 7.3 ml +/- 1.5 ml) at flow rates under 300 ml/min. The low prime HE-3 was the poorest at trapping air; less than 1 ml at a 400 ml/min pump flow rate. Thermal analysis indicated that the D1079 had the highest performance factor, though all four heat exchangers had similar heat transfer rates and were capable of warming perfusate from 34 degrees to 37 degrees C on a single pass at pump flow rates of 500 ml/min.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiac performance in ECMO candidates: echocardiographic predictors for ECMO.

Twenty-one neonates with severe respiratory failure, who met criteria in this center for extracorporeal membrane oxygenation (ECMO), underwent echocardiographic examinations to assess the role of cardiac dysfunction in determining the need for ECMO. The echocardiographic indexes of function included peak aortic and pulmonary flow velocity, aortic and pulmonary acceleration, shortening fraction, velocity of circumferential fiber shortening, right ventricular output, and left ventricular output. Patients were offered a staged treatment protocol using high-frequency oscillatory ventilation (HFOV), followed by ECMO if failing HFOV rescue. Nine patients demonstrated progressive deterioration and required ECMO (group 1); 12 patients recovered without ECMO (group 2). There were no significant intergroup differences in AaDO2, age, weight, gestational age, inotropic support, mean airway pressure, systemic blood pressure, or arterial blood gas parameters. Group 1 had significantly lower pulmonary and aortic peak flow velocities, lower pulmonary acceleration, lower shortening fraction, and lower velocity of circumferential fiber shortening (P less than .05). We found that values for peak pulmonary velocity less than 0.70 m/s with pulmonary acceleration less than 14 m/s2 would predict the need for ECMO in 7 of 9 group 1 patients and recovery without ECMO in 11 of 12 group 2 patients (P less than .01, Fisher's Exact test). We conclude that on initial echocardiographic evaluation, cardiac performance was impaired in those patients who subsequently required ECMO compared with a group of patients with similar severity in gas exchange who recovered without ECMO. We speculate that echocardiographic assessment of cardiac performance in ECMO candidates may prove useful in prediction of the subsequent need for ECMO or expedient transfer to an ECMO center.     

Role of extracorporeal lung assist in the treatment of acute respiratory failure

For patients with most severe acute respiratory distress syndrome (ARDS) conservative treatment with lung protective ventilation is often not sufficient to prevent life-threatening hypoxemia and additional strategies are necessary. Extracorporeal lung assist (ECLA) or extracorporeal membrane oxygenation (ECMO) using capillary membrane oxygenators can provide sufficient gas exchange and lung rest. In 2 randomized trials mortality was unchanged for ECMO. Today an technically enhanced ECMO is used for most severe ARDS using clinical algorithm and different case studies demonstrated a survival rate about 56%. Today miniaturized ECMO with optimized blood pumps and oxygenators are available and could enhance safety and clinical management. Another approach is an arterio-venous pumpless interventional lung assist (ILA) with a low resistance oxygenator. Advantages seem a simplified clinical management and less blood trauma. At present new devices are developed for chronic respiratory failure or bridge to lung transplant. Oxygenators with even less flow resistance could be implanted paracorporeal using the right ventricle as driving force. An intravascular oxygenator has been developed using the combination of a miniaturized blood pump and an oxygenator for implantation in the vena cava. Well designed clinical trials are necessary to demonstrate a clinical benefit for these experimental devices.     

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.     

Clinical experiences with a new membrane oxygenator with low priming volume (D702 MASTER FLO 51), studies during pulsatile and constant flow perfusion

The newly developed oxygenator "D702" is a compact hollow fiber membrane oxygenator with a priming volume of 170 ml. The maximum flow allowance is 4 liters per/minute. We used this oxygenator in 16 patients (11 infants and children, and 5 adults) undergoing various open heart surgery, and function of this oxygenator was studied. Pulsatile cardiopulmonary bypass was performed in 8 patients and nonpulsatile constant flow perfusion was employed in the remaining 8 patients. Our clinical experience showed excellent maintenance of PaO2 and PaCO2 during both pulsatile and constant flow bypasses. A low pressure drop was encountered across the membrane oxygenator, and therefore, this oxygenator is applicable for pulsatile cardiopulmonary bypass. The D702 is a very useful and applicable for a wide range of patients from infants to adults with a small body structure.     

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.     

A simple method of extracorporeal membrane oxygenation (ECMO)--3. The effects of pumpless ECMO (arterio-venous shunt) on arterial blood gas measured for 24 hours

In eight anesthetized mongrel dogs, the pumpless ECMO applied between the femoral artery and vein was performed under the condition of hypoventilation for 24 hours. The methods were same as the first and second reports, except the pumpless ECMO was used. The abnormal parameters in the cardiovascular and respiratory system (blood gas analysis and end expiratory gas analysis), induced by hypoventilation, recovered to almost normal ranges, by operation of the pumpless ECMO for 24 hours. The pumpless ECMO might have such advantages over ECMO with pump as the less destruction of blood cell, easy performance and simple apparatus. In conclusion, pumpless ECMO using arterio-venous shunt may be applied clinically on respiratory distress conditions.     

New Generation Extracorporeal Membrane Oxygenation With MedTech Mag‐Lev,a Single‐Use,Magnetically Levitated,Centrifugal Blood Pump: Preclinical Evaluation in Calves

We have evaluated the feasibility of a newly developed single‐use, magnetically levitated centrifugal blood pump, MedTech Mag‐Lev, in a 3‐week extracorporeal membrane oxygenation (ECMO) study in calves against a Medtronic Bio‐Pump BPX‐80. A heparin‐ and silicone‐coated polypropylene membrane oxygenator MERA NHP Excelung NSH‐R was employed as an oxygenator. Six healthy male Holstein calves with body weights of about 100 kg were divided into two groups, four in the MedTech group and two in the Bio‐Pump group. Under general anesthesia, the blood pump and oxygenator were inserted extracorporeally between the main pulmonary artery and the descending aorta via a fifth left thoracotomy. Postoperatively, both the pump and oxygen flow rates were controlled at 3 L/min. Heparin was continuously infused to maintain the activated clotting time at 200–240 s. All the MedTech ECMO calves completed the study duration. However, the Bio‐Pump ECMO calves were terminated on postoperative days 7 and 10 because of severe hemolysis and thrombus formation. At the start of the MedTech ECMO, the pressure drop across the oxygenator was about 25 mm Hg with the pump operated at 2800 rpm and delivering 3 L/min flow. The PO₂ of the oxygenator outlet was higher than 400 mm Hg with the PCO₂ below 45 mm Hg. Hemolysis and thrombus were not seen in the MedTech ECMO circuits (plasma‐free hemoglobin [PFH] < 5 mg/dL), while severe hemolysis (PFH > 20 mg/dL) and large thrombus were observed in the Bio‐Pump ECMO circuits. Plasma leakage from the oxygenator did not occur in any ECMO circuits. Three‐week cardiopulmonary support was performed successfully with the MedTech ECMO without circuit exchanges. The MedTech Mag‐Lev could help extend the durability of ECMO circuits by the improved biocompatible performances.     

Pumpless extracorporeal lung assist - experience with the first 20 cases.

OBJECTIVE: Long-term extracorporeal lung assist is limited by a significant mechanical blood trauma resulting in bleeding and hemolysis. To reduce the drawbacks of extracorporeal lung assist a new technique has been developed, by which the driving force for the extracorporeal circuit derives from the patients arterio-venous pressure gradient (pumpless extracorporeal lung assist). The aim of this clinical study was to test the feasibilty and effectiveness of pumpless extracorporeal lung assist in patients with acute respiratory distress syndrome. METHODS: Twenty patients (41+/-16 years) with acute respiratory distress syndrome of various causes and failing respirator therapy were enrolled. The minimum hemodynamic requirements included a cardiac output (CO) >6 l/min and mean arterial pressure (MAP) >70 mmHg. Pumpless extracorporeal lung assist was established using a short circuit arterio-venous shunt including a special designed low-resistance membrane oxygenator which was placed between the patients legs. RESULTS: At the time of inclusion FiO(2) in all patients was 1.0 (paO(2) 45.9+/-7 mmHg, paCO(2) 58.9+/-17 mmHg). After 24 h of pumpless extracorporeal lung assist FiO(2) was reduced to 0.8+/-0.1. A significant improvement in oxygenation (paO(2) 84.1+/-21 mmHg, P<0.05) and CO(2) removal (paCO(2) 32.7+/-5 mmHg, P<0.05) was notable. The mean extracorporeal flow was 2.6+/-0.6 l/min, which represented approximately 25% of the patients mean CO (10.8+/-2 l/min). The median assist time was 12+/-8 (1-32) days. Fifteen out of twenty patients were weaned off pumpless extracorporeal lung assist. Five out of twenty patients died while on the system (four sepsis, one ventricular fibrillation). Three out of twenty patients died after successful weaning on day 8, 30, and 50, respectively. Twelve out of twenty patients were discharged in a healthy state (overall survival 60%). Technical problems included thrombosis of the venous cannula (n=5), thrombus formation within the membrane oxygenator (n=2), membrane oxygenator plasma leakage (n=2), and membrane oxygenator contamination with Candida albicans. No bleeding complication was observed. CONCLUSION: Pumpless extracorporeal lung assist is feasible and effective in a selected group of patients with acute respiratory distress syndrome but preserved hemodynamic function. By eliminating the pump and reducing the tubing length blood trauma can be minimized. Being very simple the system entails fewer risks of technical complications and also facilitates nursing care.     

Pressure drop, shear stress, and activation of leukocytes during cardiopulmonary bypass: a comparison between hollow fiber and flat sheet membrane oxygenators

The membrane oxygenator is known to be superior to the bubble oxygenator, but little information is available about the difference between the hollow fiber and flat sheet membrane oxygenators with regard to pressure drop, shear stress, and leukocyte activation. In this study, we compared these 2 types of membrane oxygenators in patients undergoing cardiopulmonary bypass (CPB) surgery with special focus on leukocyte activation and pressure drop across the oxygenators. Plasma concentration of elastase, a marker indicating leukocyte activation, increased to 593+/-68% in the flat sheet oxygenator group versus 197+/-42% in the hollow fiber oxygenator group (p<0.01) at the end of CPB compared to their respective baseline concentrations before CPB. Pressure drop across the oxygenator was significantly higher in the flat sheet group than in the hollow fiber group throughout the entire period of CPB (p<0.01). High pressure drop across the oxygenator as well as the calculated shear stress was positively correlated with the release of elastase at the end of CPB (r = 0.760, p<0.01, r = 0.692, p<0.01). However, this positive correlation existed in the flat sheet oxygenator but not in the hollow fiber oxygenator. Clinically, both membrane oxygenators have satisfactory performance in O2 and CO2 transfer. These results suggest that a higher pressure drop across the flat sheet oxygenator is associated with more pronounced activation of leukocytes in patients undergoing cardiopulmonary bypass.