静脉-动脉体外膜肺氧合过程发生氧合器假性氧合不良的识别与处理

目的总结主动脉夹层患者在接受体外膜氧合(ECMO)支持过程中发生氧合器假性氧合不良的处理。方法1例患者清醒、自主呼吸、因心衰以“心肌炎”于外院行静脉-动脉(V-A)ECMO治疗60 h后完善彩超等检查,怀疑“马凡综合征”转入我科,ECMO辅助至第70 h患者自述呼吸困难,痰多,经皮血氧饱和度(SpO2)进行性下降至89%,调节ECMO氧浓度至100%后监测氧合器后动脉血气氧分压(PaO2)为92 mmHg,怀疑氧合器“假性氧合不良”,于氧合器动、静脉段先后使用分流量为0.7 L/min和1.4 L/min的旁路处理,并适当安抚患者,辅助至第94 h确诊主动脉夹层后,于急诊下行Bentall+二尖瓣成形+冠状动脉旁路移植术。结果ECMO总辅助时间94 h,其中院外60 h,院内34 h,平均血流量为3.5 L/min,平均氧浓度为60%,辅助至第70 h出现假性氧合不良,经处理后患者SpO2上升至100%,患者诉症状减轻,外科手术顺利,术毕顺利脱离心肺转流,经评估无需继续ECMO辅助,术后28 h苏醒,50 h脱离呼吸机,10 d后康复出院。结论熟悉插管、氧合器等参数有助于鉴别ECMO辅助过程的“假性氧合不良”现象,避免更换氧合器,节约医疗成本的同时保障了患者安全。     

Establishment of a novel miniature veno‐venous extracorporeal membrane oxygenation model in the rat

Recently, veno‐venous extracorporeal membrane oxygenation (V‐V ECMO) has been commonly used in the world to support patients with severe respiratory failure. However, V‐V ECMO is a new technology compared to veno‐arterial extracorporeal membrane oxygenation and cardiopulmonary bypass, and there are few reports of basic research. Although continuing research is desired, clinical research that standardizes conditions such as patients’ background characteristics is difficult. The purpose of this study was to establish a simple and stably maintainable miniature V‐V ECMO model to study the mechanisms of the biological reactions in circulation during V‐V ECMO. The V‐V ECMO system consisted of an original miniature membrane oxygenator, polyvinyl chloride tubing line, and roller pump. The priming volume of this system was only 8 mL. Polyethylene tubing was used to cannulate the right femoral vein as the venous return cannula for the V‐V ECMO system. A 16‐G cannula was passed through the right internal jugular vein and advanced into the right atrium as the conduit for venous uptake. The animals were divided into 2 groups: SHAM group and V‐V ECMO group. V‐V ECMO was initiated and maintained at 50‐60 mL/kg/min, and oxygen was added into the oxygenator during V‐V ECMO at a concentration of 100% (pump flow:oxygen = 1:10). Blood pressure was measured continuously, and blood cells were measured by blood collection. During V‐V ECMO, the blood pressure and hemodilution rate were maintained around 80 mm Hg and 20%, respectively. Hb was kept at >10 g/dL, and V‐V ECMO could be maintained without blood transfusion. It was possible to confirm oxygenation of and carbon dioxide removal from the blood. Likewise, the pH was adequately maintained. There were no problems with this miniature V‐V ECMO system, and extracorporeal circulation progressed safely. In this study, a novel miniature V‐V ECMO model was established in the rat. A miniature V‐V ECMO model appears to be very useful for studying the mechanisms of the biological reactions during V‐V ECMO and to perform basic studies of circulation assist devices.     

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.     

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.     

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.     

Impact of high mechanical shear stress and oxygenator membrane surface on blood damage relevant to thrombosis and bleeding in a pediatric ECMO circuit

The roles of the large membrane surface of the oxygenator and the high mechanical shear stress (HMSS) of the pump in the extracorporeal membrane oxygenation (ECMO) circuit were examined under a pediatric support setting. A clinical centrifugal pump and a pediatric oxygenator were used to construct the ECMO circuit. An identical circuit without the oxygenator was constructed for comparison. Fresh human blood was circulated in the two circuits for 4 hours under the identical pump speed and flow. Blood samples were collected hourly for blood damage assessment, including platelet activation, generation of platelet-derived microparticles (PDMP), losses of key platelet hemostasis receptors (glycoprotein (GP) Ibα (GPIbα) and GPVI), and high molecular weight multimers (HMWM) of von Willebrand factor (VWF) and plasma free hemoglobin (PFH). Platelet adhesion on fibrinogen, VWF, and collagen was further examined. The levels of platelet activation and generation of PDMP and PFH exhibited an increasing trend with circulation time while the expression levels of GPIbα and GPVI receptors on the platelet surface decreased. Correspondingly, the platelets in the blood samples exhibited increased adhesion capacity to fibrinogen and decreased adhesion capacities on VWF and collagen with circulation time. Loss of HMWM of VWF occurred in both circuits. No statistically significant differences were found in all the measured parameters for blood damage and platelet adhesion function between the two circuits. The results indicate that HMSS from the pump played a dominant role in blood damage associated with ECMO and the impact of the large surface of the oxygenator on blood damage was insignificant.     

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.     

Extracorporeal membrane oxygenation for postoperative cardiac support in children

Prolonged circulatory support for cardiac failure has been increasingly successful in adults but has had very limited use in children. From January 1982 to December 1985, 13 children with postoperative cardiac failure refractory to conventional therapy were treated with extracorporeal membrane oxygenation. Ages ranged from 9 days to 17.6 years (mean = 3.8 years); weights ranged from 2.8 to 50 kg (mean = 13.8 kg). Seven patients had obstructive lesions of the right ventricle, such as pulmonary stenosis and tetralogy; the other patients had tricuspid atresia, truncus arteriosus, complete transposition, total anomalous pulmonary venous connection, pericardial tamponade, and a drug reaction after heart transplantation. One patient (nonsurvivor), who could not be separated from cardiopulmonary bypass, required extracorporeal membrane oxygenation in the operating room. In the remaining 12, the interval between operation and the start of extracorporeal membrane oxygenation ranged from 9 to 50 hours (mean = 22.2 hours). Four patients were cannulated through the groin and nine through the chest. Peak flows ranged from 1.05 to 2.74 L/min/m2 (mean 1.92 L/min/m2). Duration of oxygenator support ranged from 12 hours to 9 days (mean = 3.4 days). Seven patients required reexploration for bleeding. Renal insufficiency developed in five patients, four of whom underwent hemodialysis or ultrafiltration during extracorporeal membrane oxygenation. Two patients had evidence of clots in the oxygenator circuit. Seven patients were weaned from extracorporeal membrane oxygenation. Failure to wean from the oxygenator was related to neurologic sequelae of prolonged hypotension before institution of oxygenation in three patients. Mediastinitis developed in three of the seven patients who were weaned. One of these three died in the hospital 74 days after being weaned from the oxygenator. There has been one late death 6 months after oxygenator support was withdrawn. At most recent examination, five children were well, with normal cardiac function 7 months to 4.3 years postoperatively (mean = 32 months). This series suggests that profound cardiac insufficiency in children after cardiac operations can be successfully managed with extracorporeal membrane oxygenation with excellent functional recovery, although major complications are common in this critically ill group of patients.     

At least thirty-four days of animal continuous perfusion by a newly developed extracorporeal membrane oxygenation system without systemic anticoagulants

We developed an extracorporeal membrane oxygenation (ECMO) system with high antithrombogenicity and durability characteristics for prolonged continuous cardiopulmonary support. The oxygenator consists of a special hollow-fiber-type polyolefin gas-exchange membrane, which has an ultrathin dense layer in contact with the blood, in order to prevent plasma leakage during protracted use (Platinum Cube NCVC). The centrifugal pump (RotaFlow) is free of seals. The entire blood-contacting surface of the system is coated with a newly developed heparin material (Toyobo-NCVC coating). We performed a venoarterial bypass in a goat, and the ECMO system was driven for 34 days without systemic anticoagulants. Plasma leakage from the oxygenator did not occur, and sufficient gas exchange performance was maintained. Thrombus formation was hardly observed in the ECMO system except in the casing margins of the oxygenator. This ECMO system showed potential for long-term cardiopulmonary support with minimal or no use of systemic anticoagulants.     

A description of a prototype miniature extracorporeal membrane oxygenation circuit using current technologies in a sheep model

In the United States, standardization of neonatal extracorporeal membrane oxygenation (ECMO) circuit was achieved during the 1980s. Since that time, the consoles and components of the ECMO circuit have remained fundamentally unchanged (bladder, rollerpump, silicone membrane oxygenator). Extracorporeal technology, however, has witnessed many significant advancements in components during the past two decades. These new technologies have characteristics that may improve outcomes when applied in the ECMO arena. Understanding how these technologies perform in long-term applications is necessary. Therefore, the purpose of this project is to evaluate the performance of a miniature ECMO circuit consisting of current generation technologies in an animal model. An ECMO circuit (prime volume 145 mL) was designed that included a hollow fiber oxygenator and a remote mounted centrifugal pump. All circuit tubing and components were surface coated. Three sheep (approx 13 kg) were placed on ECMO using standard neck cannulation techniques and maintained according to clinical protocols. Technical implementation, oxygenator function, and hematological parameters were accessed. Duration of ECMO was 20, 48, and 58 hours. There was no evidence of oxygenator failure, as measured by pressure drop and oxygen transfer, in any of the procedures. No plasma leak was observed in any oxygenators. Platelet count trended downward after 24 hours. Visual inspection after ECMO showed very little evidence of gross thrombosis. This ECMO circuit design departs dramatically from the typical North American systems. The use of this console and components facilitated a 70% reduction in priming volume over a traditional ECMO circuit. Further investigations should be conducted to determine if circuit miniaturization can reduce the morbidity associated with blood product consumption and the bloods contact with the artificial surfaces of the ECMO circuitry.     

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.     

Extracorporeal gas exchange with the DeltaStream rotary blood pump in experimental lung injury

In most severe cases of the acute respiratory distress syndrome, veno-venous extracorporeal membrane oxygenation (ECMO) can be used to facilitate gas exchange. However, the clinical use is limited due to the size and the concomitant risk of severe adverse events of conventionally-used centrifugal blood pumps with high extracorporeal blood volumes. The DeltaStream blood pump is a small-sized rotary blood pump that may reduce extracorporeal blood volume, foreign surfaces, contact activation of the coagulation system, and blood trauma. The aim of the present study was to test the safety and efficacy of the DeltaStream pump for ECMO in animals with normal lung function and experimental acute lung injury (ALI). Therefore, veno-venous ECMO was performed for 6 hours in mechanically ventilated pigs with normal lung function (n=6) and with ALI induced by repeated lung lavage (n=6) with a blood flow of 30% of the cardiac output. Gas flow with a FiO2 of 1.0 was set to equal blood flow. With a mean activated clotting time of 121 +/- 22 s, no circulatory impairment or thrombus formation was revealed during ECMO. Furthermore, free plasma Hb did not increase. In controls, hemodynamics and gas exchange remained unchanged. In animals with ALI, hemodynamics remained stable and gas transfer across the extracorporeal oxygenators was optimal, but only in 2 animals was a marked increase in PaO2 observed. CO2 removal was efficacious in all animals. We concluded that the DeltaStream blood pump may be used for veno-venous ECMO without major blood damage or hemodynamic impairment.     

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.     

Feasibility of a tiny centrifugal blood pump (TinyPump) for pediatric extracorporeal circulatory support

Abstract: In this study, the performances of the TinyPump (priming volume 5 mL) system including the pediatric cannulae (Stöckert Pediatric Arterial Cannulae 2.6, 3.0, and 4.0 mm, Stöckert Instruments GmbH, Munich, Germany; Polystan 20‐Fr Venous Catheter, MAQUET GmbH, Rastatt, Germany) and an oxygenator (Terumo Capiox RX05 Baby‐RX, Terumo Cardiovascular Systems Co., Tokyo, Japan) were studied in vitro followed with preliminary ex vivo studies in 20‐kg piglets. In vitro results revealed that the TinyPump system met the requirements for pump speed, pump flow, and pressure drop as extracorporeal circulatory support during open heart surgery and extracorporeal membrane oxygenation (ECMO) in pediatric patients. In 2‐h ex vivo studies using 20‐kg piglets where the blood contacting surface of the TinyPump was coated with a biocompatible phospholipid polymer, the plasma‐free hemoglobin levels remained less than 5.0 mg/dL and no thrombus formation was observed inside the pump. The TinyPump system including the oxygenator and connecting circuits resulted in an overall priming volume of 68 mL, the smallest ever reported. The TinyPump can be a safe option for pediatric circulatory support during open heart surgery and ECMO without requiring blood transfusion.     

Cephalic jugular venous blood gas measurement during neonatal venoarterial extracorporeal membrane oxygenation

Cannulation of the cephalic portion of the right internal jugular vein during extracorporeal membrane oxygenation (ECMO) allows for increased venous return flow to the circuit. This procedure also allows access to venous drainage from the brain. We reviewed data from simultaneous blood gases obtained from the cephalic jugular vein and the mixed venous return in 5 neonates during venoarterial ECMO. Cephalic venous pO 2 values were significantly lower than mixed venous pO 2 values (P less than .001). The values for pH and pCO 2 did not vary between the sites. Our experience with 34 infants using cephalic jugular drainage is reviewed. Since the institution of right jugular venous drainage, the intracranial hemorrhage rate in neonates undergoing ECMO at our center has decreased from 34% to 6% (p less than .01).     

Bedside exclusion of clinically significant recirculation volume during venovenous ECMO using conventional blood gas analyses

STUDY OBJECTIVE: To investigate prospectively whether blood gas samples drawn from extracorporeal membrane oxygenation (ECMO) cannulae help to exclude at least clinically significant recirculation volumes in patients with acute respiratory failure. DESIGN: Feasibility study. SETTING: Intensive care unit at a university-affiliated hospital. PATIENTS: Ten consecutive adult patients suffering from severe respiratory failure and undergoing ECMO. INTERVENTIONS: The drawing (venous) ECMO cannula was placed into the inferior vena cava via a femoral vein, and the oxygenated blood was returned via the right subclavian vein by supraclavicular access directly into the right atrium. Blood gas samples were obtained from both cannulae. MEASUREMENTS AND MAIN RESULTS: The median arterial oxygen tension (PaO(2)) obtained from the arterial cannula was 537 mmHg (range, 366 to 625 mmHg), the median mixed venous oxygen tension (PvO(2)) drawn from the venous cannula was 42 mmHg (range, 25 to 54 mmHg), which was less than 10% of that observed in the arterial cannula, and also within the physiologic range of PvO(2). The ECMO flow necessary to maintain patients' oxygen saturation above 90% (4.1 L/min; range, 1.95 to 5.8 L/min) was significantly lower than the patients' cardiac output (CO; 6.2 L/min; range, 4.1 to 7.9 L/min; p < 0.001). CONSLUSIONS; We recommend obtaining blood gas samples-immediately after initiation of ECMO-from both cannulae. A PvO(2) within physiologic range and below 10% of PaO(2) rules out any clinically relevant recirculation volume.     

Temporary fenestration using venoatrial extracorporeal membrane oxygenation after the Fontan operation

A 28.7-month-old male child who had undergone a Norwood operation and bidirectional cavopulmonary shunt at the age of 5 days and 6.6 months, respectively, underwent the extracardiac conduit Fontan operation. After the operation, high-volume resuscitation was needed, which led to high central venous pressure (CVP) and low arterial oxygen saturation. Venoatrial extracorporeal membrane oxygenation (ECMO) was initiated between the superior vena cava and the right atrium with one third of the expected normal cardiac output. This low-flow venoatrial ECMO immediately terminated the vicious cycle caused by high venous pressure in the Fontan circulation. He was weaned from ECMO and discharged home.     

Evaluation of an autoregulatory ECMO system for total respiratory support in an acute ovine model

Extracorporeal membrane oxygenation (ECMO) has become a mainstay of therapy for patients suffering from severe respiratory failure. Ambulatory ECMO systems aim to provide long-term out-of-hospital respiratory support. As a patient’s activity level changes, the required level of ECMO support varies with oxygen consumption and metabolic fluctuations. To compensate for such changes, an autoregulatory ECMO system (AR-ECMO) has been developed and its performance was evaluated as a proof of concept in an acute ovine model. The AR-ECMO system consists of a regular ECMO circuit and an electromechanical control system. A custom fuzzy logic control algorithm was implemented to adjust the blood flow and sweep gas flow of the ECMO circuit to meet the varying respiratory demand by utilizing two noninvasive sensors for venous oxyhemoglobin saturation and the oxygenator exhaust gas CO₂ concentration. Disturbance responses of the AR-ECMO to induced acute respiratory distress were assessed for six hours in four juvenile sheep cannulated with a veno-pulmonary artery ECMO configuration, including acute ventilator shutoff, ventilator step change (off-on-off), and forced desaturation. All sheep survived for the study duration. The AR-ECMO system was able to respond and maintain stable hemodynamics and physiological blood gas contents (SpO₂ = 96.3 % ± 4.29, pH 7.44 ± 0.09, pCO₂ = 38.9 ± 9.9 mm Hg, and pO₂ =237.9 ± 123.6 mm Hg) during simulated respiratory distress. Acceptable correlation between oxygenator exhaust gas CO₂ and oxygenator outlet pCO₂ were observed (R² = 0.84). In summary, the AR-ECMO system successfully maintained physiologic control of peripheral oxygenation and carbon dioxide over the study period, utilizing only measurements taken directly from the ECMO circuit. The range of system response necessitates an adaptable system in the setting of variable metabolic demands. The ability of this system to respond to significant disturbances in ventilator support is encouraging. Future work to evaluate our AR-ECMO system in long-term, awake animal studies is necessary for further refinement.     

Troubleshooting adult ECMO

The following scenarios explore some of the common problems encountered during extracorporeal membrane oxygenation (ECMO) in adults. In each scenario, the circuit is comprised of a centrifugal pump and a polymethylpentene oxygenator.     

Arteriovenous ECMO for neonatal respiratory support. A study in perigestational lambs.

A study was undertaken to investigate the applicability of the arteriovenous mode of perfusion for partial support of neonatal respiration. Perigestational lambs, delivered by cesarean section, served as the animal model of respiratory distress. Arteriovenous flow was accomplished between a single umbilical artery and vein. A microchannel membrane oxygenator was used to provide partial respiratory support to the newborn lambs. Total systemic flow, pulmonary blood flow, and pulmonary vascular resistance were assessed at various rates of arteriovenous perfusion and correlated with systemic oxygenation. A reduction in right-to-left shunting of blood and pulmonary vascular resistance occurred as arterial oxygenation rose from conditions of hypoxemia to PaO2 values higher than 50 torr. Myocardial performance was not impaired at rates of arteriovenous perfusion below 30 percent of the total systemic flow, as evidenced by normal electrocardiographic tracings, pulmonary capillary wedge pressures, and central venous pressures. Arteriovenous extracorporeal membrane oxgenation (ECMO) may be particularly suitable for use in infants with hypoxia and high pulmonary vascular resistance.