Development of extrauterine fetal incubation system using extracorporeal membrane oxygenator

Transferring an extremely premature infant to an extra-uterine life support system: a prospective view on the obstetric procedure

To improve care for extremely premature infants, the development of an extrauterine environment for newborn development is being researched, known as Artificial Placenta and Artificial Womb (APAW) technology. APAW facilitates extended development in a liquid-filled incubator with oxygen and nutrient supply through an oxygenator connected to the umbilical vessels. This setup is intended to provide the optimal environment for further development, allowing further lung maturation by delaying gas exposure to oxygen. This innovative treatment necessitates interventions in obstetric procedures to transfer an infant from the native to an artificial womb, while preventing fetal-to-neonatal transition. In this narrative review we analyze relevant fetal physiology literature, provide an overview of insights from APAW studies, and identify considerations for the obstetric procedure from the native uterus to an APAW system. Lastly, this review provides suggestions to improve sterility, fetal and maternal well-being, and the prevention of neonatal transition.

The alterations of cardiac function during venovenous artificial placenta support in fetal goats

INTRODUCTION

Venovenous artificial placenta (VVAP) may mimic the intrauterine environment for maintaining fetal circulation. However, changes in ventricular function in fetal goats undergoing VVAP support remain unclear.

METHODS

Pump-assisted VVAPs were established in five fetal goats for 9 h. The myocardial performance index (Tei index), cardiac output (CO), and blood biochemical parameters were measured during VVAP support.

RESULTS

An increasing trend of the right ventricular (RV) Tei index was seen during VVAP support (p for trend < 0.01). The right ventricular cardiac output (RVCO) increased after the initiation of VVAP, while a significant trend of reduction was observed after 3 h (p for trend = 0.03). During VVAP support, we observed remarkable elevations of plasma cTnI and arterial lactic acid, which were positively correlated with the RV Tei index, but not the left ventricular (LV) Tei index, LVCO, and RVCO.

CONCLUSIONS

The RVCO increases initially while a tendency of decrease could be observed during VVAP support. Special attention should be paid to right ventricular dysfunction during VVAP support.

Artificial placenta technology: History, potential and perception

As presently conceptualised, the artificial placenta (AP) is an experimental life support platform for extremely preterm infants (i.e. 400-600 g; 21-23+6 weeks of gestation) born at the border of viability. It is based around the oxygenation of the periviable fetus using gas-exchangers connected to the fetal vasculature. In this system, the lung remains fluid-filled and the fetus remains in a quiescent state. The AP has been in development for some sixty years. Over this time, animal experimental models have evolved iteratively from employing external pump-driven systems used to support comparatively mature fetuses (generally goats or sheep) to platforms driven by the fetal heart and used successfully to maintain extremely premature fetuses weighing around 600 g. Simultaneously, sizable advances in neonatal and obstetric care mean that the nature of a potential candidate patient for this therapy, and thus the threshold success level for justifying its adoption, have both changed markedly since this approach was first conceived. Five landmark breakthroughs have occurred over the developmental history of the AP: i) the first human studies reported in the 1950's; ii) foundation animal studies reported in the 1960's; iii) the first extended use of AP technology combined with fetal pulmonary resuscitation reported in the 1990s; iv) the development of AP systems powered by the fetal heart reported in the 2000's; and v) the adaption of this technology to maintain extremely preterm fetuses (i.e. 500-600 g body weight) reported in the 2010's. Using this framework, the present paper will provide a review of the developmental history of this long-running experimental system and up-to-date assessment of the published field today. With the apparent acceleration of AP technology towards clinical application, there has been an increase in the attention paid to the field, along with some inaccurate commentary regarding its potential application and merits. Additionally, this paper will address several misrepresentations regarding the potential application of AP technology that serve to distract from the significant potential of this approach to greatly improve outcomes for extremely preterm infants born at or close to the present border of viability.

Report of an Experiment With a Fetal Ex-Utero Support System in Piglets

Extreme prematurity remains one of the leading causes of neonatal death. An ex-utero treatment strategy that allows the fetus to develop beyond this period until capable of tolerating the transition to post-natal physiology would significantly impact the quality of care offered for this pre-viable patient population. In this study, we report our experience with an ex-utero support system for fetal pigs with the goal of support and survival for eight hours. Our experiment included two pigs at a gestational age equivalent to a 32-week human fetus. Following ultrasound assessment and delivery via hysterotomy, the fetuses were transferred to a 40 L glass aquarium filled with warmed lactated Ringer's solution and connected to an arteriovenous (AV) circuit that included a centrifugal pump and a pediatric oxygenator. Fetus 1 was successfully cannulated and survived for seven hours (expected maximum duration of eight hours). Fetus 2 died shortly after hysterotomy, secondary to failure at the cannulation stage. Our results suggest that ex-utero support of the premature fetal pig is feasible, contributing to a scarce body of evidence. However, further studies are needed before effectively translating an artificial placenta system into the clinical arena.

Impact of the Addition of a Centrifugal Pump in a Preterm Miniature Pig Model of the Artificial Placenta

The recent demonstration of normal development of preterm sheep in an artificial extrauterine environment has renewed interest in artificial placenta (AP) systems as a potential treatment strategy for extremely preterm human infants. However, the feasibility of translating this technology to the human preterm infant remains unknown. Here we report the support of 13 preterm fetal pigs delivered at 102 ± 4 days (d) gestation, weighing 616 ± 139 g with a circuit consisting of an oxygenator and a centrifugal pump, comparing these results with our previously reported pumpless circuit (n = 12; 98 ± 4 days; 743 ± 350 g). The umbilical vessels were cannulated, and fetuses were supported for 46.4 ± 46.8 h using the pumped AP versus 11 ± 13 h on the pumpless AP circuit. Upon initiation of AP support on the pumped system, we observed supraphysiologic circuit flows, tachycardia, and hypertension, while animals maintained on a pumpless AP circuit exhibited subphysiologic flows. On the pumped AP circuit, there was a progressive decline in umbilical vein (UV) flow and oxygen delivery. We conclude that the addition of a centrifugal pump to the AP circuit improves survival of preterm pigs by augmenting UV flow through the reduction of right ventricular afterload. However, we continued to observe the development of heart failure within a matter of days.

Development of an artificial placenta for support of premature infants: narrative review of the history, recent milestones, and future innovation

Over 50 years ago, visionary researchers began work on an extracorporeal artificial placenta to support premature infants. Despite rudimentary technology and incomplete understanding of fetal physiology, these pioneering scientists laid the foundation for future work. The research was episodic, as medical advances improved outcomes of premature infants and extracorporeal life support (ECLS) was introduced for the treatment of term and near-term infants with respiratory or cardiac failure. Despite ongoing medical advances, extremely premature infants continue to suffer a disproportionate burden of mortality and morbidity due to organ immaturity and unintended iatrogenic consequences of medical treatment. With advancing technology and innovative approaches, there has been a resurgence of interest in developing an artificial placenta to further diminish the mortality and morbidity of prematurity. Two related but distinct platforms have emerged to support premature infants by recreating fetal physiology: a system based on arteriovenous (AV) ECLS and one based on veno-venous (VV) ECLS. The AV-ECLS approach utilizes only the umbilical vessels for cannulation. It requires immediate transition of the infant at the time of birth to a fluid-filled artificial womb to prevent umbilical vessel spasm and avoid gas ventilation. In contradistinction, the VV-ECLS approach utilizes the umbilical vein and the internal jugular vein. It would be applied after birth to infants failing maximal medical therapy or preemptively if risk stratified for high mortality and morbidity. Animal studies are promising, demonstrating prolonged support and ongoing organ development in both systems. The milestones for clinical translation are currently being evaluated.

Conventional revolution: the ethical implications of the natural progress of neonatal intensive care to artificial wombs

Research teams have used extra-uterine systems (Biobags) to support premature fetal lambs and to bring them to maturation in a way not previously possible. The researchers have called attention to possible implications of these systems for sustaining premature human fetuses in a similar way. Some commentators have pointed out that perfecting these systems for human fetuses might alter a standard expectation in abortion practices: that the termination of a pregnancy also (inevitably) entails the death of the fetus. With Biobags, it might be possible, some argue, that no woman has the right to expect that outcome if the technology is able to sustain fetal life after an abortion. In order to protect the expectation that the termination of a pregnancy always entails the death of the fetus, Elizabeth Romanis has argued that fetuses sustained in Biobags have a status different than otherwise 'born' children. In support of that view, she argues that these 'gestatelings' are incapable of independent life. This argument involves a misunderstanding of the gestational support involved, as well as a misapprehension of neonatology practice. Here, we argue that any human fetus sustained in a Biobag would be as 'independent' as any other premature infant, and just as 'born'. Neonatologists would seem to have certain presumptive moral responsibilities toward any human fetus gestating in a Biobag. It remains a separate question whether the perfection and widespread application of Biobags for premature human beings would or should alter the expectation that ending a pregnancy also entails fetal death.

Artificial lungs--Where are we going with the lung replacement therapy?

Lung transplantation may be a final destination therapy in lung failure, but limited donor organ availability creates a need for alternative management, including artificial lung technology. This invited review discusses ongoing developments and future research pathways for respiratory assist devices and tissue engineering to treat advanced and refractory lung disease. An overview is also given on the aftermath of the coronavirus disease 2019 pandemic and lessons learned as the world comes out of this situation. The first order of business in the future of lung support is solving the problems with existing mechanical devices. Interestingly, challenges identified during the early days of development persist today. These challenges include device-related infection, bleeding, thrombosis, cost, and patient quality of life. The main approaches of the future directions are to repair, restore, replace, or regenerate the lungs. Engineering improvements to hollow fiber membrane gas exchangers are enabling longer term wearable systems and can be used to bridge lung failure patients to transplantation. Progress in the development of microchannel-based devices has provided the concept of biomimetic devices that may even enable intracorporeal implantation. Tissue engineering and cell-based technologies have provided the concept of bioartificial lungs with properties similar to the native organ. Recent progress in artificial lung technologies includes continued advances in both engineering and biology. The final goal is to achieve a truly implantable and durable artificial lung that is applicable to destination therapy.

Artificial placenta and womb technology: Past, current, and future challenges towards clinical translation

Extreme prematurity remains a major cause of neonatal mortality and severe long-term morbidity. Current neonatal care is associated with significant morbidity due to iatrogenic injury and developmental immaturity of extreme premature infants. A more physiologic approach, replacing placental function and providing a womb-like environment, is the foundational principle of artificial placenta (AP) and womb (AW) technology. The concept has been studied during the past 60 years with limited success. However, recent technological advancements and a greater emphasis on mimicking utero-placental physiology have improved the success of experimental models, bringing the technology closer to clinical translation. Here, we review the rationale for and history of AP and AW technology, discuss the challenges that needed to be overcome, and compare recent successful models. We conclude by outlining some remaining challenges to be addressed on the path towards clinical translation and opportunities for future research.

An EXTrauterine environment for neonatal development: EXTENDING fetal physiology beyond the womb

Extreme prematurity is a major cause of neonatal mortality and morbidity, and remains an unsolved clinical challenge. The development of an artificial womb, an extrauterine system recreating the intrauterine environment, would support ongoing growth and organ maturation of the extreme preterm fetus and would have the potential to substantially improve survival and reduce morbidity. Previous efforts toward the development of such a system have demonstrated the ability to maintain the isolated fetus for short periods of support, but have failed to achieve the long-term stability required for clinical application. Here we describe our initial experiments demonstrating the stable support of fetal lambs developmentally equivalent to the extreme premature infant for up to four weeks with stable hemodynamics, growth, and development. The achievement of long-term physiologic support of the fetus in an extrauterine system has the potential to fundamentally change the management and clinical outcome of the extreme premature infant.

Examination of the Relationship between Umbilical Cord Blood Gas Values and Hearing Function in Neonates

Objective

The aim of the present study was to examine the relationship between the results of the transient otoacoustic emission (TEOAE) test used in neonatal hearing screening and the results of the umbilical cord blood (UCB) analysis in neonates.

Methods

This retrospective study included 209 neonates born in the obstetric unit at the 37^th gestational week. Based on the results of the TEOAE test, the neonates included in the study were divided into two groups as the study group composed of those "REFER" (n=141) and the control group consisting those "PASS" (n=68) the test. The UCB sampling procedure was performed on all neonates. In the blood samples, the pH parameters were evaluated by using glass electrodes, and the pCO₂ and pO₂ parameters were evaluated directly by using sensitive electrodes.

Results

When the additional maternal diseases were compared with the TEOAE results, the ratio of hypothyroidism was found to be statistically higher in the study group (p<0.05). In terms of the pO₂, pCO₂, HCO₃, and pH values obtained as a result of analyzing the UCB samples, there was no statistically significant difference between the groups (p>0.05).

Conclusion

The results of the present study showed that there was no statistically significant difference between the results of UCB analysis and the TEOAE test. However, we believe that conducting a larger study evaluating other parameters and employing UCB analysis would be useful, and UCB evaluation, which is an inexpensive, easy and effective method in determining hypoxia in neonates, might be a significant marker in cases at risk of hearing loss.

Artificial placenta: Recent advances and potential clinical applications

Lung immaturity remains a major cause of morbidity and mortality in extremely premature infants. Positive-pressure mechanical ventilation, the method of choice for respiratory support in premature infants, frequently promotes by itself lung injury and a negative impact in the circulatory function. Extracorporeal lung support has been proposed for more than 50 years as a potential alternative to mechanical ventilation in the treatment of severe respiratory failure of extremely premature infants. Recent advances in this field included the development of miniaturized centrifugal pumps and polymethylpentene oxygenators, as well as the successful use of pump-assisted veno-venous extracorporeal gas exchange systems in experimental artificial placenta models. This review, which includes studies published from 1958 to 2015, presents an update on the artificial placenta concept and its potential clinical applications. Special focus will be devoted to the milestones achieved so far and to the limitations that must be overcome before its clinical application. Notwithstanding, the artificial placenta stands as a promising alternative to mechanical ventilation in extremely premature infants. Pediatr Pulmonol. 2016;51:643-649. © 2016 Wiley Periodicals, Inc.

Placenta: the forgotten organ

The placenta sits at the interface between the maternal and fetal vascular beds where it mediates nutrient and waste exchange to enable in utero existence. Placental cells (trophoblasts) accomplish this via invading and remodeling the uterine vasculature. Amazingly, despite being of fetal origin, trophoblasts do not trigger a significant maternal immune response. Additionally, they maintain a highly reliable hemostasis in this extremely vascular interface. Decades of research into how the placenta differentiates itself from embryonic tissues to accomplish these and other feats have revealed a previously unappreciated level of complexity with respect to the placenta's cellular composition. Additionally, novel insights with respect to roles played by the placenta in guiding fetal development and metabolism have sparked a renewed interest in understanding the interrelationship between fetal and placental well-being. Here, we present an overview of emerging research in placental biology that highlights these themes and the importance of the placenta to fetal and adult health.

An extracorporeal artificial placenta supports extremely premature lambs for 1 week

PURPOSE

The treatment of extreme prematurity remains an unsolved problem. We developed an artificial placenta (AP) based on extracorporeal life support (ECLS) that simulates the intrauterine environment and provides gas exchange without mechanical ventilation (MV) and compared it to the current standard of neonatal care.

METHODS

Extremely premature lambs (110-120 days; term=145d) were used. AP lambs (n=9) were cannulated (jugular drainage, umbilical vein reinfusion) for ECLS. Control lambs (n=7) were intubated, ventilated, given surfactant, and transitioned to high-frequency oscillatory ventilation. All lambs received parenteral nutrition, antibiotics, and steroids. Hemodynamics, blood gases, hemoglobin, and circuit flows were measured.

RESULTS

Four premature lambs survived for 1 week on the AP, with one surviving 6 days. Adequate oxygenation and ventilation were provided by the AP. The MV lambs survived 2-8 hours. Each of these lambs experienced a transient improvement with surfactant, but developed progressive hypercapnea and hypoxia despite high airway pressures and HFOV.

CONCLUSIONS

Extremely premature lambs were supported for 1 week with the AP with hemodynamic stability and adequate gas exchange. Mechanically ventilated lambs succumbed within 8 hours. Further studies will assess control of fetal circulation and organ maturation on the AP.

A paradigm shift in the treatment of extreme prematurity: the artificial placenta

PURPOSE OF REVIEW

Extremely low gestational age newborns (ELGANs), born at less than 28 weeks' estimated gestational age, suffer the greatest consequences of prematurity. There have been significant advances in their care over the last several decades, but the prospects for major advances within traditional treatment modalities appear limited. An artificial placenta using extracorporeal life support (ECLS) has been investigated in the laboratory as a new advance in the treatment of ELGANs. We review the concept of an artificial placenta, the purported benefits, and the most recent research efforts in this area.

RECENT FINDINGS

For 50 years, researchers have attempted to develop an artificial placenta based on ECLS. Traditional artificial placenta strategies have been based on arteriovenous ECLS using the umbilical vessels with moderate success. Recently, the use of venovenous ECLS and miniaturization of ECLS components have shown potential for creating a next-generation artificial placenta.

SUMMARY

ELGANs suffer the greatest morbidity and mortality of prematurity, and are poised to benefit from a paradigm shift in the treatment. Although challenges remain, the artificial placenta is feasible. An artificial placenta would not only protect ELGANs from the complications of mechanical ventilation, but also support their development until a stage of greater maturity, preparing them for a life free of the sequelae of prematurity.

ECLS for preemies: the artificial placenta

The high mortality and morbidity associated with respiratory failure among extremely low gestational age newborns (ELGANs) remains an unsolved problem. A logical strategy to avoid these complications would involve re-creating the intrauterine environment with extracorporeal membrane oxygenation (ECMO) instead of mechanical ventilation. Such a device, termed an artificial placenta, was first researched over 50 years ago. AP models vary, but all incorporate ECMO involving the umbilical vessels, lack of mechanical ventilation, and low partial pressure of oxygen to preserve fetal circulation. Current research has focused on low-volume pumpless arteriovenous circuits as well as pump-driven venovenous circuits.

Development of an artificial placenta IV: 24 hour venovenous extracorporeal life support in premature lambs

An extracorporeal artificial placenta would change the paradigm of treating extremely premature infants. We hypothesized that a venovenous extracorporeal life support (VV-ECLS) artificial placenta would maintain fetal circulation, hemodynamic stability, and adequate gas exchange for 24 hours. A near-term neonatal lamb model (130 days; term = 145 days) was used (n = 9). The right jugular vein was cannulated for VV-ECLS outflow, and an umbilical vein was used for inflow. The circuit included a peristaltic roller pump and a 0.5 m(2) hollow fiber oxygenator. Lambs were maintained on VV-ECLS in an "amniotic bath" for up to 24 hours. Five of nine fetuses survived for 24 hours. In the survivors, average mean arterial pressure was 69 ± 10 mm Hg for the first 4 hours and 36 ± 8 mm Hg for the remaining 20 hours. The mean fetal heart rate was 202 ± 30. Mean VV-ECLS flow was 94 ± 20 ml/kg/min. Using a gas mixture of 50% O(2)/3% CO(2) and sweep flow of 1-2 L/min, the mean pH was 7.27 ± 0.09, with Po(2) of 35 ± 12 mm Hg and Pco(2) of 48 ± 12 mm Hg. Necropsy revealed a patent ductus arteriosus in all cases, and there was no gross or microscopic intracranial hemorrhage. Complications in failed attempts included technically difficult cannulation and multisystem organ failure. Future studies will enhance stability and address the factors necessary for long-term support.

Advances in neonatal extracorporeal support: the role of extracorporeal membrane oxygenation and the artificial placenta

This review addresses the history and evolution of neonatal extracorporeal membrane oxygenation (ECMO), with a discussion of the indications, contraindications, modalities, outcomes, and impact of ECMO. Controversies surrounding novel uses of ECMO in neonates, namely ECMO for premature infants and ex utero intrapartum therapy with transition to ECMO, are discussed. The development of an extracorporeal artificial placenta for support of premature infants is presented, including the rationale, research, and challenges. ECMO has had a dramatic effect on the care of critically ill neonates over the past 4 decades, and there is great potential to expand these benefits in the future.

The artificial womb

The availability of computer-controlled artificial hearts, kidneys, and lungs, as well as the possibility of implanting human embryos in ex vivo uterus models or an artificial endometrium, presents new perspectives for creating an artificial uterus. Survival rates have also improved, with fetuses surviving from as early as 24 weeks of gestation. These advances bring new opportunities for complete or partial ectogenesis through the creation of an artificial womb, one that could sustain the growth and development of fetuses outside of the human body.

Development of an artificial placenta I: pumpless arterio-venous extracorporeal life support in a neonatal sheep model

PURPOSE

Effective treatment of respiratory failure in premature infants remains an unsolved problem. The development of an artificial placenta, in the form of a pumpless arteriovenous extracorporeal life support (AV-ECLS) circuit that maintains fetal circulation, is an appealing alternative.

METHODS

A near-term (140 d/term = 145 days) neonatal lamb model was used (n = 7). Fetuses were exposed by hysterotomy, and flow probes were placed on the ductus arteriosus, aorta, and carotid artery. Catheters were placed into the umbilical vessels, and pumpless AV-ECLS was initiated. Fetuses were submerged in a warm saline bath, and support was maintained for up to 4 hours.

RESULTS

Mean initial device flow was 383 mL/min but steadily declined to 177 mL/min at 4 hours. Mean initial pO(2) was 24 mm Hg and 18 mm Hg at 4 hours. Initial mean pCO(2) was 60 mm Hg and declined to 42 mm Hg at 4 hours. Mean arterial pressure was initially 43 mm Hg and decreased to 34 mm Hg at 4 hours. Flow in the ductus arteriosus was maintained for 4 hours. Of 7 fetuses, 5 survived 4 hours of support.

CONCLUSIONS

Pumpless AV-ECLS can support gas exchange and maintain fetal circulation in a neonatal lamb model for a 4-hour period. Prolonged support (>4 hours) is hampered by high cannula resistance and declining device flow.

Power Spectral Analysis of the Heart Rate Variability of Goat Fetuses During Extrauterine Incubation

Our aim is to determine the relationship between heart rate and behavioral states of a fetal goat using power spectral analysis. Electrocardiograms, electrocortical activity, and fetal breathing movements are recorded from 7 goat fetuses during extrauterine incubation. The heart rate power spectrum is classified into very low, low, and high frequency bands, and behavioral states are classified into low-voltage electrocortical activity with fetal breathing movements (LVB), low-voltage electrocortical activity without fetal breathing movements (LVN), and high-voltage electrocortical activity (HVN). There is a significant difference in total power spectral density in the high frequency band between LVN and HVN, and LVN and LVB. The relationship between each fetal behavioral state is assessed by power spectral analysis.

Effect of hypoxia on the auditory system of goat fetuses during extrauterine incubation

AIM

To investigate the effect of hypoxia on the auditory system in fetuses, we attempted to analyze the auditory brainstem response, the middle latency response, and changes of several physiological parameters of goat fetuses during extrauterine incubation.

METHODS

We conducted extrauterine incubation of five goat fetuses at around 127days of gestation (term = 148 days). Their physiological parameters, such as fetal heart rate, mean blood pressure, flow rate of carotid artery, as well as the auditory brainstem response and middle latency response, were recorded prior to and during hypoxia, and the two sets of data were compared with each other.

RESULTS

In all five cases, the fetal heart rate decreased from 178 +/- 12.2 b.p.m. to 144 +/- 15.2 b.p.m. during hypoxia, while mean blood pressure and flow rate of carotid artery increased from 37.3 +/- 3.7 mmHg to 43.2 +/- 5.1 mmHg, and from 38.5 +/- 5.5mL/min to 47.0 +/- 5.1 mL/min, respectively. The latency of the auditory brainstem response's wave V and of the middle latency response's Pa wave elongated from 5.24 +/- 0.24 ms to 5.69 +/- 0.20 ms, and from 19.2 +/- 1.6 ms to 20.9 +/- 1.4 ms, respectively.

CONCLUSIONS

Although fetal compensatory reactions, such as increases in mean blood pressure and flow rate of carotid artery during hypoxia were recognized, elongation of latency, and decrement of amplitude were observed in the auditory brainstem response and middle latency response. These results suggest that hypoxia itself influences the auditory system of the fetus.

Regional blood flow distribution from the proximal arterial cannula during veno-arterial extracorporeal membrane oxygenation in neonatal dog

Extracorporeal membrane oxygenation (ECMO) is frequently used for treatment of patients with severe hypoxemia due to life-threatening respiratory failure. Due to this hypoxemia, the myocardium of these patients is insufficiently provided with oxygen, and consequently their cardiac function commonly deteriorates. But veno-arterial (V-A) ECMO provides oxygenated blood to the coronary arteries from ECMO circuit insufficiently. To increase the coronary blood flow distributed from ECMO, we placed the arterial cannula 1 cm above the aortic valve and evaluated the regional blood from the proximal arterial cannula in comparison with the distal cannula. Eight neonatal dogs weighting 1.8-2.5 kg were supported by V-A ECMO. The regional blood flow from the arterial cannula was measured by injection of colored microspheres into ECMO circuit. The site of the arterial cannula was changed under fluoroscopy. The bypass flow was maintained at either 50 or 100 ml/min/kg. We found that the coronary blood flow distributed from the proximal arterial cannula was significantly higher than that from the distal cannula. The proximal arterial cannula appears necessary to provide sufficient oxygenated blood to the coronary circulation during V-A ECMO. Therefore, it is expected that the increased cardiac function may improved, and that the survival rate of the patients with retarded cardiac function due to severe hypoxemia may increase by proximal placement of the arterial cannula during V-A ECMO.

An evaluation of the system to control blood flow in maintaining goat fetuses on arterio-venous extracorporeal membrane oxygenation: a novel approach to the development of an artificial placenta

We compared various methods to control blood flow for extrauterine incubation of goat fetuses without lung respiration using arterio-venous extracorporeal membrane oxygenation via umbilical vessels to develop a suitable system for a long-term life support system for premature neonates. In twenty-seven consecutive preparations of goat fetuses, 4 designs (System 1, manual flow control without a reservoir; System 2, manual flow control with an arterial open-top reservoir; System 3, semiautomatic flow control with an arterial open top reservoir; and System 4, semiautomatic flow control with a tube occluder and an arterial open top reservoir) were tested in terms of the duration of incubation periods during which fetuses were kept under stable conditions. The incubation periods became prolonged with the advancement of the system (System 1, 5.4 h; System 2, 11.6 h; System 3, 64.8 h; and System 4, 159.8 h medians of the incubation periods). The incubation periods with System 4 were significantly longer compared to those with System 1 and System 2. These results suggest that, for extrauterine incubation of goat fetuses using arterio-venous extracorporeal membrane oxygenation via umbilical vessels, the method to control blood flow is of utmost importance for long-term maintenance, and thus a control system with the fixed vascular resistance of the extracorporeal circuit is applicable to long-term maintenance of premature goat fetuses.

Oxygenation in fetal lambs supported by extrauterine right atrium to artery extracorporeal membrane oxygenation

OBJECTIVE

Our purpose was to determine the adequacy of oxygenation, particularly cranial and cardiac oxygenation, in exteriorized fetal lambs on right atrium to artery extracorporeal membrane oxygenation.

STUDY DESIGN

Thirteen fetal lambs were placed on right atrium to artery extracorporeal membrane oxygenation between the gestational ages of 113 and 133 days. Various PO2 and oxygen saturation (SO2) values were obtained by varying the oxygen concentrations at the oxygenator membrane. Blood gases, pH, and SO2 were observed on samples taken before and after membrane oxygenation from the left ventricle and through the cranial carotid arterial catheter. These were compared with control values obtained before the cessation of umbilical circulation. Fetal coronary oxygenation was represented by left ventricle PO2 and SO2 and cranial oxygen by carotid artery PO2 and SO2.

RESULTS

We classified oxygen saturation as low, medium, and high on the basis of the level of postmembrane SO2. Carotid artery cranial oxygenation in the low SO2 group was equivalent to control values, but that in the medium and high SO2 groups was significantly higher than in the control group. Left ventricle oxygenation was consistently lower than cranial oxygenation in any SO2 group. In the low group left ventricle oxygenation was significantly lower than the control values.

CONCLUSIONS

Right atrium to artery extracorporeal membrane oxygenation appears sufficient to oxygenate the fetal cranial circulation but may be inadequate for the efficient distribution of oxygenated blood into the left ventricle and thus the coronary circulation.

Artificial placenta: long-term extrauterine incubation of isolated goat fetuses

Previously, this group reported on a system of extrauterine incubation of a goat fetus, in which the fetus is surrounded by artificial amniotic fluid and connected to the circuit with an ECMO (extracorporeal membrane oxygenator) by the umbilical arteries and veins. The following is a summary of recent progress using an improved method of catheterization and a new system that included a dialyzer within the circuit. Nine goat fetuses were used in this experiment. Six goats were successfully incubated; the duration of their incubation was 146.5 +/- 61.3 h (mean +/- SD). The longest one was 236 h. Slowly progressive circulatory depression was thought to be the main cause of fetal death. Marked tendencies to bleeding and water retention were not observed in any cases. Stable serum electrolyte levels were maintained.