Arterio-venous extracorporeal membrane oxygenation of fetal goat incubated in artificial amniotic fluid (artificial placenta): influence on lung growth and maturation

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.

The artificial uterus: on the way to ectogenesis

The inability to support the growth and development of a mature fetus up to delivery results in significant human suffering. Current available solutions include adoption, surrogacy, and uterus transplantation. However, these options are subject to several ethical, religious, economic, social, and medical concerns. Ectogenesis is the process in which an embryo develops in an artificial uterus from implantation through to the delivery of a live infant. This current narrative review summarizes the state of recent research focused on human ectogenesis. First, a literature search was performed to identify published reports of previous experiments and devices used for embryo implantation in an extracorporeally perfused human uterus. Furthermore, studies fitting that aim were selected and critically evaluated. Results were synthesized, interpreted, and used to design a prospective strategy for future research. Therefore, this study suggests that full ectogenesis might be obtained using a computer-controlled system with extracorporeal blood perfusion provided by a digitally controlled heart-lung-kidney system. From a clinical perspective, patients who will derive significant benefits from this technology are mainly those women diagnosed with anatomical abnormalities of the uterus and those who have undergone previous hysterectomies, numerous abortions, and experienced premature birth. Ectogenesis is the complete development of an embryo in an artificial uterus. It represents the solutions for millions of women suffering from premature deliveries, and the inability to supply growth and development of embryos/fetuses in the womb. In the future, ectogenesis might replace uterine transplantation and surrogacy.

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.

Congenital diaphragmatic hernia-associated pulmonary hypertension

Congenital diaphragmatic hernia (CDH) is a neonatal pathology in which intrathoracic herniation of abdominal viscera via diaphragmatic defect results in aberrant pulmonary and cardiovascular development. Despite decades of study and many advances in the diagnosis and treatment of CDH, morbidity and mortality remain high, largely due to pulmonary hypertension (PH), along with pulmonary hypoplasia and cardiac dysfunction. In patients with CDH, hypoplastic pulmonary vasculature and alterations in multiple molecular pathways lead to pathophysiologic pulmonary vasculopathy and, for severe CDH, sustained, elevated pulmonary arterial pressures. This review addresses the multiple anatomic and physiologic changes that underlie CDH-associated PH (CDH-PH), along with the multimodal treatment strategies that exist currently and future therapies currently under investigation.

The artificial placenta: Continued lung development during extracorporeal support in a preterm lamb model

PURPOSE

An artificial placenta (AP) utilizing extracorporeal life support (ECLS) could avoid the harm of mechanical ventilation (MV) while allowing the lungs to develop.

METHODS

AP lambs (n = 5) were delivered at 118 days gestational age (GA; term = 145 days) and placed on venovenous ECLS (VV-ECLS) with jugular drainage and umbilical vein reinfusion. Lungs remained fluid-filled. After 10 days, lambs were ventilated. MV control lambs were delivered at 118 ("early MV"; n = 5) or 128 days ("late MV"; n = 5), and ventilated. Compliance and oxygenation index (OI) were calculated. After sacrifice, lungs were procured and H&E-stained slides scored for lung injury. Slides were also immunostained for PDGFR-α and α-actin; alveolar development was quantified by the area fraction of alveolar septal tips staining double-positive for both markers.

RESULTS

Compliance of AP lambs was 2.79 ± 0.81 C_dyn compared to 0.83 ± 0.19 and 3.04 ± 0.99 for early and late MV, respectively. OI in AP lambs was lower than early MV lambs (6.20 ± 2.10 vs. 36.8 ± 16.8) and lung injury lower as well (1.8 ± 1.6 vs. 6.0 ± 1.2). Double-positive area fractions were higher in AP lambs (0.012 ± 0.003) than early (0.003 ± 0.0005) and late (0.004 ± 0.002) MV controls.

CONCLUSIONS

Lung development continues and lungs are protected from injury during AP support relative to mechanical ventilation.

LEVEL OF EVIDENCE

n/a (basic/translational science).

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.

An extra-uterine system to physiologically support the extreme premature lamb

In the developed world, extreme prematurity is the leading cause of neonatal mortality and morbidity due to a combination of organ immaturity and iatrogenic injury. Until now, efforts to extend gestation using extracorporeal systems have achieved limited success. Here we report the development of a system that incorporates a pumpless oxygenator circuit connected to the fetus of a lamb via an umbilical cord interface that is maintained within a closed 'amniotic fluid' circuit that closely reproduces the environment of the womb. We show that fetal lambs that are developmentally equivalent to the extreme premature human infant can be physiologically supported in this extra-uterine device for up to 4 weeks. Lambs on support maintain stable haemodynamics, have normal blood gas and oxygenation parameters and maintain patency of the fetal circulation. With appropriate nutritional support, lambs on the system demonstrate normal somatic growth, lung maturation and brain growth and myelination.

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.

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.

Artificial Placenta - Lung Assist Devices for Term and Preterm Newborns with Respiratory Failure

Respiratory insufficiency is a major cause of neonatal mortality and long-term morbidity, especially in very low birth weight infants. Today, non-invasive and mechanical ventilation are commonly accepted procedures to provide respiratory support to newborns, but they can reach their limit of efficacy. To overcome this technological plateau and further reduce mortality rates, the technology of an “artificial placenta”, which is a pumpless lung assist device connected to the umbilical vessels, would serve to expand the therapeutic spectrum when mechanical ventilation becomes inadequate to treat neonates with severe respiratory insufficiency.

The first attempts to create such an artificial placenta took place more than 60 years ago. However, there has been a recent renaissance of this concept, including developments of its major components like the oxygenator, vascular access via umbilical vessels, flow control, as well as methods to achieve hemocompatibility in extracorporeal circuits. This paper gives a review of past and current development, animal experiments and human case studies of artificial placenta technology.

Development of an artificial placenta V: 70 h veno-venous extracorporeal life support after ventilatory failure in premature lambs

PURPOSE

An artificial placenta would change the paradigm of treating extremely premature infants. We hypothesized that using a veno-venous extracorporeal life support (VV-ECLS) artificial placenta after ventilatory failure would stabilize premature lambs and maintain normal fetal physiologic parameters for 70 h.

METHODS

A near-term neonatal lamb model (130 days; term=145) was used. The right jugular vein (drainage) and umbilical vein (reinfusion) were cannulated with 10-12 Fr cannulas. Lambs were then transitioned to an infant ventilator. After respiratory failure, the endotracheal tube was filled with amniotic fluid, and VV-ECLS total artificial placenta support (TAPS) was initiated. Lambs were maintained on TAPS for 70 h.

RESULTS

Six of seven lambs survived for 70 h. Mean ventilation time was 57 ± 22 min. During ventilation, mean MAP was 51 ± 14 mmHg, compared to 44 ± 14 mmHg during TAPS (p=0.001). Mean pH and lactate during ventilation were 7.06 ± 0.15 and 5.7 ± 2.3 mmol/L, compared to 7.33 ± 0.07 and 2.0 ± 1.8 mmol/L during TAPS (p<0.001 for both). pO(2) and pCO(2) remained within normal fetal parameters during TAPS, and mean carotid blood flow was 25 ± 7.5 mL/kg/min. Necropsy showed a patent ductus arteriosus and no intracranial hemorrhage in all animals.

CONCLUSIONS

The artificial placenta stabilized premature lambs after ventilatory failure and maintained fetal circulation, hemodynamic stability, gas exchange, and cerebral perfusion for 70 h.

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.

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.

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.

Angiogenesis and morphogenesis of murine fetal distal lung in an allograft model

Neovascularization is crucial to lung morphogenesis; however, factors determining vessel growth and formation are poorly understood. The goal of our study was to develop an allograft model that would include maturation of the distal lung, thereby ultimately allowing us to study alveolar development, including microvascular formation. We transplanted 14-day gestational age embryonic mouse lung primordia subcutaneously into the back of nude mice for 3.5-14 days. Lung morphogenesis and neovascularization were evaluated by light microscopy, in situ hybridization, and immunohistochemical techniques. Embryonic 14-day gestational age control lungs had immature structural features consistent with pseudoglandular stage of lung development. In contrast, 14 days after subcutaneous transplantation of a 14-day gestational age lung, the allograft underwent significant structural morphogenesis and neovascularization. This was demonstrated by continued neovascularization and cellular differentiation, resulting in mature alveoli similar to those noted in the 2-day postnatal neonatal lung. Confirmation of maturation of the allograft was provided by progressive type II epithelial cell differentiation as evidenced by enhanced local expression of mRNA for surfactant protein C and a threefold (P < 0.008) increase in vessel formation as determined by immunocytochemical detection of platelet endothelial cell adhesion molecule-1 expression. Using the tyrosine kinase Flk-1 receptor (flk-1) LacZ transgene embryos, we determined that the neovascularization within the allograft was from the committed embryonic lung endothelium. Therefore, we have developed a defined murine allograft model that can be used to study distal lung development, including neovascularization. The model may be useful when used in conjunction with an altered genetic background (knockout or knock in) of the allograft and has the further decided advantage of bypassing placental barriers for introduction of pharmacological agents or DNA directly into the lung itself.