Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M1/00—Suction or pumping devices for medical purposes; Devices for carrying-off, for treatment of, or for carrying-over, body-liquids; Drainage systems
  • A61M1/14—Dialysis systems; Artificial kidneys; Blood oxygenators ; Reciprocating systems for treatment of body fluids, e.g. single needle systems for hemofiltration or pheresis
  • A61M1/16—Dialysis systems; Artificial kidneys; Blood oxygenators ; Reciprocating systems for treatment of body fluids, e.g. single needle systems for hemofiltration or pheresis with membranes
  • A61M1/1698—Blood oxygenators with or without heat-exchangers
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61G—TRANSPORT, PERSONAL CONVEYANCES, OR ACCOMMODATION SPECIALLY ADAPTED FOR PATIENTS OR DISABLED PERSONS; OPERATING TABLES OR CHAIRS; CHAIRS FOR DENTISTRY; FUNERAL DEVICES
  • A61G11/00—Baby-incubators; Couveuses
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M1/00—Suction or pumping devices for medical purposes; Devices for carrying-off, for treatment of, or for carrying-over, body-liquids; Drainage systems
  • A61M1/36—Other treatment of blood in a by-pass of the natural circulatory system, e.g. temperature adaptation, irradiation ; Extra-corporeal blood circuits
  • A61M1/3621—Extra-corporeal blood circuits
  • A61M1/3623—Means for actively controlling temperature of blood
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M1/00—Suction or pumping devices for medical purposes; Devices for carrying-off, for treatment of, or for carrying-over, body-liquids; Drainage systems
  • A61M1/14—Dialysis systems; Artificial kidneys; Blood oxygenators ; Reciprocating systems for treatment of body fluids, e.g. single needle systems for hemofiltration or pheresis
  • A61M1/16—Dialysis systems; Artificial kidneys; Blood oxygenators ; Reciprocating systems for treatment of body fluids, e.g. single needle systems for hemofiltration or pheresis with membranes
  • A61M1/168—Sterilisation or cleaning before or after use
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M2205/00—General characteristics of the apparatus
  • A61M2205/33—Controlling, regulating or measuring
  • A61M2205/3331—Pressure; Flow
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M2205/00—General characteristics of the apparatus
  • A61M2205/33—Controlling, regulating or measuring
  • A61M2205/3331—Pressure; Flow
  • A61M2205/3334—Measuring or controlling the flow rate
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M2205/00—General characteristics of the apparatus
  • A61M2205/33—Controlling, regulating or measuring
  • A61M2205/3368—Temperature
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M2205/00—General characteristics of the apparatus
  • A61M2205/75—General characteristics of the apparatus with filters
  • A61M2205/7518—General characteristics of the apparatus with filters bacterial
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M2240/00—Specially adapted for neonatal use

Definitions

• the present invention relates to the field of neonatal care. More specifically, the invention provides apparati and methods for the maintenance of homeostasis in the pre-viable fetus outside of the womb.
• an extracorporeal membrane oxygenation system (artificial placenta) is provided.
• the system is pumpless and comprises a very low resistance oxygenator.
• system/apparatus may further comprise an incubation chamber for holding the subject and sterile liquid in which to submerge the subject.
• the system/apparatus may further comprise a pump and filtration system for the sterile liquid. Examples of a system/apparatus of the instant invention are shown in Figures 1 and 7 A.
• the method comprises connecting the subject to the extracorporeal membrane oxygenation system of the instant invention.
• the subject may be connected to the oxygenator via vessels in the neck.
• the subject is a premature fetus, extreme premature fetus, or a pre-viable fetus.
• the oxygenator is primed with fetal blood.
• the subject may also be maintained submerged in an incubation chamber comprising sterile liquid, particularly where the sterile liquid is heated and continually pumped through a filtration system.
• Figure 1 provides a photo of an example of an apparatus of the instant invention.
• Figure 2 provides a photo of an example of the incubation chamber.
• Four ports in the chamber are clearly identified. Two of the ports are for circulation of the sterile liquid in the chamber (labeled “amniotic in” and “amniotic out”). The other two ports are for circulating warm liquid into an enclosed unit within the chamber to maintain the subject's body temperature.
• Figure 3 provides a photo of an example of a dry chamber comprising an oxygenator.
• Figure 4 provides a photo of a filtration system.
• Figure 5 provides a photo of a circuit design with the oxygenator.
• Figure 6A provides a photo of a premature lamb connected to the apparatus of the instant invention.
• Figure 6B provides a photo of the lamb after 5 days of growth.
• Figure 7A provides a schematic diagram of an example of the apparatus of the instant invention.
• Figure 7B provides a photograph of an example of the apparatus of the instant invention.
• Figure 7C provides a a photograph of an example of the circuit of the apparatus of the instant invention.
• Figures 8A-8F show the stability of fetal biochemical and hemodynamic parameters.
• Carotid arterial sampling for pH (Fig. 8A) and partial pressure of C0 2 and 0 2 (Fig. 8B) are shown.
• the recorded fetal heart rate (Fig. 8C), systolic blood pressure (Fig. 8D), Fi0 2 delivery to oxygenator (Fig. 8E), and circuit flow rates (Fig. 8F) over the course of 300 hours are shown. Error bars represent five independent experiments.
• Figure 9 provides a graph showing a linear relationship between systolic blood pressure (mmHg) and circuit flow rates (ml/min). Error bars represent four independent experiments.
• Figures 10A-10D show fetal growth and metabolism with the instant invention.
• Figure 1 OA shows weight gain over the course of fetal incubation.
• Figure 10B shows fetal breathing response to increased arterial PaC0 2 levels.
• Figure IOC shoes the patency of the ductusarteriosis (white arrow) confirmed by fetal
• Figure 10D shows the fetal oxygen consumption over the course of the incubation.
• Figures 11 A-l ID show the growth and development of the lamb.
• Figure 1 1 A provides a photograph of the fetal lamb on day 1 (GA 120 days).
• Figure 1 IB provides a photograph of the fetal lamb on day 14 (GA 134 days)
• Figure 11C provides an image of hematoxylin and eosin (H&E) staining of paraffin-embedded fetal lung following day 14.
• Figure 1 ID provides a photograph of the normal growth and development of the lamb 6 months after incubation.
• Premature birth may occur due to any one of a multitude of reasons. For example, premature birth may occur spontaneously due to preterm rupture of the membranes (PROM), structural uterine features such as shortened cervix, secondary to traumatic or infectious stimuli, or due to multiple gestations. Preterm labor and delivery is also frequently encountered in the context of fetoscopy or fetal surgery, where instrumentation of the uterus often stimulates uncontrolled labor despite maximal tocolytic therapy.
• the 2010 CDC National Vital Statistics Report notes birth rates at a gestational age of less than 28 weeks in the U.S. over the past decade have remained stable at approximately 0.7%, or 30,000 births annually. Similarly, birth rates at gestational ages 28-32 weeks over the past decade in the U.S. have been stable at 1.2%, or 50,000 births annually. Patients with pulmonary hypoplasia secondary to congenital diaphragmatic hernia, oligohydramnios, or abdominal wall defects are also significant.
• the National Birth Defects Prevention Network reports an annual incidence of congenital diaphragmatic hernia between 0.9 to 5.8 per 10,000 live births in the U.S., or approximately 375-2,500 births annually. The incidence of other causes of pulmonary hypoplasia is not well documented.
• the system of the instant invention allows for the support and ongoing growth and organ maturation of the fetus while maintaining fetal physiology in an
• the fetal heart is used to drive flow through the circuit and oxygenator (i.e., it is a pumpless system).
• the use of a pumpless system avoids exposure of the fetal heart to excess preload encountered in non-pulsatile pump-assisted circuits.
• the pumpless system also permits intrinsic fetal circulatory regulation of flow dynamics.
• the oxygenator of the instant invention is preferably very low resistance, has low priming volume and low transmembrane pressure drops, and provides efficient gas exchange.
• the oxygenator has a pressure drop of less than about 50 mmHg or about 40 mmHg at 1.5 1/min of blood flow.
• the priming volume of the oxygenator is less than about 100 ml, particularly less than about 85 ml.
• the oxygenator has a blood flow range up to about 2.0 1/min, about 2.5 1/min, about 2.8 1/min, or greater.
• the oxygenator has a gas transfer rate of about 150 ml/min, about 160 ml/min, about 180 ml/min, or greater for 0 2 .
• the oxygenator is a hollow fiber membrane oxygenator (e.g., a polymethyl pentene hollow fiber membrane oxygenator).
• the oxygenator is lined with anti-clotting measures/compounds (e.g., immobilized polypeptide and/or heparin).
• the oxygenator is the Quadrox-iDTM pediatric oxygenator (Maquet; Wayne, NJ).
• the subjects of the instant invention may be infants, including term and preterm infants.
• the preterm infant may be premature infants (i.e., less than 37 weeks estimated gestational age, particularly 28 - 32 weeks), extreme premature infants (i.e., 24 - 28 weeks), or pre-viable fetuses (e.g., 20 - 24 weeks).
• the gestation periods are provided for humans, though corresponding preterm infants of other animals may be used.
• the preterm infant has no underlying congenital disease.
• the term or preterm infants has limited capacity for pulmonary gas exchange, for example, due to pulmonary hypoplasia or a congenital anomaly affecting lung development, such as congenital diaphragmatic hernia.
• the subject is a preterm or term neonate awaiting lung transplantation, for example, due to congenital pulmonary disease (e.g., bronchioalveolar dysplasia, surfactant protein B deficiency, and the like).
• congenital pulmonary disease e.g., bronchioalveolar dysplasia, surfactant protein B deficiency, and the like.
• Such transplantation surgeries are currently rarely performed in the U.S. (Huddleston et al. (2002) Ann Surg., 236:270-6). However, the number of transplantation surgeries would be increased with the more stable method for pulmonary support provided by the instant invention.
• the subject may also be a candidate for ex utero intrapartum treatment (EXIT) delivery, including patients with severe airway lesions and a long expected course before definitive resection.
• EXIT ex utero intrapartum treatment
• the subject may also be a fetal surgical or fetoscopic procedure patient, particularly with preterm labor precipitating early delivery.
• the subject may be maintained in the apparatus of the instant invention for as long as needed (e.g., for days, weeks or months).
• cannulae are placed in the great neck vessels (e.g., carotid) of the subject to connect the circulatory system of the subject to the oxygenator.
• the placement in the great neck vessels avoids issues of vasospasm and cannula instability in umbilical vessels.
• the connective tubing e.g., silicone
• the connective tubing e.g., silicone
• the tubing is about 12 inches or less from the cannula to the oxygenator.
• the tubing is lined with anti-clotting measures/compounds (e.g., immobilized polypeptide and/or heparin) (i.e., the tubing is clot resistant).
• anti-clotting measures/compounds e.g., immobilized polypeptide and/or heparin
• the external portion of the cannulas may be fitted with a sleeve (e.g., to permit increased tension of the stabilizing sutures).
• the sleeve may be made of silicone and may be, for example, about 1-10 cm in length, particularly about 3-5 cm in length.
• the cannulae may be sutured to the animal (e.g., via the fitted sleeve) to secure them to the neck of the animal.
• the oxygenator device is primed with blood.
• the oxygenatoer device may be primed with, for example, maternal blood and/or fetal blood.
• the priming of the oxygenator with fetal hemoglobin permits optimal oxygen exchange across the membrane. Indeed, the fetal oxygen dissociation curve is shifted to the left meaning that fetal arterial oxygen pressures are lower than adult arterial oxygen pressures.
• the blood comprises heparin.
• the gas inflow to the oxygenator is mixed medical air and oxygen.
• the subject is placed with an incubator.
• the incubator is a chamber filled with a sterile liquid such that the subject is submerged (e.g., approximating the in utero environment).
• the incubation chamber may be sealed to prevent contamination of the sterile liquid on the inside.
• the top of the chamber is removable or is a lid to allow access to the subject. However, the top should be sealable to the remainder of the chamber (e.g., via a gasket).
• the chamber is a rigid structure such as a box or bowl made out of glass, metal, or an inert medical grade plastic or silicone.
• the chamber is a bag or sac (e.g., made out of an inert medical grade plastic or silicone; water-tight), thereby replicating the amniotic sac.
• the chamber may comprise a hanging or suspended mesh or hammock to place the subject on within the chamber (see, e.g., Figs. 1 1 A and 1 IB).
• the hanging/suspended mesh e.g., a sling or hammock
• the hanging/suspended mesh (e.g., sling or hammock) may be made out of a sterile and inert medical grade material such as metal or nylon.
• the incubation chamber may also comprise glove ports to allow sterile access to the subject (e.g., for swaddling of the subject to calm or to gain access to objects within the interior of the chamber).
• the sterile liquid within the incubation chamber may be amniotic fluid, sterile artificial/synthetic amniotic fluid, Lactated Ringer's solution, or the like.
• the sterile liquid may contain antibiotics (e.g., penicillin) and/or lysozyme.
• the sterile liquid and/or incubator may be heated to maintain the body temperature of the subject.
• the sterile liquid may be heated outside of the incubator and pumped in warm and/or may be heated within the chamber.
• a warm liquid e.g., water
• a closed unit e.g., tubing (e.g., silicone), particularly in a loop or coiled shape
• the warm liquid is pumped into the heating coil at about 50°C.
• the fluid within the incubator chamber is connected to a pump and one or more filters (e.g., to remove particulate matter excreted from the subject in the chamber).
• the apparatus comprises a series of filters which may optionally have pressure gauges in between them to allow for rapid identification of any filter clogs.
• the filtration system may also comprise a UV fluid filter.
• An example of a filter system is shown in Figure 4. Depicted in Figure 4 is a gross debris filter connected in succession with a 30 micron filter, a 5 micron filter, and a 0.15 micron filter.
• the filtration system may comprise any number of filters of varying pore size.
• the filtration system may comprise a gross debris filter connected in succession with a 1 micron filter, a 30 micron filter, a 1 micron filter, a 5 micron filter, 0.2 micron filter, and a 0.15 micron filter.
• a gross debris filter connected in succession with a 1 micron filter, a 30 micron filter, a 1 micron filter, a 5 micron filter, 0.2 micron filter, and a 0.15 micron filter.
• FIG. 7A An example of another filter system is shown in Figure 7A wherein a pump is connected to a 100 ⁇ filter and a UV light.
• the fluid within the incubator chamber is exchanged about 1 to about 10 times daily, particularly about 1 to about 5 times daily or about 2 to about 4 times daily.
• Sterile fluid may be pumped into the chamber by at least one port.
• Fluid may be removed from the chamber through at least one port, wherein the fluid may be removed from the chamber with the assistance of a pump.
• An example of the exchange system is shown in Figure 7A, wherein a pump moves sterile fluid into the chamber at a first port and a second pump removes old fluid from the chamber through a second port.
• the apparatus and methods of the instant invention use fluid exchange and/or filtration for maintaining the sterility of the fluid (e.g., fluid exchange may be used without supplemental filtration, although the combined use will increase sterility).
• the subject receives nutritional support through feeding tubes or IV while in the incubation chamber.
• the subject may also be administered sedatives in order to limit movements, but the instant invention does allow for some movements within the chamber so it may not be necessary.
• the subject may also be administered antibiotics (e.g., ampicillin, gentamycin, etc.).
• the subject may also be administered an anticoagulant (e.g., heparain).
• the subject may also be administered a prostaglandin (e.g., prostaglandin-El or E2).
• the subject's vital signs, weight, liver function, and blood flow are also typically monitored.
• Bilirubin levels may also be monitored.
• Figures 1 and 7 show examples of the apparatus of the instant invention.
• Figure 7A provides a schematic of an example of an apparatus of the instant invention.
• the apparatus may be a single unit or comprise separate housing units with interconnecting tubing.
• the apparatus shown is an appropriate size for a lamb.
• the apparatus can be sized appropriately for the size of the subject. For example, the apparatus may about 1/3 the size for a human subject.
• the incubation chamber may comprise any number of inlets and outlets.
• the chamber comprises at least one inlet and one outlet to circulate the sterile liquid within.
• the incubation chamber may also comprise glove ports to allow sterile access to the subject (e.g., for swaddling of the subject to calm or to gain access to objects within the interior of the chamber).
• the chamber may also comprise at least one port for an IV line to the subject.
• the chamber may also have a variety of ports (e.g., resealable ports) to allow access for any of a variety of monitoring devices.
• the chamber may have ports to allow access for an ultrasound device and/or a dialysis unit.
• the chamber may also comprise a UV light unit (e.g., to treat/inhibit jaundice).
• Figure 3 provides an image of the oxygenator contained within an optional dry chamber.
• Figures 5 and 7C show an example of the circuit design with the oxygenator without the dry chamber. While this chamber is shown as being separated from the incubator chamber by a divider in a single unit, the two can be separated into individual units (albeit connected by the necessary tubing and the like).
• the cannulas from the subject may connected directly to the oxygenator within the dry chamber or through ports in the dry chamber.
• the dry chamber may also comprise at least one port to attach the gas flow to the oxgenator. The port may connect to the oxygenator via tubing within the dry chamber.
• Figure 3 also shows additional ports for the addition of a heater (e.g., via a warm liquid and tubing) to the dry chamber to help maintain the temperature of the blood being circulated through the tubing and the oxygenator.
• a heater e.g., via a warm liquid and tubing
• the tubing to and/or from the oxygenator may be attached to monitors (e.g., temperature monitors, gas content monitors, etc.).
• Figure 7A provides a schematic of an example of an apparatus of the instant invention.
• the chamber is depicted as a bowl located within a water bath to maintain the temperature of the system.
• the incubation chamber is depicted with two glove/hand ports on the top of the chamber (though the ports could be located anywhere, including the sides of the chamber) for sterile access to the interior of the chamber.
• the chamber comprises an inlet port for the pumping in of sterile amniotic fluid and an exit port for the removal of used/old amniotic fluid.
• the chamber is also depicted as having a filtration system comprising a pump, at least one filter, and a UV filter for elimination of bacteria and contaminants.
• the chamber also depicts a mesh upon which the subject may be placed.
• Figure 7 A also depicts the oxygenator (Ox) in fluid connection with the blood system of the subject, particularly through cannulae into the neck vessels of the subject.
• the oxygenator is connected to a gas mixer drawing upon air and oxygen.
• the tubing of the oxygentor system may comprise at least one port for the introduction of compounds (e.g., nutrients, antibiotics, drugs, etc.) into the blood stream of the subject.
• Monitors such as for determining pressure, flow, and temperature may connected to the oxygentor system and/or the subject directly.
• the terms "host,” “subject,” and “patient” refer to any animal, particularly mammals including humans.
• a pre-term lamb (28 weeks) was maintained in the apparatus using the methods of the instant invention.
• 8F to 10F arterial ECMO cannulas were placed in carotid artery and internal jugular vein (size chosen at time of surgery).
• Figure 6A provides an image of the lamb connected to the apparatus and Figure 6B shows the lamb after 5 days of growth. The growth of the premature lamb for five days demonstrates the ability of the instant invention to maintain a fetus outside of the womb.
• extracorporeal membrane oxygenation (ECMO) of the fetus is appealing due to the similarities to innate fetal physiology, in which extracorporeal gas exchange is performed by the placenta.
• the artificial placenta has been a subject of experimental trials since the 1960's, with a series of short experiments in which fetal lambs were cannulated via the umbilical vessels and perfused by first-generation bubble membrane oxygenators, with perfusion supported for 40 minutes to 2 days (Callaghan et al. (1963) Circulation 27:686-690; Zapol et al. (1969) Science 166:617- 618).
• a pumpless circuit may offer advantages over current ECMO technology including reduced priming and distribution volumes, shorter exposure of blood to thrombogenic surfaces, and achieving innate regulation of blood flow and pressure by the fetal heart itself.
• the MaquetQuadrox-ID Pediatric Oxygenator supports the possibility of achieving pumpless oxygenation of fetal blood using the native heart to drive flow through the circuit. This oxygenator has been applied as a pumpless artificial lung in pediatric patients with good success (Boston et al. (2013) J. Thorac. Cardiovasc. Surg., 146:e42-e43).
• an approach was sought to maintain fetal blood oxygenation and stable hemodynamics using a modified pumpless circuit that permits the fetal heart to act as the pump, replicating innate fetal hemodynamics.
• Major challenges included achieving stable perfusion autoregulated by the innate fetal circulation, replicating the sterile fluid-immersed intrauterine environment, and facilitating appropriate fetal growth and development.
• PFLS pumpless extrauterine fetal life support
• Intraoperative hemodynamic monitoring included pulse oximetry, with a constant infusion of isotonic saline administered via a central venous line placed in the right jugular vein to maintain maternal fluid balance.
• a lower midline laparotomy was created to expose the uterus, with a small hysterotomy performed to expose the fetal sheep head and neck.
• fetal blood was collected from the donor animal to prime the circuit.
• Donor animals underwent creation of a small right neck incision to expose the jugular vein, and were administered one intramuscular dose of buprenorphine (0.005 mg/kg) and one intravenous dose of sodium heparin (150 USP units, APP Pharmaceuticals, Schaumburg, IL), followed by creation of a small right neck incision to expose the jugular vein and placement of a catheter to permit collection of the entire blood volume of the animal.
• singleton lambs maternal blood was collected to prime the circuit. In all animals, maternal blood was collected and stored for subsequent transfusion requirements during the run.
• mice underwent creation of a small right neck incision to expose the carotid artery and jugular vein. Animals received one intramuscular dose of buprenorphine (0.005 mg/kg) and one intravenous dose of sodium heparin (300 USP units). After determination of the maximal cannula size accommodated by each vessel, ECMO cannulae were placed (size range 8-12Fr, Avalon Laboratories, LLC, Collinso Dominguez, CA), with stabilizing sutures placed along the external length of cannulae at the neck. In a subset of animals, the external portion of the cannulas were fitted with a silicone 'sleeve' of 3-5 cm to permit increased tension of the stabilizing sutures.
• EMG ocular electromyography
• EEG electroencephalography
• connection of the cannulas to the circuit was performed under continuous ultrasonographic visualization of the fetal heart. Occlusion of the umbilical cord was performed immediately following establishment of blood flow through the circuit, with administration of additional blood volume and/or atropine (0.1 mg) and/or epinephrine (0.1 mg) in a subset of animals demonstrating poor cardiac contractility immediately after establishment of circuit flow.
• catheters were implanted in the fetal carotid artery and jugular vein, in addition to a reference catheter placed in the amniotic sac, followed by placement of EOG and dural EEG wire electrodes as described above.
• EMG wire electrodes were placed in the nuchal and diaphragm muscles.
• the posterior left diaphragm was approached from a mid- axillary incision with two electrodes sewn 1.0 cm apart, while a single electrode was sewn into a long muscle of the neck to record nuchalactivity.
• Fetal catheters and electrodes were exteriorized through the maternal flank, and the uterus and abdomen were closed. Following a 48-72 hour recovery period, ewes were transferred to a holding cage for fetal monitoring.
• the pumpless extrauterine fetal life support (P-EFLS) circuit consisted of a low-resistance hollow fiber oxygenator (Quadrox-ID, Maquet, Rastatt, Germany) connected to the ECMO cannulae with 3/16" BIOLINE heparin-coated Medtronic tubing (Medtronic, Minneapolis Minesotta). Connections were established as an arterial-venous extracorporeal oxygenation circuit, with the carotid arterial outflow under pulsatile systemic pressure connected to the oxygenator inflow port and return flow connected to the outflow port.
• the priming volume was 81 mL, and heparinized fetal blood was used when available, with maternal blood utilized in singleton pregnancies. Circuit flow was measured with a flow probe (Transonic Systems Inc, Ithaca NY), and sweep gas supplied to the oxygenator was a blended mixture of medical air and oxygen titrated to fetal blood gas values.
• Trial incubator designs included a 30-liter heated stainless steel reservoir filled with sterile synthetic amniotic fluid ("still reservoir”), a 40-liter polycarbonate tank with continuous recirculation of fluid through a series of sterile filters ("recirculated filtration”), and finally a 60-liter tank within flow and outflow tubing mounted on a double-head peristaltic pump to facilitate continuous exchange of sterile fluid (“continuous exchange”).
• the complete volume of the tank is replaced three-fold with sterile inflow from a 180-liter reservoir over a 24-hour period.
• Synthetic amniotic fluid was composed of a balanced salt solution containing Na + (109 mM), CI “ (104 niM), HC0 3 " (19 mM), K + (6.5 niM), Ca 2 + (1.6 mM), pH 7.0- 7.1, osmolarity 235.8 mOsm/kg water. Antibiotics were added to a final
• heparin 80-200 USP units per hour
• prostaglandin El 0.1 mcg/kg/min, Pfizer Inc, New York, NY
• Blood was drawn every 1 -4 hours for blood gas, electrolyte and coagulation values using an i- Stat® System (Abbott Point of Care Inc, Princeton, NJ), with titration of the heparin infusion to a target Activated Clotting Time of 180-200 seconds (100-400 USP units per hour), and titration of the oxygenator sweep gas to target fetal partial pressures of 0 2 (Pa0 2 20-30 mmHg) and C0 2 (PaC0 2 35-45 mmHg) (Fi0 2 21-55%, sweep gas 0.125-1.5 L/min). Stored whole maternal blood was used to maintain fetal hemoglobin levels above 9 mg/dL.
• i- Stat® System Abbott Point of Care Inc, Princeton, NJ
• Analgesics (buprenorphine, 0.005 mg/kg IV every 3-5 hours as needed) and anxiolytics (midazolam, 0.4 mg/kg IV every 3-5 hours as needed) were administered during periods of perceived fetal distress (restless repetitive fetal movements, tachycardia, hypertension).
• Total parenteral nutrition was administered throughout the duration of fetal incubation, with a dosage of 3.5 g/kg amino acids (TrophAmine® 10%), 5-10% dextrose, and 3 g/kg lipids (Intralipid® 20%).
• Oxygen Delivery Post-membrane 0 2 C x Circuit Flow/100/body weight
• Oxygen Consumption (OC) (Post-membrane 0 2 C - Pre-membrane 0 2 C) x Circuit Flow/100
• Oxygen Extraction Rate (OER) (OC/OD) x 100.
• OER Oxygen Extraction Rate
• the fluid incubator was subsequently designed to a closed system with recirculation of amniotic fluid containing antibiotics (Ciprofloxacin 30 mg/L, Gentamycin 18 mg/L) through a series of filters with increasingly fine pore size (1 mm, 10 ⁇ , 5 ⁇ , 2 ⁇ , 0.2 ⁇ ) to eliminate gross debris and maintain sterility.
• antibiotics Ciprofloxacin 30 mg/L, Gentamycin 18 mg/L
• filters with increasingly fine pore size (1 mm, 10 ⁇ , 5 ⁇ , 2 ⁇ , 0.2 ⁇
• Fetal flows during PEFLS are linearly related to the systolic blood pressure of the animal ( Figure 9) and are pulsatile and directly correlate with the measured cardiac output. Autoregulation of circuit flow was consistently demonstrated in response to hypoxia, with compensatory increases in systolic blood pressure and circuit flow in response to reduced sweep gas flow to the oxygenator and
• a pumpless circuit to permit long-term support of the extrauterine fetus may be the optimal design for an artificial placenta.
• previous efforts have been limited by low flow rates and poor perfusion.
• PEF pumpless extrauterine fetal life support
• a superior oxygenator with extremely low resistance and low priming volumes, a circuit has been created which more closely approximates the placenta itself.
• the reported placental blood volume of the sheep is 23.1 to 48.1 ml/kg (Creasy et al. (1970) Circ.
• priming of the oxygenator circuit with fetal blood might provide advantages with respect to oxygen unloading and maintaining peripheral perfusion.
• priming of the circuit was completed with fetal blood in the case of twin gestations and with maternal blood in the event of singleton lambs (Tables 1 and 2), and no differences were observed in arterial oxygen content, lactic acid production, or cardiac function over the course of long-term fetal incubation.
• a pumpless circuit in which innate hemodynamics can be maintained by autoregulation may be advantageous for normal fetal development.
• the longest extrauterine fetal incubation experiments was with animals maintained on a circuit employing a silicone hollow fiber membrane oxygenator and a roller pump and animals cannulated via the umbilical vessels (Kuwabara et al. (1986) Artificial Organs 1 1 :224-277; Kuwabara et al. (1989) Artificial Organs 13:527-531).
• the maximum duration of incubation was 8 hours, with rapid onset of cardiac failure accounting for fetal demise in the majority of experiments.
• this reservoir-supported circuit was modified by the addition of hemodialysis to improve fluid and electrolyte balance, achieving incubation lengths of up to 236 hours with flow rates between 50 to 100 ml/min/kg. Again, while three animals died due to catheter malfunctions, cardiac failure was the cause of all nontechnical deaths, with progressive circulatory depression and eventual demise on the circuit.
• One advantage of a pumpless system for fetal perfusion is the maintenance of regulation of cerebral blood flow by innate autoregulatory pathways. Ensuring adequate oxygenation of the developing brain is a key consideration in the design of an artificial placenta, with cerebral autoregulation felt to represent one important component of cerebral perfusion. Cerebral autoregulation has been well described in the population of neonatal infants who require intensive care, but is poorly understood. Significant individual variability exists with respect to measured ranges of cerebral artery blood flow rates, vasoreactivity, and autoregulatory thresholds, to the extent that normative values for these patients remain undefined (Vutskis, L. (2014) Pediatr. Anesth., 24:22-29).
• Cerebral autoregulation has also been observed in the human fetus, with increased middle cerebral artery peak systolic velocity described in fetuses with intrauterine growth restriction (Hanif et al. (2007) Am. J. Perinatol, 24:501-505).
• the effects of conventional pump-supported ECMO on cerebral perfusion in neonates have demonstrated a well-documented loss of autoregulation in response to fetal hypoxia in a number of systems, including lamb models of veno-arterial ECMO (Short et al. (1993) Pediatr. Res., 33:289-294; Stolar et al. (1988) J. Pediatr.
• TEFLS total extrauterine fetal life support

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