The role of fetal hemoglobin in the artificial placenta: A premature ovine model.

INTRODUCTION: A radical paradigm shift in the treatment of premature infants failing conventional treatment is to recreate fetal physiology using an extracorporeal Artificial Placenta (AP). The aim of this study is to evaluate the effects of changing fetal hemoglobin percent (HbF%) on physiology and circuit function during AP support in an ovine model. METHODS: Extremely premature lambs (n = 5) were delivered by cesarean section at 117-121 d estimated gestational age (EGA) (term = 145d), weighing 2.5 ± 0.35 kg. Lambs were cannulated using 10-14Fr cannulae for drainage via the right jugular vein and reinfusion via the umbilical vein. Lambs were intubated and lungs were filled with perfluorodecalin to a meniscus with a pressure of 5-8 cm H2O. The first option for transfusion was fetal whole blood from twins followed by maternal red blood cells. Arterial blood gases were used to titrate AP support to maintain fetal blood gas values. RESULTS: The mean survival time on circuit was 119.6 ± 39.5 h. Hemodynamic parameters and lactate were stable throughout. As more adult blood transfusions were given to maintain hemoglobin at 10 mg/dL, the HbF% declined, reaching 40% by post operative day 7. The HbF% was inversely proportional to flow rates as higher flows were required to maintain adequate oxygen saturation and perfusion. CONCLUSIONS: Transfusion of adult blood led to decreased fetal hemoglobin concentration during AP support. The HbF% was inversely proportional to flow rates. Future directions include strategies to decrease the priming volume and establishing a fetal blood bank to have blood rich in HbF.

Nitric Oxide-Releasing Insert for Disinfecting the Hub Region of Tunnel Dialysis Catheters.

The use of tunneled dialysis catheters (TDCs) for patients in need of hemodialysis treatments (HDs) causes a significant number of bloodstream infections (BSIs), with very few viable preventative/treatment methods. Use of antibiotics is relatively ineffective due to the development of multidrug-resistant bacterial strains and the inability to penetrate bacterial biofilms. Nitric oxide (NO) is an endogenous gas molecule that has broad-spectrum antimicrobial/antibiofilm activity. In this study, the potential of creating a NO-releasing insert device that is attached onto the hub region cap of TDCs and locally releases NO within the TDC hub is evaluated for its antimicrobial/antibiofilm effectiveness. The NO-releasing insert contains the natural NO donor S-nitrosoglutathione (GSNO), along with zinc oxide (ZnO) nanoparticles to accelerate NO release from the GSNO, within a short silicone tube that is sealed at both ends and attached to the catheter cap. An in vitro 3-d-long antimicrobial study using catheter hubs yielded >6.6 log reductions of both Pseudomonas aeruginosa and Staphylococcus aureus for the NO-releasing insert device compared to controls. Two 14-d-long sheep studies demonstrated that the NO-releasing insert devices are exceptionally potent at preventing bacteria/biofilm growth on the inner lumen walls of TDCs compared to controls that have no preventative treatment devices as well as implanted TDCs that have commercially available chlorhexidine-treated insert devices placed within the hub regions.

Evaluation of an Anti-Thrombotic Continuous Lactate and Blood Pressure Monitoring Catheter in an In Vivo Piglet Model undergoing Open-Heart Surgery with Cardiopulmonary Bypass.

Blood lactate and blood pressure measurements are important predictors of life-threatening complications after infant open-heart surgeries requiring cardiopulmonary bypass (CPB). We have developed an intravascular nitric oxide (NO)-releasing 5-Fr catheter that contains a lactate sensor for continuous in-blood lactate monitoring and a dedicated lumen for third-party pressure sensor attachment. This device has antimicrobial and antithrombotic properties and can be implanted intravascularly. The importance of this design is its ability to inhibit thrombosis, due to the slow release of NO through the surface of the catheter and around the electrochemical lactate sensors, to allow continuous data acquisition for more than 48 h. An in vivo study was performed using six piglets undergoing open-heart surgery with CPB and cardioplegic arrest, in order to mimic intra-operative conditions for infants undergoing cardiac surgery with CPB. In each study of 3 h, two 5-Fr NO-releasing lactate and blood-pressure monitoring catheters were implanted in the femoral vessels (arteries and veins) and the CPB circuitry to monitor changing lactate levels and blood pressures during and immediately after aortic cross-clamp removal and separation from CBP. Electrical signals continuously acquired through the sensors were processed and displayed on the device's display and via Bluetooth to a computer in real-time with the use of a two-point in vivo calibration against blood gas results. The study results show that lactate levels measured from those sensors implanted in the CPB circuit during CPB were comparable to those acquired by arterial blood gas measurements, whereas lactate levels measured from sensors implanted in the femoral artery were closely correlated with those acquired intermittently by blood gas prior to CPB initiation, but not during CPB. Blood pressure sensors attached to one lumen of the device displayed accurate blood pressure readings compared to those measured using an FDA approved pressure sensor already on the market. We recommend that the sensor be implanted in the CPB's circuit to continuously monitor lactate during CPB, and implanted in the femoral arteries or jugular veins to monitor lactate before and after CPB. Blood pressures dramatically drop during CPB due to lower blood flow into the lower body, and we suspect that the femoral arteries are likely collapsing or constricting on the implanted catheter and disrupting the sensor-to-blood contact. This study shows that the device is able to accurately and continuously monitor lactate levels during CPB and potentially prevent post-surgery complications in infants.

Tidal Flow Perfusion for the Artificial Placenta: A Paradigm Shift.

The modalities of vascular access for the extracorporeal artificial placenta (AP) have undergone many iterations over the past decade. We hypothesized that single lumen cannulation (SLC) of the jugular vein using tidal flow extracorporeal life (ECLS) support is a feasible alternative to venovenous (VV) umbilical-jugular cannulation and double lumen cannulation (DLC) and can maintain fetal circulation, stable hemodynamics, and adequate gas exchange for 24 hours. After in vitro evaluation of the tidal flow system, six preterm lambs at estimated gestational age 118-124 days (term 145 days) were delivered and underwent VV-ECLS. Three were supported using DLC and three with SLC utilizing tidal flow AP support. Hemodynamics, circuit flow, and gas exchange were monitored. Target fetal parameters were as follows: mean arterial pressure 40-60 mmHg, heart rate 140-240 beats per minute (bpm), SatO2% 60-80%, PaO2 25-50 mmHg, PaCO2 30-55 mmHg, oxygen delivery >5 ml O2/dl/kg/min, and circuit flow 100 ± 25 ml/kg/min. All animals survived 24 hours and maintained fetal circulation with stable hemodynamics and adequate gas exchange. Parameters of the tidal flow group were comparable with those of DLC. Single lumen jugular cannulation using tidal flow is a promising vascular access strategy for AP support. Successful miniaturization holds great potential for clinical translation to support extremely premature infants.

Evaluation of Continuous Lactate Monitoring Systems within a Heparinized In Vivo Porcine Model Intravenously and Subcutaneously.

We present an animal model used to evaluate the in vivo performance of electrochemical amperometric continuous lactate sensors compared to blood gas instruments. Electrochemical lactate sensors were fabricated, placed into 5 Fr central venous catheters (CVCs), and paired with wireless potentiostat devices. Following in vivo evaluation and calibration, sensors were placed within the jugular and femoral veins of a porcine subject as a preliminary assessment of in vivo measurement accuracy. The mobile electronic circuit potentiostat devices supplied the operational voltage for the sensors, measured the resultant steady-state current, and recorded the sensor response values in internal memory storages. An in vivo time trace of implanted intravenous (IV) sensors demonstrated lactate values that correlated well with the discrete measurements of blood samples on a benchtop point-of-care sensor-based instrument. Currents measured continuously from the implanted lactate sensors over 10 h were converted into lactate concentration values through use of a two-point in vivo calibration. Study shows that intravenously implanted sensors had more accurate readings, faster peak-reaching rates, and shorter peak-detection times compared to subcutaneously placed sensors. IV implanted and subcutaneously placed sensors closer to the upper body (in this case neck) showed faster response rates and more accurate measurements compared to those implanted in the lower portion of the porcine model. This study represents an important milestone not only towards continuous lactate monitoring for early diagnosis and intervention in neonatal patients with congenital heart disease undergoing cardiopulmonary bypass surgeries, but also in the intervention of critical ill patients in the Intensive Care Units or during complex surgical procedures.

Development of a Model of Pediatric Lung Failure Pathophysiology.

A pediatric artificial lung (PAL) is under development as a bridge to transplantation or lung remodeling for children with end-stage lung failure (ESLF). To evaluate the efficiency of a PAL, a disease model mimicking the physiologic derangements of pediatric ESLF is needed. Our previous right pulmonary artery (rPA) ligation model (rPA-LM) achieved that goal, but caused immediate mortality in nearly half of the animals. In this study, we evaluated a new technique of gradual postoperative right pulmonary artery occlusion using a Rummel tourniquet (rPA-RT) in seven (25-40 kg) sheep. This technique created a stable model of ESLF pathophysiology, characterized by high alveolar dead space (58.0% ± 3.8%), pulmonary hypertension (38.4 ± 2.2 mm Hg), tachypnea (79 ± 20 breaths per minute), and intermittent supplemental oxygen requirement. This improvement to our technique provides the necessary physiologic derangements for testing a PAL, whereas avoiding the problem of high immediate perioperative mortality.

Large Animal Model of Pumpless Arteriovenous Extracorporeal CO2 Removal Using Room Air via Subclavian Vessels.

End-stage lung disease (ESLD) causes progressive hypercapnia and dyspnea and impacts quality of life. Many extracorporeal support (ECS) configurations for CO2 removal resolve symptoms but limit ambulation. An ovine model of pumpless ECS using subclavian vessels was developed to allow for ambulatory support. Vascular grafts were anastomosed to the left subclavian vessels in four healthy sheep. A low-resistance membrane oxygenator was attached in an arteriovenous (AV) configuration. Device function was evaluated in each animal while awake and spontaneously breathing and while mechanically ventilated with hypercapnia induced. Sweep gas (FiO2 = 0.21) to the device was increased from 0 to 15 L/min, and arterial and postdevice blood gases, as well as postdevice air, were sampled. Hemodynamics remained stable with average AV shunt flows of 1.34 ± 0.14 L/min. In awake animals, CO2 removal was 3.4 ± 1.0 ml/kg/min at maximum sweep gas flow. Respiratory rate decreased from 60 ± 25 at baseline to 30 ± 11 breaths per minute. In animals with induced hypercapnia, PaCO2 increased to 73.9 ± 15.1. At maximum sweep gas flow, CO2 removal was 3.4 ± 0.4 ml/kg/min and PaCO2 decreased to 49.1 ± 6.7 mm Hg. Subclavian AV access is effective in lowering PaCO2 and respiratory rate and is potentially an effective ambulatory destination therapy for ESLD patients.

The Implantable Pediatric Artificial Lung: Interim Report on the Development of an End-Stage Lung Failure Model.

An implantable pediatric artificial lung (PAL) may serve as a bridge to lung transplantation for children with end-stage lung failure (ESLF); however, an animal model of pediatric lung failure is needed to evaluate the efficacy of PAL before it can enter clinical trials. The objective of this study was to assess ligation of the right pulmonary artery (rPA) as a model for pediatric ESLF. Seven lambs weighing 20-30 kg underwent rPA ligation and were recovered and monitored for up to 4 days. Intraoperatively, rPA ligation significantly increased physiologic dead space fraction (Vd/Vt; baseline = 48.6 ± 5.7%, rPA ligation = 60.1 ± 5.2%, p = 0.012), mean pulmonary arterial pressure (mPPA; baseline = 17.4 ± 2.2 mm Hg, rPA ligation = 28.5 ± 5.2 mm Hg, p < 0.001), and arterial partial pressure of carbon dioxide (baseline = 40.4 ± 9.3 mm Hg, rPA ligation = 57.3 ± 12.7 mm Hg, p = 0.026). Of the seven lambs, three were unable to be weaned from mechanical ventilation postoperatively, three were successfully weaned but suffered cardiorespiratory failure within 4 days, and one survived all 4 days. All four animals that were successfully weaned from mechanical ventilation had persistent pulmonary hypertension (mPPA = 28.6 ± 2.2 mm Hg) and remained tachypneic (respiratory rate = 63 ± 21 min). Three of the four recovered lambs required supplemental oxygen. We conclude that rPA ligation creates the physiologic derangements commonly seen in pediatric ESLF and may be suitable for testing and implanting a PAL.

Successful Porcine Renal Transplantation After 60 Minutes of Donor Warm Ischemia: Extracorporeal Perfusion and Thrombolytics.

Donation from uncontrolled circulatory determination of death donors (uDCD) is impractical in United States because of the time needed to organize procurement before irreversible organ damage. Salvaging organs after prolonged warm ischemic time (WIT) may address this limitation. We evaluated the combination of extracorporeal support (ECS) and thrombolytics in a porcine uDCD renal transplant model. Nonanticoagulated uDCD sustained 60 min of WIT, and two groups were studied. Rapid recovery (RR)-uDCD renal grafts procured using the standard quick topical cooling and renal flush, and ECS-assisted donation (E-uDCD), 4 hr ECS plus thrombolytics for in situ perfusion before procurement. All kidneys were flushed and cold stored, followed by transplantation into healthy nephrectomized recipients without immunosuppression. Delayed graft function (DGF) was defined as creatinine more than 5.0 mg/dl on any postoperative day. Twelve kidneys in E-uDCD and 6 in RR-uDCD group were transplanted. All 12 E-uDCD recipients had urine production and adequate function in the first 48 hr, but two grafts (16.7%) had DGF at 96 hr. All six recipients from RR-uDCD group had DGF at 48 hr and were killed. Creatinine and blood urea nitrogen (BUN) levels were significantly lower in E-uDCD compared with RR-uDCD group at 24 hr (2.9 ± 0.7 mg/dl vs. 5.2 ± 0.9 mg/dl) and 48 hr (3.2 ± 0.9 mg/dl vs. 7.2 ± 1.0 mg/dl); BUN levels at 24 and 48 hr were 28.3 ± 6.7 mg/dl vs. 39.5 ± 7.5 mg/dl and 23.9 ± 5.0 mg/dl vs. 46 ± 12.9 mg/dl, respectively. Thrombolytics plus ECS precondition organs in situ yielding functional kidneys in a porcine model of uDCD with 60 min of WIT. This procurement method addresses logistical limitations for uDCD use in the United States and could have a major impact on the organ donor pool.