Slowing lung deflation by increasing the expiratory resistance enhances FRC in preterm rabbits.

BACKGROUND: As very preterm infants have surfactant-deficient and highly incompliant lungs, slowing lung deflation during expiration might help preserve functional residual capacity(FRC) during lung aeration. In this study, we investigated the effect of expiratory resistance(Re) on lung aeration during positive pressure ventilation in preterm rabbits immediately after birth. METHODS: Preterm rabbit pups were delivered at 29 days gestation, mechanically ventilated from birth and simultaneously imaged to measure lung aeration using phase-contrast X-ray. Re was varied by altering the length (0, 60 or 1000 mm) of the expiratory circuit. RESULTS: Increasing Re led to a decrease in lung deflation rates and both peak expiratory flows and flow rates at mid-deflation. As a result, the rate of de-acceleration(slowing) in lung deflation when approaching FRC was markedly reduced with increasing resistance. During lung aeration, FRC was significantly different between resistance groups and was significantly higher over time in the high compared to the low resistance group. While FRC values tended to be higher with higher Re, they were not significantly different at end-ventilation (t = 7 min). CONCLUSION: Increasing Re of the ventilation circuit during lung aeration in preterm rabbits immediately after birth decreased lung deflation rates and increased the accumulation of FRC over time. IMPACT: The expiratory phase of the ventilatory cycle has been largely overlooked as an opportunity to improve ventilation in preterm infants after birth. Increasing the expiratory resistance of the ventilator circuit during lung aeration in preterm rabbits immediately after birth markedly decreased lung deflation rates and increased FRC accumulation, compared to a low expiratory resistance. This indicates that ventilation devices that reduce the "work of breathing" by reducing the expiratory resistance, may have the unintended effect of reducing FRC, particularly in extremely preterm infants that have surfactant deficient highly incompliant lungs.

The effect of vibrotactile stimulation on hypoxia-induced irregular breathing and apnea in preterm rabbits.

BACKGROUND: Manual tactile stimulation is used to counteract apnea in preterm infants, but it is unknown when this intervention should be applied. We compared an anticipatory to a reactive approach using vibrotactile stimulation to prevent hypoxia induced apneas. METHODS: Preterm rabbit kittens were prematurely delivered and randomized to either group. All kittens breathed spontaneously with a positive airway pressure of 8 cmH2O while they were imaged using phase contrast X-ray. Irregular breathing (IB) was induced using gradual hypoxia. The anticipatory group received stimulation at the onset of IB and the reactive group if IB transitioned into apnea. Breathing rate (BR), heart rate (HR) and functional residual capacity (FRC) were compared. RESULTS: Anticipatory stimulation significantly reduced apnea incidence and maximum inter-breath intervals and increased BR following IB, compared to reactive stimulation. Recovery in BR but not HR was more likely with anticipatory stimulation, although both BR and HR were significantly higher at 120 s after stimulation onset. FRC values and variability were not different. CONCLUSIONS: Anticipated vibrotactile stimulation is more effective in preventing apnea and enhancing breathing when compared to reactive stimulation in preterm rabbits. Stimulation timing is likely to be a key factor in reducing the incidence and duration of apnea. IMPACT: Anticipated vibrotactile stimulation can prevent apnea and stimulate breathing effort in preterm rabbits. Anticipated vibrotactile stimulation increases the likelihood of breathing rate recovery following hypoxia induced irregular breathing, when compared to reactive stimulation. Automated stimulation in combination with predictive algorithms may improve the treatment of apnea in preterm infants.

Sustained inflation improves initial lung aeration in newborn rabbits with a diaphragmatic hernia.

BACKGROUND: Infants with a congenital diaphragmatic hernia (DH) have underdeveloped lungs and require mechanical ventilation after birth, but the optimal approach is unknown. We hypothesised that sustained inflation (SI) increases lung aeration in newborn kittens with a DH. METHODS: In pregnant New Zealand white rabbits, a left-sided DH was induced in two fetal kittens per doe at 24-days gestation (term = 32 days); litter mates acted as controls. DH and control kittens were delivered by caesarean section at 30 days, intubated and mechanically ventilated (7-10 min) with either an SI followed by intermittent positive pressure ventilation (IPPV) or IPPV throughout. The rate and uniformity of lung aeration was measured using phase-contrast X-ray imaging. RESULTS: Lung weights in DH kittens were ~57% of controls. An SI increased the rate and uniformity of lung aeration in DH kittens, compared to IPPV, and increased dynamic lung compliance in both control and DH kittens. However, this effect of the SI was lost when ventilation changed to IPPV. CONCLUSION: While an SI improved the rate and uniformity of lung aeration in both DH and control kittens, greater consideration of the post-SI ventilation strategy is required to sustain this benefit. IMPACT: Compared to intermittent positive pressure ventilation (IPPV), an initial sustained inflation (SI) increased the rate and uniformity of lung aeration after birth. However, this initial benefit is rapidly lost following the switch to IPPV. The optimal approach for ventilating CDH infants at birth is unknown. While an SI improves lung aeration in immature lungs, its effect on the hypoplastic lung is unknown. This study has shown that an SI greatly improves lung aeration in the hypoplastic lung. This study will guide future studies examining whether an SI can improve lung aeration in infants with a CDH.

Higher CPAP levels improve functional residual capacity at birth in preterm rabbits.

BACKGROUND: Preterm infants are commonly supported with 4-8 cm H2O continuous positive airway pressures (CPAP), although higher CPAP levels may improve functional residual capacity (FRC). METHODS: Preterm rabbits delivered at 29/32 days (~26-28 weeks human) gestation received 0, 5, 8, 12, 15 cm H2O of CPAP or variable CPAP of 15 to 5 or 15 to 8 cm H2O (decreasing ~2 cm H2O/min) for up to 10 min after birth. RESULTS: FRC was lower in the 0 (6.8 (1.0-11.2) mL/kg) and 5 (10.1 (1.1-16.8) mL/kg) compared to the 15 (18.8 (10.9-22.4) mL/kg) cm H2O groups (p = 0.003). Fewer kittens achieved FRC > 15 mL/kg in the 0 (20%), compared to 8 (36%), 12 (60%) and 15 (73%) cm H2O groups (p = 0.008). While breathing rates were not different (p = 0.096), apnoea tended to occur more often with CPAP < 8 cm H2O (p = 0.185). CPAP belly and lung bulging rates were similar whereas pneumothoraces were rare. Lowering CPAP from 15 to 5, but not 15 to 8 cm H2O, decreased FRC and breathing rates. CONCLUSION: In all, 15 cm H2O of CPAP improved lung aeration and reduced apnoea, but did not increase the risk of lung over-expansion, pneumothorax or CPAP belly immediately after birth. FRC and breathing rates were maintained when CPAP was decreased to 8 cm H2O. IMPACT: Although preterm infants are commonly supported with 4-8 cm H2O CPAP at birth, preclinical studies have shown that higher PEEP levels improve lung aeration. In this study, CPAP levels of 15 cm H2O improved lung aeration and reduced apnoea in preterm rabbit kittens immediately after birth. In all, 15 cm H2O CPAP did not increase the risk of lung over-expansion (indicated by bulging between the ribs), pneumothorax, or CPAP belly. These results can be used when designing future studies on CPAP strategies for preterm infants in the delivery room.

Why Do the Fetal Membranes Rupture Early after Fetoscopy? A Review.

Iatrogenic preterm premature rupture of the fetal membranes (iPPROM) remains the Achilles' heel of keyhole fetal surgery (fetoscopy) despite significant efforts in preclinical models to develop new therapies. This limited success is partially due to incomplete understanding why the fetal membranes rupture early after fetoscopy and notable differences in membrane physiology between humans and domestic species. In this review, we summarize aspects of fetoscopy that may contribute to iPPROM, the previous efforts to develop new therapies, and limitations of preclinical models commonly used in fetal membrane research.

Glucocorticoids influence versican and chondroitin sulphate proteoglycan levels in the fetal sheep lung.

BACKGROUND: Prenatal glucocorticoid treatment decreases alveolar tissue volumes and facilitates fetal lung maturation, however the mechanisms responsible are largely unknown. This study examines whether changes in versican levels or sulphation patterns of chondroitin sulphate (CS) side chains, are associated with glucocorticoid-induced reductions in peri-alveolar tissue volumes. METHODS: Lung tissue was collected from 1) fetal sheep at 131 ± 0.1 days gestational age (GA) infused with cortisol (122-131d GA) to prematurely induce a pre-parturient-like rise in circulating cortisol, 2) fetal sheep at 143d GA bilaterally adrenalectomised (ADX) at 112d GA to remove endogenous cortisol and 3) fetal sheep at 124d GA in which bolus doses (2 × 11.4 mg) of betamethasone were administered to the pregnant ewe. The level and distribution of versican and CS glycosaminoglycans (GAG) were determined using immunohistochemistry (IHC). Fluorophore assisted carbohydrate electrophoresis (FACE) was used to determine changes in CS sulphation patterns. RESULTS: Cortisol infusion significantly decreased chondrotin-6-sulphate levels (C-6-S) to 16.4 ± 0.7 AU, compared with saline-infused fetuses (18.9 ± 0.7 AU: p = 0.04) but did not significantly alter the level of versican or chondroitin-4-sulphate (C-4-S). ADX significantly increased the level of C-4-S (28.2 ± 2.2 AU), compared with sham-operated fetuses (17.8 ± 2.0 AU; p = 0.006) without altering versican or C-6-S levels. Betamethasone significantly decreased versican, C-4-S and C-6-S in the fetal sheep lung (19.2 ± 0.9 AU, 24.9 ± 1.4 AU and 23.2 ± 1.0 AU, respectively), compared with saline-exposed fetuses (24.3 ± 0.4 AU, p = 0.0004; 33.3±0.6 AU, p = 0.0003; 29.8±1.3 AU, 0.03, respectively). CONCLUSIONS: These results indicate that glucocorticoids alter versican levels and CS side chain microstructure in alveolar lung tissue. Betamethasone appears to have a greater impact on versican and CS side chains than cortisol.

Differential short-term regional effects of early high dose erythropoietin on white matter in preterm lambs after mechanical ventilation.

Inadvertently injurious ventilation of preterm neonates in the delivery room can cause cerebral white matter (WM) inflammation and injury. We investigated the impact of an early high dose of recombinant human erythropoietin (EPO) on ventilation-induced WM changes in preterm lambs. Injurious ventilation, targeting a V(T) of 15 ml kg(-1) with no positive end-expiratory pressure, was initiated for 15 min in preterm lambs (0.85 gestation). Conventional ventilation was continued for a further 105 min. Lambs received either 5000 IU kg(-1) of EPO (EPREX®; Vent+EPO; n = 6) or vehicle (Vent; n = 8) via an umbilical vein at 4 ± 2 min. Markers of WM injury and inflammation were assessed using quantitative real-time PCR (qPCR) and immunohistochemistry and compared to a group of unventilated controls (UVC; n = 4). In Vent+EPO lambs compared to Vent lambs: (i) interleukin (IL)-1ß and IL-6 mRNA levels in the periventricular WM and IL-8 mRNA levels in the subcortical WM were higher (P < 0.05 for all); (ii) the density of microglia within the aggregations was not different in the periventricular WM and was lower in the subcortical WM (P = 0.001); (iii) the density of astrocytes was lower in the subcortical WM (P = 0.002); (iv) occludin and claudin-1 mRNA levels were higher in the periventricular WM (P < 0.02 for all) and (vi) the number of blood vessels with protein extravasation was lower (P < 0.05). Recombinant human EPO had variable regional effects within the WM when administered during injurious ventilation. The adverse short-term outcomes discourage the use of early high dose EPO administration in preterm ventilated babies.

Human Amnion Epithelial Cells Modulate Ventilation-Induced White Matter Pathology in Preterm Lambs.

BACKGROUND: Preterm infants can be inadvertently exposed to high tidal volumes (VT) during resuscitation in the delivery room due to limitations of available equipment. High VT ventilation of preterm lambs produces cerebral white matter (WM) pathology similar to that observed in preterm infants who develop cerebral palsy. We hypothesized that human amnion epithelial cells (hAECs), which have anti-inflammatory and regenerative properties, would reduce ventilation-induced WM pathology in neonatal late preterm lamb brains. METHODS: Two groups of lambs (0.85 gestation) were used, as follows: (1) ventilated lambs (Vent; n = 8) were ventilated using a protocol that induces injury (VT targeting 15 ml/kg for 15 min, with no positive end-expiratory pressure) and were then maintained for another 105 min, and (2) ventilated + hAECs lambs (Vent+hAECs; n = 7) were similarly ventilated but received intravenous and intratracheal administration of 9 × 10(7) hAECs (18 × 10(7) hAECs total) at birth. Oxygenation and ventilation parameters were monitored in real time; cerebral oxygenation was measured using near-infrared spectroscopy. qPCR (quantitative real-time PCR) and immunohistochemistry were used to assess inflammation, vascular leakage and astrogliosis in both the periventricular and subcortical WM of the frontal and parietal lobes. An unventilated control group (UVC; n = 5) was also used for qPCR analysis of gene expression. Two-way repeated measures ANOVA was used to compare physiological data. Student's t test and one-way ANOVA were used for immunohistological and qPCR data comparisons, respectively. RESULTS: Respiratory parameters were not different between groups. Interleukin (IL)-6 mRNA levels in subcortical WM were lower in the Vent+hAECs group than the Vent group (p = 0.028). IL-1ß and IL-6 mRNA levels in periventricular WM were higher in the Vent+hAECs group than the Vent group (p = 0.007 and p = 0.001, respectively). The density of Iba-1-positive microglia was lower in the subcortical WM of the parietal lobes (p = 0.010) in the Vent+hAECs group but not in the periventricular WM. The number of vessels in the WM of the parietal lobe exhibiting protein extravasation was lower (p = 0.046) in the Vent+hAECs group. Claudin-1 mRNA levels were higher in the periventricular WM (p = 0.005). The density of GFAP-positive astrocytes was not different between groups. CONCLUSIONS: Administration of hAECs at the time of birth alters the effects of injurious ventilation on the preterm neonatal brain. Further studies are required to understand the regional differences in the effects of hAECs on ventilation-induced WM pathology and their net effect on the developing brain.

Endotracheal epinephrine at standard versus high dose for resuscitation of asystolic newborn lambs.

INTRODUCTION: Endotracheal (ET) epinephrine administration is an option during neonatal resuscitation, if the preferred intravenous (IV) route is unavailable. OBJECTIVES: We assessed whether endotracheal epinephrine achieved return of spontaneous circulation (ROSC), and maintained physiological stability after ROSC, at standard and higher dose, in severely asphyxiated newborn lambs. METHODS: Near-term fetal lambs were asphyxiated until asystole. Resuscitation was commenced with ventilation and chest compressions. Lambs were randomly allocated to: IV Saline placebo (5 ml/kg), IV Epinephrine (20 micrograms/kg), Standard-dose ET Epinephrine (100 micrograms/kg), and High-dose ET Epinephrine (1 mg/kg). After three allocated treatment doses, rescue IV Epinephrine was administered if ROSC had not occurred. Lambs achieving ROSC were monitored for 60 minutes. Brain histology was assessed for microbleeds. RESULTS: ROSC in response to allocated treatment (without rescue IV Epinephrine) occurred in 1/6 Saline, 9/9 IV Epinephrine, 0/9 Standard-dose ET Epinephrine, and 7/9 High-dose ET Epinephrine lambs respectively. Blood pressure during CPR increased after treatment with IV Epinephrine and High-dose ET Epinephrine, but not Saline or Standard-dose ET Epinephrine. After ROSC, both ET Epinephrine groups had lower pH, higher lactate, and higher blood pressure than the IV Epinephrine group. Cortex microbleeds were more frequent in High-dose ET Epinephrine lambs (8/8 lambs examined, versus 3/8 in IV Epinephrine lambs). CONCLUSIONS: The currently recommended dose of ET Epinephrine was ineffective in achieving ROSC. Without convincing clinical or preclinical evidence of efficacy, use of ET Epinephrine at this dose may not be appropriate. High-dose ET Epinephrine requires further evaluation before clinical translation.

Assessing the influence of abdominal compression on time to return of circulation during resuscitation of asphyxiated newborn lambs: a randomised preclinical study.

OBJECTIVE: During neonatal resuscitation, the return of spontaneous circulation (ROSC) can be achieved using epinephrine which optimises coronary perfusion by increasing diastolic pressure. Abdominal compression (AC) applied during resuscitation could potentially increase diastolic pressure and therefore help achieve ROSC. We assessed the use of AC during resuscitation of asystolic newborn lambs, with and without epinephrine. METHODS: Near-term fetal lambs were instrumented for physiological monitoring and after delivery, asphyxiated until asystole. Resuscitation was commenced with ventilation followed by chest compressions. Lambs were randomly allocated to: intravenous epinephrine (20 µg/kg, n=9), intravenous epinephrine+continuous AC (n=8), intravenous saline placebo (5 mL/kg, n=6) and intravenous saline+AC (n=9). After three allocated treatment doses, rescue intravenous epinephrine was administered if ROSC had not occurred. Time to achieve ROSC was the primary outcome. Lambs achieving ROSC were ventilated and monitored for 60 min before euthanasia. Brain histology was assessed for micro-haemorrhage. RESULTS: Use of AC did not influence mean time to achieve ROSC (epinephrine lambs 177 s vs epinephrine+AC lambs 179 s, saline lambs 602 s vs saline+AC lambs 585 s) or rate of ROSC (nine of nine lambs, eight of eight lambs, one of six lambs and two of eight lambs, respectively). Application of AC was associated with higher diastolic blood pressure (mean value >10 mm Hg), mean and systolic blood pressure and carotid blood flow during resuscitation. Cortex and deep grey matter micro-haemorrhage was more frequent in AC lambs. CONCLUSION: Use of AC during resuscitation increased diastolic blood pressure, but did not impact time to ROSC.

Influence of the chest wall on respiratory function at birth in near-term lambs.

Airway liquid is cleared into lung tissue after birth, which becomes edematous and forces the chest wall to expand to accommodate both the cleared liquid and incoming air. This study investigated how changing chest wall mechanics affects respiratory function after birth in near-term lambs with different airway liquid volumes. Surgically instrumented near-term lambs (139 ± 2 days) were randomized into Control (n = 7) or Elevated Liquid (EL; n = 6) groups. Control lambs had lung liquid drained to simulate expected volumes following vaginal delivery. EL lambs had airway liquid drained and 30 mL/kg liquid returned to simulate expected airway liquid volumes after elective cesarean section. Lambs were delivered, transferred to a Perspex box, and ventilated (30 min). Pressure in the box was adjusted to apply positive (7-8 cmH2O above atmospheric pressure) or negative (7-8 cmH2O below atmospheric pressure) pressures for 30 min before pressures were reversed. External negative pressures expanded the chest wall, reduced chest wall compliance (CCW) and increased lung compliance (CL) in Control and EL lambs. External positive pressures compressed the chest wall, increased CCW and reduced CL in Control and EL lambs. External negative pressure improved pulmonary oxygen exchange, reducing the alveolar-arterial difference in oxygen (AaDO2) by 69 mmHg (95% CI [13, 125]; P = 0.016) in Control lambs and by 300 mmHg (95% CI [233, 367]; P < 0.001) in EL lambs. In contrast, external positive pressures impaired pulmonary gas exchange, increasing the AaDO2 by 179 mmHg (95% CI [73, 285]; P = 0.002) in Control and by 215 mmHg (95% CI [89, 343]; P < 0.001) in EL lambs. The application of external thoracic pressures influences respiratory function after birth.NEW & NOTEWORTHY This study investigated how changes in chest wall mechanics influence respiratory function after birth. Our data indicate that the application of continuous external subatmospheric pressure greatly improves respiratory function in near-term lambs with respiratory distress, whereas external positive pressures impair respiratory function. Our findings indicate that, during neonatal resuscitation at birth, the forces applied to the chest wall should not be ignored as they can have a major impact on neonatal respiratory function.

Evaluating the efficacy of endotracheal and intranasal epinephrine administration in severely asphyxic bradycardic newborn lambs: a randomised preclinical study.

OBJECTIVE: Intravenous epinephrine administration is preferred during neonatal resuscitation, but may not always be rapidly administered due to lack of equipment or trained staff. We aimed to compare the time to return of spontaneous circulation (ROSC) and post-ROSC haemodynamics between intravenous, endotracheal (ET) and intranasal (IN) epinephrine in severely asphyxic, bradycardic newborn lambs. METHODS: After instrumentation, severe asphyxia (heart rate <60 bpm, blood pressure ~10 mm Hg) was induced by clamping the cord in near-term lambs. Resuscitation was initiated with ventilation followed by chest compressions. Lambs were randomly assigned to receive intravenous (0.02 mg/kg), ET (0.1 mg/kg) or IN (0.1 mg/kg) epinephrine. If ROSC was not achieved after three allocated treatment doses, rescue intravenous epinephrine was administered. After ROSC, lambs were ventilated for 60 min. RESULTS: ROSC in response to allocated treatment occurred in 8/8 (100%) intravenous lambs, 4/7 (57%) ET lambs and 5/7 (71%) IN lambs. Mean (SD) time to ROSC was 173 (32) seconds in the intravenous group, 360 (211) seconds in the ET group and 401 (175) seconds in the IN group (p<0.05 intravenous vs IN). Blood pressure and cerebral oxygen delivery were highest in the intravenous group immediately post-ROSC (p<0.05), whereas the ET group sustained the highest blood pressure over the 60-min observation (p<0.05). CONCLUSION: Our study supports neonatal resuscitation guidelines, highlighting intravenous administration as the most effective route for epinephrine. ET and IN epinephrine should only be considered when intravenous access is delayed or not feasible.

Multicentre, randomised controlled trial of physiological-based cord clamping versus immediate cord clamping in infants with a congenital diaphragmatic hernia (PinC): statistical analysis plan.

BACKGROUND: Infants born with congenital diaphragmatic hernia (CDH) are at high risk of respiratory insufficiency and pulmonary hypertension. Routine practice includes immediate clamping of the umbilical cord and endotracheal intubation. Experimental animal studies suggest that clamping the umbilical cord guided by physiological changes and after the lungs have been aerated, named physiological-based cord clamping (PBCC), could enhance the fetal-to-neonatal transition in CDH. We describe the statistical analysis plan for the clinical trial evaluating the effects of PBCC versus immediate cord clamping on pulmonary hypertension in infants with CDH (PinC trial). DESIGN: The PinC trial is a multicentre, randomised controlled trial in infants with isolated left-sided CDH, born ≥ 35.0 weeks of gestation. The primary outcome is the incidence of pulmonary hypertension in the first 24 h after birth. Maternal outcomes include estimated maternal blood loss. Neonatal secondary outcomes include mortality before discharge, extracorporeal membrane oxygenation therapy, and number of days of mechanical ventilation. Infants are 1:1 randomised to either PBCC or immediate cord clamping using variable random permutated block sizes (4-8), stratified by treatment centre and estimated severity of pulmonary hypoplasia (i.e. mild/moderate/severe). At least 140 infants are needed to detect a relative reduction in pulmonary hypertension by one third, with 80% power and 0.05 significance level. A chi-square test will be used to evaluate the hypothesis that PBCC decreases the occurrence of pulmonary hypertension. This plan is written and submitted without knowledge of the collected data. The trial has been ethically approved. TRIAL REGISTRATION: ClinicalTrials.gov NCT04373902 (registered April 2020).

Delaying cord clamping until ventilation onset improves cardiovascular function at birth in preterm lambs.

Delayed cord clamping improves circulatory stability in preterm infants at birth, but the underlying physiology is unclear. We investigated the effects of umbilical cord clamping, before and after ventilation onset, on cardiovascular function at birth. Prenatal surgery was performed on lambs (123 days) to implant catheters into the pulmonary and carotid arteries and probes to measure pulmonary (PBF), carotid (CaBF) and ductus arteriosus blood flows. Lambs were delivered at 126 ± 1 days and: (1) the umbilical cord was clamped at delivery and ventilation was delayed for about 2 min (Clamp 1st; n = 6), and (2) umbilical cord clamping was delayed for 3-4 min, until after ventilation was established (Vent 1st; n = 6). All lambs were subsequently ventilated for 30 min. In Clamp 1st lambs, cord clamping rapidly (within four heartbeats), but transiently, increased pulmonary and carotid arterial pressures (by ∼30%) and CaBF (from 30.2 ± 5.6 to 40.1 ± 4.6 ml min(-1) kg(-1)), which then decreased again within 30-60 s. Following ventilation onset, these parameters rapidly increased again. In Clamp 1st lambs, cord clamping reduced heart rate (by ∼40%) and right ventricular output (RVO; from 114.6 ± 14.4 to 38.8 ± 9.7 ml min(-1) kg(-1)), which were restored by ventilation. In Vent 1st lambs, cord clamping reduced RVO from 153.5 ± 3.8 to 119.2 ± 10.6 ml min(-1) kg(-1), did not affect heart rates and resulted in stable blood flows and pressures during transition. Delaying cord clamping for 3-4 min until after ventilation is established improves cardiovascular function by increasing pulmonary blood flow before the cord is clamped. As a result, cardiac output remains stable, leading to a smoother cardiovascular transition throughout the early newborn period.

Lung aeration reduces blood pressure surges caused by umbilical cord milking in preterm lambs.

Background: Umbilical cord milking (UCM) at birth causes surges in arterial blood pressure and blood flow to the brain, which may explain the high risk of intraventricular haemorrhage (IVH) in extremely preterm infants receiving UCM. This high risk of IVH has not been reported in older infants. Objective: We hypothesized that lung aeration before UCM, reduces the surge in blood pressure and blood flow induced by UCM. Methods: At 126 days' gestation, fetal lambs (N = 8) were exteriorised, intubated and instrumented to measure umbilical, pulmonary, cerebral blood flows, and arterial pressures. Prior to ventilation onset, the umbilical cord was briefly (2-3 s) occluded (8 times), which was followed by 8 consecutive UCMs when all physiological parameters had returned to baseline. Lambs were then ventilated. After diastolic pulmonary blood flow markedly increased in response to ventilation, the lambs received a further 8 consecutive UCMs. Ovine umbilical cord is shorter than the human umbilical cord, with ∼10 cm available for UCMs. Therefore, 8 UCMs/occlusions were done to match the volume reported in the human studies. Umbilical cord clamping occurred after the final milk. Results: Both umbilical cord occlusions and UCM caused significant increases in carotid arterial blood flow and pressure. However, the increases in systolic and mean arterial blood pressure (10 ± 3 mmHg vs. 3 ± 2 mmHg, p = 0.01 and 10 ± 4 mmHg vs. 6 ± 2 mmHg, p = 0.048, respectively) and carotid artery blood flow (17 ± 6 ml/min vs. 10 ± 6 ml/min, p = 0.02) were significantly greater when UCM occurred before ventilation onset compared with UCM after ventilation. Conclusions: UCM after ventilation onset significantly reduces the increases in carotid blood flow and blood pressure caused by UCM.

Effect of prenatal diaphragmatic hernia on pulmonary arterial morphology.

Congenital diaphragmatic hernia (CDH) is a major cause of severe lung hypoplasia and pulmonary hypertension in the newborn. While the pulmonary hypertension is thought to result from abnormal vascular development and arterial vasoreactivity, the anatomical changes in vascular development are unclear. We have examined the 3D structure of the pulmonary arterial tree in rabbits with a surgically induced diaphragmatic hernia (DH). Fetal rabbits (n = 6) had a left-sided DH created at gestational day 23 (GD23), delivered at GD30, and briefly ventilated; sham-operated litter mates (n = 5) acted as controls. At postmortem the pulmonary arteries were filled with a radio-opaque resin before the lungs were scanned using computed tomography (CT). The 3D reconstructed images were analyzed based on vascular branching hierarchy using the software Avizo 2020.2. DH significantly reduced median number of arteries (2,579 (8440) versus 576 (442), p = .017), artery numbers per arterial generation, mean total arterial volume (43.5 ± 8.4 vs. 19.9 ± 3.1 µl, p = .020) and mean total arterial cross-sectional area (82.5 ± 2.3 vs. 28.2 ± 6.2 mm2 , p =.036). Mean arterial radius was increased in DH kittens between the eighth and sixth branching generation and mean arterial length between the sixth and 28th branching generation. A DH in kittens resulted in threefold reduction in pulmonary arterial cross-sectional area, primarily due to reduced arterial branching. Thus, the reduction in arterial cross-sectional area could be a major contributor to pulmonary hypertension infants with CDH.

The effects of intrauterine growth restriction and antenatal glucocorticoids on ovine fetal lung development.

INTRODUCTION: Intrauterine growth restriction (IUGR) is associated with high rates of neonatal morbidity. IUGR babies are often born preterm and are, therefore, exposed to antenatal glucocorticoids. Antenatal glucocorticoids significantly improve overall survival rates of preterm infants, but there is a paucity of information about their effects on IUGR Infants. METHODS: We induced IUGR in sheep by single umbilical artery ligation (SUAL), or sham in control fetuses. To half the ewes, we administered betamethasone (BM) on d 5 (BM1) and 6 (BM2) following surgery, and collected fetal lung tissue on d 7. RESULTS: SUAL alone was associated with higher circulating fetal cortisol levels (2.8 ± 0.4 vs. 1.0 ± 0.4, P = 0.001) as compared with controls but not with changes in lung morphology or surfactant protein (SP) gene expression. BM was associated with a significant reduction in lung tissue density (P = 0.048). There were no significant differences between groups in lung DNA concentration or septal crest density. SP-A, SP-B, and SP-C gene expressions were significantly increased in control and SUAL fetuses that were administered BM. DISCUSSION: These results show that in SUAL fetuses, maternal BM is associated with acceleration of fetal lung structure, as occurs in normally grown fetuses, and that BM induces SP production, an effect not observed in SUAL-induced IUGR fetuses alone.

Effects of caffeine on renal and pulmonary function in preterm newborn lambs.

INTRODUCTION: Caffeine administration is associated with a reduction in bronchopulmonary dysplasia, assisted ventilation, patent ductus arteriosus (DA) and cerebral palsy in preterm infants, but the mechanisms are unknown. Our aim was to determine the effects of acute caffeine administration on renal and pulmonary function in preterm lambs. METHODS: Lambs were delivered by caesarean section at ~126 days of gestation and ventilated with a tidal volume of 5 ml/kg, 60 breaths/min and 5 cmH(2)O positive end-expiratory pressure. After 30 minutes, lambs received 40 mg/kg caffeine i.v (n=7) or saline (controls; n=6) over 30 minutes and were ventilated for 2 hours. RESULTS: Arterial caffeine concentrations reached 35.9 ± 7.8 mg/l. Urine output was significantly higher after caffeine treatment than in controls (5.86 ± 1.95 vs 0.76 ± 0.94 ml/kg, area under curve p=0.041). Mean heart rate was significantly higher after caffeine treatment than in controls (211 ± 8 vs 169 ± 15 beats per minute, p<0.05) and remained higher for the experimental period. DISCUSSION: Caffeine did not affect pulmonary artery or DA blood flows or other renal, respiratory or cardiovascular parameters examined. Neonatal caffeine administration increased heart rate and urine output but had little effect on pulmonary function in ventilated preterm lambs.

Comparison of intraosseous and intravenous epinephrine administration during resuscitation of asphyxiated newborn lambs.

OBJECTIVE: Intraosseous access is recommended as a reasonable alternative for vascular access during newborn resuscitation if umbilical access is unavailable, but there are minimal reported data in newborns. We compared intraosseous with intravenous epinephrine administration during resuscitation of severely asphyxiated lambs at birth. METHODS: Near-term lambs (139 days' gestation) were instrumented antenatally for measurement of carotid and pulmonary blood flow and systemic blood pressure. Intrapartum asphyxia was induced by umbilical cord clamping until asystole. Resuscitation commenced with positive pressure ventilation followed by chest compressions and the lambs received either intraosseous or central intravenous epinephrine (10 µg/kg); epinephrine administration was repeated every 3 min until return of spontaneous circulation (ROSC). The lambs were maintained for 30 min after ROSC. Plasma epinephrine levels were measured before cord clamping, at end asphyxia, and at 3 and 15 min post-ROSC. RESULTS: ROSC was successful in 7 of 9 intraosseous epinephrine lambs and in 10 of 12 intravenous epinephrine lambs. The time and number of epinephrine doses required to achieve ROSC were similar between the groups, as were the achieved plasma epinephrine levels. Lambs in both groups displayed a similar marked overshoot in systemic blood pressure and carotid blood flow after ROSC. Blood gas parameters improved more quickly in the intraosseous lambs in the first 3 min, but were otherwise similar over the 30 min after ROSC. CONCLUSIONS: Intraosseous epinephrine administration results in similar outcomes to intravenous epinephrine during resuscitation of asphyxiated newborn lambs. These findings support the inclusion of intraosseous access as a route for epinephrine administration in current guidelines.