Effect of lung hypoplasia on birth-related changes in the pulmonary circulation in sheep

Increased airway liquid volumes at birth impairs cardiorespiratory function in preterm and near-term lambs

Respiratory distress is relatively common in infants born at or near-term, particularly in infants delivered following elective cesarean section. The pathophysiology underlying respiratory distress at term has largely been explained by a failure to clear airway liquid, but recent physiological evidence has indicated that it results from elevated airway liquid at the onset of air-breathing. We have investigated the effect of elevated airway liquid volumes at birth on cardiorespiratory function in preterm and near-term lambs. Preterm (130 ± 0 days gestation, term ~147 days gestation; n=13) and near-term (139 ± 1 days gestation; n=13) lambs were instrumented (to measure blood pressure, blood flow and blood gas status) and at delivery airway liquid volumes were adjusted to mimic levels expected following vaginal delivery (Controls; ~7mL/kg) or elective caesarean section with no labour (elevated liquid; EL; 37mL/kg). Lambs were delivered, mechanically ventilated and monitored for blood gas status, oxygenation, ventilator requirements, blood flows (carotid artery and pulmonary artery) and blood pressure during the first few hours of life. Preterm and near-term EL lambs had poorer gas exchange and required greater ventilatory support to maintain adequate oxygenation. Pulmonary blood flow was reduced and carotid artery blood flow, mean arterial blood pressure and heart rate were reduced in EL near-term but not preterm lambs. These data provide further evidence that greater airway liquid volumes at birth adversely effects newborn cardiorespiratory function, with the effects being greater in near-term newborns.

Non-invasive carbon dioxide monitoring in neonates: methods, benefits, and pitfalls

Wide fluctuations in partial pressure of carbon dioxide (PaCO2) can potentially be associated with neurological and lung injury in neonates. Blood gas measurement is the gold standard for assessing gas exchange but is intermittent, invasive, and contributes to iatrogenic blood loss. Non-invasive carbon dioxide (CO2) monitoring has become ubiquitous in anesthesia and critical care and is being increasingly used in neonates. Two common methods of non-invasive CO2 monitoring are end-tidal and transcutaneous. A colorimetric CO2 detector (a modified end-tidal CO2 detector) is recommended by the International Liaison Committee on Resuscitation (ILCOR) and the American Academy of Pediatrics to confirm endotracheal tube placement. Continuous CO2 monitoring is helpful in trending PaCO2 in critically ill neonates on respiratory support and can potentially lead to early detection and minimization of fluctuations in PaCO2. This review includes a description of the various types of CO2 monitoring and their applications, benefits, and limitations in neonates.

Effect of lung hypoplasia on the cardiorespiratory transition in newborn lambs

Newborns with lung hypoplasia (LH) commonly have limited respiratory function and often require ventilatory assistance after birth. We aimed to characterize the cardiorespiratory transition and respiratory function in newborn lambs with LH. LH was induced by draining fetal lung liquid in utero [110-133 days (d), term = 147d, n = 6]. At ~133d gestation, LH and Control lambs (n = 6) were instrumented and ventilated for 3 h to monitor blood-gas status, oxygenation, ventilator requirements, and hemodynamics during the transition from fetal to newborn life. Lambs with LH had significantly reduced relative wet and dry lung weights indicating hypoplastic lungs compared with Control lambs. LH lambs experienced persistent hypercapnia and acidosis during the ventilation period, had lower lung compliance, and had higher alveolar-arterial differences in oxygen and oxygenation index compared with Control lambs. As a result, LH lambs required greater respiratory support and more supplemental oxygen. Following delivery, LH lambs experienced periods of significantly lower pulmonary artery blood flow and higher carotid artery blood flow in association with the lower oxygenation levels. The detrimental effects of LH can be attributed to a reduction in lung size and poorer gas exchange capabilities. This study has provided greater understanding of the effect of LH itself on the physiology underpinning the transition from fetal to newborn life. Advances in this area is the key to identifying improved or novel management strategies for babies with LH starting in the delivery room, to favorably alter the fetal-to-newborn transition toward improved outcomes and reduced lifelong morbidity.NEW & NOTEWORTHY Current clinical management of newborns with lung hypoplasia (LH) is largely based on expert opinion rather than scientific evidence. We have generated physiological evidence for detrimental effects of LH on hemodynamics and respiratory function in newborn lambs, which mimics the morbidity observed in LH newborns clinically. The unfavorable consequences of LH can be attributed to a reduction in lung size and poorer gas exchange capabilities.

Nitric Oxide in Pulmonary Hypoplasia: Results from the European iNO Registry

OBJECTIVES

The aim of this work was to describe treatment response and outcome data for preterm infants with pulmonary hypoplasia treated with inhaled nitric oxide (iNO). We hypothesised that an acute oxygenation response to iNO would be associated with survival.

DESIGN

A retrospective observational study design was used to identify cases of pulmonary hypoplasia in preterm infants <34 weeks' gestation reported to the European iNO Registry. Demographic and clinical data were collected including oxygenation and echocardiographic parameters. The primary outcome was acute oxygenation response defined as a reduction in fractional inspired oxygen of >0.15. Outcome data included chronic lung disease (CLD) and death.

RESULTS

Seventy-two infants with pulmonary hypoplasia were treated with iNO during a 10-year period (2007-2016). In total, 30/69 (43%) of the infants showed a significant improvement in oxygenation and were categorised as "responders." Thirty-one treated infants died, and 19 survivors developed CLD. Although there were no differences in demographics and baseline cardiorespiratory parameters between responders and non-responders, an acute response was significantly associated with survival. Neither pulmonary hypertension nor PPHN (persistent pulmonary hypertension of the newborn) physiology predicted the acute response to iNO or survival.

CONCLUSION

Although the acute oxygenation response to iNO therapy in pulmonary hypoplasia is comparable to other respiratory disorders in preterm infants, mortality in this group remains very high. An acute response is associated with survival and suggests that a short therapeutic trial of iNO therapy is warranted in this population. This study underscores the value of registries in evaluating therapies for rare neonatal disorders, although their limitations must be recognised.

Contemporary neonatal outcome following rupture of membranes prior to 25 weeks with prolonged oligohydramnios

BACKGROUND

Prolonged oligohydramnios following early preterm prelabour rupture of membranes (PPROM) is traditionally associated with high neonatal mortality and significant risk of pulmonary hypoplasia. However, recent evidence points to an apparent improvement in outcome.

AIMS

To document current neonatal outcomes following rupture of membranes prior to 25 weeks with severe persistent oligohydramnios and a latency to delivery of at least 14 days.

METHODS

A retrospective case note analysis over a 28-month period at Saint Luc University Hospital, Brussels.

RESULTS

From 23 pregnancies that were complicated by PPROM prior to 25 weeks, 15 infants were born after 24 weeks with a latency of more than 14 days and persistent oligohydramnios. Nine infants (60%) had severe respiratory failure and clinical signs compatible with pulmonary hypoplasia. Seven of these infants (78%) responded to high frequency ventilation and inhaled nitric oxide therapy with good clinical outcome but two died from severe respiratory failure. Five infants showed no clinical signs of pulmonary hypoplasia and responded to conventional neonatal management. One of these infants died at 77 days of age of necrotising enterocolitis. One infant was not resuscitated and died within minutes of birth, following prior discussion with the perinatal team and the parents. Survivors in this high-risk group (73%) had low morbidity at the time of discharge.

SUMMARY

The favourable neonatal survival and morbidity figures are in keeping with recent published evidence. This study confirms improved outcome even amongst the highest risk infants with documented persistent oligohydramnios.

The effect of fetal tracheal occlusion on lung tissue mechanics and tissue composition

Fetal tracheal occlusion (TO) is currently used to treat severe cases of congenital diaphragmatic hernia (DH). Clinical and experimental studies suggest an improved postnatal outcome, but lung tissue mechanics after TO have not been studied. We determined the effect of TO on mechanical impedance and lung tissue components in a rabbit model for DH. At 23 days of gestation (term = 31 days) either a sham thoracotomy or a diaphragmatic defect was induced. DH fetuses were randomly assigned to undergo 5 days later TO. Fetuses were delivered by term cesarean section to determine lung to body weight ratio (LBWR), dynamic lung mechanics and lung impedance. Airway resistance (R(aw)), elastance (H(L)), tissue damping (G(L)) and hysteresivity (G(L)/H(L)) were calculated from impedance data. Collagen I and III and elastin were quantified histologically. LBWR was significantly increased by TO compared to DH (P < 0.001) and resistance and compliance of the respiratory system (R(rs), C(rs)) were improved as well. TO resulted in a significant decrease of R(aw) comparable to observations in sham-fetuses, without effect on lung tissue mechanics H(L), G(L) and hysteresivity. This coincides with a significant decrease of collagen I, III and elastin in comparison to DH fetuses. In this first report on lung tissue mechanics in a rabbit model of DH, TO had a substantial effect on tissue morphology yet this was not mirrored in lung mechanics. We conclude that the effect of TO on lung mechanics without in utero reversal of occlusion, is dominated by airway remodeling.

Effects of antenatal corticosteroid treatment on pulmonary ventilation and circulation in neonatal lambs with hypoplastic lungs

Our aim was to determine whether antenatal corticosteroids improve perinatal adaptation of the pulmonary circulation in lambs with lung hypoplasia (LH). LH was induced in 12 ovine fetuses between 105 and 140 days gestation (term approximately 147 days); in 6 of these the ewe was given a single dose of betamethasone (11.4 mg im) 24 hr before delivery (LH + B). All lambs, including a control group (n = 6), were delivered at approximately 140 days and ventilated for 2 hr during which arterial pressures, pulmonary blood flow (PBF), and ventilating pressure and flow were recorded. During ventilation, respiratory system compliance was lower in both LH + B and LH groups than in controls. Pulmonary vascular resistance (PVR) was lower in LH + B lambs than in LH lambs and similar to controls; PBF was reduced in LH lambs but was restored to control levels by betamethasone. The mean density of small arteries of LH + B lambs was similar to that of LH lambs (P = 0.06) and lower than in controls; the thickness of the media of small pulmonary arteries from LH + B lambs was similar to that in LH lambs and thicker than in controls. VEGF mRNA levels were not different between groups. PDGF mRNA levels in LH + B lambs were higher than in LH lambs; a similar trend (P = 0.06) was seen for PECAM-1. SP-C mRNA levels were greater in both LH and LH + B lambs than in controls. Effects of betamethasone were greater on indices of pulmonary circulation than ventilation. We conclude that a single dose of maternal betamethasone 24 hr prior to birth has significant favorable effects on the postnatal adaptation of the pulmonary circulation in lambs with LH.