An update on the diagnosis and management of bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension

Optimizing management of chronic pulmonary hypertension in preterm infants: strategies for a complex population

PURPOSE OF REVIEW

Pulmonary hypertension (PH) is commonly observed in premature infants with bronchopulmonary dysplasia (BPD) and is associated with poor outcomes and increased mortality. This review explores the management of this intricate condition of the pulmonary vasculature, which exhibits heterogeneous effects and may involve both arterial and postcapillary components.

RECENT FINDINGS

Current management of BPD-PH should focus on optimizing ventilatory support, which involves treatment of underlying lung disease, transitioning to a chronic phase ventilation strategy and evaluation of the airway. Data on management is limited to observational studies. Diuretics are considered a part of the initial management, particularly in infants with right ventricular dilation. In many cases, pulmonary vasodilator therapy is required to induce pulmonary arterial vasodilation, reduce right ventricular strain, and prevent coronary ischemia and heart failure. Echocardiography plays a pivotal role in guiding treatment decisions and monitoring disease progression.

SUMMARY

BPD-PH confers a heightened risk of mortality and long-term cardio-respiratory adverse outcomes. Echocardiography has been advocated for screening, while catheterization allows for confirmation in select more complex cases. Successful management of BPD-PH requires a multidisciplinary approach, focusing on optimizing BPD treatment and addressing underlying pathologies.

Guidelines and Recommendations for Targeted Neonatal Echocardiography and Cardiac Point-of-Care Ultrasound in the Neonatal Intensive Care Unit: An Update from the American Society of Echocardiography

Targeted neonatal echocardiography (TNE) involves the use of comprehensive echocardiography to appraise cardiovascular physiology and neonatal hemodynamics to enhance diagnostic and therapeutic precision in the neonatal intensive care unit. Since the last publication of guidelines for TNE in 2011, the field has matured through the development of formalized neonatal hemodynamics fellowships, clinical programs, and the expansion of scientific knowledge to further enhance clinical care. The most common indications for TNE include adjudication of hemodynamic significance of a patent ductus arteriosus, evaluation of acute and chronic pulmonary hypertension, evaluation of right and left ventricular systolic and/or diastolic function, and screening for pericardial effusions and/or malpositioned central catheters. Neonatal cardiac point-of-care ultrasound (cPOCUS) is a limited cardiovascular evaluation which may include line tip evaluation, identification of pericardial effusion and differentiation of hypovolemia from severe impairment in myocardial contractility in the hemodynamically unstable neonate. This document is the product of an American Society of Echocardiography task force composed of representatives from neonatology-hemodynamics, pediatric cardiology, pediatric cardiac sonography, and neonatology-cPOCUS. This document provides (1) guidance on the purpose and rationale for both TNE and cPOCUS, (2) an overview of the components of a standard TNE and cPOCUS evaluation, (3) disease and/or clinical scenario-based indications for TNE, (4) training and competency-based evaluative requirements for both TNE and cPOCUS, and (5) components of quality assurance. The writing group would like to acknowledge the contributions of Dr. Regan Giesinger who sadly passed during the final revisions phase of these guidelines. Her contributions to the field of neonatal hemodynamics were immense.

Macrophage Polarizations in the Placenta and Lung are Associated with Bronchopulmonary Dysplasia

The intricate interplay between macrophage polarization and placenta vascular dysfunction has garnered increasing attention in the context of placental inflammatory diseases. This study delves into the complex relationship between macrophage polarization within the placenta and its potential impact on the development of vascular dysfunction and inflammatory conditions. The placenta, a crucial organ in fetal development, relies on a finely tuned balance of immune responses for proper functioning. Disruptions in this delicate equilibrium can lead to pathological conditions, including inflammatory diseases affecting the fetus and newborn infant. We explored the interconnectedness between placental macrophage polarization and its relevance to lung macrophages, particularly in the context of early life lung development. Bronchopulmonary dysplasia (BPD), the most common chronic lung disease of prematurity, has been associated with abnormal immune responses, and understanding the role of macrophages in this context is pivotal. The investigation aims to shed light on how alterations in placental macrophage polarization may contribute to lung macrophage behavior and, consequently, influence the development of BPD. By unraveling the intricate mechanisms linking macrophage polarization, placental dysfunction and BPD, this research seeks to provide insights that could pave the way for targeted therapeutic interventions. The findings may offer novel perspectives on preventing and managing placental and lung-related pathologies, ultimately contributing to improved maternal and neonatal health outcomes.

Bronchopulmonary dysplasia - associated pulmonary hypertension: An updated review

Bronchopulmonary dysplasia (BPD) is the leading cause of chronic lung disease in infants and the commonest complication of prematurity. Advances in respiratory and overall neonatal care have increased the survival of extremely low gestational age newborns, leading to the continued high incidence of BPD. Pulmonary hypertension (PH) represents the severe form of the pulmonary vascular disease associated with BPD, and affects almost one-third of infants with moderate to severe BPD. PH responds suboptimally to pulmonary vasodilators and increases morbidity and mortality in BPD infants. An up-to-date knowledge of the pathogenesis, pathophysiology, diagnosis, treatment, and outcomes of BPD-PH can be helpful to develop meaningful and novel strategies to improve the outcomes of infants with this disorder. Therefore, our multidisciplinary team has attempted to thoroughly review and summarize the latest advances in BPD-PH in preventing and managing this morbid lung disorder of preterm infants.

Recent Advances in Pediatric Pulmonary Hypertension: Implications for Diagnosis and Treatment

PURPOSE

Pediatric pulmonary hypertension (PH) is a condition characterized by elevated pulmonary arterial pressure, which has the potential to be life-limiting. The etiology of pediatric PH varies. When compared with adult cohorts, the etiology is often multifactorial, with contributions from prenatal, genetic, and developmental factors. This review aims to provide an up-to-date overview of the causes and classification of pediatric PH, describe current therapeutics in pediatric PH, and discuss upcoming and necessary research in pediatric PH.

METHODS

PubMed was searched for articles relating to pediatric pulmonary hypertension, with a particular focus on articles published within the past 10 years. Literature was reviewed for pertinent areas related to this topic.

FINDINGS

The evaluation and approach to pediatric PH are unique when compared with that of adults, in large part because of the different, often multifactorial, causes of the disease in children. Collaborative registry studies have found that the most common disease causes include developmental lung disease and subsets of pulmonary arterial hypertension, which includes genetic variants and PH associated with congenital heart disease. Treatment with PH-targeted therapies in pediatrics is often guided by extrapolation of adult data, small clinical studies in pediatrics, and/or expert consensus opinion. We review diagnostic considerations and treatment in some of the more common pediatric subpopulations of patients with PH, including developmental lung diseases, congenital heart disease, and trisomy 21.

IMPLICATIONS

The care of pediatric patients with PH requires consideration of unique pediatric-specific factors. With significant variability in disease etiology, ongoing efforts are needed to optimize treatment strategies based on disease phenotype and guide evidence-based practices.

Efficacy of Sildenafil in Infants with Bronchopulmonary Dysplasia-Associated Pulmonary Hypertension

Background: Pulmonary hypertension (PH) is a common comorbidity in infants with bronchopulmonary dysplasia (BPD). Sildenafil is a widely recognized therapy for PH, but its efficacy in infants with BPD is questionable. We propose to assess the efficacy of sildenafil in BPD-associated PH as evaluated based on transthoracic echocardiography (TTE) changes and clinical measures. Methods: Data were retrospectively and prospectively collected. Inclusion criteria were gestational age (GA) < 32 weeks, birth weight (BW) < 1500 g with severe BPD, diagnosis of PH via TTE on sildenafil treatment. PH was evaluated via TTE, which was performed monthly after 36 weeks post-menstrual age (PMA) as a standard of care, and re-reviewed by a single pediatric cardiologist, who was blind to the initial reading. Results: In total, 19 patients were enrolled in the study, having a median GA of 24 3/7 weeks (IQR 23 5/7-25 5/7) and a median BW of 598 g (IQR 572-735). Sildenafil treatment was started at a median PMA of 40.4 weeks. The median respiratory severity score (RSS) at 28 d was 6.5, RSS and FiO2 showed improvement about 12 weeks after starting sildenafil treatment. Conclusions: Improvement in PH was noted via TTE, and patients had improvement in their RSS and FiO2 after prolonged therapy. However, TTE improvements did not correlate with clinical improvements.

Patent ductus arteriosus and the risk of bronchopulmonary dysplasia-associated pulmonary hypertension

BACKGROUND

The aim of the study was to determine whether prolonged exposure to a moderate/large patent ductus arteriosus left-to-right shunt (PDA) increases the risk of late (beyond 36 weeks) pulmonary hypertension (BPD-PH) and pulmonary vascular disease (BPD-PVD) during the neonatal hospitalization in preterm infants (<28 weeks' gestation) with bronchopulmonary dysplasia (BPD).

METHODS

All infants requiring respiratory support ≥36 weeks had systematic echocardiographic evaluations for BPD-PH at planned intervals. Infants were classified as having either flow-associated BPD-PH (BPD-flow-PH) or BPD-PVD.

RESULTS

256 infants survived ≥36 weeks: 105 had NO BPD (were off respiratory support by 36 weeks); 151 had BPD. 22/151 had BPD-PH (12/22 had BPD-flow-PH from a PDA that persisted beyond 36 weeks; 10/22 had BPD-PVD). Moderate/large PDA shunts that persisted beyond 36 weeks were significantly associated with an increased incidence of BPD-PH due to BPD-flow-PH. We found no association between the duration of PDA exposure and the incidence of BPD-PVD.

CONCLUSIONS

Moderate/large PDA shunts increase the risk of flow-associated BPD-PH when present beyond 36 weeks. Although term infants with PDA-congenital heart disease can develop pulmonary vascular remodeling and PVD after months of PDA exposure, we found no echocardiographic evidence in preterm infants that prolonged PDA exposure increases the incidence of BPD-PVD during the neonatal hospitalization.

IMPACT

In our study, preterm infants (<28 weeks' gestation) with bronchopulmonary dysplasia (BPD) had a 15% incidence of pulmonary hypertension (PH) beyond 36 weeks' postmenstrual age as a comorbidity. Moderate/large patent ductus arteriosus (PDA) shunts increased the risk of flow-associated PH when present beyond 36 weeks. Although months of prolonged PDA exposure can cause pulmonary vascular remodeling and pulmonary vascular disease (PVD) in term infants with PDA-congenital heart disease, we found no echocardiographic evidence for an association between the duration of PDA exposure and the incidence of late PVD during the neonatal hospitalization in preterm infants with BPD.

A multidisciplinary approach to severe bronchopulmonary dysplasia is associated with resolution of pulmonary hypertension

Objective

To describe our multidisciplinary bronchopulmonary dysplasia (BPD) consult team's systematic approach to BPD associated pulmonary hypertension (PH), to report our center outcomes, and to evaluate clinical associations with outcomes.

Study design

Retrospective cohort of 60 patients with BPD-PH who were referred to the Seattle Children's Hospital BPD team from 2018 to 2020. Patients with critical congenital heart disease were excluded. Demographics, comorbidities, treatments, closure of hemodynamically relevant intracardiac shunts, and clinical outcomes including time to BPD-PH resolution were reviewed.

Results

Median gestational age of the 60 patients was 25 weeks (IQR: 24-26). 20% were small for gestational age (SGA), 65% were male, and 25% received a tracheostomy. With aggressive cardiopulmonary management including respiratory support optimization, patent ductus arteriosus (PDA) and atrial septal defect (ASD) closure (40% PDA, 5% ASD, 3% both), and limited use of pulmonary vasodilators (8%), all infants demonstrated resolution of PH during the follow-up period, including three (5%) who later died from non-BPD-PH morbidities. Neither SGA status nor the timing of PH diagnosis (<36 vs. ≥36 weeks PMA) impacted the time to BPD-PH resolution in our cohort [median 72 days (IQR 30.5-166.5)].

Conclusion

Our multidisciplinary, systematic approach to BPD-PH management was associated with complete resolution of PH with lower mortality despite less sildenafil use than reported in comparable cohorts. Unique features of our approach included aggressive PDA and ASD device closure and rare initiation of sildenafil only after lack of BPD-PH improvement with respiratory support optimization and diagnostic confirmation by cardiac catheterization.

Tracheostomy in the extremely premature neonate - Long term outcomes in a multi-institutional study

OBJECTIVES

To describe the long-term outcomes related to breathing, feeding, and neurocognitive development in extremely premature infants requiring tracheostomy.

STUDY DESIGN

Pooled cross-sectional survey.

SETTING

Multi-institutional academic children's hospitals.

METHODS

Extremely premature infants who underwent tracheostomy between January 1, 2012, and December 31, 2019, at four academic hospitals were identified from an existing database. Information was gathered from responses to a questionnaire by caregivers regarding airway status, feeding, and neurodevelopment 2-9 years after tracheostomy.

RESULTS

Data was available for 89/91 children (96.8%). The mean gestational age was 25.5 weeks (95% CI 25.2-25.7) and mean birth weight was 0.71 kg (95% CI 0.67-0.75). Mean post gestational age at tracheostomy was 22.8 weeks (95% CI 19.0-26.6). At time of the survey, 18 (20.2%) were deceased. 29 (40.8%) maintained a tracheostomy, 18 (25.4%) were on ventilatory support, and 5 (7%) required 24-h supplemental oxygen. Forty-six (64.8%) maintained a gastrostomy tube, 25 (35.2%) had oral dysphagia, and 24 (33.8%) required a modified diet. 51 (71.8%) had developmental delay, 45 (63.4%) were enrolled in school of whom 33 (73.3%) required special education services.

CONCLUSIONS

Tracheostomy in extremely premature neonates is associated with long term morbidity in the pulmonary, feeding, and neurocognitive domains. At time of the survey, about half are decannulated, with a majority weaned off ventilatory support indicating improvement in lung function with age. Feeding dysfunction is persistent, and a significant number will have some degree of neurocognitive dysfunction at school age. This information may help caregivers regarding expectations and plans for resource management.

Inhaled Nitric Oxide Therapy in the Post-Acute Phase in Extremely Preterm Infants: A Japanese Cohort Study

OBJECTIVE

To determine the trends in inhaled nitric oxide (iNO) utilization in the late phase of hospitalization in a large Japanese cohort of extremely preterm infants and evaluate its benefit on long-term outcomes.

STUDY DESIGN

This was a retrospective multicenter cohort study of 15 977 extremely preterm infants born at <28 weeks of gestational age between 2003 and 2016, in the Neonatal Research Network, Japan. Demographic characteristics, morbidity, and mortality were compared between extremely preterm infants with and without post-acute iNO therapy. Multivariable logistic analysis was performed to determine factors associated with post-acute iNO and its impact on neurodevelopmental outcomes at 3 years of age.

RESULTS

Post-acute iNO utilization rates increased from 0.3% in 2009 to 1.9% in 2016, even under strict insurance coverage rules starting in 2009. Gestational age (1-week increment; aOR 0.82, 95% CI 0.76-0.88), small for gestational age (1.47, 1.08-1.99), histologic chorioamnionitis (1.50, 1.21-1.86), 5-minute Apgar score <4 (1.51, 1.10-2.07), air leak (1.92, 1.30-2.83), and bubbly/cystic appearance on chest X-Ray (1.68, 1.37-2.06) were associated with post-acute iNO. Post-acute iNO was not associated with neurodevelopmental outcomes at 3 years of age.

CONCLUSIONS

The increasing post-acute iNO utilization rate among extremely preterm infants has been concurrent with improved survival rates of extremely preterm infants in Japan. Infants treated with post-acute iNO had more severe disease and complications than the comparison group, but there were no differences in neurodevelopmental outcome at 3 years. This suggests post-acute iNO may benefit extremely preterm infants.

Effects of less invasive surfactant administration versus intubation-surfactant-extubation on bronchopulmonary dysplasia in preterm infants with respiratory distress syndrome: a single-center, retrospective study from China

BACKGROUND

This study evaluated the effects of less invasive surfactant administration (LISA) and intubation-surfactant-extubation (InSurE) on bronchopulmonary dysplasia (BPD) in preterm infants with respiratory distress syndrome (RDS).

METHODS

Neonates with respiratory distress syndrome requiring surfactant, with gestational age < 32 weeks and birth weight < 1500 g admitted to our neonatal intensive care unit from January 2018 to December 2019, were retrospectively analyzed. LISA and InSurE were used independently. The incidence of BPD at 36 weeks postmenstrual age, pre-discharge mortality, and need for mechanical ventilation (MV) within 72 h of birth were compared between LISA and InSurE group. Secondary outcomes including necrotizing enterocolitis requiring surgery, retinopathy of prematurity ≥ stage 3, patent ductus arteriosus requiring medical therapy or surgery, and length of hospitalization were analyzed.

RESULTS

Among the 148 included neonates, there were 46 and 102 infants in LISA group and InSurE group, respectively. There were no significant differences in BPD incidence, the severity of BPD at 36 weeks postmenstrual age, and the rate of MV within the first 72 h after birth between the two groups (P > 0.05, respectively). The incidences of necrotizing enterocolitis requiring surgery, retinopathy of prematurity ≥ stage 3, patent ductus arteriosus requiring medical therapy or surgery, and length of hospitalization did not differ significantly between the two groups (P > 0.05, respectively).

CONCLUSIONS

For surfactant administration among preterm infants with respiratory distress syndrome, LISA did not decrease bronchopulmonary dysplasia and severity of BPD at 36 weeks postmenstrual age. The benefits of LISA would require further evaluations.

Safety and Feasibility of Riociguat Therapy for the Treatment of Chronic Pulmonary Arterial Hypertension in Infancy

The effects of riociguat, an oral-soluble guanylate-cyclase stimulator, were studied in 10 infants with chronic pulmonary arterial hypertension. Respiratory status (n = 8/10), right heart dilation (n = 7/10), function (n = 9/10), and chronic pulmonary arterial hypertension (n = 8/10) improved. Median decrement in systolic (12 [4, 14]), diastolic (14 [7, 20]), and mean arterial (14 [10, 17]) pressures were noted; no critical hypotension or hypoxemia occurred.

The role of bedside functional echocardiography in the assessment and management of pulmonary hypertension

Pulmonary hypertension is an emergency in neonatal intensive care units with high morbidity and mortality. Its timely assessment and management is crucial for intact survival. Over the last couple of decades, there have been significant advances in management and techniques, which have resulted in improved survival. The use of neonatologist-performed echocardiography (NPE) is now increasingly utilized on neonatal intensive care units to understand the pathophysiology of the disease and to direct the treatment to the underlying cause. Its use is now established not only in cases of congenital diaphragmatic hernia and in the newborn with refractory hypoxemia, but also in other conditions such as bronchopulmonary dysplasia and the premature infant with difficulty in oxygenation. The use of NPE, however, requires the availability of trained personnel, equipment, and a close working relationship with pediatric cardiology.

Mortality after 36 weeks postmenstrual age of extremely preterm infants in neonatal care: The impact of growth impairment and bronchopulmonary dysplasia

BACKGROUND

A small group of extremely preterm infants survive to 36 weeks postmenstrual age (PMA), but die before discharge from neonatal care.

AIMS

To investigate which epidemiological and clinical parameters were related to death after 36 weeks PMA in extremely preterm infants.

STUDY DESIGN

Retrospective whole-population study.

SUBJECTS

All infants born <28 weeks of gestation admitted to a neonatal unit in England between 2014 and 2018.

OUTCOME MEASURES

Mortality after 36 weeks PMA and before discharge from neonatal care. Bronchopulmonary dysplasia (BPD) defined as any respiratory support at 36 weeks PMA.

RESULTS

Death after 36 weeks PMA occurred in 156 of a total of 11.747 included infants (1.3 %) and at a median (IQR) age of 130 (93-164) days. A lower gestational age [Odds Ratio: 0.82, 95 % CI:0.72-0.94, adjusted p = 0.005], lower birth weight z-score [Odds Ratio: 0.45, 95 % CI:0.36-0.56, adjusted p < 0.001], greater absolute difference in weight z-score from birth to 36 weeks PMA [Odds Ratio: 0.46, 95 % CI:0.38-0.56, adjusted p < 0.001] were independently associated with death after 36 weeks PMA. A diagnosis of BPD [Odds Ratio: 4.57, 95 % CI:2.19-9.54, adjusted p < 0.001] and of necrotising enterocolitis requiring surgery [Odds Ratio: 2.81, 95 % CI:1.82-4.34, adjusted p < 0.001] were also independently associated with death after 36 weeks PMA.

CONCLUSIONS

Mortality of extremely preterm infants after 36 weeks postmenstrual age is associated with lower gestational age and more impaired growth. The diagnoses of bronchopulmonary dysplasia and necrotising enterocolitis were associated with a higher risk of death after 36 weeks postmenstrual age and before discharge from neonatal care.

Extracellular Signal-Regulated Kinase 1 Alone Is Dispensable for Hyperoxia-Mediated Alveolar and Pulmonary Vascular Simplification in Neonatal Mice

Bronchopulmonary dysplasia (BPD) is a morbid lung disease distinguished by lung alveolar and vascular simplification. Hyperoxia, an important BPD causative factor, increases extracellular signal-regulated kinases (ERK)-1/2 expression, whereas decreased lung endothelial cell ERK2 expression reduces angiogenesis and potentiates hyperoxia-mediated BPD in mice. However, ERK1′s role in experimental BPD is unclear. Thus, we hypothesized that hyperoxia-induced experimental BPD would be more severe in global ERK1-knockout (ERK1^-/-) mice than their wild-type (ERK1^+/+ mice) littermates. We determined the extent of lung development, ERK1/2 expression, inflammation, and oxidative stress in ERK1^-/- and ERK1^+/+ mice exposed to normoxia (FiO₂ 21%) or hyperoxia (FiO₂ 70%). We also quantified the extent of angiogenesis and hydrogen peroxide (H₂O₂) production in hyperoxia-exposed neonatal human pulmonary microvascular endothelial cells (HPMECs) with normal and decreased ERK1 signaling. Compared with ERK1^+/+ mice, ERK1^-/- mice displayed increased pulmonary ERK2 activation upon hyperoxia exposure. However, the extent of hyperoxia-induced inflammation, oxidative stress, and interrupted lung development was similar in ERK1^-/- and ERK1^+/+ mice. ERK1 knockdown in HPMECs increased ERK2 activation at baseline, but did not affect in vitro angiogenesis and hyperoxia-induced H₂O₂ production. Thus, we conclude ERK1 is dispensable for hyperoxia-induced experimental BPD due to compensatory ERK2 activation.

Ascorbic Acid and the Premature Infant

Little information exists about the plasma target nutritional needs of the >15 million premature infants <37 weeks gestation. Investigating ascorbic acid’s (AscA) role in infant health, our study details the relationship of infant characteristics and maternal health on infant plasma AscA level (pAscA) during postnatal development. Furthermore, we determined pAscA influence during the first week of life (EpAscA) with later infant morbidities. We hypothesize that pAscA is influenced by gestational organ immaturity, as well as maternal factors, with EpAscA associated with greater morbidity risk. We conducted a prospective longitudinal observational study of pAscA, demographics and hospital course detailed in infants ≤34 weeks. Sixty-three subjects were included, with >200 urine and plasma data points analyzed. Maternal smoking, exposure to magnesium sulfate (MgSO4) and advancing gestational and postnatal age were associated with lower pAscA. Non-white infants and those ≤30 weeks that developed bronchopulmonary dysplasia or retinopathy of prematurity had lower pAscA. Prenatal smoking, MgSO4, birth gestational age and race negatively influence pAscA. These results show prenatal and postnatal developmental factors influencing initial pAscA and metabolism, potentially setting the stage for organ health and risk for disease. Assessment of dietary targets may need adjustment in this population.

Moving Bronchopulmonary Dysplasia Research from the Bedside to the Bench

Although advances in the respiratory management of extremely preterm infants have led to improvements in survival, this progress has not yet extended to a reduction in the incidence of bronchopulmonary dysplasia (BPD). BPD is a complex multifactorial condition that primarily occurs due to disturbances in the regulation of normal pulmonary airspace and vascular development. Preterm birth and exposure to invasive mechanical ventilation also compromises large airway development, leading to significant morbidity and mortality. Although both predisposing and protective genetic and environmental factors have been frequently described in the clinical literature, these findings have had limited impact on the development of effective therapeutic strategies. This gap is likely because the molecular pathways that underlie these observations are yet not fully understood, limiting the ability of researchers to identify novel treatments that can preserve normal lung development and/or enhance cellular repair mechanisms. In this review article, we will outline various well-established clinical observations whilst identifying key knowledge gaps that need to be filled with carefully designed pre-clinical experiments. We will address these issues by discussing controversial topics in the pathophysiology, the pathology and the treatment of BPD, including an evaluation of existing animal models that have been used to answer important questions.

Molecular Mechanism of Caffeine in Preventing Bronchopulmonary Dysplasia in Premature Infants

Bronchopulmonary dysplasia (BPD) is a chronic respiratory complication commonly seen in premature infants. Following continuous advances in neonatal intensive care diagnosis and treatment technology, an increasing number of premature babies are being treated successfully. Despite these remarkable improvements, there has been no significant decline in the incidence of BPD; in fact, its incidence has increased as more extremely preterm infants survive. Therefore, in view of the impact of BPD on the physical and mental health of children and the increased familial and social burden on these children, early prevention of BPD is emphasized. In recent decades, the clinical application of caffeine in treating primary apnea in premature infants was shown not only to stimulate the respiratory center but also to confer obvious protection to the nervous and respiratory systems. Numerous clinical cross-sectional and longitudinal studies have shown that caffeine plays a significant role in the prevention and treatment of BPD, but there is a lack of overall understanding of its potential molecular mechanisms. In this review, we summarize the possible molecular mechanisms of caffeine in the prevention or treatment of BPD, aiming to better guide its clinical application.

Extremely premature infants born at 23-25 weeks gestation are at substantial risk for pulmonary hypertension

OBJECTIVE

Extremely low gestational age newborns (ELGANs) represent an especially vulnerable population. Herein, we aimed to determine incidence and severity of pulmonary hypertension associated with bronchopulmonary dysplasia (BPD-PH) in extremely immature ELGANs (gestational age: 23^0/6-25^6/7 weeks).

METHODS

In this prospective observational cohort study, we assessed BPD-PH by means of several echocardiography markers and serum N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels at 3 and 12 months of chronological age. In addition, we analyzed incidence and efficacy of pharmacologic treatment for BPD-PH.

RESULTS

At 3 months 15/34 ELGANs had echocardiographic evidence of BPD-PH, while at 12 months of age 6/34 still had PH. PH-targeted therapy consisted of sildenafil monotherapy in 11 and dual oral combination therapy (sildenafil and macitentan) in four ELGANs at 3 and 12 months.

CONCLUSION

44% (15/34) of ELGANs developed BPD-PH. All received PH-targeted pharmacotherapy at 3 months, leading to hemodynamic improvements at 12 months in most infants.

Inhibition of miR-21 improves pulmonary vascular responses in bronchopulmonary dysplasia by targeting the DDAH1/ADMA/NO pathway

miR-21 has been confirmed to be overexpressed in neonatal rat lungs with hyperoxia-mediated bronchopulmonary dysplasia (BPD). The specific function of miR-21 in BPD is still unclear. We established the hyperoxia-induced BPD rat model in vivo and the hyperoxia-induced pulmonary microvascular endothelial cells (PMVECs) model in vitro. Transwell assay was utilized to detect the migratory capability of PMVECs. Tube formation assay was utilized to measure angiogenesis ability. ELISA was utilized to test nitric oxide (NO) production and the intracellular and extracellular Asymmetric Dimethylarginine (ADMA) concentration. Furthermore, the interaction between miR-21 and dimethylarginine dimethylaminohydrolase 1 (DDAH1) was evaluated using luciferase reporter assay. We found that miR-21 expression in PMVECs was increased by hyperoxia stimulation. Inhibition of miR-21 improved the migratory and angiogenic activities of PMVECs and overexpression of miR-21 exerted the opposite effects. Furthermore, knockdown of miR-21 increased NO production and decreased intracellular and extracellular ADMA concentration in hyperoxia-treated PMVECs. Next we proved that miR-21 could bind to DDAH1 and negatively regulate its expression. Rescues assays showed that DDAH1 knockdown reversed the effects of miR-21 depletion on hyperoxia-mediated PMVEC functions, NO production, and ADMA concentration. Importantly, miR-21 downregulation restored alveolarization and vascular density in BPD rats. This study demonstrates that inhibition of miR-21 improves pulmonary vascular responses in BPD by targeting the DDAH1/ADMA/NO pathway.

Relationship between bronchopulmonary dysplasia phenotypes with high-resolution computed tomography score in early preterm infants

OBJECTIVE

To assess the relationship between high-resolution computed tomography (HRCT) abnormalities and clinical phenotypes of bronchopulmonary dysplasia (BPD).

METHODS

A retrospective, single-center study was carried out at the Children's Hospital of Fudan University between 2013 and 2020. Preterm infants born at ≤ 32 weeks' gestation who were diagnosed with BPD and had HRCT between 40 and 50 weeks postmenstrual age (PMA)were included in the study. HRCT images from six pulmonary lobes were scored based on seven types of pulmonary lesions from two categories: hyperaeration lesions and parenchymal lesions. The hyperaeration score (HS) included scores of decreased attenuation, mosaic attenuation, and bulla/bleb, while the parenchymal score (PS) included those of linear lesion, consolidation, bronchial wall thickening, and bronchiectasis. All seven scores were summed up to create the total score (TS). One-way ANOVA testing or Kruskal-Wallis testing was adopted for the comparison of HRCT scores with BPD severity and clinical phenotypes. The correlation between HRCT scores and clinical phenotypes was evaluated by Spearman's correlation analysis.

RESULTS

A total of 81 cases were included in the study. Cases with more severe BPD had a higher TS (p = 0.01), HS (p = 0.02), PS (p = 0.02), mosaic attenuation score (p = 0.03), bulla/Bleb score (p = 0.03), and linear density score (p = 0.01). TS (r = 0.28), PS (r = 0.35), linear density (r = 0.34), and consolidation (r = 0.24) were correlated with pulmonary hypertension (PH). However, no HRCT score was significantly different between the patients with or without tracheobronchomalacia (TBM). BPD patients with a combination of lung parenchymal disease, PH, and TBM had the highest TS and HS.

CONCLUSION

HRCT scores correlated with BPD severity and PH in our study. HS might be a useful tool in the assessment of BPD severity while linear densities and consolidation might be helpful in predicting PH.

Comparisons of two definitions of bronchopulmonary dysplasia for the premature infants

OBJECTIVE

Bronchopulmonary dysplasia (BPD) is a very common respiratory disease in premature infants, but there is still a different understanding of the definition of BPD. Therefore, this study is intended to compare are main clinical results and health economic expenditures under different BPD definitions.

METHODS

This study included premature infants who came into the neonatal intensive care unit (NICU) from January 2018 to January 2020, who were not more than 32 weeks of premenstrual age. The main clinical consequences and health economic expenditures were analyzed by the National Institute of Health and Human Development definition (Workshop) and Jensen definition.

RESULTS

Total 303 survivors were evaluated at 36 weeks. BPD was performed in 47.5% and 37.6% of infants, respectively, with Workshop's and Jensen's definitions. The percentage of unclassified BPD infants was 0.9% in Workshop's and 3.3% in Jensen's definitions. Further discussing the health economic burden and found that Jensen's definitions had a significantly correlated with NICU charges than the Workshop's definitions.

CONCLUSION

Comparing the Workshop definition of BPD, the Jensens definition was better correlated to health expenditure.

Impact of early respiratory care for extremely preterm infants

Despite advances in neonatal intensive care, more than half of surviving infants born extremely preterm (EP; < 28 weeks' gestation) develop bronchopulmonary dysplasia (BPD). Prevention of BPD is critical because of its associated mortality and morbidity, including adverse neurodevelopmental outcomes and respiratory health in later childhood and beyond. The respiratory care of EP infants begins before birth, then continues in the delivery room and throughout the primary hospitalization. This chapter will review the evidence for interventions after birth that might improve outcomes for infants born EP, including the timing of umbilical cord clamping, strategies to avoid or minimize exposure to mechanical ventilation, modes of mechanical ventilation and non-invasive respiratory support, oxygen saturation targets, postnatal corticosteroids and other adjunct therapies.

Weaning from the Ventilator in Bronchopulmonary Dysplasia

For the newborns needing respiratory support at 36 weeks postmenstrual age, regardless of the type of ventilation used, it is critical to take into account the mechanics properties of both airways and lungs affected by severe bronchopulmonary dysplasia (sBPD). Ventilator strategies, settings, and weaning must change dramatically after sBPD is established, but to date there is almost no high-quality evidence base supporting a specific approach to guide the optimal ventilator management and weaning in patients with sBPD. Weaning from invasive mechanical ventilation, management of the immediately postextubation period, and weaning from noninvasive ventilation in patients with sBPD are the topics covered in this chapter.

Pulmonary hypertension in the child with bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the most common chronic lung disease of prematurity resulting from complex interactions of perinatal factors that often lead to prolonged respiratory support and increased pulmonary morbidity. There is also growing appreciation for the dysmorphic pulmonary bed characterized by vascular growth arrest and remodeling, resulting in pulmonary vascular disease and its most severe form, pulmonary hypertension (PH) in children with BPD. In this review, we comprehensively discuss the pathophysiology of PH in children with BPD, evaluate the current recommendations for screening and diagnosis of PH, discern associated comorbid conditions, and outline the current treatment options.

Pulmonary Function Tests in Very Low Birth Weight Infants Screened for Pulmonary Hypertension: A Pilot Study

OBJECTIVE

To compare pulmonary function tests (PFTs), specifically respiratory system resistance (Rrs) and compliance (Crs), in very low birth weight (VLBW) infants with and without pulmonary hypertension.

STUDY DESIGN

Infants were included who underwent PFTs at 34-38 weeks postmenstrual age (PMA) as part of our pulmonary hypertension screening guidelines for infants born at ≤1500 g requiring respiratory support at ≥34 weeks PMA. One pediatric cardiologist reviewed and estimated right ventricular or pulmonary arterial pressure and defined pulmonary hypertension as an estimated pulmonary arterial pressure or right ventricular pressure greater than one-half the systemic pressure. Rrs and Crs were measured with the single breath occlusion technique and functional residual capacity with the nitrogen washout method according to standardized criteria.

RESULTS

Twelve VLBW infants with pulmonary hypertension and 39 without pulmonary hypertension were studied. Those with pulmonary hypertension had significantly lower birth weight and a trend toward a lower gestational age. There were no other demographic differences between the groups. The infants with pulmonary hypertension had significantly higher Rrs (119 vs 78 cmH₂O/L/s; adjusted P = .012) and significantly lower Crs/kg (0.71 vs 0.92 mL/cmH₂O/kg; P = .04).

CONCLUSIONS

In this pilot study of VLBW infants screened for pulmonary hypertension at 34-38 weeks PMA, those with pulmonary hypertension had significantly increased Rrs and decreased Crs compared with those without pulmonary hypertension. Additional studies are needed to further phenotype infants with evolving BPD and pulmonary hypertension.

Pediatric Pulmonary Hypertension: Definitions, Mechanisms, Diagnosis, and Treatment

Pediatric pulmonary hypertension (PPH) is a multifactorial disease with diverse etiologies and presenting features. Pulmonary hypertension (PH), defined as elevated pulmonary artery pressure, is the presenting feature for several pulmonary vascular diseases. It is often a hidden component of other lung diseases, such as cystic fibrosis and bronchopulmonary dysplasia. Alterations in lung development and genetic conditions are an important contributor to pediatric pulmonary hypertensive disease, which is a distinct entity from adult PH. Many of the causes of pediatric PH have prenatal onset with altered lung development due to maternal and fetal conditions. Since lung growth is altered in several conditions that lead to PPH, therapy for PPH includes both pulmonary vasodilators and strategies to restore lung growth. These strategies include optimal alveolar recruitment, maintaining physiologic blood gas tension, nutritional support, and addressing contributing factors, such as airway disease and gastroesophageal reflux. The outcome for infants and children with PH is highly variable and largely dependent on the underlying cause. The best outcomes are for neonates with persistent pulmonary hypertension (PPHN) and reversible lung diseases, while some genetic conditions such as alveolar capillary dysplasia are lethal. © 2021 American Physiological Society. Compr Physiol 11:2135-2190, 2021.

Association Analysis in Children Born from Normal and Complicated Pregnancies-Cardiovascular Disease Associated microRNAs and the Incidence of Prehypertension/Hypertension, Overweight/Obesity, Valve Problems and Heart Defects

The goal was to assess how a history of any kind of pregnancy-related complication altered expression profile of microRNAs played a role in the pathogenesis of diabetes, cardiovascular and cerebrovascular diseases in the peripheral blood leukocytes of children at the age of 3–11 years. The prior exposure to gestational hypertension, preeclampsia, fetal growth restriction, gestational diabetes mellitus, preterm prelabor rupture of membranes or spontaneous preterm birth causes that a significant proportion of children (57.42% to 90.0% specifically) had a substantially altered microRNA expression profile, which might be the origin of a lifelong cardiovascular risk. A total of 23 out of 29 tested microRNAs were upregulated in children born from such complicated gestation. The occurrence of overweight, obesity, valve problems and heart defects even intensified upregulation of microRNAs already present in children exposed to such pregnancy complications. The occurrence of overweight/obesity (miR-92a-3p, and miR-210-3p) and valve problems or heart defects (miR-342-3p) induced microRNA upregulation in children affected with pregnancy complications. Overall, 42.86% overweight/obese children and 27.36% children with valve problems or heart defects had even higher microRNA levels than children with normal clinical findings after complicated pregnancies. In addition, the microRNA expression profile was also able to differentiate between children descending from normal gestation in relation to the occurrence of overweight and obesity. Screening on the base of the combination of 19 microRNAs identified 70.0% overweight/obese children at 90.0% specificity. In general, children after complicated pregnancies, just as children after normal pregnancies, with abnormal findings are at a higher risk of the onset of cardiovascular complications, and their dispensarization, with the aim to implement primary prevention strategies, would be beneficial.

Interactive and independent effects of early lipopolysaccharide and hyperoxia exposure on developing murine lungs

Bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension (PH) is a chronic infantile lung disease that lacks curative therapies. Infants with BPD-associated PH are often exposed to hyperoxia and additional insults such as sepsis that contribute to disease pathogenesis. Animal models that simulate these scenarios are necessary to develop effective therapies; therefore, we investigated whether lipopolysaccharide (LPS) and hyperoxia exposure during saccular lung development cooperatively induce experimental BPD-PH in mice. C57BL/6J mice were exposed to normoxia or 70% O₂ (hyperoxia) during postnatal days (PNDs) 1-5 and intraperitoneally injected with varying LPS doses or a vehicle on PNDs 3-5. On PND 14, we performed morphometry, echocardiography, and gene and protein expression studies to determine the effects of hyperoxia and LPS on lung development, vascular remodeling and function, inflammation, oxidative stress, cell proliferation, and apoptosis. LPS and hyperoxia independently and cooperatively affected lung development, inflammation, and apoptosis. Growth rate and antioxidant enzyme expression were predominantly affected by LPS and hyperoxia, respectively, while cell proliferation and vascular remodeling and function were mainly affected by combined exposure to LPS and hyperoxia. Mice treated with lower LPS doses developed adaptive responses and hyperoxia exposure did not worsen their BPD phenotype, whereas those mice treated with higher LPS doses displayed the most severe BPD phenotype when exposed to hyperoxia and were the only group that developed PH. Collectively, our data suggest that an additional insult such as LPS may be necessary for models utilizing short-term exposure to moderate hyperoxia to recapitulate human BPD-PH.

Bronchopulmonary Dysplasia: Then, Now, and Next

Bronchopulmonary dysplasia (BPD) has evolved considerably since its first description over 50 years ago. This review aims to provide a historical framework for conceptualizing BPD and a current understanding of the changing definition, epidemiology, pathophysiology, treatment, and outcomes of BPD. The transdisciplinary approach that led to the initial phenotypic description of BPD continues to hold promise today. Investigators are refining the definition of BPD in light of changes in clinical care and increasing survival rates of very preterm infants. Despite improvements in perinatal care the incidence of BPD continues to increase. There is growing recognition that antenatal risk factors play a key role in the development of BPD. Strategies designed to prevent or limit neonatal lung injury continue to evolve. Defining the phenotype of infants with BPD can meaningfully direct treatment. Infants with BPD benefit from an interdisciplinary approach to longitudinal care with a focus on growth and neurocognitive development. While the ultimate impact of BPD on long-term pulmonary morbidity remains an active area of investigation, current data indicate that most children and adolescents with a history of BPD have a quality of life comparable to that of other preterm infants.

Tie-2 Cre-Mediated Deficiency of Extracellular Signal-Regulated Kinase 2 Potentiates Experimental Bronchopulmonary Dysplasia-Associated Pulmonary Hypertension in Neonatal Mice

Bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension (PH) is a significant lung morbidity of infants, and disrupted lung angiogenesis is a hallmark of this disease. We observed that extracellular signal-regulated kinases (ERK) 1/2 support angiogenesis in vitro, and hyperoxia activates ERK1/2 in fetal human pulmonary microvascular endothelial cells (HPMECs) and in neonatal murine lungs; however, their role in experimental BPD and PH is unknown. Therefore, we hypothesized that Tie2 Cre-mediated deficiency of ERK2 in the endothelial cells of neonatal murine lungs would potentiate hyperoxia-induced BPD and PH. We initially determined the role of ERK2 in in vitro angiogenesis using fetal HPMECs. To disrupt endothelial ERK2 signaling in the lungs, we decreased ERK2 expression by breeding ERK2^flox/flox mice with Tie-Cre mice. One-day-old endothelial ERK2-sufficient (eERK2^+/+) or –deficient (eERK2^+/−) mice were exposed to normoxia or hyperoxia (FiO₂ 70%) for 14 d. We then performed lung morphometry, gene and protein expression studies, and echocardiography to determine the extent of inflammation, oxidative stress, and development of lungs and PH. The knockdown of ERK2 in HPMECs decreased in vitro angiogenesis. Hyperoxia increased lung inflammation and oxidative stress, decreased lung angiogenesis and alveolarization, and induced PH in neonatal mice; however, these effects were augmented in the presence of Tie2-Cre mediated endothelial ERK2 deficiency. Therefore, we conclude that endothelial ERK2 signaling is necessary to mitigate hyperoxia-induced experimental BPD and PH in neonatal mice. Our results indicate that endothelial ERK2 is a potential therapeutic target for the management of BPD and PH in infants.

Extracorporeal Life Support in Pediatric Patients with Bronchopulmonary Dysplasia and Associated Pulmonary Hypertension

This retrospective study reviews outcomes of 281 pediatric patients with bronchopulmonary dysplasia (BPD) managed with extracorporeal life support (ECLS). Data from 1982 to 2018 from the Extracorporeal Life Support Organization (ELSO) registry were queried for children aged 60 days to 18 years with a prior diagnosis of BPD, and all patients with secondary pulmonary hypertension (PH) were identified. Overall survival of patients with and without PH was 86.7% and 68.0%, respectively (p = 0.23). There was no report of patients with PH before 2004. Patients with BPD + PH were more likely to have associated intraventricular hemorrhage (p = 0.002) and retinopathy of prematurity (p = 0.05), as well as a greater reported use of sildenafil (p = 0.0001) and milrinone (p = 0.008) before ECLS. The most common primary diagnosis in patients with BPD was viral respiratory infection (45.3%) and in patients with BPD + PH was respiratory failure without mention of infection (40.0%). Inotrope use was the most common complication reported (36.7%) with survival of 54.4%. We conclude that data from the ELSO registry demonstrate reasonable survival in both, patients with BPD and BPD + PH. Thus, patients with BPD and associated PH should be considered candidates for ECLS.

Adrenomedullin Is Necessary to Resolve Hyperoxia-Induced Experimental Bronchopulmonary Dysplasia and Pulmonary Hypertension in Mice

Bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension (PH) is an infantile lung disease characterized by aberrant angiogenesis and impaired resolution of lung injury. Adrenomedullin (AM) signals through calcitonin receptor-like receptor and receptor activity-modifying protein 2 and modulates lung injury initiation. However, its role in lung injury resolution and the mechanisms by which it regulates angiogenesis remain unclear. Consequently, we hypothesized that AM resolves hyperoxia-induced BPD and PH via endothelial nitric oxide synthase (NOS3). AM-sufficient (ADM^+/+) or -deficient (ADM^+/-) mice were exposed to normoxia or hyperoxia through postnatal days (PNDs) 1 to 14, and the hyperoxia-exposed mice were allowed to recover in normoxia for an additional 56 days. Lung injury and development and PH were quantified at different time points. Human pulmonary microvascular endothelial cells were also used to examine the effects of AM signaling on the NOS3 pathway and angiogenesis. Lung blood vessels and NOS3 expression decreased and the extent of hyperoxia-induced BPD and PH increased in ADM^+/- mice compared with ADM^+/+ mice. Hyperoxia-induced apoptosis and PH resolved by PND14 and PND70, respectively, in ADM^+/+ mice but not in ADM^+/- mice. Knockdown of ADM, calcitonin receptor-like receptor, and receptor activity-modifying protein 2 in vitro decreased NOS3 expression, nitric oxide generation, and angiogenesis. Furthermore, NOS3 knockdown abrogated the angiogenic effects of AM. Collectively, these results indicate that AM resolves hyperoxic lung injury via NOS3.

Validation of a new predictive model to improve risk stratification in bronchopulmonary dysplasia

We need a better risk stratification system for the increasing number of survivors of extreme prematurity suffering the most severe forms of bronchopulmonary dysplasia (BPD). However, there is still a paucity of studies providing scientific evidence to guide future updates of BPD severity definitions. Our goal was to validate a new predictive model for BPD severity that incorporates respiratory assessments beyond 36 weeks postmenstrual age (PMA). We hypothesized that this approach improves BPD risk assessment, particularly in extremely premature infants. This is a longitudinal cohort of premature infants (≤32 weeks PMA, n = 188; Washington D.C). We performed receiver operating characteristic analysis to define optimal BPD severity levels using the duration of supplementary O2 as predictor and respiratory hospitalization after discharge as outcome. Internal validation included lung X-ray imaging and phenotypical characterization of BPD severity levels. External validation was conducted in an independent longitudinal cohort of premature infants (≤36 weeks PMA, n = 130; Bogota). We found that incorporating the total number of days requiring O2 (without restricting at 36 weeks PMA) improved the prediction of respiratory outcomes according to BPD severity. In addition, we defined a new severity category (level IV) with prolonged exposure to supplemental O2 (≥120 days) that has the highest risk of respiratory hospitalizations after discharge. We confirmed these findings in our validation cohort using ambulatory determination of O2 requirements. In conclusion, a new predictive model for BPD severity that incorporates respiratory assessments beyond 36 weeks improves risk stratification and should be considered when updating current BPD severity definitions.

Novel Strategies to Reduce Pulmonary Hypertension in Infants With Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is a developmental lung disorder of preterm infants primarily caused by the failure of host defense mechanisms to prevent tissue injury and facilitate repair. This disorder is the most common complication of premature birth, and its incidence remains unchanged over the past few decades. Additionally, BPD increases long-term cardiopulmonary and neurodevelopmental morbidities of preterm infants. Pulmonary hypertension (PH) is a common morbidity of BPD. Importantly, the presence of PH increases both the short- and long-term morbidities and mortality in BPD infants. Further, there are no curative therapies for this complex disease. Besides providing an overview of the pathogenesis and diagnosis of PH associated with BPD, we have attempted to comprehensively review and summarize the current literature on the interventions to prevent and/or mitigate BPD and PH in preclinical studies. Our goal was to provide insight into the therapies that have a high translational potential to meaningfully manage BPD patients with PH.

Recent advances in our understanding of the mechanisms of lung alveolarization and bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the most common cause of morbidity and mortality in preterm infants. A key histopathological feature of BPD is stunted late lung development, where the process of alveolarization-the generation of alveolar gas exchange units-is impeded, through mechanisms that remain largely unclear. As such, there is interest in the clarification both of the pathomechanisms at play in affected lungs, and the mechanisms of de novo alveoli generation in healthy, developing lungs. A better understanding of normal and pathological alveolarization might reveal opportunities for improved medical management of affected infants. Furthermore, disturbances to the alveolar architecture are a key histopathological feature of several adult chronic lung diseases, including emphysema and fibrosis, and it is envisaged that knowledge about the mechanisms of alveologenesis might facilitate regeneration of healthy lung parenchyma in affected patients. To this end, recent efforts have interrogated clinical data, developed new-and refined existing-in vivo and in vitro models of BPD, have applied new microscopic and radiographic approaches, and have developed advanced cell-culture approaches, including organoid generation. Advances have also been made in the development of other methodologies, including single-cell analysis, metabolomics, lipidomics, and proteomics, as well as the generation and use of complex mouse genetics tools. The objective of this review is to present advances made in our understanding of the mechanisms of lung alveolarization and BPD over the period 1 January 2017-30 June 2019, a period that spans the 50th anniversary of the original clinical description of BPD in preterm infants.

Optimal oxygenation and role of free radicals in PPHN

Effective ventilation of the lungs is essential in mediating pulmonary vasodilation at birth to allow effective gas exchange and an increase in systemic oxygenation. Unsuccessful transition prevents the increase in pulmonary blood flow after birth resulting in hypoxemia and persistent pulmonary hypertension of the newborn (PPHN). Management of neonates with PPHN includes ventilation of the lungs with supplemental oxygen to correct hypoxemia. Optimal oxygenation should meet oxygen demand to the tissues and avoid hypoxic pulmonary vasoconstriction (HPV) while preventing oxidative stress. The optimal target for oxygenation in PPHN is not known. Animal models have demonstrated that PaO₂<45 mmHg exacerbates HPV. However, there are no practical methods of assessing oxygen levels associated with oxidant stress. Oxidant stress can be due to free radical generation from underlying lung disease or from free radicals generated by supplemental oxygen. Free radicals act on the nitric oxide pathway reducing cGMP and promoting pulmonary vasoconstriction. Antioxidant therapy improves systemic oxygenation in an animal model of PPHN but there are no clinical trials to support such therapy. Targeting preductal SpO₂ between 90 and 97% and PaO₂ at 50-80 mmHg appears prudent in PPHN but clinical trials to support this practice are lacking. Preterm infants with PPHN present unique challenges due to lack of antioxidant defenses and functional and structural immaturity of the lungs. This review highlights the need for additional studies to mitigate the impact of oxidative stress in the lung and pulmonary vasculature in PPHN.

Hemodynamic management in chronically ventilated infants

Positive pressure ventilation can significantly alter hemodynamics. The reduction in systemic venous return and increase in right ventricular afterload in response to an inappropriately high mean airway pressure can decrease pulmonary blood flow and compromise systemic perfusion as a result. In addition to ventilator parameters, the degree of hemodynamic effects depends on the baseline cardiac function and lung compliance. Furthermore, the chronically ventilated infants often have a multitude of comorbidities which may also impact hemodynamics. These include pulmonary and systemic hypertension which can lead to myocardial dysfunction as a result of the increase in the right and left ventricular afterload, respectively. In this section, we aim to outline the hemodynamic changes associated with chronic lung disease and mechanical ventilation and discuss management options.

Paving the Road for Mesenchymal Stem Cell-Derived Exosome Therapy in Bronchopulmonary Dysplasia and Pulmonary Hypertension

Bronchopulmonary dysplasia (BPD) is a chronic neonatal lung disease characterized by inflammation and arrest of alveolarization. Its common sequela, pulmonary hypertension (PH), presents with elevated pulmonary vascular resistance associated with remodeling of the pulmonary arterioles. Despite notable advancements in neonatal medicine, there is a severe lack of curative treatments to help manage the progressive nature of these diseases. Numerous studies in preclinical models of BPD and PH have demonstrated that therapies based on mesenchymal stem/stromal cells (MSCs) can resolve pulmonary inflammation and ameliorate the severity of disease. Recent evidence suggests that novel, cell-free approaches based on MSC-derived exosomes (MEx) might represent a compelling therapeutic alternative offering major advantages over treatments based on MSC transplantation. Here, we will discuss the development of MSC-based therapies, stressing the centrality of paracrine action as the actual vector of MSC therapeutic functionality, focusing on MEx. We will briefly present our current understanding of the biogenesis and secretion of MEx, and discuss potential mechanisms by which they afford such beneficial effects, including immunomodulation and restoration of homeostasis in diseased states. We will also review ongoing clinical trials using MSCs as treatment for BPD that pave the way for bringing cell-free, MEx-based therapeutics from the bench to the NICU setting.