Surfactant function and composition in premature infants treated with inhaled nitric oxide

Late surfactant administration after 48 hours of age in preterm neonates with respiratory insufficiency: a systematic review and meta-analysis

OBJECTIVE

To systematically review and meta-analyse the effect of late surfactant administration versus placebo in reducing the incidence of death or bronchopulmonary dysplasia (BPD) in preterm infants.

DESIGN

PubMed, EMBASE, CINAHL and Cochrane CENTRAL were searched until 30 May 2023, for randomised controlled trials (RCTs) comparing administration of surfactant after 48 hours of age versus placebo in preterm ventilator-dependent neonates. The primary outcome was incidence of death or BPD at 36 weeks' postmenstrual age (PMA). Secondary outcomes included incidence of BPD at 36 weeks PMA, pre-discharge mortality, use of postnatal steroids, post-discharge respiratory support, treatment with steroids or hospitalisation prior to 1-year corrected age.

RESULTS

Pooled analyses of four RCTs (N=850) showed no statistically significant difference between groups in the incidence of death or BPD at 36 weeks' PMA (relative risk (RR) 0.99; 95% CI 0.90 to 1.10; Grades of Recommendation, Assessment, Development and Evaluation (GRADE): moderate). Late surfactant administration significantly decreased the need for post-discharge respiratory support prior to 1-year corrected age (two RCTs; N=522; RR 0.72; 95% CI 0.59 to 0.89; GRADE: low). Other secondary outcomes did not differ significantly between the groups.

CONCLUSIONS

Administration of late surfactant does not improve the rates of death or BPD at 36 weeks when administered to preterm infants with prolonged respiratory insufficiency. Additional adequately powered trials are needed to establish the efficacy of late surfactant therapy in preterm infants.

PROSPERO REGISTRATION NUMBER

CRD42023432463.

Surfactant status and respiratory outcome in premature infants receiving late surfactant treatment

BACKGROUND

Many premature infants with respiratory failure are deficient in surfactant, but the relationship to occurrence of bronchopulmonary dysplasia (BPD) is uncertain.

METHODS

Tracheal aspirates were collected from 209 treated and control infants enrolled at 7-14 days in the Trial of Late Surfactant. The content of phospholipid, surfactant protein B, and total protein were determined in large aggregate (active) surfactant.

RESULTS

At 24 h, surfactant treatment transiently increased surfactant protein B content (70%, p < 0.01), but did not affect recovered airway surfactant or total protein/phospholipid. The level of recovered surfactant during dosing was directly associated with content of surfactant protein B (r = 0.50, p < 0.00001) and inversely related to total protein (r = 0.39, p < 0.0001). For all infants, occurrence of BPD was associated with lower levels of recovered large aggregate surfactant, higher protein content, and lower SP-B levels. Tracheal aspirates with lower amounts of recovered surfactant had an increased proportion of small vesicle (inactive) surfactant.

CONCLUSIONS

We conclude that many intubated premature infants are deficient in active surfactant, in part due to increased intra-alveolar metabolism, low SP-B content, and protein inhibition, and that the severity of this deficit is predictive of BPD. Late surfactant treatment at the frequency used did not provide a sustained increase in airway surfactant.

Review shows that using surfactant a number of times or as a vehicle for budesonide may reduce the risk of bronchopulmonary dysplasia

AIM

Bronchopulmonary dysplasia (BPD) remains the most common respiratory morbidity in immature infants. This review describes the diagnosis of BPD has evolved and summarises the therapeutic approaches that have made it possible to limit the incidence of BPD.

METHOD

We reviewed the literature from the first definition of BPD by Northway in 1967 to the surfactant treatment policies that are currently in use, drawing on more than 50 papers up to 2017.

RESULTS

Our review showed that improvements in neonatal survival have been associated with an increased risk of severe BPD, significant levels of long-term morbidity and the increased use of healthcare resources. These issues have encouraged researchers to explore potential new treatments that limit the incidence of BPD. Repeated surfactant instillation and the use of surfactant as a vehicle for budesonide are promising strategies for alleviating the burden of chronic lung disease. Ongoing research on surfactant or stem cell therapy may further improve the respiratory prognosis for prematurely born children.

CONCLUSION

Considerable research has been carried out into the increase in BPD, which has resulted from improvements in neonatal survival. Key areas of research include repeated surfactant administration, using surfactant as a vehicle for budesonide and stem cell therapy.

Inflammatory Mediators in Tracheal Aspirates of Preterm Infants Participating in a Randomized Trial of Inhaled Nitric Oxide

BACKGROUND

Ventilated preterm infants frequently develop bronchopulmonary dysplasia (BPD) which is associated with elevated inflammatory mediators in their tracheal aspirates (TA). In animal models of BPD, inhaled nitric oxide (iNO) has been shown to reduce lung inflammation, but data for human preterm infants is missing.

METHODS

Within a European multicenter trial of NO inhalation for preterm infants to prevent BPD (EUNO), TA was collected to determine the effects of iNO on pulmonary inflammation. TA was collected from 43 premature infants randomly assigned to receive either iNO or placebo gas (birth weight 530-1230 g, median 800 g, gestational age 24 to 28 2/7 weeks, median 26 weeks). Interleukin (IL)-1β, IL-6, IL-8, transforming growth factor (TGF)-β1, interferon γ-induced protein 10 (IP-10), macrophage inflammatory protein (MIP)-1α, acid sphingomyelinase (ASM), neuropeptide Y and leukotriene B4 were measured in serial TA samples from postnatal day 2 to 14. Furthermore, TA levels of nitrotyrosine and nitrite were determined under iNO therapy.

RESULTS

The TA levels of IP-10, IL-6, IL-8, MIP-1α, IL-1β, ASM and albumin increased with advancing postnatal age in critically ill preterm infants, whereas nitrotyrosine TA levels declined in both, iNO-treated and placebo-treated infants. The iNO treatment generally increased nitrite TA levels, whereas nitrotyrosine TA levels were not affected by iNO treatment. Furthermore, iNO treatment transiently reduced early inflammatory and fibrotic markers associated with BPD development including TGF-β1, IP-10 and IL-8, but induced a delayed increase of ASM TA levels.

CONCLUSION

Treatment with iNO may have played a role in reducing several inflammatory and fibrotic mediators in TA of preterm infants compared to placebo-treated infants. However, survival without BPD was not affected in the main EUNO trial.

TRIAL REGISTRATION

NCT00551642.

Surfactant Replacement Therapy Beyond Respiratory Distress Syndrome in Neonates

BACKGROUND

Surfactant replacement therapy is an established modality of treatment in preterm neonates with respiratory distress syndrome. In addition, there are various neonatal respiratory disorders which are characterized by surfactant deficiency in which surfactant therapy can be a feasible and safe option.

OBJECTIVE

To collate the literature on the use of surfactant replacement therapy in neonates beyond respiratory distress syndrome and examine the evidence and newer developments.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library), MEDLINE, and EMBASE up to June 2015; and previous reviews, including cross-references, abstracts, and conference proceedings.

RESULTS

Evidence supports surfactant administration via bolus route in neonates with meconium aspiration syndrome, but additional robust evidence is required before its adoption in clinical practice. There is limited evidence to support surfactant therapy in neonates with pneumonia, pulmonary hemorrhage and bronchopulmonary dysplasia. Large multicenter randomized trials are needed to cement or refute the role of surfactant therapy in these disorders.

Randomized Trial of Late Surfactant Treatment in Ventilated Preterm Infants Receiving Inhaled Nitric Oxide

OBJECTIVE

To assess whether late surfactant treatment in extremely low gestational age (GA) newborn infants requiring ventilation at 7-14 days, who often have surfactant deficiency and dysfunction, safely improves survival without bronchopulmonary dysplasia (BPD).

STUDY DESIGN

Extremely low GA newborn infants (GA ≤28 0/7 weeks) who required mechanical ventilation at 7-14 days were enrolled in a randomized, masked controlled trial at 25 US centers. All infants received inhaled nitric oxide and either surfactant (calfactant/Infasurf) or sham instillation every 1-3 days to a maximum of 5 doses while intubated. The primary outcome was survival at 36 weeks postmenstrual age (PMA) without BPD, as evaluated by physiological oxygen/flow reduction.

RESULTS

A total of 511 infants were enrolled between January 2010 and September 2013. There were no differences between the treated and control groups in mean birth weight (701 ± 164 g), GA (25.2 ± 1.2 weeks), percentage born at GA <26 weeks (70.6%), race, sex, severity of lung disease at enrollment, or comorbidities of prematurity. Survival without BPD did not differ between the treated and control groups at 36 weeks PMA (31.3% vs 31.7%; relative benefit, 0.98; 95% CI, 0.75-1.28; P = .89) or 40 weeks PMA (58.7% vs 54.1%; relative benefit, 1.08; 95% CI, 0.92-1.27; P = .33). There were no between-group differences in serious adverse events, comorbidities of prematurity, or severity of lung disease to 36 weeks.

CONCLUSION

Late treatment with up to 5 doses of surfactant in ventilated premature infants receiving inhaled nitric oxide was well tolerated, but did not improve survival without BPD at 36 or 40 weeks. Pulmonary and neurodevelopmental assessments are ongoing.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01022580.

Use of inhaled nitric oxide in preterm infants

Nitric oxide, an important signaling molecule with multiple regulatory effects throughout the body, is an important tool for the treatment of full-term and late-preterm infants with persistent pulmonary hypertension of the newborn and hypoxemic respiratory failure. Several randomized controlled trials have evaluated its role in the management of preterm infants ≤ 34 weeks' gestational age with varying results. The purpose of this clinical report is to summarize the existing evidence for the use of inhaled nitric oxide in preterm infants and provide guidance regarding its use in this population.

Current Issues and Challenges in the Use of Aerosolized Surfactant for Respiratory Distress Syndrome in the Newborns

BACKGROUND: Surfactant replacement therapy is a recognized treatment for respiratory distress syndrome (RDS) in the newborns. Over the past 30 years, human and animal trials have been performed regarding administration of aerosolized surfactant to the injured lung, however the result has been unsatisfactory when compared with instilled surfactant delivery via endotracheal tube (ETT). This review aims to investigate the current issues, challenges and future recommendation of aerosolized surfactant therapy.CONTENT: Five randomized clinical trials in humans and 13 animal trials met the inclusion criteria and were reviewed. Most animal trials agree that this method of treatment is feasible. However, human trials presented conflicting results, and generally showed it to be ineffective. When compared with surfactant delivery via ETT, aerosolized surfactant is less effective in improving respiratory function.SUMMARY: The current data from human trials does not support the implementation of aerosolized surfactant therapy to treat newborns with RDS. Further research is necessary to improve nebulization, delivery, distribution and deposition in the lung, to investigate aerosolized surfactant delivery via ETT and to determine the appropriate dose.KEYWORDS: surfactant, aerosol, prematurity, respiratory distress syndrome

Late administration of surfactant replacement therapy increases surfactant protein-B content: a randomized pilot study

BACKGROUND

Surfactant dysfunction may contribute to the development of bronchopulmonary dysplasia (BPD) in persistently ventilated preterm infants. We conducted a multicenter randomized, blinded, pilot study to assess the safety and efficacy of late administration of doses of a surfactant protein-B (SP-B)-containing surfactant (calfactant) in combination with prolonged inhaled nitric oxide (iNO) in infants ≤1,000 g birth weight (BW).

METHODS

We randomized 85 preterm infants ventilated at 7-14 d after birth to receive either late administration of surfactant (up to 5 doses) plus prolonged iNO or iNO alone. Large aggregate surfactant was isolated from daily tracheal aspirates (TAs) for measurement of SP-B content, total protein, and phospholipid (PL).

RESULTS

Late administration of surfactant had minimal acute adverse effects. Clinical status as well as surfactant recovery and SP-B content in tracheal aspirate were transiently improved as compared to the controls; these effects waned after 1 d. The change in SP-B content with surfactant dosing was positively correlated with SP-B levels during treatment (r = 0.50, P = 0.02).

CONCLUSION

Low SP-B values increased with calfactant administration, but the relationship of this response to SP-B levels suggests that degradation is a contributing mechanism for SP-B deficiency and surfactant dysfunction. We conclude that late therapy with surfactant in combination with iNO is safe and transiently increases surfactant SP-B content, possibly leading to improved short- and long-term respiratory outcomes.

Can nitric oxide-based therapy prevent bronchopulmonary dysplasia?

A growing understanding of endogenous nitric oxide (NO) biology is helping to explain how and when exogenous NO may confer benefit or harm; this knowledge is also helping to identify new better-targeted NO-based therapies. In this review, results of the bronchopulmonary dysplasia clinical trials that used inhaled NO in the preterm population are placed in context, the biologic basis for novel NO therapeutics is considered, and possible future directions for NO-focused clinical and basic research in developmental lung disease are identified.

Pulmonary Collectins in Diagnosis and Prevention of Lung Diseases

Pulmonary surfactant is a complex mixture of lipids and proteins, and is synthesized and secreted by alveolar type II epithelial cells and bronchiolar Clara cells. It acts to keep alveoli from collapsing during the expiratory phase of the respiratory cycle. After its secretion, lung surfactant forms a lattice structure on the alveolar surface, known as tubular myelin. Surfactant proteins (SP)-A, B, C and D make up to 10% of the total surfactant. SP-B and SPC are relatively small hydrophobic proteins, and are involved in the reduction of surface-tension at the air-liquid interface. SP-A and SP-D, on the other hand, are large oligomeric, hydrophilic proteins that belong to the collagenous Ca²⁺-dependent C-type lectin family (known as “Collectins”), and play an important role in host defense and in the recycling and transport of lung surfactant (Awasthi 2010) (Fig. 43.1). In particular, there is increasing evidence that surfactant-associated proteins A and -D (SP-A and SP-D, respectively) contribute to the host defense against inhaled microorganisms (see 10.1007/978-3-7091-1065_24 and 10.1007/978-3-7091-1065_25). Based on their ability to recognize pathogens and to regulate the host defense, SP-A and SP-D have been recently categorized as “Secretory Pathogen Recognition Receptors”. While SP-A and SP-D were first identified in the lung; the expression of these proteins has also been observed at other mucosal surfaces, such as lacrimal glands, gastrointestinal mucosa, genitourinary epithelium and periodontal surfaces. SP-A is the most prominent among four proteins in the pulmonary surfactant-system. The expression of SP-A is complexly regulated on the transcriptional and the chromosomal level. SP-A is a major player in the pulmonary cytokine-network and moreover has been described to act in the pulmonary host defense. This chapter gives an overview on the understanding of role of SP-A and SP-D in for human pulmonary disorders and points out the importance for pathology-orientated research to further elucidate the role of these molecules in adult lung diseases. As an outlook, it will become an issue of pulmonary pathology which might provide promising perspectives for applications in research, diagnosis and therapy (Awasthi 2010).

Etiology of Bronchopulmonary Dysplasia: Before Birth

Bronchopulmonary dysplasia affects thousands of infants annually with high attendant morbidity, mortality, and healthcare costs. Respiratory outcomes for preterm infants may be widely disparate even within the same medical center for infants of similar gestational ages. Given the high estimates for the heritability for bronchopulmonary dysplasia as measured at 36 weeks of postmenstrual age, the course of disease for a particular infant is likely heavily influenced by factors that operate prenatally or in the early postnatal period. In this review we discuss the etiologies of lung disease in the premature infant, including in utero, genetic, and epigenetic factors that may influence pulmonary outcomes.

Two-year neurodevelopmental outcomes of ventilated preterm infants treated with inhaled nitric oxide

OBJECTIVE

In a randomized multi-center trial, we demonstrated that inhaled nitric oxide begun between 7 and 21 days and given for 24 days significantly increased survival without bronchopulmonary dysplasia (BPD) in ventilated premature infants weighing <1250 g. Because some preventative BPD treatments are associated with neurodevelopmental impairment, we designed a follow-up study to assess the safety of nitric oxide.

STUDY DESIGN

Our hypothesis was that inhaled nitric oxide would not increase neurodevelopmental impairment compared with placebo. We prospectively evaluated neurodevelopmental and growth outcomes at 24 months postmenstrual age in 477 of 535 surviving infants (89%) enrolled in the trial.

RESULTS

In the treated group, 109 of 243 children (45%) had neurodevelopmental impairment (moderate or severe cerebral palsy, bilateral blindness, bilateral hearing loss, or score <70 on the Bayley Scales II), compared with 114 of 234 (49%) in the placebo group (relative risk, 0.92; 95% CI, 0.75-1.12; P = .39). No differences on any subcomponent of neurodevelopmental impairment or growth variables were found between inhaled nitric oxide or placebo.

CONCLUSIONS

Inhaled nitric oxide improved survival free of BPD, with no adverse neurodevelopmental effects at 2 years of age.

Inhaled nitric oxide in premature infants: effect on tracheal aspirate and plasma nitric oxide metabolites

OBJECTIVE

Inhaled nitric oxide (iNO) is a potential new therapy for prevention of bronchopulmonary dysplasia and brain injury in premature infants. This study examined dose-related effects of iNO on NO metabolites as evidence of NO delivery.

STUDY DESIGN

A subset of 102 premature infants in the NO CLD trial, receiving 24 days of iNO (20 p.p.m. decreasing to 2 p.p.m.) or placebo, were analyzed. Tracheal aspirate (TA) and plasma samples collected at enrollment and at intervals during study gas were analyzed for NO metabolites.

RESULT

iNO treatment increased NO metabolites in TA at 20 and 10 p.p.m. (1.7- to 2.3-fold vs control) and in plasma at 20, 10, and 5 p.p.m. (1.6- to 2.3-fold). In post hoc analysis, treated infants with lower metabolite levels at entry had an improved clinical outcome.

CONCLUSION

iNO causes dose-related increases in NO metabolites in the circulation as well as lung fluid, as evidenced by TA analysis, showing NO delivery to these compartments.

Epidemiology of bronchopulmonary dysplasia

First described more than 40 years ago, bronchopulmonary dysplasia (BPD) remains one of the most serious and vexing challenges in the care of very preterm infants. Affecting approximately one-quarter of infants born <1500g birth weight, BPD is associated with prolonged neonatal intensive care unit hospitalization, greater risk of neonatal and post-neonatal mortality and a host of associated medical and neurodevelopmental sequelae. This seminar focuses on the epidemiology and definition of BPD as well as the current evidence pertaining to a number of potential preventive treatments for BPD: non-invasive respiratory support technologies, inhaled nitric oxide, vitamin A, and caffeine.

Clinical and economic effects of iNO in premature newborns with respiratory failure at 1 year

BACKGROUND

The long-term consequences of inhaled nitric oxide (iNO) use in premature newborns with respiratory failure are unknown. We therefore studied the clinical and economic outcomes to 1 year of corrected age after a randomized controlled trial of prophylactic iNO.

METHODS

Premature newborns (gestational age <or=34 w, birth weight 500-1250 g) with respiratory failure randomly received 5 ppm iNO or placebo within 48 h of birth until 21 d or extubation. We assessed clinical outcomes via in-person neurodevelopmental evaluation at 1 y corrected age and telephone interviews every 3 m. We estimated costs from detailed hospital bills and interviews, converting all costs to 2008 US$. Of 793 trial subjects, 631 (79.6%) contributed economic data, and 455 (77.1% of survivors) underwent neurodevelopmental evaluation.

RESULTS

At 1 y corrected age, survival was not different by treatment arm (79.2% iNO vs. 74.5% placebo, P = .12), nor were other post-discharge outcomes. For subjects weighing 750-999 g, those receiving iNO had greater survival free from neurodevelopmental impairment (67.9% vs. 55.6%, P = .04). However, in subjects weighing 500-749 g, iNO led to greater oxygen dependency (11.7% vs. 4.0%, P = .04). Median total costs were similar ($235,800 iNO vs. $198,300 placebo, P = .19). Quality-adjusted survival was marginally better with iNO (by 0.011 quality-adjusted life-years/subject). The incremental cost-effectiveness ratio was $2.25 million/quality-adjusted life-year.

CONCLUSIONS

Subjects in both arms commonly experienced neurodevelopmental and pulmonary morbidity, consuming substantial health care resources. Prophylactic iNO beginning in the first days of life did not lower costs and had a poor cost-effectiveness profile.

Pitfalls, problems, and progress in bronchopulmonary dysplasia

Bronchopulmonary dysplasia is a chronic lung disease associated with premature birth and characterized by early lung injury. In this review we discuss some pitfalls, problems, and progress in this condition over the last decade, focusing mainly on the last 5 years, limited to studies in human neonates. Changes in the definition, pathogenesis, genetic susceptibility, and recent biomarkers associated with bronchopulmonary dysplasia will be discussed. Progress in current management strategies, along with novel approaches/therapies, will be critically appraised. Finally, recent data on long-term pulmonary and neurodevelopmental outcomes of infants with bronchopulmonary dysplasia will be summarized.

Respiratory function during infancy in survivors of the INNOVO trial

RATIONALE

Despite encouraging reports suggesting that inhaled nitric oxide (iNO) appear to improve outcome in hypoxemic term and near term infants by improving oxygenation and reducing need for ECMO, the long-term benefits of iNO remain unclear. This study aimed to compare lung function at approximately 1 year in infants who were and were not randomly allocated to iNO as part of their neonatal management for severe respiratory failure at birth. Furthermore, results were compared to lung function of healthy infants.

METHODS

Maximal expiratory flow at functional residual capacity (V'maxFRC) was measured at approximately 1 year of age (corrected for any prematurity) in survivors of the INNOVO trial. Results were expressed as Z-scores, adjusted for sex and body size, based on data from healthy controls using identical techniques.

RESULTS

Technically satisfactory results were obtained in 30 infants (53% < 34 weeks gestation), 19 of whom were randomized to receive iNO V'maxFRC. Z-score was significantly reduced in infants with prior respiratory failure, whether or not they had been allocated to iNO (mean (SD) Z-score: -2.0 (1.2) and -2.6 (1.1), respectively, 95% CI difference; iNO vs. no iNO: -0.3; 1.6, P = 0.2). There was significant respiratory morbidity in both groups during the first year of life.

CONCLUSIONS

These results suggest that airway function remains reduced at 1 year of age following severe respiratory failure at birth, whether or not iNO is administered.

Role of iNO in the modulation of pulmonary vascular resistance

Inhaled nitric oxide (iNO) has quickly become a standard therapy for term and near-term infants with hypoxic respiratory failure and persistent pulmonary hypertension. Its effect on the lung is believed to be through the stimulation of soluble guanylyl cyclase and the increased production of cyclic guanosine 3',5'-monophosphate (cGMP). However, in addition to pulmonary vasodilation and a decrease in pulmonary vascular resistance, nitric oxide (NO) shows several additional potential beneficial effects on the lung. This article reviews NO mechanisms of action, early clinical trial of iNO and clinical aspects for the use of iNO in acute respiratory failure of the term and near-tem neonates.

Inhaled nitric oxide in the treatment of preterm infants

Inhaled nitric oxide (iNO) has been used successfully in select term and near-term infants with respiratory failure. The use of iNO in the premature infant population, however, remains controversial. This article will review some of the current literature regarding the use of iNO in premature infants and discuss current recommendations and future research directions.