Substrate utilization and kinetics of surfactant metabolism in evolving bronchopulmonary dysplasia

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.

Bronchopulmonary dysplasia: then and now

When bronchopulmonary dysplasia (BPD) was first described in 1967, the use of assisted ventilation in neonates was in its infancy. High concentrations of oxygen were implicated, and BPD was equated with 'pulmonary oxygen toxicity'. The etiologic role of not only oxygen but also peak inspiratory pressures and the duration of exposure to both was emphasized in the 1970s, but BPD remained a dreaded complication of managing respiratory distress syndrome in the 1980s. It was only after exogenous surfactant became commercially available for endotracheal administration that 'classical' BPD began to disappear and was replaced by the 'new' BPD. 'Classical' BPD was seen in more mature preterm infants (>28 weeks' gestational age) and in its severe form was characterized radiographically by micro- and macrocysts of the lung, lung hyperinflation and flattening of the diaphragms. In contrast, 'new' BPD is seen in less mature infants (<28 weeks' gestational age), has comparatively mild radiographic abnormalities and has been defined as continued oxygen requirement at 36 weeks' postmenstrual age. Pathologically, 'classical' BPD frequently revealed obstructive bronchiolitis and fibrosis of lung parenchyma, whereas 'new' BPD demonstrates minimal fibrosis but uniform arrest of development. Herein, factors which may contribute to the etiology of BPD are described, as well as possible preventative and therapeutic strategies.

Detection of pepsinogen in the neonatal lung and stomach by immunohistochemistry

OBJECTIVE

Evaluate the hypothesis that the same pepsinogen C molecule produced in the stomach is also produced by the lung.

PATIENTS AND METHODS

Pulmonary and gastric tissues collected postmortem were immunohistochemically stained for pepsinogen C and pepsinogen A.

RESULTS

Sixteen patients with diverse causes of death were evaluated. Gestational age at birth ranged between 21 and 37 weeks. Pepsinogen A was detected in 12 of the 13 stomach sections, mainly in the chief cells, but not in any lung sections. Pepsinogen C was detected in all stomach sections in chief and mucus cells and in 9 of the 16 lung sections, mainly in type II pneumocytes. Pepsinogen C was not detected in the 3 lung cases with a gestational age <23 weeks.

CONCLUSIONS

The same pepsinogen C molecule is produced in the stomach and in the lung. These findings potentially affect previous study results that used an enzymatic pepsin detection assay to evaluate for and associate gastroesophageal reflux disease with other morbidities.

Metabolic precursors of surfactant disaturated-phosphatidylcholine in preterms with respiratory distress

Our objective was to study the metabolic precursors of surfactant disaturated-phosphatidylcholine (DSPC) in preterm infants with respiratory distress syndrome (RDS) on mechanical ventilation. We performed 46 DSPC kinetic studies in 23 preterms on fat-free parenteral nutrition and mechanical ventilation (birth weight = 1167 +/- 451 g, gestational age = 28.5 +/- 2.0 weeks). Eight infants received a simultaneous intravenous infusion of U(13)C-glucose and [16,16,16](2)H-palmitate, eight infants received U(13)C-glucose and (2)H(2)O, and seven received U(13)C-palmitate and (2)H(2)O. Surfactant DSPC kinetics were calculated from the isotopic enrichments of DSPC-palmitate from sequential tracheal aspirates and its metabolic precursors in plasma or urine. DSPC fractional synthesis rate (FSR) was 17 +/- 11, 21 +/- 16, and 15 +/- 6%/day from glucose, palmitate, and body water, respectively (P = 0.36). DSPC-FSR from U(13)C-glucose and (2)H(2)O were significantly correlated and yielded similar estimates (difference of -0.1 +/- 3%) (P = 0.91). The difference in the 15 infants receiving palmitate versus (2)H(2)O or palmitate versus glucose was +6.0 +/- 12%/day (P = 0.21). There was a significant correlation between DSPC-FSRs from plasma glucose and plasma FFA. The contribution of glucose versus palmitate to DSPC-FSR was 49 +/- 20% versus 51 +/- 20%, respectively. Plasma glucose and FFA showed similar contributions to DSPC-FSR in infants with RDS and fat-free parenteral nutrition. FSRs from (2)H(2)O or glucose were highly correlated.

Surfactant status in preterm neonates recovering from respiratory distress syndrome

OBJECTIVE

The goal was to establish whether reduced amounts of pulmonary surfactant contribute to postextubation respiratory failure in preterm infants recovering from respiratory distress syndrome.

METHODS

We prospectively recruited preterm infants who needed mechanical ventilation and exogenous surfactant for treatment of moderate/severe respiratory distress syndrome and could not be extubated before day 3 of life. (13)C-labeled dipalmitoyl-phosphatidylcholine was administered endotracheally as tracer before extubation, for estimation of surfactant disaturated phosphatidylcholine pool size and half-life. Patients were retrospectively divided into 3 groups, that is, extubation failure if, after extubation, they needed reintubation or continuous positive airway pressure treatment of >or=6 cmH(2)O and fraction of inspired oxygen of >0.4, extubation success if they did not meet the failure criteria, and not extubated if they needed ongoing ventilation. Clinical and respiratory parameters were recorded hourly.

RESULTS

Reliable kinetic data could be obtained for 63 of the 88 enrolled neonates. Sixteen, 23, and 24 neonates were categorized in the extubation failure, extubation success, and not extubated groups, respectively. Clinical and demographic characteristics did not differ between the extubation failure and extubation success groups. Disaturated phosphatidylcholine pool size was smaller in the extubation failure group than in the extubation success group (25 +/- 12 vs 43 +/- 24 mg/kg) and was 37 +/- 32 mg/kg in the not extubated group. Disaturated phosphatidylcholine half-life was 19 +/- 7, 24 +/- 12, and 28 +/- 18 hours in the extubation failure, extubation success, and not extubated groups, respectively.

CONCLUSIONS

In a selected population of preterm infants with moderate/severe respiratory distress syndrome who could not be extubated in the first 3 days of life, infants who were reintubated or needed high continuous positive airway pressure settings after extubation had a smaller disaturated phosphatidylcholine pool size than did those who were successfully extubated or needed low continuous positive airway pressure settings.

What's new in surfactant? A clinical view on recent developments in neonatology and paediatrics

Surfactant therapy has significantly changed clinical practice in neonatology over the last 25 years. Recent trials in infants with respiratory distress syndrome (RDS) have not shown superiority of any natural surfactant over another. Advancements in the development of synthetic surfactants are promising, yet to date none has been shown to be superior to natural preparations. Ideally, surfactant would be administered without requiring mechanical ventilation. An increasing number of studies investigate the roles of alternative modes of administration and the use of nasal continuous positive airway pressure to minimise the need for mechanical ventilation. Whether children with other lung diseases benefit from surfactant therapy is less clear. Evidence suggests that infants with meconium aspiration syndrome and children with acute lung injury/acute respiratory distress syndrome may benefit, while no positive effect of surfactant is seen in infants with congenital diaphragmatic hernia. However, more research is needed to establish potential beneficial effects of surfactant administration in children with lung diseases other than RDS. Furthermore, genetic disorders of surfactant metabolism have recently been linked to respiratory diseases of formerly unknown origin. It is important to consider these disorders in the differential diagnosis of unexplained respiratory distress although no established treatment is yet available besides lung transplantation for the most severe cases.

CONCLUSION

Research around surfactant is evolving and recent developments include further evolution of synthetic surfactants, evaluation of surfactant as a therapeutic option in lung diseases other than RDS and the discovery of genetic disorders of surfactant metabolism. Ongoing research is essential to continue to improve therapeutic prospects for children with serious respiratory disease involving disturbances in surfactant.