Pulmonary surfactant therapy

Animal derived surfactant extract for treatment of respiratory distress syndrome

BACKGROUND

Respiratory distress syndrome (RDS) is caused by a deficiency or dysfunction of pulmonary surfactant. A wide variety of surfactant products have been formulated and studied in clinical trials. These include synthetic surfactants and animal derived surfactant extracts. Trials of surfactant replacement have either tried to prevent the development of respiratory distress in high-risk premature infants or treat established respiratory distress in premature infants.

OBJECTIVES

To assess the effect of administration of animal derived surfactant extract on mortality, chronic lung disease and other morbidities associated with prematurity in preterm infants with established respiratory distress syndrome. Subgroup analysis were planned according to the specific surfactant product, the degree of prematurity, and the severity of disease.

SEARCH STRATEGY

Searches were made of the Oxford Database of Perinatal Trials, MEDLINE, EMBASE, and CINAHL from 1975 through December 2008. In addition, searches were made of previous reviews including cross references, abstracts, conference and symposia proceedings, expert informants and journal hand searching in the English language.

SELECTION CRITERIA

Randomized or quazi-randomized controlled trials that compared the effect of animal derived surfactant extract treatment administered to infants with established respiratory distress syndrome in order to prevent complications of prematurity and mortality.

DATA COLLECTION AND ANALYSIS

Data regarding clinical outcomes were excerpted from the reports of the clinical trials by the review authors. Data analysis was done in accordance with the standards of the Cochrane Neonatal Review Group.

MAIN RESULTS

Thirteen randomized controlled trials were included in the analysis. The studies demonstrated an initial improvement in respiratory status (improved oxygenation and decreased need for ventilator support). The meta-analysis supports a significant decrease in the risk of any air leak (typical relative risk 0.47, 95% CI 0.39, 0.58; typical risk difference -0.16, 95% CI -0.21, -0.12), pneumothorax (typical relative risk 0.42, 95% CI 0.34, 0.52; typical risk difference -0.17, 95% CI -0.21, -0.13), and a significant decrease in the risk of pulmonary interstitial emphysema (typical relative risk 0.45, 95% CI 0.37, 0.55; typical risk difference -0.20, 95% CI -0.25, -0.15). There is a significant decrease in the risk of neonatal mortality (typical relative risk 0.68, 95% CI 0.57, 0.82; typical risk difference -0.09, 95% CI -0.13, -0.05), a significant decrease in the risk of mortality prior to hospital discharge (typical relative risk 0.63, 95% CI 0.44, 0.90; typical risk difference -0.10, 95% CI -0.18, -0.03) and a significant decrease in the risk of bronchopulmonary dysplasia (BPD) or death at 28 days of age (typical relative risk 0.83, 95% CI 0.77, 0.90; typical risk difference -0.11, 95 CI -0.16, -0.06). No differences are reported in the risk of patent ductus arteriosus, necrotizing enterocolitis, intraventricular hemorrhage, BPD or retinopathy of prematurity.

AUTHORS' CONCLUSIONS

Infants with established respiratory distress syndrome who receive animal derived surfactant extract treatment have a decreased risk of pneumothorax, a decreased risk of pulmonary interstitial emphysema, a decreased risk of mortality, and a decreased risk of bronchopulmonary dysplasia or death.

Role of lung surfactant in respiratory disease: current knowledge in large animal medicine

Lung surfactant is produced by type II alveolar cells as a mixture of phospholipids, surfactant proteins, and neutral lipids. Surfactant lowers alveolar surface tension and is crucial for the prevention of alveolar collapse. In addition, surfactant contributes to smaller airway patency and improves mucociliary clearance. Surfactant-specific proteins are part of the innate immune defense mechanisms of the lung. Lung surfactant alterations have been described in a number of respiratory diseases. Surfactant deficiency (quantitative deficit of surfactant) in premature animals causes neonatal respiratory distress syndrome. Surfactant dysfunction (qualitative changes in surfactant) has been implicated in the pathophysiology of acute respiratory distress syndrome and asthma. Analysis of surfactant from amniotic fluid allows assessment of fetal lung maturity (FLM) in the human fetus and exogenous surfactant replacement therapy is part of the standard care in premature human infants. In contrast to human medicine, use and success of FLM testing or surfactant replacement therapy remain limited in veterinary medicine. Lung surfactant has been studied in large animal models of human disease. However, only a few reports exist on lung surfactant alterations in naturally occurring respiratory disease in large animals. This article gives a general review on the role of lung surfactant in respiratory disease followed by an overview of our current knowledge on surfactant in large animal veterinary medicine.

Complications of the late preterm infant

One of the goals of Healthy People 2010 (set in 1998) was to reduce preterm birthrates from 11.6% to 7.6%. However, in 2004, the preterm birthrate of 12.5% was actually higher than the rate in 1998. Approximately 65% of this increase in prematurity rate is attributed to the increasing birthrate of the late preterm infant. Care of the late preterm infant is far more complicated than many hospital policies and clinical guidelines imply. It cannot be stressed enough to frontline clinicians that late preterm infants are not full-term infants. Their care should not be defined by the same policies and practices that govern term infants. The purpose of this article is to explore the complications that accompany late preterm birth. The following complications will be discussed: thermoregulation challenges, feeding difficulty, late neonatal sepsis, prolonged physiologic jaundice, hypoglycemia, possible neurodevelopmental differences, and respiratory problems.

Effect of covalent antithrombin-heparin complex on developmental mechanisms in the lung

We have developed a potent antithrombin (AT)-heparin conjugate (ATH) that is retained in the lung to prevent pulmonary thrombosis associated with respiratory distress in premature newborns. During continuing maturation, pulmonary angiogenesis in premature infants would be a crucial process in lung development. A naturally occurring latent form of antithrombin (L-AT) has antiangiogenic effects on lung vascularization. However, impact of latent ATH (L-ATH) on developing lung vascularization is unknown. Thus, effects of L-AT and L-ATH on fetal murine lung development were compared. Lung buds from embryonic day 11.5 (E11.5) Tie2-LacZ mouse embryos were incubated in DMEM plus FBS supplemented with PBS, AT, L-AT, heparin, ATH, or L-ATH. Vasculature of cultured explants was quantified by X-galactosidase staining. RNA was analyzed with murine gene probes for angiopoietin (Ang)-1, Ang-2, fibroblast growth factor 2 (FGF2), platelet endothelial cell adhesion molecule (PECAM), and vascular endothelial growth factor (VEGF). FGF2-supplemented medium was used to test contribution to effects of L-AT and L-ATH on angiogenesis. Epithelial branching morphogenesis was inhibited by L-AT (P = 0.003) and heparin (P < 0.001). L-AT and heparin decreased relative vascular area compared with PBS, ATH, and L-ATH. Expressions of all genes studied were downregulated by L-AT. However, L-AT and L-ATH inhibited branching morphogenesis and vasculature with added FGF2. These findings indicate that covalent linkage of AT to heparin negates disruptive effects of these moieties on lung morphology, vascularization, and growth factor gene expression. ATH may have enhanced safety as an anticoagulant during vascular development.

Macrophage dysfunction and susceptibility to pulmonary Pseudomonas aeruginosa infection in surfactant protein C-deficient mice

To determine the role of surfactant protein C (SP-C) in host defense, SP-C-deficient (Sftpc-/-) mice were infected with the pulmonary pathogen Pseudomonas aeruginosa by intratracheal injection. Survival of young, postnatal day 14 Sftpc-/- mice was decreased in comparison to Sftpc+/+ mice. The sensitivity to Pseudomonas bacteria was specific to the 129S6 strain of Sftpc-/- mice, a strain that spontaneously develops interstitial lung disease-like lung pathology with age. Pulmonary bacterial load and leukocyte infiltration were increased in the lungs of Sftpc-/- mice 24 h after infection. Early influx of polymorphonuclear leukocytes in the lungs of uninfected newborn Sftpc-/- mice relative to Sftpc+/+ mice indicate that the lack of SP-C promotes proinflammatory responses in the lung. Mucin expression, as indicated by Alcian blue staining, was increased in the airways of Sftpc-/- mice following infection. Phagocytic activity of alveolar macrophages from Sftpc-/- mice was reduced. The uptake of fluorescent beads in vitro and the number of bacteria phagocytosed by alveolar macrophages in vivo was decreased in the Sftpc-/- mice. Alveolar macrophages from Sftpc-/- mice expressed markers of alternative activation that are associated with diminished pathogen response and advancing pulmonary fibrosis. These findings implicate SP-C as a modifier of alveolar homeostasis. SP-C plays an important role in innate host defense of the lung, enhancing macrophage-mediated Pseudomonas phagocytosis, clearance and limiting pulmonary inflammatory responses.

Protein containing synthetic surfactant versus animal derived surfactant extract for the prevention and treatment of respiratory distress syndrome

BACKGROUND

Respiratory distress syndrome (RDS) is a significant cause of morbidity and mortality in preterm infants. RDS is caused by a deficiency, dysfunction, or inactivation of pulmonary surfactant. Numerous surfactants of either animal extract or synthetic design have been shown to improve outcomes. New surfactant preparations that include peptides or whole proteins that mimic endogenous surfactant protein have recently been developed and tested.

OBJECTIVES

To assess the effect of administration of synthetic surfactant containing surfactant protein mimics compared to animal derived surfactant extract on the risk of mortality, chronic lung disease, and other morbidities associated with prematurity in preterm infants at risk for or having RDS.

SEARCH STRATEGY

Standard search methods of the Cochrane Neonatal Review Group were used. The search included MEDLINE (1966 - May 2007) and the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library) in all languages. In addition, published abstracts of the Society of Pediatric Research were searched electronically. For abstract books that did not include key words, the search was limited to the relevant sections on pulmonary and neonatology. The bibliography cited in each publication was obtained and searched in order to identify additional relevant articles.

SELECTION CRITERIA

Randomized and quasi-randomized controlled clinical trials were considered for this review. Studies that enrolled preterm infants or low birth weight infants at risk for or having RDS who were treated with either a synthetic surfactant containing surfactant protein mimics or an animal-derived surfactant preparation were included for this review. Studies that either attempted to treat or prevent respiratory distress syndrome were included.

DATA COLLECTION AND ANALYSIS

Primary outcome measures, including mortality, chronic lung disease and multiple secondary outcome measures were abstracted by the reviewers. Statistical analysis was performed using Review Manager software. Categorical data was analyzed using relative risk, risk difference, and number needed to treat. 95% confidence intervals reported. A fixed effects model was used for the meta-analysis. Heterogeneity was assessed using the I-squared statistic.

MAIN RESULTS

Two studies were identified that compared protein containing synthetic surfactants to animal derived surfactant preparations. In a meta-analysis of these two studies, infants who received protein containing synthetic surfactant compared to animal derived surfactant extract did not demonstrate significantly different risks of prespecified primary outcomes: mortality at 36 weeks [typical RR 0.81 (95% CI 0.64, 1.03)], chronic lung disease at 36 weeks [typical RR 0.99 (95% CI 0.84, 1.18)], or the combined outcome of mortality or chronic lung disease at 36 weeks [typical RR 0.96 (95% CI 0.82, 1.12)]. There were also no differences in any of the secondary outcomes regarding complications of prematurity between the two surfactant groups with the exception of necrotizing enterocolitis. A decrease in the risk of necrotizing enterocolitis was noted in infants who received protein containing synthetic surfactants compared to animal derived surfactant extract [typical RR 0.60 (95% CI 0.42, 0.86)]. However, this was a secondary outcome in both of the primary studies and there was moderate heterogeneity between the studies.

AUTHORS' CONCLUSIONS

In two trials of protein containing synthetic surfactants compared to animal derived surfactant extract, no statistically different clinical differences in death and chronic lung disease were noted. In general, clinical outcomes between the two groups were similar. Further well designed studies of adequate size and power will help confirm and refine these findings.

Outcome and hospital cost for infants weighing less than 500 grams: a tertiary centre experience in Taiwan

AIM

To determine the outcome and hospital cost for infants weighing < or =500 g at a tertiary centre in Taiwan.

METHODS

We retrospectively reviewed the medical records of infants who were born alive with birthweight < or =500 g at the National Taiwan University Hospital from 1997 to 2004. Their outcome and hospital cost were analysed.

RESULTS

A total of 168 infants were included for analysis that 146 of them died after compassionate care in the delivery room and 22 received postnatal resuscitation. The infants who received resuscitation were more likely to have higher birthweights, older gestational ages and multiple births compared with those who received compassionate care. After resuscitation, five of the infants died and 17 were admitted to neonatal intensive care unit (NICU) for further management. Subsequently, 12 infants died and five infants survived to discharge. Two infants were discharged against advice and died within days. After exclusion of those receiving compassionate care, the NICU survival rate was 22.7% and the long-term survival rate was 13.6%. The most common early morbidities were respiratory distress syndrome, intraventricular haemorrhage and patent ductus arteriosus, whereas the late morbidities included cholestatic jaundice, retinopathy of prematurity and chronic lung disease. The average total hospital costs for the NICU survivors with birthweight < or =500 g was US $42,411 and the average hospital cost per day was US $350.

CONCLUSION

Exclusive compassionate care was given to the majority of the infants weighing < or =500 g in Taiwan. The survival rate remained low in these marginally viable infants.

Protein containing synthetic surfactant versus animal derived surfactant extract for the prevention and treatment of respiratory distress syndrome

BACKGROUND

Respiratory distress syndrome (RDS) is a significant cause of morbidity and mortality in preterm infants. RDS is caused by a deficiency, dysfunction, or inactivation of pulmonary surfactant. Numerous surfactants of either animal extract or synthetic design have been shown to improve outcomes. New surfactant preparations that include peptides or whole proteins that mimic endogenous surfactant protein have recently been developed and tested.

OBJECTIVES

To assess the effect of administration of synthetic surfactant containing surfactant protein mimics compared to animal derived surfactant extract on the risk of mortality, chronic lung disease, and other morbidities associated with prematurity in preterm infants at risk for or having RDS.

SEARCH STRATEGY

Standard search methods of the Cochrane Neonatal Review Group were used. The search included MEDLINE (1966 - May 2007) and the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library) in all languages. In addition, published abstracts of the Society of Pediatric Research were searched electronically. For abstract books that did not include key words, the search was limited to the relevant sections on pulmonary and neonatology. The bibliography cited in each publication was obtained and searched in order to identify additional relevant articles.

SELECTION CRITERIA

Randomized and quasi-randomized controlled clinical trials were considered for this review. Studies that enrolled preterm infants or low birth weight infants at risk for or having RDS who were treated with either a synthetic surfactant containing surfactant protein mimics or an animal-derived surfactant preparation were included for this review. Studies that either attempted to treat or prevent respiratory distress syndrome were included.

DATA COLLECTION AND ANALYSIS

Primary outcome measures, including mortality, chronic lung disease and multiple secondary outcome measures were abstracted by the reviewers. Statistical analysis was performed using Review Manager software. Categorical data was analyzed using relative risk, risk difference, and number needed to treat. 95% confidence intervals reported. A fixed effects model was used for the meta-analysis. Heterogeneity was assessed using the I-squared statistic.

MAIN RESULTS

Two studies were identified that compared protein containing synthetic surfactants to animal derived surfactant preparations. In a meta-analysis of these two studies, infants who received protein containing synthetic surfactant compared to animal derived surfactant extract did not demonstrate significantly different risks of prespecified primary outcomes: mortality at 36 weeks [typical RR 0.81 (95% CI 0.64, 1.03)], chronic lung disease at 36 weeks [typical RR 0.99 (95% CI 0.84, 1.18)], or the combined outcome of mortality or chronic lung disease at 36 weeks [typical RR 0.96 (95% CI 0.82, 1.12)]. There were also no differences in any of the secondary outcomes regarding complications of prematurity between the two surfactant groups with the exception of necrotizing enterocolitis. A decrease in the risk of necrotizing enterocolitis was noted in infants who received protein containing synthetic surfactants compared to animal derived surfactant extract [typical RR 0.60 (95% CI 0.42, 0.86)]. However, this was a secondary outcome in both of the primary studies and there was moderate heterogeneity between the studies.

AUTHORS' CONCLUSIONS

In two trials of protein containing synthetic surfactants compared to animal derived surfactant extract, no statistically different clinical differences in death and chronic lung disease were noted. Further well designed studies of adequate size and power will be needed to confirm and refine these findings.

Level and volume of neonatal intensive care and mortality in very-low-birth-weight infants

BACKGROUND

There has been a large increase in both the number of neonatal intensive care units (NICUs) in community hospitals and the complexity of the cases treated in these units. We examined differences in neonatal mortality among infants with very low birth weight (below 1500 g) among NICUs with various levels of care and different volumes of very-low-birth-weight infants.

METHODS

We linked birth certificates, hospital discharge abstracts (including interhospital transfers), and fetal and infant death certificates to assess neonatal mortality rates among 48,237 very-low-birth-weight infants who were born in California hospitals between 1991 and 2000.

RESULTS

Mortality rates among very-low-birth-weight infants varied according to both the volume of patients and the level of care at the delivery hospital. The effect of volume also varied according to the level of care. As compared with a high level of care and a high volume of very-low-birth-weight infants (more than 100 per year), lower levels of care and lower volumes (except for those of two small groups of hospitals) were associated with significantly higher odds ratios for death, ranging from 1.19 (95% confidence interval [CI], 1.04 to 1.37) to 2.72 (95% CI, 2.37 to 3.12). Less than one quarter of very-low-birth-weight deliveries occurred in facilities with NICUs that offered a high level of care and had a high volume, but 92% of very-low-birth-weight deliveries occurred in urban areas with more than 100 such deliveries.

CONCLUSIONS

Mortality among very-low-birth-weight infants was lowest for deliveries that occurred in hospitals with NICUs that had both a high level of care and a high volume of such patients. Our results suggest that increased use of such facilities might reduce mortality among very-low-birth-weight infants.

Solubility versus electrostatics: what determines lipid/protein interaction in lung surfactant

Mammalian lung surfactant is a complex lipid/protein mixture covering the alveolar interface and has the crucial function of reducing the surface tension at this boundary to minimal values. Surfactant protein SP-B plays an important role for this purpose and was the focus of many recent studies. However, the specificity of lipid/SP-B interactions is controversial. Since these investigations were accomplished at varying pH conditions (pH 5.5 and 7.0), we studied the specificity of these interactions in a dipalmitoylphosphatidylcholine (DPPC)/dipalmitoylphosphatidylglycerol (DPPG)/SP-B (4:1:0.2 mol %) model system at either pH. Mainly fluorescence microscopy and laterally resolved time-of-flight secondary ion mass spectrometry were used to reveal information about the phase behavior of the lipids and the molecular distribution of SP-B in the lipid mixture. DPPG forms separated condensed domains due to a strong hydrogen-bond network, from which the protein is mainly excluded. Considering the protein as an impurity of the lipid mixture leads to the principle of the zone melting process: an impurity is highly more soluble in a liquid phase than in a solid phase. The phase behavior effect of the lipids mainly outperforms the electrostatic interactions between DPPG and SP-B, leading to a more passively achieved colocalization of DPPC and SP-B.

Improvement in neonatal intensive care in Northern Ireland through sharing of audit data

PROBLEM

Ten percent of infants born will require admission to a neonatal facility. Coordinated activity to monitor and improve the quality of care for this high risk, high cost group of infants is considered a high priority. At the time of initiation of this project no system for collection and analysis of neonatal data existed in Northern Ireland.

DESIGN

In 1994 an ongoing prospective centralised data collection system was implemented to facilitate quality improvement and research in neonatal care. We aim to ascertain if there has been a demonstrable improvement in the quality of care provided since the initiation of this system.

SETTING

All nine Northern Ireland neonatal intensive care units returned prospectively collected socioeconomic, obstetric and neonatal episode data.

KEY MEASURES FOR IMPROVEMENT

Achievement of the agreed quality indicators relating to transfer patterns, thermoregulation, antenatal steroid administration, and timing of administration of surfactant during the period 1 April 1999 to 31 March 2000 were compared with data for the period 1 April 1994 to 31 March 1996.

STRATEGIES FOR CHANGE

Monitoring included audit and annual feedback of timely clear and relevant data where results were provided confidentially as standardised reports, together with anonymised comparisons with other similar sized units. Draft recommendations were made at regional level and units were asked to adopt finalized consensus guidelines at the local level and to implement changes to clinical practice.

EFFECTS OF CHANGE

The proportion of transfers taking place in utero increased from 26% to 42% and antenatal steroid administration from 68% to 82%. Normothermia on first admission improved from 66% to 71% for inborn infants. The proportion of infants receiving surfactant where the first dose was given within an hour of birth increased from 13% to 66%.

LESSONS LEARNT

A multi-professional regional care network can facilitate the development of agreed standards and a culture of regular evaluation leading to quality improvement.

Comparison of surfactant protein B polymorphisms of healthy term newborns with preterm newborns having respiratory distress syndrome

Polymorphisms and mutations in the surfactant protein B (SP-B) gene have been associated with the pathogenesis of respiratory distress syndrome (RDS). The objective of the present study was to compare the frequencies of SP-B gene polymorphisms between preterm babies with RDS and healthy term newborns. We studied 50 preterm babies with RDS (inclusion criteria - newborns with RDS and gestational age between 28 and 33 weeks and 6 days), and 100 healthy term newborns. Four SP-B gene polymorphisms were analyzed: A/C at nucleotide -18, C/T at nucleotide 1580, A/G at nucleotide 9306, and G/C at nucleotide 8714, by PCR amplification of genomic DNA and genotyping by cRFLP. The healthy newborns comprised 42 female and 58 male neonates; 39 were white and 61 non-white. The RDS group comprised 21 female and 29 male preterm neonates; 28 were white and 22 non-white. Weight ranged from 640 to 2080 g (mean: 1273 g); mean gestational age was 31 weeks and 2 days (range: 28-33 weeks and 6 days). When white children were analyzed separately, a statistically significant difference in the G/C polymorphism at 8714 was observed between groups (P = 0.028). All other genotype frequencies were similar for both groups when sex and race were analyzed together. Analysis of the SP-B polymorphism G/C at nucleotide 8714 showed that among white neonates the GG genotype was found only in the RDS group at a frequency of 17% and the GC genotype was more frequently found in healthy term newborns. These data demonstrate an association of GG genotype with RDS.

Low birth weight in the United States

Pregnancy outcomes in the United States and other developed countries are considerably better than those in many developing countries. However, adverse pregnancy outcomes are generally more common in the United States than in other developed countries. Low-birth-weight infants, born after a preterm birth or secondary to intrauterine growth restriction, account for much of the increased morbidity, mortality, and cost. Wide disparities exist in both preterm birth and growth restriction among different population groups. Poor and black women, for example, have twice the preterm birth rate and higher rates of growth restriction than do most other women. Low birth weight in general is thought to place the infant at greater risk of later adult chronic medical conditions, such as diabetes, hypertension, and heart disease. Of interest, maternal thinness is a strong predictor of both preterm birth and fetal growth restriction. However, in the United States, several nutritional interventions, including high-protein diets, caloric supplementation, calcium and iron supplementation, and various other vitamin and mineral supplementations, have not generally reduced preterm birth or growth restriction. Bacterial intrauterine infections play an important role in the etiology of the earliest preterm births, but, at least to date, antibiotic treatment either before labor for risk factors such as bacterial vaginosis or during preterm labor have not consistently reduced the preterm birth rate. Most interventions have failed to reduce preterm birth or growth restriction. The substantial improvement in newborn survival in the United States over the past several decades is mostly due to better access to improved neonatal care for low-birth-weight infants.

Criteria supporting the study of drugs in the newborn

BACKGROUND

Profound changes in the development and the maturation of neonates' organs and organ systems over variable periods of time potentially place neonates at increased risk and/or at different risks compared with adults or older children on exposure to pharmaceutical agents. Most studies of drugs in neonates focus on pharmacokinetic and pharmacodynamic end points and include insufficient numbers of patients to permit evaluation of safety. Only one fourth to one third of approved drugs have received adequate pediatric study to permit labeling for treatment of all appropriate pediatric populations.

OBJECTIVE

The initial goal of the Newborn Drug Prioritization Group was to develop a reproducible, objective process for evaluating drugs most in need of study in the neonatal population based on a universally acceptable priority ranking. The criteria would be applicable across therapeutic classes and would identify those drugs for which immediate study was most needed.

METHODS

Because the therapeutic requirements of the neonate are unique in comparison to older infants and children, the National Institute of Child Health and Human Development and the US Food and Drug Administration (FDA) developed the Newborn Drug Development Initiative to address the limited study of off-patent drugs in newborns. In March 2003, they convened a meeting of pediatric pharmacologists and pediatric specialists from the FDA, the American Academy of Pediatrics, the National Institutes of Health, and academic institutions to discuss how to increase the study of drugs for the newborn. One of the working groups was charged to develop generic criteria for overall prioritization of drugs for study in newborns. Because resources are limited, and not all drugs identified by the 4 clinically focused working groups can receive study at the same time, a process for priority ranking is necessary.

RESULTS

The panel identified 4 general categories containing different numbers of criteria as important for ranking drugs for priority investigation: (1) the disease and indication, including elements such as the potential for adverse outcomes, frequency in newborns, and level of evidence for treatment of newborns; (2) drug characteristics, including elements such as duration of dosing, lack of age-appropriate formulation, clinically relevant drug-drug and drug-disease interactions, and drug disposition in newborns; (3) feasibility and methodology for newborn studies, including both analytical considerations and clinical end points; and (4) the ethical basis for study, including elements to address benefit or harm due to exposure to the study drug, study methodology, and benefit of the new treatment relative to established standard therapy. Based on these categories, a list of criteria to warrant study of a drug in newborns was developed.

CONCLUSION

A process for judicious use of limited resources to rectify these deficiencies remains an urgent public health need.

Effect of viscosity on instilled perfluorocarbon distribution in rabbit lungs

The effect of viscosity on the distribution of perfluorocarbon instilled into the lungs for liquid ventilation was investigated. Perfluorocarbon (either perfluorodecalin or FC-3283) was instilled into the trachea during ventilation at a constant infusion rate of 40 ml/min and radiographic images were obtained at 30 frames/s. Image analysis was performed and the homogeneity index of the distribution was computed for images at the end of inspiration of each breath to evaluate the evolution of perfluorocarbon distribution during filling. The higher viscosity perfluorocarbon (perfluorodecalin) resulted in a more homogeneous distribution. This was attributed to perfluorodecalin's higher propensity to form liquid plugs in large airways and to those plugs leaving behind a thicker liquid layer as they propagated through the lungs.

The changing risk of infant mortality by gestation, plurality, and race: 1989-1991 versus 1999-2001

OBJECTIVE

Our aim was to quantify contemporary infant mortality risks and to evaluate the change by plurality, gestation, and race during the most recent decade.

PATIENTS AND METHODS

The study population included live births of 20 to 43 weeks' gestation from the 1989-1991 and 1999-2001 US Birth Cohort Linked Birth/Infant Death Data Sets, including 11,317,895 and 11,181,095 live births and 89,823 and 67,129 infant deaths, respectively. Adjusted odds ratios and 95% confidence intervals were calculated to evaluate the change in risk by plurality and gestation and to compare the change with that for singletons.

RESULTS

Overall, the infant mortality risk decreased significantly for singletons, twins, and triplets but nonsignificantly for quadruplets and quintuplets. Compared with singletons, significantly greater reductions were experienced by twins overall and at <37 weeks and triplets at <29 weeks. The largest reduction was for triplets at 20 to 24 weeks and for quadruplets and quintuplets at 25 to 28 weeks. For white infants, significant reductions were achieved overall for singletons, twins, and triplets and at every gestation. For black infants, significant reductions occurred for singletons overall and at every gestation, for twins at <37 weeks, and for triplets at 25 to 28 weeks. Compared with white infants, black infants had significantly lower risks before and higher risks after 33 weeks, although between 1989-1991 and 1999-2001 this survival advantage at earlier ages diminished, and the risk at later gestations increased.

CONCLUSIONS

The improvements in survival were greater for multiples versus singletons and for white versus black infants. Within each plurality, at each gestation the racial disparity in mortality has widened.

Haplotypes of surfactant protein C are associated with common paediatric lung diseases

Surfactant protein C is part of the surfactant complex lining up the alveoles and thereby inhibiting collapse of the airways. In addition it is involved in innate immune responses. Rare polymorphisms within surfactant protein C have been linked to sporadic paediatric lung diseases, like proteinosis or interstitial lung diseases. One study in the Finnish population described association of common polymorphisms with neonatal respiratory syndrome. Other common lung diseases have not yet been investigated for association with this gene. The aim of this study was to test surfactant protein C for association with bronchial asthma and with severe respiratory syncytial virus associated diseases in infancy. The two common amino acid variants Asn138Thr and Asn186Ser were genotyped on 322 children with asthma, 131 children with severe respiratory syncytial virus associated diseases and 270 controls. Statistical analyses of single polymorphisms made use of the Armitage's trend test; haplotypes were calculated with FAMHAP and FASTEHPLUS. Polymorphisms were in Hardy-Weinberg equilibrium and in tight linkage equilibrium in all populations. Single polymorphisms showed no association with the diseases, however, surfactant protein C haplotypes were associated with severe respiratory syncytial virus associated diseases (p = 0.013). Furthermore, an inverse haplotype distribution was found between children with asthma and respiratory syncytial virus infection (p = 0.00025). The results of our study might suggest opposing roles of surfactant Protein C in the genetic predisposition for respiratory syncytial virus associated diseases vs. asthma. The causal mechanism for this observation has still to be shown.

Exogenous surfactant therapy for ARDS

Regardless of the cause, a common pathophysiological feature of patients with acute respiratory distress syndrome is a dysfunction of the endogenous surfactant system. Although exogenous surfactant therapy has proven to be an effective treatment for neonatal respiratory distress syndrome, no similar current effective therapy exists for patients with acute respiratory distress syndrome. This is mainly due to the complexity of the lung injury that is involved with this disorder. Results from clinical trials, to date, have failed to show an improvement in patient survival after administration of exogenous surfactant; however, ongoing and future research efforts suggest that this therapy may eventually be feasible.

Lung surfactants

PURPOSE

The pharmacology, clinical efficacy, and cost considerations of exogenous lung surfactants are reviewed.

SUMMARY

Exogenous pulmonary surfactants, along with advancements in ventilatory care, have significantly reduced the incidence of respiratory distress syndrome (RDS) and its related complications in infants. The following exogenous surfactants are approved for the prophylaxis and treatment (rescue) of neonatal RDS: beractant, a modified natural surfactant; calfactant and poractant, both natural surfactants; and colfosceril, a synthetic surfactant that is not currently available in the United States. Lucinactant, a synthetic surfactant, is under investigation and received approvable status from the Food and Drug Administration in February 2005. The surfactants are delivered directly to their site of action, and only small amounts reach the systemic circulation. Bioavailability to the distal airways and alveoli depends on the method of delivery, the stage and severity of pulmonary disease, and the properties of the particular surfactant. According to data from clinical trials, the use of exogenous surfactant therapy for rescue within the first two hours of life appears to be as efficacious as prophylaxis in most premature infants.

CONCLUSION

Comparative trials of surfactants have proven the efficacy of both synthetic and natural surfactants in the prevention and treatment of RDS. However, these trials have universally demonstrated greater reduction in the immediate need for ventilator support in infants who receive natural surfactants. Natural preparations cause less pneumothorax, bronchopulmonary dysplasia, and mortality compared with synthetic preparations. Synthetic agents offer the potential advantages of an unlimited supply with consistent pharmaceutical quality and no risk of transmitting infectious disease or causing immunologic sensitization.

Surfactant therapy for bronchiolitis in critically ill infants

BACKGROUND

Viral bronchiolitis is a common cause of respiratory failure in infants and children, and accounts for a significant portion of intensive care unit (ICU) admissions during seasonal epidemics. Currently there is no evidence to support the use of anything but supportive care for this disease. Surfactant is a potentially promising therapy; alterations in its composition have been described in bronchiolitis, and it may play a role in the host immunity for this disease.

OBJECTIVES

The objective of this review was to assess the efficacy of exogenous surfactant for the treatment of bronchiolitis in mechanically ventilated infants and children.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 1, 2006); MEDLINE (1966 to Week 1, February 2006); and EMBASE (1990 to September 2005). We reviewed reference lists of relevant articles and contacted experts in the field.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing surfactant with placebo or surfactant with no surfactant in mechanically ventilated infants and children with viral bronchiolitis.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted data and assessed trial quality. Unpublished data were requested from trial authors when necessary.

MAIN RESULTS

Three trials containing a total of 79 patients met the inclusion criteria. No mortality or adverse effects associated with surfactant administration were reported in any of these trials. In the three trials, use of surfactant was associated with a decrease in duration of mechanical ventilation by 2.6 days (95% confidence interval (CI) -5.34 to 0.18 days; P value 0.07) and a decrease in ICU length of stay by 3.3 days (95% CI -6.38 to -0.23 days; P value 0.04). In two studies with 59 patients, in which duration of mechanical ventilation in the control groups was more comparable, surfactant was associated with a decrease in ventilator days by 1.21 days (95% CI 0.75 to 1.67 days) and a decrease in ICU stay by 1.81 days (95% CI 1.19 days to 2.42 days). Individually the studies reported some short term benefit of surfactant on pulmonary mechanics and gas exchange.

AUTHORS' CONCLUSIONS

Available data on surfactant were not sufficient to provide reliable estimates of its effects in mechanically ventilated infants and children with bronchiolitis. Future studies should be adequately powered and will need to address unresolved questions regarding which surfactant preparation may be best suited for the treatment of bronchiolitis, the appropriate dose and administration interval, and how the choice of ventilator strategy may modify its effects.

Genetics of pediatric interstitial lung disease

PURPOSE OF REVIEW

The interstitial lung diseases are a heterogeneous group of rare disorders of largely unknown etiology. The occurrence of familial cases of pediatric interstitial lung diseases with the onset of symptoms developing early in infancy has suggested a genetic basis for some forms of interstitial lung diseases in children.

RECENT FINDINGS

Mutations in the genes encoding surfactant protein C, SFTPC, and a member of the adenosine triphosphate-binding cassette family of proteins, ABCA3, have been shown to result in pediatric interstitial lung diseases inherited in autosomal-dominant and autosomal-recessive patterns, respectively. There is overlap in both the clinical and histopathologic features of these disorders.

SUMMARY

Identification of genes responsible for pediatric interstitial lung diseases provides the opportunity for noninvasive testing to establish an etiologic diagnosis, to counsel family members for their recurrence risk, and to classify these rare disorders more accurately. A better understanding of the cause and pathophysiology of these disorders may provide additional insights into the causes of other forms of pediatric interstitial lung diseases, and may suggest novel treatment approaches.

Recent clinical trials of surfactant treatment for neonates

OBJECTIVE

To search for recent clinical trials of neonatal surfactant treatment and report their findings.

METHODS

Recent was defined as published between 2000 and 2005. An online search on PubMed was made on 30th December 2005 using the following terms: surfactant treatment, clinical trials and neonate, with limits of years 2000 to 2005 and age - newborn from birth to 1 month. Randomised clinical trials (RCTs) and systematic reviews of RCTs were prioritised and studies in children and animals were excluded from further analysis.

RESULTS

175 papers were found in this search. Only about half of these papers were directly related to some aspect of surfactant treatment and of these just over one-half were either RCTs or systematic reviews of RCTs. Of the 34 RCTs of surfactant treatment, 3 were excluded as they involved children or animals rather than neonates. Twenty-nine trials studied preterm babies with respiratory distress syndrome (RDS) and 2 were for meconium aspiration syndrome (MAS) in term infants. The median sample sizes of these studies were RDS (92, range 19-1,361) and MAS (42, range 22-61). Eighteen of the RDS trials compared two or more surfactant preparations, the most frequently studied being Curosurf and Survanta but altogether 11 different surfactants were compared. These new RCTs need to be analysed by meta-analyses in systematic reviews. Twelve systematic reviews were found and these demonstrated the superiority of prophylactic over selective use of surfactant in babies <30 weeks, natural over synthetic surfactant and the absence of an increase in long-term developmental sequelae. Surfactant for MAS may reduce the severity of respiratory illness and the need for extracorporeal membrane oxygenation. Of the non-randomised trials' novel delivery methods, failure to use evidence-based guidelines and the benefit of surfactant for babies <25 weeks were the most interesting.

CONCLUSIONS

Surfactant remains one of the most effective and safest interventions in neonatology. Prophylactic natural surfactant seems to be the most evidence-based treatment for babies <30 weeks. Of the newer synthetic surfactants, only Surfaxin has been compared with currently used surfactants and systematic reviews are needed to establish if it has a role in treatment of RDS. The improvement in outcome for babies <25 weeks has been due to a number of interventions: prenatal steroids, prenatal antibiotics and postnatal surfactant. Clinical trials of surfactant replacement in the neonate continue to be published with remarkable frequency.

Effects of Inertia and Gravity on Liquid Plug Splitting at a Bifurcation

Liquid plugs may form in pulmonary airways during the process of liquid instillation or removal in many clinical treatments. During inspiration the plug may split at airway bifurcations and lead to a nonuniform final liquid distribution, which can adversely affect treatment outcomes. In this paper, a combination of bench top experimental and theoretical studies is presented to study the effects of inertia and gravity on plug splitting in an airway bifurcation model to simulate the liquid distributions in large airways. The splitting ratio, Rs, is defined as the ratio of the plug volume entering the upper (gravitationally opposed) daughter tube to the lower (gravitationally favored) one. Rs is measured as a function of parent tube Reynolds number, Rep; gravitational orientations for roll angle, ϕ, and pitch angle, γ; parent plug length LP; and the presence of pre-existing plug blockages in downstream daughter tubes. Results show that increasing Rep causes more homogeneous splitting. A critical Reynolds number Rec is found to exist so that when Rep⩽Rec, Rs=0, i.e., no liquid enters the upper daughter tube. Rec increases while Rs decreases with increasing the gravitational effect, i.e., increasing ϕ and γ. When a blockage exists in the lower daughter, Rec is only found at ϕ=60deg in the range of Rep studied, and the resulting total mass ratio can be as high as 6, which also asymptotes to a finite value for different ϕ as Rep increases. Inertia is further demonstrated to cause more homogeneous plug splitting from a comparison study of Rs versus Cap (another characteristic speed) for three liquids: water, glycerin, and LB-400X. A theoretical model based on entrance flow for the plug in the daughters is developed and predicts Rs versus Rep. The frictional pressure drop, as a part of the total pressure drop, is estimated by two fitting parameters and shows a linear relationship with Rep. The theory provides a good prediction on liquid plug splitting and well simulates the liquid distributions in the large airways of human lungs.

SERPINB1 upregulation is associated with in vivo complex formation with neutrophil elastase and cathepsin G in a baboon model of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) continues to be a major cause of morbidity in premature infants. An imbalance between neutrophil elastase and its inhibitors has been implicated in BPD. Serine protease inhibitor (SERPIN)B1 is an inhibitor of neutrophil proteases, including neutrophil elastase (NE) and cathepsin G (cat G). Recent studies suggest that SERPINB1 could provide protection in the airways by regulating excess protease activity associated with inflammatory lung disorders. In this study, we determined the distribution and ontogeny of SERPINB1 in the baboon lung and characterized the expression of SERPINB1 in baboon models of BPD. SERPINB1 expression was detected in the conducting airway and glandular epithelial cells in addition to neutrophils, macrophages, and mast cells. SERPINB1 mRNA and protein expression increased with advancing gestational age and in the new BPD model. In contrast, SERPINB1 expression levels were decreased in the old BPD model. Furthermore, SERPINB1 was detected as a high-molecular-mass (HMM) complex in lung tissue and bronchoalveolar lavage fluid samples from the BPD group. Analysis of the HMM complex by coimmunoprecipitation showed that these complexes were formed between SERPINB1 and NE or cat G. High-performance liquid chromatography (HPLC) ion trap mass spectrometry verified the presence of SERPINB1 in HMM complexes. Finally, NE activity level was compared between new and old baboon models of BPD and was found to be significantly lower in new BPD. Thus SERPINB1 upregulation in new BPD may be protective by contributing to the regulation of neutrophil proteases NE and cat G.

Effect of gravity on liquid plug transport through an airway bifurcation model

Many medical therapies require liquid plugs to be instilled into and delivered throughout the pulmonary airways. Improving these treatments requires a better understanding of how liquid distributes throughout these airways. In this study, gravitational and surface mechanisms determining the distribution of instilled liquids are examined experimentally using a bench-top model of a symmetrically bifurcating airway. A liquid plug was instilled into the parent tube and driven through the bifurcation by a syringe pump. The effect of gravity was adjusted by changing the roll angle (phi) and pitch angle (gamma) of the bifurcation (phi = gamma =0 deg was isogravitational). Phi determines the relative gravitational orientation of the two daughter tubes: when phi not equal to 0 deg, one daughter tube was lower (gravitationally favored) compared to the other. Gamma determines the component of gravity acting along the axial direction of the parent tube: when gamma not equal to 0 deg, a nonzero component of gravity acts along the axial direction of the parent tube. A splitting ratio Rs, is defined as the ratio of the liquid volume in the upper daughter to the lower just after plug splitting. We measured the splitting ratio, Rs, as a function of: the parent-tube capillary number (Cap); the Bond number (Bo); phi; gamma; and the presence of pre-existing plugs initially blocking either daughter tube. A critical capillary number (Cac) was found to exist below which no liquid entered the upper daughter (Rs = 0), and above which Rs increased and leveled off with Cap. Cac increased while Rs decreased with increasing phi, gamma, and Bo for blocked and unblocked cases at a given Cap > Ca,. Compared to the nonblockage cases, Rs decreased (increased) at a given Cap while Cac increased (decreased) with an upper (lower) liquid blockage. More liquid entered the unblocked daughter with a blockage in one daughter tube, and this effect was larger with larger gravity effect. A simple theoretical model that predicts Rs and Cac is in qualitative agreement with the experiments over a wide range of parameters.

Surfactant administration by transient intubation in infants 29 to 35 weeks' gestation with respiratory distress syndrome decreases the likelihood of later mechanical ventilation: a randomized controlled trial

OBJECTIVE

To assess, among premature infants with early respiratory distress syndrome (RDS), the effect of one dose of intratracheally administered surfactant followed by extubation to nasal continuous positive airway pressure (NCPAP) on subsequent mechanical ventilation (MV), when compared with NCPAP alone.

STUDY DESIGN

Randomized, blinded trial in infants 29 to 35 weeks' gestation with mild-to-moderate RDS requiring supplemental oxygen and NCPAP. Infants were randomized to intubation, surfactant treatment, and immediate extubation (surfactant group N=52), or to no intervention (control group N=53). All infants were subsequently managed with NCPAP.

RESULTS

Need for later MV was 70% in the control group and 50% in the surfactant group. Surfactant group subjects had lower inspired oxygen fraction (FiO(2)) after study intervention and were less likely to require subsequent surfactant. Overall surfactant use, duration of O(2) therapy, length of stay, and bronchopulmonary dysplasia were unaffected.

CONCLUSION

Among premature infants with mild-to-moderate RDS, transient intubation for surfactant administration reduces later MV.

Caudal anesthesia for vascular access procedures in two extremely small premature neonates

With advances in neonatology, there is an increasing need for central vascular access in extremely small (<1,000 g) premature infants. Although the use of peripherally inserted central venous lines have become common practice, surgeons still frequently perform central venous line placements via cut-down in difficult access patients. The advantages of general anesthesia for vascular access procedures are obvious for optimal pain control and ideal operative exposure; however, extremely premature infants are at significant risk for prolonged endotracheal intubation with postoperative apneas. We report two cases where regional caudal anesthesia with bupivacaine and clonidine without intubation was successfully utilized at bedside during central venous line placements in premature infants weighing <600 g. The operative field was ideal with adequate motor and sensory block with caudal anesthesia and both infants received only oxygen by nasal cannula.

Laryngeal Mask Airway Used as a Delivery Conduit for the Administration of Surfactant to Preterm Infants with Respiratory Distress Syndrome

BACKGROUND

The laryngeal mask airway (LMA(TM), Laryngeal Mask Co. Ltd, Jersey, UK) is a supraglottic device used to administer positive pressure ventilation (PPV) in adults, pediatric and neonatal patients.

OBJECTIVES

To avoid endotracheal intubation, we evaluated the feasibility and practicality of administering surfactant via the LMA(TM) in preterm infants with respiratory distress syndrome (RDS).

METHODS

Infants less than 72 h old with a gestational age of < or =35 weeks and a birth weight of >800 g, treated with nasal continuous positive airway pressure (CPAP, 5 cm H2O) for RDS were eligible for inclusion in the study if the arterial-to-alveolar oxygen tension ratio (a/APO2) was <0.20 over a period of >60 min.

RESULTS

Eight preterm infants, median gestational age 31 (range 28-35) weeks; birth weight 1,700 (880-2,520) g, treated with nasal CPAP for RDS were enrolled. Three hours after surfactant instillation, the mean a/APO2 was significantly increased (0.13 +/- 0.04 to 0.34 +/- 0.11; p < 0.01) without complications.

CONCLUSIONS

The LMA may be a useful and noninvasive conduit for the administration of surfactant therapy. A large randomized comparative clinical trial will be required to confirm the efficacy of this technique.

A randomized trial comparing beractant and poractant treatment in neonatal respiratory distress syndrome

AIM

To compare the effects of beractant and poractant in neonatal respiratory distress syndrome (RDS).

METHODS

Infants with RDS were randomized to receive beractant or poractant. The primary outcome measure was fraction of inspired oxygen (FiO2) requirement in the first 48 h after surfactant therapy.

RESULTS

58 infants completed the study. The mean gestational ages for the poractant and beractant groups were 29.6+/-3.6 and 29.3+/-2.9 wk, with average birthweights of 1394+/-699 and 1408+/-534 g, respectively. In the first 48 h, infants who received poractant had a lower FiO2 requirement compared to those who received beractant (p=0.018). The prevalence of patent ductus arteriosus (PDA) was lower in the group of infants that received poractant (17%) compared to the group that received beractant (45%) (p=0.02).

CONCLUSIONS

Infants with RDS treated with poractant had a lower FiO2 requirement during the first 48 h compared to infants who received beractant. Infants who received poractant also had fewer PDAs than infants who received beractant. The difference in FiO2 was not associated with a difference in age of first extubation, total intubation time, or incidence of bronchopulmonary dysplasia between groups.

Trends in severe bronchopulmonary dysplasia rates between 1994 and 2002

OBJECTIVE

To examine temporal trends in the rates of severe bronchopulmonary dysplasia (BPD) between 1994 and 2002.

STUDY DESIGN

In a retrospective cohort study, all infants with a gestational age (GA) <33 weeks in a large managed care organization were identified. Annual rates of BPD (defined as an oxygen requirement at 36 weeks corrected GA), severe BPD (defined as respiratory support at 36 weeks corrected GA), and death before 36 weeks corrected GA were examined.

RESULTS

Of the 5115 infants in the study cohort, 603 (12%) had BPD, including 246 (4.9%) who had severe BPD. There were 481 (9.5%) deaths before 36 weeks corrected GA. Although the decline in BPD in this period was not significant, the rates of severe BPD declined from 9.7% in 1994 to 3.7% in 2002. Controlling for gestational age, the odds ratio (95% CI) for annual rate of decline in severe BPD was 0.890 (0.841-0.941). Controlling for gestational age, deaths before 36 weeks corrected GA also declined, with the odds ratio (CI) for the annual decline being 0.944 (0.896-0.996).

CONCLUSIONS

In this study population, the odds of having of BPD remained constant after controlling for GA. However, the odds of having severe BPD declined on average 11% per year between 1994 and 2002.

Immunoregulatory functions of surfactant proteins

Because the lungs function as the body's gas-exchange organ, they are inevitably exposed to air that is contaminated with pathogens, allergens and pollutants. Host-defence mechanisms within the lungs must facilitate clearance of inhaled pathogens and particles while minimizing an inflammatory response that could damage the thin, delicate gas-exchanging epithelium. Pulmonary surfactant is a complex of lipids and proteins that enhances pathogen clearance and regulates adaptive and innate immune-cell functions. In this article, I review the structure and functions of the surfactant proteins SP-A and SP-D in regulating host immune defence and in modulating inflammatory responses.

Improved outcome for very low birth weight multiple births

This study describes time trends for very low birth weight multiple births in relation to very low birth weight singletons. Two cohorts of very low birth weight (less than 1250 gm) children recruited between 1983-85 (cohort 1, n = 115) and 1992-94 (cohort 2, n = 144) were compared. The Bayley Scales of Infant Development and a standardized neurologic examination were administered at 2 years corrected age. Neurodevelopmental outcome did not change between cohort 1 and 2 for singletons. For multiple births, mean Mental Developmental Index increased after adjustment for neonatal risk factors [adjusted mean (standard deviation) 81.8 (11.7) to 96.5 (18.6), analysis of covariance P = 0.007]. The prevalence of cerebral palsy decreased, however not significantly [adjusted odds ratio (95% confidence interval) 0.3 (0.1-1.5), P = 0.14]. The proportion of disease-free survival (no cerebral palsy and no developmental delay) increased for multiple births (7-37%, P = 0.002), but not for singletons. In cohort 2, neurodevelopmental outcome of multiple births was similar to that of singletons. The cognitive outcome of very low birth weight multiple births improved, possibly because of changes in perinatal practice. However, neurodevelopmental outcome was similar to that of very low birth weight singletons who were unaffected by changes in neonatal care with high proportions of motor delay and cerebral palsy.

Surfactant Therapy for Meconium Aspiration Syndrome

Meconium aspiration syndrome (MAS) is an important cause of respiratory distress in the term infant. Therapy for the disease remains problematic, and newer treatments such as high-frequency ventilation and inhaled nitric oxide are being applied with increasing frequency. There is a significant disturbance of the pulmonary surfactant system in MAS, with a wealth of experimental data indicating that inhibition of surfactant function in the alveolar space is an important element of the pathophysiology of the disease. This inhibition may be mediated by meconium, plasma proteins, haemoglobin and oedema fluid, and, at least in vitro, can be overcome by increasing surfactant phospholipid concentration. These observations have served as the rationale for administration of exogenous surfactant preparations in MAS, initially as standard bolus therapy and, more recently, in association with therapeutic lung lavage. Bolus surfactant therapy in ventilated infants with MAS has been found to improve oxygenation in most studies, although there are a significant proportion of nonresponders and in many cases the effect is transient. Pooled data from randomised controlled trials of surfactant therapy suggest a benefit in terms of a reduction in the requirement for extracorporeal membrane oxygenation (relative risk 0.48 in surfactant-treated infants) but no diminution of air leak or ventilator days. Current evidence would support the use of bolus surfactant therapy on a case by case basis in nurseries with a relatively high mortality associated with MAS, or the lack of availability of other forms of respiratory support such as high-frequency ventilation or nitric oxide. If used, bolus surfactant should be administered as early as practicable to infants who exhibit significant parenchymal disease, at a phospholipid dose of at least 100 mg/kg, rapidly instilled into the trachea. Natural surfactant or a third-generation synthetic surfactant should be used and the dosage repeated every 6 hours until oxygenation has improved. Lung lavage with dilute surfactant has recently emerged as an alternative to bolus therapy in MAS, which has the advantage of removing surfactant inhibitors from the alveolar space in addition to augmenting surfactant phospholipid concentration. Combined animal and human data suggest that lung lavage can remove significant amounts of meconium and alveolar debris, and thereby improve oxygenation and pulmonary mechanics. Arterial oxygen saturation inevitably falls during lavage but has been noted to recover relatively rapidly, even in infants with severe disease. Several randomised controlled trials of surfactant lavage in MAS are underway, and until the results are known, lavage must be considered an unproven and experimental therapy.

Effect of antitubercular drugs on dipalmitoylphosphatidylcholine monolayers: implications for drug loaded surfactants

The year long chemotherapy in pulmonary tuberculosis results in dose related side effects and may not reach atelectatic areas. On account of its spreading properties and the ability to re-expand atelectatic areas, exogenous surfactant may act as a pulmonary drug delivery agent. We investigated the interactions between antitubercular drugs and the main surfactant component, dipalmitoylphosphatidylcholine (DPPC) with the aim of developing more effective antitubercular drug loaded surfactants. The surface properties were evaluated using a Langmuir-Blodgett trough and Wilhelmy balance at 37 degrees C. Lung surfactant was modeled as DPPC monolayers. The isoniazid (INH)-DPPC combination in 1:1 ratio by weight significantly improved the adsorption of DPPC, reached a minimum surface tension of zero, formed a low compressibility film and required 32.7% area change to decrease surface tension from 30 to 10 mN/m. The triple drug (INH-rifampicin-ethambutol in 1:2:3 ratio by weight) DPPC combination when used in 1:1 or 1:2 ratios by weight also achieved surface properties superior to those of DPPC alone. A significant improvement in the adsorption was observed (surface tensions of 34.7 mN/m for 1:1 and 32.0 mN/m for 1:2 triple drug: DPPC combinations in the first second), and the films had low compressibility reaching a minimum surface tension of zero on compression. Thus, we observed statistically significant improvements in all the surface parameters and we feel encouraged to continue developing a tuberculosis therapy consisting of surfactant liposomes carrying antitubercular drugs.

Simple, Helical Peptoid Analogs of Lung Surfactant Protein B

The helical, amphipathic surfactant protein, SP-B, is a critical element of pulmonary surfactant and hence is an important therapeutic molecule. However, it is difficult to isolate from natural sources in high purity. We have created and studied three different, nonnatural analogs of a bioactive SP-B fragment (SP-B(1-25)), using oligo-N-substituted glycines (peptoids) with simple, repetitive sequences designed to favor the formation of amphiphilic helices. For comparison, a peptide with a similar repetitive sequence previously shown to be a good SP mimic was also studied, along with SP-B(1-25) itself. Surface pressure-area isotherms, surfactant film phase morphology, and dynamic adsorption behavior all indicate that the peptoids are promising mimics of SP-B(1-25). The extent of biomimicry appears to correlate with peptoid helicity and lipophilicity. These biostable oligomers could serve in a synthetic surfactant replacement to treat respiratory distress syndrome.

Influence of modified natural and synthetic surfactant preparations on bacterial killing by polymorphonuclear leucocytes

In addition to its biophysical functions, surfactant plays an important role in pulmonary host defense. In this investigation we studied the influence of various commercially available surfactants on the phagocytosis of bacteria that are common pathogens in the neonatal period. Group B streptococci (GBS), Escherichia coli and Staphylococcus aureus were cultured with isolated human polymorphonuclear leucocytes (PMN) and non-specific serum in the presence or absence of different modified natural (Curosurf, Alveofact, Survanta) or totally synthetic, protein-free surfactant preparations (Exosurf, Pumactant). Prior to and after 30 and 60 min of incubation with PMN at different surfactant concentrations (1, 10 or 20 mg/ml), the number of viable bacteria was determined by colony counting. Killing of S. aureus by PMN was not influenced by any of the surfactants. Alveofact and Curosurf had no significant negative impact on phagocytosis. At 20 mg/ml, Curosurf even reduced the number of viable E. coli. Survanta at 10 and 20 mg/ml and Exosurf at all concentrations impaired the killing of non-encapsulated GBS and E. coli. Pumactant at 1-20 mg/ml interfered with the phagocytosis of E. coli. In further experiments we demonstrated that Curosurf did not interfere with the phagocytosis of an encapsulated GBS-strain opsonised by a specific antiserum either. In additional experiments we analysed the influence of the different surfactants on the release of reactive oxygen metabolite by PMN and found that the changes in nitroblue tetrazolium reduction did not necessarily correlate with the findings of the studies on killing. In conclusion, we found that killing by PMN was influenced by the bacterial species and the composition and concentration of the different surfactant preparations. The strongest impairment in phagocytic function of PMN was observed with the protein-free synthetic surfactant Exosurf, a phospholipid preparation that contains the alcohols hexadecanol and tyloxapol as spreading agents.

Surfactant protein C gene variation in the Finnish population - association with perinatal respiratory disease

Surfactant protein C (SP-C) is a small hydrophobic protein component of alveolar surfactant, a lipid-protein complex lining the alveolar surface of the lung. Surfactant deficiency is the main cause of respiratory distress syndrome (RDS) in premature infants. RDS is a major risk factor of a chronic lung disease called bronchopulmonary dysplasia (BPD). The dominant mutations of the SP-C gene have recently been associated with interstitial lung diseases. However, the common genetic variation in the surfactant protein C gene has not been studied in detail. In the present study, the exonic variation of the SP-C gene in the Finnish population (n=472) was defined, and the association of the allelic variants with the susceptibility to RDS and BPD was examined. Conformation-sensitive gel electrophoresis (CSGE) was used to determine the extent of exonic variation in the SP-C gene. Methods of genotyping were generated for three biallelic polymorphisms of the SP-C gene's exons 1, 4 and 5, which encode proSP-C. The frequencies of these polymorphisms were evaluated in a study population consisting of 158 DNA samples from full-term infants. In addition, the linkage disequilibrium between the SP-C alleles was evaluated by haplotype analysis of parent-infant triplets. The role of SP-C gene variation in RDS and in BPD was evaluated in a high-risk population of 245 premature infants. According to the present results, the SP-C polymorphisms were associated with RDS and with very premature birth. The strength of allelic associations differed according to the gender of the premature infants.

The Effect of Airway Wall Motion on Surfactant Delivery

Soluble surfactant and airway surface liquid transport are examined using a mathematical model of Marangoni flows which accounts for airway branching and for cyclic airway stretching. Both radial and longitudinal wall strains are considered. The model allows for variation of the amplitude and frequency of the motion, as may occur under a variety of ventilatory situations occurring during surfactant replacement therapy. The soluble surfactant dynamics of the thin fluid film are modeled by linear sorption. The delivery of surfactants into the lung is handled by setting the proximal boundary condition to a higher concentration compared to the distal boundary condition. Starting with a steady-state, nonuniform, surfactant distribution, we find that transport of surfactant into the lung is enhanced for increasing strain amplitudes. However, for fixed amplitude, increasing frequency has a smaller effect. At small strain amplitudes, increasing frequency enhances transport, but at large strain amplitudes, increasing cycling frequency has the opposite effect.

Lipid peroxidation of lung surfactant in experimental neonatal group B streptococcal pneumonia

Group B streptococcal (GBS) pneumonia, with neutrophilic granulocytes immigrating into the lungs, may occur in neonates. The incidence is particularly high among preterm infants, who often are treated with exogenous surfactant. We have previously demonstrated in vitro that neutrophils stimulated by GBS cause lipid peroxidation (LPO) and functional impairment of lung surfactant. The present study aimed at evaluating LPO of exogenous lung surfactant (Curosurf) and the protective effect of the natural antioxidant, vitamin E in immature ventilated newborn rabbits with experimental neonatal GBS pneumonia. There was a prominent proliferation of GBS in the lungs of animals treated with surfactant and ventilated for 5 h. GBS-infected rabbits had a higher LPO of lung lavage fluid than non-infected ones. The LPO could be diminished using vitamin E, which, however, did not affect bacterial proliferation. During the 5-h incubation period, mean lung-thorax compliance values were significantly lower in GBS-infected than in noninfected animals. We speculate that addition of vitamin E to exogenous surfactant preparations may improve their resistance to LPO and make them more suitable for treatment of neonates with pneumonia.

Effect of ventilation rate on instilled surfactant distribution in the pulmonary airways of rats

Liquid can be instilled into the pulmonary airways during medical procedures such as surfactant replacement therapy, partial liquid ventilation, and pulmonary drug delivery. For all cases, understanding the dynamics of liquid distribution in the lung will increase the efficacy of treatment. A recently developed imaging technique for the study of real-time liquid transport dynamics in the pulmonary airways was used to investigate the effect of respiratory rate on the distribution of an instilled liquid, surfactant, in a rat lung. Twelve excised rat lungs were suspended vertically, and a single bolus (0.05 ml) of exogenous surfactant (Survanta, Ross Laboratories, Columbus, OH) mixed with radiopaque tracer was instilled as a plug into the trachea. The lungs were ventilated with a 4-ml tidal volume for 20 breaths at one of two respiratory rates: 20 or 60 breaths/min. The motion of radiodense surfactant was imaged at 30 frames/s with a microfocal X-ray source and an image intensifier. Dynamics of surfactant distribution were quantified for each image by use of distribution statistics and a homogeneity index. We found that the liquid distribution depended on the time to liquid plug rupture, which depends on ventilation rate. At 20 breaths/min, liquid was localized in the gravity-dependent region of the lung. At 60 breaths/min, the liquid coated the airways, providing a more vertically uniform liquid distribution.

Low expression of human epithelial sodium channel in airway epithelium of preterm infants with respiratory distress

OBJECTIVE

Active ion transport is critical to postnatal clearance of lung fluid. The importance of epithelial sodium channel (ENaC) in this clearance has been demonstrated in animal studies in which alpha-ENaC knockout mice died postnatally as a result of respiratory insufficiency. In animals, the expression of alpha-ENaC in respiratory epithelium is dependent on gestational age, but when assessed by in situ hybridization in the human (h), the mRNA is present from the earliest stages of pulmonary development. Therefore, the purpose of the present investigation was to quantify mRNA of the alpha-, beta-, and gamma-hENaC subunits of newborn preterm infants with respiratory distress and compare the gene expression data against those detected in healthy term infants. In addition, the effect of systemic dexamethasone therapy on the 3 hENaC subunits was studied in 4 preterm infants who received prolonged assisted ventilation.

METHODS

The expression of subunits of hENaC was determined in samples taken from nasal respiratory epithelium of 7 healthy term infants (gestation age: 39.3 +/- 0.9 weeks [mean +/- standard deviation) and 5 preterm infants (gestational age: 27.2 +/- 0.9 weeks) with respiratory distress syndrome within 5 hours of birth. Betamethasone had been given to all mothers of preterm infants. In 4 additional preterm infants who still required assisted ventilation at 43 +/- 6 days postnatal age, the expression of alpha-hENaC was determined in samples taken before and during treatment with dexamethasone.

RESULTS

Preterm infants with respiratory distress syndrome had low expression of all hENaC subunits relative to healthy term infants (alpha-hENaC: 5.38 +/- 2.01 [amol/fmol cytokeratin 18] vs 9.13 +/- 2.26; beta-hENaC: 2.44 +/- 1.43 vs 4.25 +/- 1.10; gamma-hENaC: 2.43 +/- 0.11 vs 6.81 +/- 3.24). Each of the 4 preterm infants who were treated with dexamethasone at approximately 1 month of age showed an increase in expression of alpha-hENaC and beta-hENaC subunit normalized to cytokeratin 18.

CONCLUSION

All 3 subunits of the hENaC are low in preterm relative to full-term infants. alpha-hENaC mRNA in respiratory epithelium is increased by therapeutic doses of glucocorticosteroid. Low expression of alpha-hENaC in human respiratory epithelium may play a role in the pathogenesis of respiratory distress in preterm infants.

Surfactant from diving aquatic mammals

Diving mammals that descend to depths of 50-70 m or greater fully collapse the gas exchanging portions of their lungs and then reexpand these areas with ascent. To investigate whether these animals may have evolved a uniquely developed surfactant system to facilitate repetitive alveolar collapse and expansion, we have analyzed surfactant in bronchoalveolar lavage fluid (BAL) obtained from nine pinnipeds and from pigs and humans. In contrast to BAL from terrestrial mammals, BAL from pinnipeds has a higher concentration of phospholipid and relatively more fluidic phosphatidylcholine molecular species, perhaps to facilitate rapid spreading during alveolar reexpansion. Normalized concentrations of hydrophobic surfactant proteins B and C were not significantly different among pinnipeds and terrestrial mammals by immunologic assay, but separation of proteins by gel electrophoresis indicated a greater content of surfactant protein B in elephant seal surfactant than in human surfactant. Remarkably, surfactant from the deepest diving pinnipeds produced moderately elevated in vitro minimum surface tension measurements, a finding not explained by the presence of protein or neutral lipid inhibitors. Further study of the composition and function of pinniped surfactants may contribute to the design of optimized therapeutic surfactants.

Interaction between surfactant and ventilatory support in newborns with primary surfactant deficiency

The interaction between exogenous surfactant and various modes of ventilatory support in terms of timing, quality and quantity can influence both short- and long-term outcomes of immature infants. Alterations to the pulmonary surfactant system can occur with all forms of mechanical ventilation. Experimental data suggest possible interaction between ventilatory support and exogenous surfactant even during the first breaths in the delivery room. The adverse effect on surfactant function at this time can increase the need for and duration of ventilatory support. The logical approach to ventilatory support is to be minimally aggressive with optimal recruitment of the lungs to avoid ventilator-induced lung injury. Nasal continuous positive airway pressure (CPAP) in combination with early prophylactic surfactant administration may be an effective and less damaging method capable of reducing the need of artificial ventilation, but its benefit has not been proven in extremely preterm infants less than 28 weeks' gestation. Because of unproven efficacy of nasal CPAP in extremely premature infants, the population most at risk for adverse pulmonary and neurologic outcome, this paper focuses on the comparison of conventional and high-frequency oscillatory ventilation (HFOV) with respect to alteration of surfactant function, and short- and long-term outcomes, in both human and experimental trials. Though the two most recent large clinical trials provide reassurance with respect to the safety of first-intention high-frequency ventilation, the reduction in the risk of chronic lung disease appears to be only modest or absent. Recent laboratory investigations suggest that the key element of HFOV, namely optimization of volume, can, under some circumstances, be replicated with low tidal volume conventional ventilation and high positive end-expiratory pressure. Recent introduction of patient-triggered volume-targeted conventional ventilation into clinical practice offers the promise of a practical means of providing gentle conventional ventilation capable of minimizing ventilator-induced lung injury. Ultimately, well-designed comparative clinical trials with long-term outcomes are essential to accurately quantify risks and benefits of any new approach to mechanical ventilation. Without such data, these experimental results should not be extrapolated into clinical practice, because of the multifactorial pathophysiology of the development of chronic pulmonary disease in extremely premature infants and the risk of unanticipated adverse effects.

Pulmonary antioxidant defenses in the preterm newborn with respiratory distress and bronchopulmonary dysplasia in evolution: implications for antioxidant therapy

Preterm neonates with respiratory distress are exposed not only to the relative hyperoxia ex utero, but also to life-saving mechanical ventilation with high inspired oxygen (O2) concentrations, which is considered a major risk factor for the development of bronchopulmonary dysplasia, also referred to as chronic lung disease of infancy. O2 toxicity is mediated through reactive oxygen species (ROS). ROS are constantly generated as byproducts of normal cellular metabolism, but their production is increased in various pathological states, and also upon exposure to exogenous oxidants, such as hyperoxia. Antioxidants, either enzymatic or nonenzymatic, protect the lung against the deleterious effects of ROS. Expression of various pulmonary antioxidants is developmentally regulated in many species so that the expression is increased toward term gestation, as if in anticipation of birth into an O2-rich extrauterine environment. Therefore, the lungs of prematurely born infants may be ill-adapted for protection against ROS. While premature birth interrupts normal lung development, the clinical condition necessitating the administration of high inhaled O2 concentrations may lead to permanent impairment of alveolar development. An understanding of the processes involved in lung growth, especially in alveolarization and vascularization, as well as in repair of injured lung tissue, may facilitate development of strategies to enhance these processes.

Protective ventilation of patients with acute respiratory distress syndrome

The majority of patients with acute respiratory distress syndrome (ARDS) require mechanical ventilation. This support provides time for the lungs to heal, but the adverse effects of mechanical ventilation significantly influence patient outcome. Traditionally, these were ascribed to mechanical effects, such as haemodynamic compromise from decreased venous return or gross air leaks induced by large transpulmonary pressures. More recently, however, the ARDS Network study has established the clinical importance of lowering the tidal volume to limit overdistension of the lung when ventilating patients with ARDS. This study suggests that ventilator-associated lung injury (VALI) caused by overdistension of the lung contributes to the mortality of patients with ARDS. Moreover, the results from clinical and basic research have revealed more subtle types of VALI, including upregulation of the inflammatory response in the injured and overdistended lung. This not only damages the lung, but the overflow of inflammatory mediators into the systemic circulation may explain why most patients who die with ARDS succumb to multi-organ failure rather than respiratory failure. The results of these studies, the present understanding of the pathophysiology of VALI, and protective ventilatory strategies are reviewed.