The role of surfactant treatment in preterm infants and term newborns with acute respiratory distress syndrome

Construction and evaluation of neonatal respiratory failure risk prediction model for neonatal respiratory distress syndrome

BACKGROUND

Neonatal respiratory distress syndrome (NRDS) is a common respiratory disease in preterm infants, often accompanied by respiratory failure. The aim of this study was to establish and validate a nomogram model for predicting the probability of respiratory failure in NRDS patients.

METHODS

Patients diagnosed with NRDS were extracted from the MIMIC-iv database. The patients were randomly assigned to a training and a validation cohort. Univariate and stepwise Cox regression analyses were used to determine the prognostic factors of NRDS. A nomogram containing these factors was established to predict the incidence of respiratory failure in NRDS patients. The area under the receiver operating characteristic curve (AUC), receiver operating characteristic curve (ROC), calibration curves and decision curve analysis were used to determine the effectiveness of this model.

RESULTS

The study included 2,705 patients with NRDS. Univariate and multivariate stepwise Cox regression analysis showed that the independent risk factors for respiratory failure in NRDS patients were gestational age, pH, partial pressure of oxygen (PO2), partial pressure of carbon dioxide (PCO2), hemoglobin, blood culture, infection, neonatal intracranial hemorrhage, Pulmonary surfactant (PS), parenteral nutrition and respiratory support. Then, the nomogram was constructed and verified.

CONCLUSIONS

This study identified the independent risk factors of respiratory failure in NRDS patients and used them to construct and evaluate respiratory failure risk prediction model for NRDS. The present findings provide clinicians with the judgment of patients with respiratory failure in NRDS and help clinicians to identify and intervene in the early stage.

The perinatal period should be considered in neonatal acute respiratory distress syndrome: comparison of the Montreux definition vs. the second pediatric acute lung injury consensus conference definition

Background

The recently developed Montreux definition for neonatal acute respiratory distress syndrome (ARDS) partially differs from the Second Pediatric Acute Lung Injury Consensus Conference (PALICC-2) definition. Here, we compare the Montreux and PALICC-2 definitions regarding morbidity, mortality, and prognosis of neonatal cases of ARDS in order to evaluate which definition is more appropriate for newborns.

Methods

Neonates admitted to our neonatal intensive care unit between 1 January 2018 and 30 September 2019 who met the Montreux or PALICC-2 definition of neonatal ARDS were retrospectively analyzed (n = 472). One comparison was made between application of the Montreux and PALICC-2 definitions to neonates outside the perinatal period (> 7 d after birth). A second comparison was made between a diagnosis of neonatal ARDS within (≤ 7 d of birth) and outside (> 7 d after birth) the perinatal period using the Montreux definition.

Results

No significant differences in morbidity, mortality, severity, therapies, or prognosis were observed between neonates in the extra perinatal group according to the Montreux and PALICC-2 definitions. However, epidemiology, clinical course, and prognosis of neonatal ARDS within the perinatal period did differ from those outside the perinatal period according to the Montreux definition.

Conclusion

Neonates with ARDS within the perinatal period have unique triggers, epidemiology, clinical course, and prognosis, yet a similar pathobiology pattern, to neonates at other ages. Therefore, it may be essential to consider the perinatal period when defining neonatal ARDS.

Comparison of the Montreux definition with the Berlin definition for neonatal acute respiratory distress syndrome

To compare the similarities and differences between the Montreux definition and the Berlin definition in terms of the prevalence, mortality, and complications of neonatal acute respiratory distress syndrome (ARDS). We retrospectively analyzed the data of neonates with respiratory failure treated in a neonatal intensive care unit (NICU) between 1 November 2019 and 31 December 2021. In total, 554 infants had neonatal ARDS (524 infants, Montreux definition; 549 infants, Berlin definition). The prevalence (3.1% vs. 3.3%, p = 0.438) and mortality (18.9% vs.18.0%, p = 0.716) of neonatal ARDS did not differ between the definitions. Among the 519 infants meeting both definitions, key clinical outcomes did not differ between the definitions such as ventilation duration, NICU stay, complication rates, and antibiotic use, except for nitric oxide inhalation. The Montreux and Berlin definitions identified an additional 5 and 30 patients, respectively, not captured by the other definition. The rate of inhaled nitric oxide treatment (20.0% vs. 0%, p = 0.013), air leaks (20.0% vs. 0%, p = 0.013), and invasive ventilation duration (110.00 vs.0.00 h, p = 0.002) significantly differed between the above two groups. Sixty-two patients had moderate and severe ARDS according to the Montreux and Berlin definitions, respectively. The rates of adverse outcomes (e.g., mortality, invasive ventilation time) among these patients were similar to the rates among patients with moderate ARDS according to both definitions than among patients with severe ARDS according to both definitions.  Conclusion: The prevalence, mortality, and most complications of neonatal ARDS were similar between the Montreux and Berlin definitions, which mainly differed in terms of the severity of neonatal ARDS. What is Known: • The Montreux definition was first proposed for the diagnosis of neonatal acute respiratory distress syndrome and was established in 2017. To date, the Montreux definition has not been compared with other diagnostic definitions of ARDS. What is New: • The study suggests that perinatal lung disease need not be excluded in the diagnosis of neonatal ARDS, and that the Montreux definition is more applicable to neonates, taking into account their specific physiological characteristics.

Management Practices During Perinatal Respiratory Transition of Very Premature Infants

The present review considers some controversial management practices during extremely premature perinatal transition. We focus on perinatal prevention and treatment of respiratory distress syndrome (RDS) in immature infants. New concerns regarding antenatal corticosteroid management have been raised. Many fetuses are only exposed to potential adverse effects of the drug. Hence, the formulation and the dosage may need to be modified. Another challenge is to increase the fraction of the high-risk fetuses that benefit from the drug and to minimize the harmful effects of the drug. On the other hand, boosting anti-inflammatory and anti-microbial properties of surfactant requires further attention. Techniques of prophylactic surfactant administration to extremely immature infants at birth may be further refined. Also, new findings suggest that prophylactic treatment of patent ductus arteriosus (PDA) of a high-risk population rather than later selective closure of PDA may be preferred. The TREOCAPA trial (Prophylactic treatment of the ductus arteriosus in preterm infants by acetaminophen) evaluates, whether early intravenous paracetamol decreases the serious cardiorespiratory consequences following extremely premature birth. Lastly, is inhaled nitric oxide (iNO) used in excess? According to current evidence, iNO treatment of uncomplicated RDS is not indicated. Considerably less than 10% of all very premature infants are affected by early persistence of pulmonary hypertension (PPHN). According to observational studies, effective ventilation combined with early iNO treatment are effective in management of this previously fatal disease. PPHN is associated with prolonged rupture of fetal membranes and birth asphyxia. The lipopolysaccharide (LPS)-induced immunotolerance and hypoxia-reperfusion-induced oxidant stress may inactivate NO-synthetases in pulmonary arterioles and terminal airways. Prospective trials on iNO in the management of PPHN are indicated. Other pulmonary vasodilators may be considered as comparison drugs or adjunctive drugs. The multidisciplinary challenge is to understand the regulation of pregnancy duration and the factors participating the onset of extremely premature preterm deliveries and respiratory adaptation. Basic research aims to identify deficiencies in maternal and fetal tissues that predispose to very preterm births and deteriorate the respiratory adaptation of immature infants. Better understanding on causes and prevention of extremely preterm births would eventually provide effective antenatal and neonatal management practices required for the intact survival.

PERINATAL CENTRILOBULAR HEPATIC NECROSIS IN GIANT PANDAS (AILUROPODA MELANOLEUCA): A RETROSPECTIVE STUDY

Between 1983 and 2012, six giant panda cubs (Ailuropoda melanoleuca) born at a zoological institution were stillborn or died between the ages of 3 and 200 h. Two of the six cubs had panhepatic centrilobular hepatic necrosis (CHN), granulocytic extramedullary hematopoiesis (GEM), positive liver culture for Staphylococcus species, and terminal liver failure. Another low-weight cub was administered oxygen therapy immediately after birth and developed hyaline membranes in air spaces and hepatic necrosis restricted to the hilar region. A retrospective analysis of liver and lung lesions, pulmonary microanatomy, blood-gas barrier ultrastructure, and hepatic myofibroblast proliferation was conducted on the six cubs. Neonates with CHN had concurrent severe periportal GEM accompanied by severe myofibroblast proliferation. The pulmonary blood-gas barrier was markedly increased in one cub with CHN. Developmentally, the lungs of all but one cub were at the late saccular stage, and the lowest-weight cub was in early saccular stage, consistent with immaturity, and had pneumonia comparable to neonatal respiratory distress syndrome (RDS). Stage of lung development was eliminated as the primary factor leading to CHN. The pathogenesis of CHN in these neonates is proposed to be transformation of hepatic stellate cells to myofibroblasts initiating blockage and microvascular constriction of hepatic sinusoids, resulting in insufficient perfusion and cellular hypoxia of hepatocytes surrounding central veins in acinar zone 3.

Surfactant therapies for pediatric and neonatal ARDS: ESPNIC expert consensus opinion for future research steps

Pediatric (PARDS) and neonatal (NARDS) acute respiratory distress syndrome have different age-specific characteristics and definitions. Trials on surfactant for ARDS in children and neonates have been performed well before the PARDS and NARDS definitions and yielded conflicting results. This is mainly due to heterogeneity in study design reflecting historic lack of pathobiology knowledge. We reviewed the available clinical and preclinical data to create an expert consensus aiming to inform future research steps and advance the knowledge in this area. Eight trials investigated the use of surfactant for ARDS in children and ten in neonates, respectively. There were improvements in oxygenation (7/8 trials in children, 7/10 in neonates) and mortality (3/8 trials in children, 1/10 in neonates) improved. Trials were heterogeneous for patients' characteristics, surfactant type and administration strategy. Key pathobiological concepts were missed in study design. Consensus with strong agreement was reached on four statements: 1. There are sufficient preclinical and clinical data to support targeted research on surfactant therapies for PARDS and NARDS. Studies should be performed according to the currently available definitions and considering recent pathobiology knowledge. 2. PARDS and NARDS should be considered as syndromes and should be pre-clinically studied according to key characteristics, such as direct or indirect (primary or secondary) nature, clinical severity, infectious or non-infectious origin or patients' age. 3. Explanatory should be preferred over pragmatic design for future trials on PARDS and NARDS. 4. Different clinical outcomes need to be chosen for PARDS and NARDS, according to the trial phase and design, trigger type, severity class and/or surfactant treatment policy. We advocate for further well-designed preclinical and clinical studies to investigate the use of surfactant for PARDS and NARDS following these principles.

Comparison of Serum Triglyceride and Cholesterol Levels in Premature Neonates with or without Respiratory Distress Syndrome (RDS)

Background

Deficiency or reduced transmission of long-chain fatty acids and essential fatty acids may inhibit lung growth and development. We aimed to evaluate and compare serum triglyceride and cholesterol levels in premature neonates with RDS.

Methods

This study is a cross-sectional study performed on premature neonates born in Beheshti Hospital in Isfahan in 2018. Immediately after birth and after umbilical cord clumping, blood samples were taken from the umbilical artery and triglyceride and total cholesterol levels were measured. Those patients with the diagnosis of RDS were transferred to the neonatal intensive care unit (NICU). Data regarding the laboratory results of the lipid profile in patients were compared to that in the other group.

Results

A total number of 100 neonates entered the study and were divided into 2 groups. Analysis of gender and mean gestational ages among the two groups showed no significant differences between the groups (P = 0.84 and P = 0.28, respectively). Further analysis showed a significant decreased serum cholesterol in the group 1 of patients (P = 0.01), but there were no significant differences between the two groups regarding triglyceride levels (P = 0.43). There was a significant direct relationship between gestational age and serum triglyceride levels in patients with RDS (r = 0.550, P < 0.001).

Conclusion

Here, we indicated significantly lower cholesterol levels in the cord serum of premature neonates with RDS compared to non-RDS premature neonates. Our data also showed a significant direct relationship between gestational age and serum triglyceride levels in patients with RDS. These data were in line with the previous studies.

DMBT1 is upregulated in lung epithelial cells after hypoxia and changes surfactant ultrastructure

BACKGROUND

Hypoxia and asphyxia are known to induce surfactant inactivation in newborns. Deleted in Malignant Brain Tumors 1 (DMBT1) is an innate immunity protein with functions in epithelial differentiation and angiogenesis. It was detected in hyaline membranes of infants with respiratory distress syndrome. Human recombinant DMBT1 is able to increase the surface tension of exogenous surfactant preparations in a dose-dependent manner.

METHODS

Immunohistochemistry was performed on lung sections of infants who died due to pre-, peri- or postnatal hypoxia. The lung epithelial cell line A549 was stably transfected with a DMBT1 (DMBT1+ cells) expression plasmid or with an empty plasmid (DMBT1- cells). The cells were cultured in normoxic or hypoxic conditions, and then DMBT1 as well as HIF-1α RNA expression were analyzed by using real-time-polymerase chain reaction. Human recombinant DMBT1 was added to the modified porcine natural surfactant Curosurf to examine the effect of DMBT1 on surfactant ultrastructure with electron microscopy.

RESULTS

DMBT1 expression was upregulated in human lung tissue after fetal/peri-/postnatal hypoxia. In addition, in vitro experiments showed increased DMBT1 RNA expression in A549 cells after hypoxia. HIF-1α was upregulated in both DMBT1+ and DMBT1- cells in response to hypoxia. The addition of human recombinant DMBT1 to Curosurf caused an impaired surfactant ultrastructure.

CONCLUSIONS

DMBT1 is upregulated in response to hypoxia and there seems to be a link between hypoxia and surfactant inactivation.

COVID-19: Endogenous Retinoic Acid Theory and Retinoic Acid Depletion Syndrome

This study presents two new concepts and definitions to the medical literature. One of those is "endogenous retinoic acid theory" and the other "retinoic acid depletion syndrome". A new classification will be provided for the immune system: "retinoic acid-dependent component" and "retinoic acid non-dependent component". If this theory is verified, all the diseases where the retinoic acid metabolism is defective and retinoic acid levels are low will be identified and new approaches will be developed fortreating such diseases. When the need for retinoic acids increases, such as acute infection, high fever, severe catabolic process, or chronic antigenic stimulation, cytochrome oxidase enzymes are inhibited by drugs or internal mechanisms. Metabolism and excretion of retinoic acids stored in the liver are prevented. In this way, retinoic acid levels in the blood are raised to therapeutic levels. This is called "Endogenous Retinoic Acid Theory". Retinoic acids also manage their metabolism through feedback mechanisms. Despite compensatory mechanisms, causes such as high fever, serious catabolic process and excessively large viral genome (SARS-CoV-2), excessive use of RIG-I and Type I interferon synthesis pathway using retinoic acid causes emptying of retinoic acid stores. As a result, the RIG-I pathway becomes ineffective, Type I IFN synthesis stops, and the congenital immune system collapses. Then the immune mechanism passes to TLR3, TLR7, TLR8, TLR9, MDA5 and UPS pathways in the monocyte, macrophage, neutrophil and dendritic cells of the adaptive immune defense system that do not require retinoic acid. This leads to excessive TNFα and cytokine discharge from the pathway. With the depletion of retinoic acid stores as a result of this overuse, the immune defense mechanism switches from the congenital immune system to the adaptive immune system, where retinoic acids cannot be used. As a result of this depletion of retinoic acids, the shift of the immune system to the NFκB arm, which causes excessive cytokine release, is called "retinoic acid depletion syndrome". COVID-19 and previously defined sepsis, SIRS and ARDS are each retinoic acid depletion syndrome. We claim that retinoic acid metabolism is defective in most inflammatory diseases, particularly COVID-19 (cytokine storm) sepsis, SIRS and ARDS. Finding a solution to this mechanism will bring a new perspective and treatment approach to such diseases.

Birth weight, neonatal care, and infant mortality: Evidence from macrosomic babies

This study demonstrates that rule-of-thumb health treatment decision-making exists when assigning medical care to macrosomic newborns with an extremely high birth weight and estimates the short-run health return to neonatal care for infants at the high end of the birth weight distribution. Using a regression discontinuity design, we find that infants born with a birth weight above 5000 grams have a 2 percentage-point higher probability of admission to a neonatal intensive care unit and a 1 percentage-point higher probability of antibiotics receipt, compared to infants with a birth weight below 5000 grams. We also find that being born above the 5000-gram cutoff has a mortality-reducing effect: infants with a birth weight larger than 5000 grams face a 0.15 percentage-point lower risk of mortality in the first week and a 0.20 percentage-point lower risk of mortality in the first month, compared to their counterparts with a birth weight below 5000 grams. We do not find any evidence of changes in health treatments and mortality at macrosomic cutoffs lower than 5000 grams, which is consistent with the idea that such treatment decisions are guided by the higher expected morbidity and mortality risk associated with infants weighing more than 5000 grams.

Surfactant Components and Tracheal Aspirate Inflammatory Markers in Preterm Infants with Respiratory Distress Syndrome

In 93 preterm infants ≤32 weeks of gestational age and 12 control infants, epithelial lining fluid disaturated-phosphatidylcholine, surfactant protein A and B, albumin, and myeloperoxidase activity were assessed after intubation and before exogenous surfactant administration. We found that disaturated-phosphatidylcholine, surfactant protein B, and myeloperoxidase were significantly higher in preterms with chorioamnionitis.

Expression of surfactant protein B is dependent on cell density in H441 lung epithelial cells

Background

Expression of surfactant protein (SP)-B, which assures the structural stability of the pulmonary surfactant film, is influenced by various stimuli, including glucocorticoids; however, the role that cell-cell contact plays in SP-B transcription remains unknown. The aim of the current study was to investigate the impact of cell-cell contact on SP-B mRNA and mature SP-B expression in the lung epithelial cell line H441.

Methods

Different quantities of H441 cells per growth area were either left untreated or incubated with dexamethasone. The expression of SP-B, SP-B transcription factors, and tight junction proteins were determined by qPCR and immunoblotting. The influence of cell density on SP-B mRNA stability was investigated using the transcription inhibitor actinomycin D.

Results

SP-B mRNA and mature SP-B expression levels were significantly elevated in untreated and dexamethasone-treated H441 cells with increasing cell density. High cell density as a sole stimulus was found to barely have an impact on SP-B transcription factor and tight junction mRNA levels, while its stimulatory ability on SP-B mRNA expression could be mimicked using SP-B-negative cells. SP-B mRNA stability was significantly increased in high-density cells, but not by dexamethasone alone.

Conclusion

SP-B expression in H441 cells is dependent on cell-cell contact, which increases mRNA stability and thereby potentiates the glucocorticoid-mediated induction of transcription. Loss of cell integrity might contribute to reduced SP-B secretion in damaged lung cells via downregulation of SP-B transcription. Cell density-mediated effects should thus receive greater attention in future cell culture-based research.

Prognostic value of funisitis and/or chorionic vasculitis compared to histologic chorioamnionitis in full-term infants

AIM

To compare pathological findings in the placenta and cord with the prognosis of full-term infants in cases of neonatal infection and microbial analyses.

METHODS

The pathological findings in the placenta and cord and microbial analyses of amniotic fluid and neonatal samples based on culture or polymerase chain reaction (PCR) were observed in 1208 full-term mother-infant pairs at our center. We also collected neonatal clinical infection data, such as the occurrence of septicemia and other infectious diseases.

RESULTS

Neonatal infection and positive identification of microorganisms were more common in the funisitis and/or chorionic vasculitis group than in the histologic chorioamnionitis group.

CONCLUSION

Funisitis and/or chorionic vasculitis is a valuable pathological marker for assessing the comparison between intrauterine infection and neonatal inflammatory conditions in infants delivered at full-term.

Nebulization of Poractant alfa via a vibrating membrane nebulizer in spontaneously breathing preterm lambs with binasal continuous positive pressure ventilation

BACKGROUND

Surfactant replacement therapy is the gold standard treatment of neonatal respiratory distress (RDS). Nebulization is a noninvasive mode of surfactant administration. We administered Poractant alfa (Curosurf) via a vibrating perforated membrane nebulizer (eFlow Neonatal Nebulizer) to spontaneously breathing preterm lambs during binasal continuous positive pressure ventilation (CPAP).

METHODS

Sixteen preterm lambs were operatively delivered at a gestational age of 133 ± 1 d (term ~150 d), and connected to CPAP applied via customized nasal prongs. Nebulization was performed (i) with saline or (ii) with surfactant for 3 h in humidified or (iii) nonhumidified air, and with surfactant (iv) for 60 min or (v) for 30 min. We measured arterial oxygenation, lung gas volumes and surfactant pool size and deposition.

RESULTS

Nebulization of surfactant in humidified air for 3 h improved oxygenation and lung function, and surfactant was preferentially distributed to the lower lung lobes. Shorter nebulization times and 3 h nebulization in dry air did not show these effects. Nebulized surfactant reached all lung lobes, however the increase of surfactant pool size missed statistical significance.

CONCLUSION

Positive effects of surfactant nebulization to spontaneously breathing preterm lambs depend on treatment duration, surfactant dose, air humidity, and surfactant distribution within the lung.

Acute Neonatal Respiratory Failure

Acute respiratory failure requiring assisted ventilation is one of the most common reasons for admission to the neonatal intensive care unit. Respiratory failure is the inability to maintain either normal delivery of oxygen to the tissues or normal removal of carbon dioxide from the tissues. It occurs when there is an imbalance between the respiratory workload and ventilatory strength and endurance. Definitions are somewhat arbitrary but suggested laboratory criteria for respiratory failure include two or more of the following: PaCO₂ > 60 mmHg, PaO₂ < 50 mmHg or O₂ saturation <80 % with an FiO₂ of 1.0 and pH < 7.25 (Wen et al. 2004).

The Efficacy of Surfactant Replacement Therapy in the Growth-Restricted Preterm Infant: What is the Evidence?

BACKGROUND

Surfactant replacement therapy (SRT) is an integral part of management of preterm surfactant deficiency respiratory distress syndrome (RDS). Its role in the management of RDS has been extensively studied. However, its efficacy in the management of lung disease in preterm infants born with intrauterine growth restriction (IUGR) has not been systematically studied.

OBJECTIVE

To evaluate the efficacy of exogenous SRT in the management of preterm IUGR lung disease.

METHODS

A systematic search of all available randomized clinical trials (RCT) of SRT in preterm IUGR infants was done according to the standard Cochrane collaboration search strategy. Neonatal respiratory outcomes were compared between the preterm IUGR and appropriately grown for gestational age (AGA) preterm infant populations in eligible studies.

RESULTS

No study was identified which evaluated the efficacy or responsiveness of exogenous SRT in preterm IUGR infants as compared to preterm AGA-infants. The only study identified through the search strategy used small for gestational age (SGA; defined as less than tenth centile for birth weight) as a proxy for IUGR. The RCT evaluated the efficacy or responsiveness of SRT in preterm SGA group as compared to AGA-infants. The rate of intubation, severity of RDS, rate of surfactant administration, pulmonary air leaks, and days on the ventilator did not differ between both groups. However, the requirement for prolonged nasal continuous positive airway pressure (p < 0.001), supplemental oxygen therapy (p < 0.01), and the incidence of bronchopulmonary dysplasia at 28 days and 36 weeks (both p < 0.01) was greater in SGA-infants.

DISCUSSION

There is currently insufficient data available to evaluate the efficacy of SRT in preterm IUGR lung disease. A variety of research strategies will be needed to enhance our understanding of the role and rationale for use of SRT in preterm IUGR lung disease.

Early births and congenital birth defects: a complex interaction

Congenital birth defects and early/premature birth are common complex conditions affecting populations throughout the world, the interaction of which accounts for a significant proportion of neonatal morbidity and mortality. The relationship between these two conditions is not well understood. Several congenital birth defects can directly lead to early delivery. In addition, certain fetal conditions may necessitate early or premature delivery, several of which are also associated with maternal conditions necessitating early birth. Further understanding of both the incidences and causes of congenital birth defects and of early and premature birth will facilitate establishment of strategies to improve neonatal mortality and morbidity.

Immunomodulatory properties of surfactant preparations

Surfactant replacement significantly decreased acute pulmonary morbidity and mortality among preterm neonates with respiratory distress syndrome. Besides improving lung function and oxygenation, surfactant is also a key modulator of pulmonary innate and acquired immunity regulating lung inflammatory processes. In this review, we describe the immunomodulatory features of surfactant preparations. Various surfactant preparations decrease the proinflammatory cytokine and chemokine release, the oxidative burst activity, and the nitric oxide production in lung inflammatory cells such as alveolar neutrophils, monocytes and macrophages; they also affect lymphocyte proliferative response and immunoglobulin production, as well as natural killer and lymphokine-activated killer cell activity. In addition, surfactant preparations are involved in airway remodeling, as they decrease lung fibroblast proliferation capacity and the release of mediators involved in remodeling. Moreover, they increase cell transepithelial resistance and VEGF synthesis in lung epithelial cells. A number of different signaling pathways and molecules are involved in these processes. Because the inhibition of local immune response may decrease lung injury, surfactant therapeutic efficacy may be related not only to its biophysical characteristics but, at least in part, to its anti-inflammatory features and its effects on remodeling processes. However, further studies are required to identify which surfactant preparation ensures the highest anti-inflammatory activity, thereby potentially decreasing the inflammatory process underlying respiratory distress syndrome. In perspective, detailed characterization of these anti-inflammatory effects could help to improve the next generation of surfactant preparations.

Surfactant therapy: past, present and future

Surfactant replacement in preterm infants with respiratory distress syndrome (RDS) has been a major therapeutic breakthrough and the most intensively studied intervention in neonatal medicine. Surfactant whether given prophylactically in the delivery room or in babies with established RDS reduces the severity of RDS, the incidence of air leaks and pneumothorax and, most importantly, neonatal death. Many randomized controlled trials have explored different strategies to optimize the effect of surfactant administration and have further improved neonatal outcome. Whenever indicated, surfactant should be administered as early as possible in the course of the RDS.

New surfactant with SP-B and C analogs gives survival benefit after inactivation in preterm lambs

BACKGROUND

Respiratory distress syndrome in preterm babies is caused by a pulmonary surfactant deficiency, but also by its inactivation due to various conditions, including plasma protein leakage. Surfactant replacement therapy is well established, but clinical observations and in vitro experiments suggested that its efficacy may be impaired by inactivation. A new synthetic surfactant (CHF 5633), containing synthetic surfactant protein B and C analogs, has shown comparable effects on oxygenation in ventilated preterm rabbits versus Poractant alfa, but superior resistance against inactivation in vitro. We hypothesized that CHF 5633 is also resistant to inactivation by serum albumin in vivo.

METHODOLOGY/PRINCIPAL FINDINGS

Nineteen preterm lambs of 127 days gestational age (term = 150 days) received CHF 5633 or Poractant alfa and were ventilated for 48 hours. Ninety minutes after birth, the animals received albumin with CHF 5633 or Poractant alfa. Animals received additional surfactant if P(a)O(2) dropped below 100 mmHg. A pressure volume curve was done post mortem and markers of pulmonary inflammation, surfactant content and biophysiology, and lung histology were assessed. CHF 5633 treatment resulted in improved arterial pH, oxygenation and ventilation efficiency index. The survival rate was significantly higher after CHF 5633 treatment (5/7) than after Poractant alfa (1/8) after 48 hours of ventilation. Biophysical examination of the surfactant recovered from bronchoalveolar lavages revealed that films formed by CHF 5633-treated animals reached low surface tensions in a wider range of compression rates than films from Poractant alfa-treated animals.

CONCLUSIONS

For the first time a synthetic surfactant containing both surfactant protein B and C analogs showed significant benefit over animal derived surfactant in an in vivo model of surfactant inactivation in premature lambs.

The pharmacology of acute lung injury in sepsis

Acute lung injury (ALI) secondary to sepsis is one of the leading causes of death in sepsis. As such, many pharmacologic and nonpharmacologic strategies have been employed to attenuate its course. Very few of these strategies have proven beneficial. In this paper, we discuss the epidemiology and pathophysiology of ALI, commonly employed pharmacologic and nonpharmacologic treatments, and innovative therapeutic modalities that will likely be the focus of future trials.

Neonatal respiratory distress syndrome: an inflammatory disease?

Surfactant substitution has been a major breakthrough in the treatment of neonatal respiratory distress syndrome (RDS), primarily caused by a lack of pulmonary surfactant; it has significantly reduced mortality and acute pulmonary morbidity in preterm infants. Some very immature infants, however, have a poor response to surfactant replacement or an early relapse. This brief article is based on the hypothesis that neonatal RDS has a complex and multifactorial pathogenesis characterized by an injurious inflammatory sequence in the immature lung. Fetal exposure to chorioamnionitis has been shown to initiate an inflammatory reaction beginning in utero. A 'low-grade' inflammatory stimulus in utero may 'prime' the fetal lung for accelerated maturation of the surfactant system, especially in conjunction with prenatal steroids, and may protect the preterm infant from developing moderate to severe RDS. Depending on the severity of inflammatory injury to the alveolar-capillary unit, however, serum proteins will leak into the airways and induce surfactant inactivation. Following this intrauterine 'first hit', the immature infant may develop severe RDS and have a poor response to surfactant substitution. Secondary insults such as traumatic stabilization techniques, oxygen toxicity, initiation of mechanical ventilation and others injure the immature lung immediately after birth and perpetuate and may aggravate the inflammatory process. Observational studies in preterm infants and animal experiments support this concept. Whenever surfactant inactivation is suspected, higher or repetitive doses of natural surfactant may help to overcome surfactant inactivation and to restore lung function.

Surfactant protein D deficiency increases lung injury during endotoxemia

Acute lung injury (ALI) and its severe form, acute respiratory distress syndrome (ARDS), are major causes of acute respiratory failure with high rates of morbidity and mortality. Although surfactant protein (SP)-D plays a critical role in pulmonary innate immunity and several clinical studies suggest that this protein may be implicated in the pathophysiology of ARDS, little is known regarding the function of SP-D in ARDS. In the present study, we induced indirect lung injury by intraperitoneal injection of LPS and direct lung injury by intratracheal injection of LPS in wild-type and Sftpd(-/-) mice to elucidate the role of SP-D during ALI/ARDS. Results indicate that pulmonary levels of IL-6 and TNF-α were higher in Sftpd(-/-) mice when compared with wild-type mice. However, the magnitude of this difference was 10-fold greater after indirect lung injury compared with direct lung injury. After indirect lung injury, there was a 2-fold increase in the number of pulmonary monocyte/macrophages in the Sftpd(-/-) mice when compared with wild-type mice, whereas pulmonary neutrophils were not increased. After indirect injury, the concentration of granulocyte-macrophage colony stimulating factor (GM-CSF) was approximately 5-fold greater in Sftpd(-/-) mice than wild-type mice. In contrast, after direct injury, the concentration of GM-CSF was 20-fold less in Sftpd(-/-) mice than wild-type mice. Despite increased inflammatory cells and markers of inflammation, survival in Sftpd(-/-) mice after indirect lung injury was paradoxically increased. In conclusion, these results suggest that SP-D inhibits pulmonary inflammation and migration of peripheral monocyte/macrophages into the lung through GM-CSF-dependent pathways during indirect lung injury.