Nebulisation of surfactants in an animal model of neonatal respiratory distress

Positive end-expiratory pressure and surfactant administration mode influence function in ex-vivo premature sheep lungs

AIM

Respiratory distress syndrome often necessitates endotracheal surfactant administration in extremely preterm infants. Our study aimed to explore a multi-modal simulation tool for investigating treatment strategies in ex vivo sheep lungs during spontaneous breathing.

METHODS

An electromechanical lung simulator (xPULM) mimicking spontaneous breathing was coupled with a non-aerated premature sheep lung, replicating a premature respiratory system. Changes in tidal volume for different positive end-expiratory pressure (PEEP) levels prior to and after either bolus or nebulised surfactant administration were compared.

RESULTS

In two preterm sheep lungs, we observed a progressive decline in tidal volume with increasing PEEP levels prior to surfactant delivery from 0.30 ± 0.01 mL at zero PEEP to 0.04 ± 0.01 mL at 15 cmH2O PEEP. Our measurements showed that both bolus (p < 0.05) and nebulised (p < 0.05) surfactant administration resulted in a significant increase in tidal volume, with no significant difference (p = 0.71) between the two methods.

CONCLUSION

The experimental setup demonstrated the feasibility of xPULM for investigating the effectiveness of different PEEP levels and modes of surfactant administration with respect to tidal volume in premature sheep lungs. The lack of adequate lung water resorption in our model warrants further investigations.

Surfactant Replacement Therapy: What’s the New Future?

Surfactant replacement therapy (SRT) can be lifesaving for preterm babies with respiratory distress because of surfactant deficiency. Attempts have been made over the last two decades to make surfactant administration as smooth and as nontraumatic as possible. Lesser invasive techniques, such as less invasive surfactant administration, minimally invasive surfactant therapy, intrapartum pharyngeal surfactant therapy, and the laryngeal mask airway, are preferred over invasive techniques like intubate surfactant extubation to reduce trauma and peridosing adverse effects. However, at present, aerosolized surfactant (AS) via nebulization remains the only truly noninvasive method of SRT. Many animal and human studies have shown promising results with the use of AS with similar clinical effects to an instilled surfactant with greater safety potential. But still AS has not been adapted to routine neonatal care. There is still scope for studies to further strengthen the role of AS. Also, SRT is a constantly changing field with new innovations revolutionizing and replacing old techniques.

Physiologic Effects of Instilled and Aerosolized Surfactant Using a Breath-Synchronized Nebulizer on Surfactant-Deficient Rabbits

Surfactant administration incorporates liquid bolus instillation via endotracheal tube catheter and use of a mechanical ventilator. Aerosolized surfactant has generated interest and conflicting data related to dose requirements and efficacy. We hypothesized that aerosolized surfactant with a novel breath-actuated vibrating mesh nebulizer would have similar efficacy and safety as instilled surfactant. Juvenile rabbits (1.50 ± 0.20 kg, n = 17) were sedated, anesthetized, intubated, and surfactant was depleted via lung lavage on mechanical ventilation. Subjects were randomized to receive standard dose liquid instillation via catheter (n = 5); low dose surfactant (n = 5) and standard dose surfactant (n = 5) via aerosol; and descriptive controls (no treatment, n = 2). Peridosing events, disease severity and gas exchange, were recorded every 30 min for 3 h following surfactant administration. Direct-Instillation group had higher incidence for peridosing events than aerosol. Standard dose liquid and aerosol groups had greater PaO₂ from pre-treatment baseline following surfactant (p < 0.05) with greater ventilation efficiency with aerosol (p < 0.05). Our study showed similar improvement in oxygenation response with greater ventilation efficiency with aerosol than liquid bolus administration at the same dose with fewer peridosing events. Breath-synchronized aerosol via nebulizer has potential as a safe, effective, and economical alternative to bolus liquid surfactant instillation.

Aerosolized Surfactant for Preterm Infants with Respiratory Distress Syndrome

Currently, the administration of surfactant to preterm infants with respiratory distress syndrome (RDS) mainly relies on intratracheal instillation; however, there is increasing evidence of aerosolized surfactant being an effective non-invasive strategy. We present a historical narrative spanning sixty years of development of aerosolization systems. We also offer an overview of the pertinent mechanisms needed to create and manage the ideal aerosolization system, with a focus on delivery, distribution, deposition, and dispersion in the context of the human lung. More studies are needed to optimize treatment with aerosolized surfactants, including determination of ideal dosages, nebulizer types, non-invasive interfaces, and breath synchronization. However, the field is rapidly evolving, and widespread clinical use may be achieved in the near future.

Nebulized Poractant Alfa Reduces the Risk of Respiratory Failure at 72 Hours in Spontaneously Breathing Surfactant-Deficient Newborn Piglets

Supplemental Digital Content is available in the text.

We have setup for the first time a long-term (72 hr) respiratory distress syndrome model in spontaneously breathing surfactant-deficient newborn piglets to investigate the continuous positive airway pressure failure rate with nebulized poractant alfa compared with that with the intubation surfactant extubation technique or continuous positive airway pressure only.

Breath-Synchronized Nebulized Surfactant in a Porcine Model of Acute Respiratory Distress Syndrome

Objectives

Effective treatment options for surfactant therapy in acute respiratory distress syndrome and coronavirus disease 2019 have not been established. To conduct preclinical studies in vitro and in vivo to evaluate efficiency, particle size, dosing, safety, and efficacy of inhaled surfactant using a breath-synchronized, nebulized delivery system in an established acute respiratory distress syndrome model.

Design

Preclinical study.

Setting

Research laboratory.

Subjects

Anesthetized pigs.

Intervention

In vitro analysis included particle size distribution and inhaled dose during simulated ventilation using a novel breath-synchronized nebulizer. Physiologic effects of inhaled aerosolized surfactant (treatment) were compared with aerosolized normal saline (control) in an adult porcine model (weight of 34.3 ± 0.6 kg) of severe acute respiratory distress syndrome (Pao₂/Fio₂ <100) with lung lavages and ventilator-induced lung injury during invasive ventilation.

Measurements and Main Results

Mass median aerosol diameter was 2.8 µm. In vitro dose delivered distal to the endotracheal tube during mechanical ventilation was 85% ± 5%. Nebulizers were functional up to 20 doses of 108 mg of surfactant. Surfactant-treated animals (n = 4) exhibited rapid improvement in oxygenation with nearly full recovery of Pao₂/Fio₂ (~300) and end-expiratory lung volumes with nominal dose less than 30 mg/kg of surfactant, whereas control subjects (n = 3) maintained Pao₂/Fio₂ less than 100 over 4.5 hours with reduced end-expiratory lung volume. There was notably greater surfactant phospholipid content and lower indicators of lung inflammation and pathologic lung injury in surfactant-treated pigs than controls. There were no peridosing complications associated with nebulized surfactant, but surfactant-treated animals had progressively higher airway resistance post treatment than controls with no differences in ventilation effects between the two groups.

Conclusions

Breath-synchronized, nebulized bovine surfactant appears to be a safe and feasible treatment option for use in coronavirus disease 2019 and other severe forms of acute respiratory distress syndrome.

Dose-Response Study on Surfactant Nebulization Therapy During Nasal Continuous Positive Airway Pressure Ventilation in Spontaneously Breathing Surfactant-Deficient Newborn Piglets

OBJECTIVES

The current clinical treatment of neonates with respiratory distress syndrome includes endotracheal intubation and intratracheal instillation of exogenous surfactant. Nebulization of surfactant offers an attractive alternative. The aims of this study were to test nebulization as a noninvasive method of administering surfactant and determine the optimal dose for the treatment of respiratory distress syndrome-associated pathophysiology of the neonatal lungs.

DESIGN

Prospective, randomized, animal model study.

SETTING

An experimental laboratory.

SUBJECTS

Thirty-six newborn piglets.

INTERVENTIONS

Different doses (100, 200, 400, and 600 mg/kg) of poractant alfa were administered via a vibrating membrane nebulizer (eFlow-Neos; Pari Pharma GmbH, Starnberg, Germany) or a bolus administration using the intubation-surfactant-extubation (Insure) technique (200 mg/kg) to spontaneously breathing newborn piglets (n = 6/group) with bronchoalveolar lavage-induced respiratory distress syndrome during nasal continuous positive airway pressure (180 min).

MEASUREMENTS AND MAIN RESULTS

Pulmonary, hemodynamic, and cerebral effects were assessed. Histologic analysis of lung and brain tissue was also performed. After repeated bronchoalveolar lavage, newborn piglets developed severe respiratory distress syndrome. Rapid improvement in pulmonary status was observed in the Insure group, whereas a dose-response effect was observed in nebulized surfactant groups. Nebulized poractant alfa was more effective at doses higher than 100 mg/kg and was associated with similar pulmonary, hemodynamic, and cerebral behavior to that in the Insure group, but improved lung injury scores.

CONCLUSIONS

In newborn piglets with severe bronchoalveolar lavage-induced respiratory distress syndrome, our results demonstrate that the administration of nebulized poractant alfa using an investigational customized eFlow-Neos nebulizer is an effective and safe noninvasive surfactant administration technique.

A novel delivery system for supraglottic atomization allows increased lung deposition rates of pulmonary surfactant in newborn piglets

BACKGROUND

Earlier attempts to deliver effective lung doses of surfactant by aerosolization were unsuccessful, mostly because of technical shortcomings. We aimed at quantifying the lung deposition of poractant alfa with a new supraglottic delivery system for surfactant atomization in an experimental neonatal model.

METHODS

The method involved six sedated 1-day-old piglets lying in the lateral decubitus, spontaneously breathing on nasal-mask continuous positive airway pressure (nCPAP). A pharyngeal cannula housing a multi-channel air-blasting atomization catheter was placed through the mouth with its tip above the glottis entrance. In all, 200 mg kg^-1 of a ^99mTc-surfactant mixture was atomized through the catheter synchronously with inspiration. Six intubated control piglets received an equal amount of intratracheally instilled ^99mTc-surfactant mixture. The percentage of the ^99mTc-surfactant mixture deposited in the lungs was estimated by scintigraphy.

RESULTS

Median (range) deposition in the lungs was 40% (24-68%) after atomization and 87% (55-95%) after instillation (p < 0.001). Overall, almost 80% of the deposited surfactant was in the dependent lung. Effective atomization time (atomizer on) was 28 (17-52) min, yielding an output rate of 0.1-0.2 mL min^-1.

CONCLUSIONS

Without endotracheal intubation, in spontaneously breathing newborn piglets, this new supraglottic atomizer delivery system attained a median lung deposition of 40% of the nominal dose of surfactant.

Update of minimally invasive surfactant therapy

To date, preterm infants with respiratory distress syndrome (RDS) after birth have been managed with a combination of endotracheal intubation, surfactant instillation, and mechanical ventilation. It is now recognized that noninvasive ventilation (NIV) such as nasal continuous positive airway pressure (CPAP) in preterm infants is a reasonable alternative to elective intubation after birth. Recently, a meta-analysis of large controlled trials comparing conventional methods and nasal CPAP suggested that CPAP decreased the risk of the combined outcome of bronchopulmonary dysplasia or death. Since then, the use of NIV as primary therapy for preterm infants has increased, but when and how to give exogenous surfactant remains unclear. Overcoming this problem, minimally invasive surfactant therapy (MIST) allows spontaneously breathing neonates to remain on CPAP in the first week after birth. MIST has included administration of exogenous surfactant by intrapharyngeal instillation, nebulization, a laryngeal mask, and a thin catheter. In recent clinical trials, surfactant delivery via a thin catheter was found to reduce the need for subsequent endotracheal intubation and mechanical ventilation, and improves short-term respiratory outcomes. There is also growing evidence for MIST as an alternative to the INSURE (intubation-surfactant-extubation) procedure in spontaneously breathing preterm infants with RDS. In conclusion, MIST is gentle, safe, feasible, and effective in preterm infants, and is widely used for surfactant administration with noninvasive respiratory support by neonatologists. However, further studies are needed to resolve uncertainties in the MIST method, including infant selection, optimal surfactant dosage and administration method, and need for sedation.

Supraglottic Atomization of Surfactant in Spontaneously Breathing Lambs Receiving Continuous Positive Airway Pressure

OBJECTIVES

To determine the short-term tolerance, efficacy, and lung deposition of supraglottic atomized surfactant in spontaneously breathing lambs receiving continuous positive airway pressure.

DESIGN

Prospective, randomized animal study.

SETTING

Animal research laboratory.

SUBJECTS

Twenty-two preterm lambs on continuous positive airway pressure (132 ± 1 d gestational age).

INTERVENTIONS

Animals receiving continuous positive airway pressure via binasal prongs at 8 cm H2O were randomized to receive atomized surfactant at approximately 60-minute of life (atom; n = 15) or not (control; n = 7). The atom group received 200 mg/kg of poractant alfa (Curosurf; Chiesi Farmaceutici SpA, Parma, Italy) over 45 minutes via a novel atomizer located in the upper pharynx that synchronized surfactant delivery with the inspiratory phase.

MEASUREMENTS AND MAIN RESULTS

Arterial blood gas, regional distribution of tidal ventilation (electrical impedance tomography), and carotid blood flow were recorded every 15 minutes until 90 minutes after stabilizing on continuous positive airway pressure. Gas exchange, respiratory rate, and hemodynamic variables, including carotid blood flow, remained stable during surfactant treatment. There was a significant improvement in arterial alveolar ratio after surfactant delivery in the atom group (p < 0.05; Sidak posttests), while there was no difference in PaCO2. Electrical impedance tomography data showed a more uniform pattern of ventilation in the atom group. In the atom group, the median (interquartile range) deposition of surfactant in the lung was 32% (22-43%) of the delivered dose, with an even distribution between the right and the left lungs.

CONCLUSIONS

In our model of spontaneously breathing lambs receiving CPAP, supraglottic atomization of Curosurf via a novel device was safe, improved oxygenation and ventilation homogeneity compared with CPAP only, and provided a relatively large lung deposition suggesting clinical utility.

Minimally Invasive Surfactant Therapy and Noninvasive Respiratory Support

Respiratory distress syndrome (RDS) caused by surfactant deficiency is major cause for neonatal mortality and short- and long-term morbidity of preterm infants. Continuous positive airway pressure and other modes of noninvasive respiratory support and intubation and positive pressure ventilation with surfactant therapy are efficient therapies for RDS. Because continuous positive airway pressure can fail in severe surfactant deficiency, and because traditional surfactant therapy requires intubation and positive pressure ventilation, this entails a risk of lung injury. Several strategies to combine noninvasive respiratory therapy with minimally invasive surfactant therapy have been described. Available data suggest that those strategies may improve outcome of premature infants with RDS.

Intratracheal atomized surfactant provides similar outcomes as bolus surfactant in preterm lambs with respiratory distress syndrome

BACKGROUND

Aerosolization of exogenous surfactant remains a challenge. This study is aimed to evaluate the efficacy of atomized poractant alfa (Curosurf) administered with a novel atomizer in preterm lambs with respiratory distress syndrome.

METHODS

Twenty anaesthetized lambs, 127 ± 1 d gestational age, (mean ± SD) were instrumented before birth and randomized to receive either (i) positive pressure ventilation without surfactant (Control group), (ii) 200 mg/kg of bolus instilled surfactant (Bolus group) at 10 min of life or (iii) 200 mg/kg of atomized surfactant (Atomizer group) over 60 min from 10 min of life. All lambs were ventilated for 180 min with a standardized protocol. Lung mechanics, regional lung compliance (electrical impedance tomography), and carotid blood flow (CBF) were measured with arterial blood gas analysis.

RESULTS

Dynamic compliance and oxygenation responses were similar in the Bolus and Atomizer groups, and both better than Control by 180 min (all P < 0.05; two-way ANOVA). Both surfactant groups demonstrated more homogeneous regional lung compliance throughout the study period. There were no differences in CBFConclusion:In a preterm lamb model, atomized surfactant resulted in similar gas exchange and mechanics as bolus administration. This study suggests evaluation of supraglottic atomization with this system when noninvasive support is warranted.

In Vitro Evaluation of a Device for Intra-Pulmonary Aerosol Generation and Delivery

For infants born with respiratory distress syndrome (RDS), liquid bolus delivery of surfactant administered through an endotracheal tube is common practice. While this method is generally effective, complications such as transient hypoxia, hypercapnia, and altered cerebral blood flow may occur. Aerosolized surfactant therapy has been explored as an alternative. Unfortunately, past efforts have led to disappointing results as aerosols were generated outside the lungs with significant pharyngeal deposition and minimal intrapulmonary instillation. A novel aerosol generator (Microjet™) is evaluated herein for intrapulmonary aerosol generation within an endotracheal tube and tested with Curosurf and Infasurf surfactants. Compared with other aerosol delivery devices, this process utilizes low air flow (range 0.01-0.2 L/min) that is ideal for limiting potential barotrauma to the premature newborn lung. The mass mean diameter (MMD) of the particles for both tested surfactants was less than 4 μm, which is ideal for both uniform and distal lung delivery. As an indicator of phospholipid function, surfactant surface tension was measured before and after aerosol formation; with no significant difference. Moreover, this device has an outside diameter of <1mm, which permits insertion into an endotracheal tube (of even 2.0 mm). In the premature infant where intravenous access is either technically challenging or difficult, aerosol drug delivery may provide an alternative route in patient resuscitation, stabilization and care. Other potential applications of this type of device include the delivery of nutrients, antibiotics, and analgesics via the pulmonary route.

Surfactant

Exogenous pulmonary surfactant, widely used in neonatal care, is one of the best-studied treatments in neonatology, and its introduction in the 1990s led to a significant improvement in neonatal outcomes in preterm infants, including a decrease in mortality. This chapter provides an overview of surfactant composition and function in health and disease and summarizes the evidence for its clinical use.

Lung deposition of nebulized surfactant in newborn piglets

BACKGROUND

It would be advantageous for the treatment of neonatal respiratory distress syndrome if effective amounts of surfactant could be delivered by nebulization.

OBJECTIVE

To investigate lung deposition and distribution of nebulized porcine surfactant using an investigational eFlow neonatal nebulizer.

METHODS

While lying on one side, 1-day-old piglets inhaled 200 mg·kg(-1) of nebulized surfactant via mask, nasal prongs, or tracheal tube. The surfactant was diluted with normal saline to 40 mg·ml(-1) and labeled with (99m)technetium-labelled nanocolloid. Undiluted surfactant (80 mg·ml(-1)) was instilled tracheally in a fourth group. Each group had 8 animals. Lung deposition was measured by gamma scintigraphy, and deposition values were presented as a percentage of the nebulized or instilled dose.

RESULTS

The median lung deposition of inhaled surfactant was 5% (range 3-16) via mask, 14% (2-40) via prongs, and 45% (25-56) via tracheal tube (p < 0.05). It was 88% (71-96) with instillation. In all groups, the surfactant preferentially went to the dependent lung. Deposition ratios (upper lung/both lungs) were 0.32 (0.13-0.58), 0.15 (0.05-0.58), 0.16 (0.11-0.23), and 0.08 (0.03-0.46).

CONCLUSIONS

Using this nebulizer, the lung depositions of porcine surfactant were 45% via endotracheal tube and 14% via nasal-continuous positive airway pressure (prongs). These figures might be physiologically relevant, but still have to be confirmed in efficacy studies.

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

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

Acute and sustained effects of aerosolized vs. bolus surfactant therapy in premature lambs with respiratory distress syndrome

BACKGROUND

Surfactant (SF) instillation may produce acute deleterious effects on gas exchange and both systemic and cerebral hemodynamics. Our aim was to compare the effects of aerosolized SF (SF-aero) with those of bolus SF (SF-bolus) administration on gas exchange, lung mechanics, and cardiovascular function in premature lambs with respiratory distress syndrome (RDS).

METHODS

Fourteen preterm lambs (85% gestation) were randomly assigned to receive SF-aero or SF-bolus. Oxygenation index (OI), PaCO2, cardiovascular parameters, carotid blood flow (CBF), lung compliance (mean dynamic compliance), and tidal volume (VT) were measured every 30 min for 6 h. Biochemical and histological analyses were performed.

RESULTS

After delivery, lambs developed severe RDS (inspiratory fraction of oxygen: 1; pH < 7.15; PaCO2 > 80 mm Hg; PaO2 < 30 mm Hg, mean dynamic compliance < 0.08 ml/cm H2O/kg). By 60 min after treatment, both groups showed an improvement in OI, PaCO2, mean dynamic compliance, and VT that was maintained until the end of the experiment. PaCO2 and CBF increased significantly in the SF-bolus group during the first 15-30 min, without concomitant changes in cardiovascular parameters, whereas in the SF-aero group, PaCO2 and CBF decreased gradually. SF-aero induced less alveolar hemorrhage and inflammation.

CONCLUSION

SF-aero produced improvements in gas exchange and lung mechanics similar to those produced by bolus administration but with less lung injury and fewer cerebral hemodynamic changes.

Novel approaches to surfactant administration

Surfactant replacement therapy has been the mainstay of treatment for preterm infants with respiratory distress syndrome for more than twenty years. For the most part, surfactant is administered intratracheally, followed by mechanical ventilation. In recent years, the growing interest in noninvasive ventilation has led to novel approaches of administration. This paper will review these techniques and the associated clinical evidence.

Nebulised surfactant in preterm infants with or at risk of respiratory distress syndrome

BACKGROUND

Nebulised surfactant has the potential to deliver surfactant to the infant lung with the goal of avoiding endotracheal intubation and ventilation, ventilator-induced lung injury and bronchopulmonary dysplasia (BPD).

OBJECTIVES

To determine the effect of nebulised surfactant administration either as prophylaxis or treatment compared to placebo, no treatment or intratracheal surfactant administration on morbidity and mortality in preterm infants with, or at risk of, respiratory distress syndrome (RDS).

SEARCH METHODS

Searches were performed of CENTRAL (The Cochrane Library, January 2012), MEDLINE and PREMEDLINE (1950 to January 2012), EMBASE (1980 to January 2012) and CINAHL (1982 to January 2012), as well as proceedings of scientific meetings, clinical trial registries, Google Scholar and reference lists of identified studies. Expert informants and surfactant manufacturers were contacted.

SELECTION CRITERIA

Randomised, cluster-randomised or quasi-randomised controlled trials of nebulised surfactant administration compared to placebo, no treatment, or other routes of administration (laryngeal, pharyngeal instillation of surfactant before the first breath, thin endotracheal catheter surfactant administration or intratracheal surfactant instillation) on morbidity and mortality in preterm infants at risk of RDS. We considered published, unpublished and ongoing trials.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for eligibility and quality, and extracted data.

MAIN RESULTS

No studies of prophylactic or early nebulised surfactant administration were found. A single small study of late rescue nebulised surfactant was included. The study is of moderate risk of bias. The study enrolled 32 preterm infants born < 36 weeks' gestation with RDS on nasal continuous positive airway pressure (nCPAP). The study reported no significant difference between nebulised surfactant administration compared to no treatment groups in chronic lung disease (risk ratio (RR) 5.00; 95% confidence interval (CI) 0.26 to 96.59) or other outcomes (oxygenation 1 to 12 hours after randomisation, need for mechanical ventilation, days of mechanical ventilation or continuous positive airways pressure (CPAP) or days of supplemental oxygen). No side effects of the nebulised surfactant therapy or aerosol inhalation were reported.

AUTHORS' CONCLUSIONS

There are insufficient data to support or refute the use of nebulised surfactant in clinical practice. Adequately powered trials are required to determine the effect of nebulised surfactant administration for prevention or early treatment of RDS in preterm infants. Nebulised surfactant administration should be limited to clinical trials.

Surfactant for bacterial pneumonia in late preterm and term infants

BACKGROUND

Pulmonary surfactant is an important part of the host defence against respiratory infections. Bacterial pneumonia in late preterm or term newborn infants often leads to surfactant deficiency or dysfunction, as surfactant is either inactivated or peroxidated. Studies of animal models of pneumonia and clinical case reports suggest that exogenous surfactant might be beneficial to infants with bacterial pneumonia.

OBJECTIVES

To assess the effect of exogenous surfactant treatment on mortality and pulmonary complications in infants with bacterial pneumonia.

SEARCH METHODS

We used standard Cochrane Collaboration methodology to conduct our search of databases. We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 6); MEDLINE (accessed via Ovid SP June 2011); EMBASE (via Ovid SP 1980 to June 2011); and CINAHL Plus (accessed via EBSCOHost June 2011).

SELECTION CRITERIA

We limited our search to randomised and quasi-randomised trials of surfactant replacement therapy in infants > 35 weeks gestation with bacterial pneumonia in the first 28 days of life. The primary outcome measures were death, time to resolution of pneumonia, incidence of chronic lung disease, pneumothoraces and pulmonary haemorrhage.

DATA COLLECTION AND ANALYSIS

We assessed all studies with predefined criteria as to whether they were eligible for inclusion. We extracted data using RevMan 5 (RevMan 2011). We used the standard Cochrane Collaboration methodology for data collection and analysis to assess risk of bias, heterogeneity, treatment effect, missing data and reporting bias where appropriate.

MAIN RESULTS

We did not identify any studies that met our inclusion criteria.

AUTHORS' CONCLUSIONS

There is no evidence from randomised controlled trials (RCTs) to support or refute the efficacy of surfactant in near-term and term infants with proven or suspected bacterial pneumonia. RCTs are still required to answer this question.

Overview of surfactant replacement trials

Clinical trials have evaluated the overall efficacy of surfactant therapy, as well as the relative efficacy of different surfactant preparations, the optimal timing of administration and the optimal dosage. Surfactant therapy leads to significant clinical improvement in infants at risk for, or having, respiratory distress syndrome (RDS). Clinical trials that compared the effects of synthetic or animal-derived surfactant preparations to placebo or no therapy demonstrate that surfactant therapy lead to rapid improvement in oxygenation, decreased ventilator support, decreased risk of pneumothorax, and mortality. Earlier treatment, prophylactic treatment of infants at high risk of developing RDS, and selective re-treatment leads to improved clinical outcome as well. Currently available animal-derived surfactants are superior to non-protein-containing synthetic surfactants. Ongoing evaluation will determine if important differences in animal-derived products are noted. Future trials will evaluate third-generation surfactant products and further refine what constitutes optimal use of surfactant.

Surfactant therapy for respiratory distress syndrome in premature neonates: a comparative review

Exogenous surfactant therapy has been part of the routine care of preterm neonates with respiratory distress syndrome (RDS) since the beginning of the 1990s. Discoveries that led to its development as a therapeutic agent span the whole of the 20th century but it was not until 1980 that the first successful use of exogenous surfactant therapy in a human population was reported. Since then, randomized controlled studies demonstrated that surfactant therapy was not only well tolerated but that it significantly reduced both neonatal mortality and pulmonary air leaks; importantly, those surviving neonates were not at greater risk of subsequent neurological impairment. Surfactants may be of animal or synthetic origin. Both types of surfactants have been extensively studied in animal models and in clinical trials to determine the optimum timing, dose size and frequency, route and method of administration. The advantages of one type of surfactant over another are discussed in relation to biophysical properties, animal studies and results of randomized trials in neonatal populations. Animal-derived exogenous surfactants are the treatment of choice at the present time with relatively few adverse effects related largely to changes in oxygenation and heart rate during surfactant administration. The optimum dose of surfactant is usually 100 mg/kg. The use of surfactant with high frequency oscillation and continuous positive pressure modes of respiratory support presents different problems compared with its use with conventional ventilation. The different components of surfactant have important functions that influence its effectiveness both in the primary function of the reduction of surface tension and also in secondary, but nonetheless just as important, role of lung defense. With greater understanding of the individual surfactant components, particularly the surfactant-associated proteins, development of newer synthetic surfactants has been made possible. Despite being an effective therapy for RDS, surfactant has failed to have a significant impact on the incidence of chronic lung disease in survivors. Paradoxically the cost of care has increased as surviving neonates are more immature and consume a greater proportion of neonatal intensive care resources. Despite this, surfactant is considered a cost-effective therapy for RDS compared with other therapeutic interventions in premature infants.

Surfactant protein-A and phosphatidylglycerol suppress type IIA phospholipase A2 synthesis via nuclear factor-kappaB

We previously showed that surfactant inhibits the synthesis of type IIA secretory phospholipase A2 (sPLA2-IIA) by alveolar macrophages. These cells have been identified as the main source of this enzyme in an animal model of acute lung injury. The aim of the present study was to identify the surfactant components involved in the inhibition of sPLA2-IIA expression in alveolar macrophages and the signaling pathways that mediate this inhibition. Our results show that various surfactant preparations can inhibit sPLA2-IIA expression in endotoxin-stimulated alveolar macrophages. Both the surfactant protein (SP)-A and the surfactant phospholipid fraction inhibit this expression. The surfactant phospholipid dioleylphosphatidylglycerol (DOPG) abolishes sPLA2-IIA expression, whereas dipalmitoylphosphatidylcholine does not. Chromatographic analysis and confocal microscopy revealed that phosphatidylglycerol was rapidly incorporated and metabolized by alveolar macrophages and that its metabolites accumulate in the cytosol. Nuclear factor-kappaB (NF-kappaB) modulates sPLA2-IIA expression in endotoxin-activated alveolar macrophages, and surfactant preparations, surfactant phospholipid fraction, SP-A, and DOPG indeed suppressed NF-kappaB activation. In summary, our results show that SP-A and DOPG play a role in the surfactant-mediated inhibition of sPLA2-IIA expression in alveolar macrophages and that this inhibition occurs via a downregulation of NF-kappaB activation.

Inhalation therapy for infants

Delivering aerosolised drugs to infants poses a number of challenges. It is clear that drug delivery is possible via the inhaled route but to date it has been difficult to demonstrate clearly therapeutic benefit from the use of any conventional therapy in the vast majority of infants. This is probably related to the nature of pulmonary disease in this age group. While most aerosol scientists focus on factors such as aerosol size and airways geometry drug delivery, as in all age groups, is most dependent upon patient behaviour. A small amount of drug reaches the lungs of distressed infants. Consideration of patient device interactions is vital if successful drug delivery is to be achieved and this includes consideration of mask design. Doses reaching the lungs are generally very low when considered in terms of the nominal dose but when considered in terms of dose delivered per kilogram body weight drug delivery to the lungs is generally similar to or greater than in adults. Upper airways deposition is relatively greater than in older subjects, in large part because of nasal breathing, and this will affect the 'therapeutic index' of some drugs.

Current surfactant use in premature infants

Exogenous surfactant therapy has been a significant advance in the management of preterm infants with RDS. It has become established as a standard part of the management of such infants. Both natural and synthetic surfactants lead to clinical improvement and decreased mortality, with natural surfactants having additional advantages over currently available synthetic surfactants. The use of prophylactic surfactant administered after initial stabilization at birth to infants at risk for RDS has benefits compared with rescue surfactant given to treat infants with established RDS. In infants who do not receive prophylaxis, earlier treatment (before 2 hours) has benefits over later treatment. The use of multiple doses of surfactant is a superior strategy to the use of a single dose, whereas the use of a higher threshold for retreatment seems to be as effective as a low threshold. Adverse effects of surfactant therapy are infrequent and usually not serious. Long-term follow-up of infants treated with surfactant in the neonatal period is reassuring. In the future we are likely to see the development of new types of surfactants. Further research is required to determine the optimal use of surfactant in conjunction with other respiratory interventions.

The present status of exogenous surfactant for the newborn

This year is the 20th anniversary of the first successful trial of exogenous surfactant for respiratory distress syndrome in the newborn and it is perhaps a good time to review recent advances in basic science and clinical practice as they relate to surfactant therapy.

Endotracheal surfactant atomization: an alternative to bolus instillation?

OBJECTIVE

To investigate the effect of an intratracheal surfactant fog on oxygenation, blood pressure, distribution, and recovery rate as a pilot study to intratracheal surfactant aerosol.

DESIGN

Prospective, randomized study.

SETTING

University laboratory.

SUBJECTS

A total of 15 New Zealand White rabbits.

INTERVENTIONS

The anesthetized ventilated rabbits were surfactant-deprived by repeated lung lavages and then received 200 mg/kg of a 99mTc-labeled porcine surfactant (Curosurf) either as bolus or as intratracheal surfactant fog.

MEASUREMENTS AND MAIN RESULTS

Blood gases and pressure were measured and distribution as well as recovery rate of the surfactant determined by means of the radio label (gamma camera images and lung processing with subsequent gamma counter measurements). Respiratory function normalized immediately, no difference could be found between the two groups with regard to PaO2, PaCO2, and blood pressure. Even distribution of the radiolabel was found with both methods, the bolus group showing a higher percentage of lung pieces with label concentrations of double average or more. Recovery rates were 82.5%+/-13.1% (mean +/- SD) in the bolus group and 86.5%+/-7.7% in the fog group.

CONCLUSION

Endotracheal surfactant fog application is as effective as bolus instillation and may have a role in the treatment of adult respiratory distress syndrome. It has to be considered as a first step in producing an effective aerosol.

Aerosolized surfactant in lung-lavaged adult rats: factors influencing the therapeutic response

OBJECTIVE

To evaluate the effect of aerosolized modified natural surfactant in adult rats with respiratory failure.

METHODS

Lung-lavaged adult rats were treated with aerosolized surfactant, aerosolized saline or a bolus of surfactant. Surfactant was labelled with dimyristoylphosphatidylcholine (DMPC) and human serum albumin was given intravenously for evaluation of lung protein leakage. Blood gases and dynamic compliance were measured intermittently. At the end of ventilation, the lungs were either fixed by vascular perfusion for histological examination or washed for determination of total phospholipids, DMPC and human albumin in the lavage fluid.

RESULTS

Treatment with bolus surfactant led to a quick and sustained restoration of pre-lavage blood gas values in most animals. The response to aerosolized surfactant varied considerably, with an overall moderate improvement of gas exchange. The saline-treated group failed to show any significant recovery of lung function. No histopathological differences were found between any of the groups. On average 0.46% of total administered aerosolized surfactant could be recovered. Vascular-to-alveolar leakage of human albumin averaged 11%, with no significant differences between the groups. Final values for PaO2 were significantly correlated with total phospholipids in the lavage fluid, and inversely related to the vascular-to-alveolar leakage of albumin.

CONCLUSION

Neither bolus nor aerosolized surfactant influenced lung morphology. Nebulized surfactant improved lung function but the effect was inferior to that obtained with bolus surfactant, and the outcome depended on the balance between the combined pool size of exogenous and endogenous surfactant and the vascular-to-alveolar leakage of serum protein.

Ultrasonic surfactant nebulization with different exciting frequencies

Intratracheal bolus instillation of natural lung surfactant is the treatment of choice in neonatal respiratory distress syndrome and an increasing part in adults' therapy. For reasons of hemodynamics, surfactant distribution and efficiency the application mode should be improved. Nebulization seems to have some advantages but its technical realization is difficult. The aim of the present study was to investigate if ultrasonic nebulization with exciting frequencies higher than 2.8 MHz can improve the efficiency of surfactant nebulization without changing the surface-active properties of the material. Exciting frequencies of 1.7, 3.3 and 4.0 MHz were used to produce a surfactant aerosol. The phospholipid content in the liquefied aerosol and particle size distinctly dropped with higher frequencies. The surface activity was not altered in the produced aerosol and neither in the surfactant remaining in the nebulizer. Although possible, ultrasonic nebulization of surfactant suspensions is ineffective because of a striking decrease in phospholipid content.