A controlled clinical comparison of four different surfactant preparations in surfactant-deficient preterm lambs

Bilayer aggregate microstructure determines viscoelasticity of lung surfactant suspensions

Neonatal respiratory distress syndrome (NRDS) is treated by intratracheal delivery of suspensions of animal-derived lung surfactant in saline. Lung surfactants are extracted via organic solvents from animal lung lavage, followed by solvent removal and surfactant re-hydration to form multi-bilayer particles suspended in saline. Following intra-tracheal administration, the surfactant suspension spreads throughout the lungs by surface tension gradient induced flow; the spreading rate is limited by suspension viscoelasticity. Here we examine the rheology of three clinical lung surfactant suspensions: Survanta (bovine lung), Curosurf (porcine lung), and Infasurf (calf lung). These surfactants have widely different rheological properties that depend on the lipid composition and bilayer organization. The steady shear viscosity is related to the bilayer particle volume fraction as for a suspension of hard spheres, but the lipid volume fraction is not simply related to the mass loading. Optical and electron microscopy and small angle X-ray scattering show that the viscosity variation is due to the temperature and composition dependent bilayer aggregate shapes and internal particle organization. Survanta forms crystalline bilayers at 37 °C, resulting in high aspect ratio asymmetric particles. Infasurf forms aggregates of unilamellar vesicles containing water pockets, while Curosurf forms onion-like multi-layered liposomes. While the mass loading of the three clinical surfactants is different, the different bilayer organization causes the particle volume fractions to be similar. Adding polyethylene glycol dehydrates and partially flocculates the bilayer aggregates in all suspensions, leading to smaller particle volume fractions and a reduced suspension viscosity even though the solvent viscosity increases almost six-fold.

The role of surfactant in respiratory distress syndrome

The key feature of respiratory distress syndrome (RDS) is the insufficient production of surfactant in the lungs of preterm infants. As a result, researchers have looked into the possibility of surfactant replacement therapy as a means of preventing and treating RDS. We sought to identify the role of surfactant in the prevention and management of RDS, comparing the various types, doses, and modes of administration, and the recent development. A PubMed search was carried out up to March 2012 using phrases: surfactant, respiratory distress syndrome, protein-containing surfactant, protein-free surfactant, natural surfactant, animal-derived surfactant, synthetic surfactant, lucinactant, surfaxin, surfactant protein-B, surfactant protein-C.Natural, or animal-derived, surfactant is currently the surfactant of choice in comparison to protein-free synthetic surfactant. However, it is hoped that the development of protein-containing synthetic surfactant, such as lucinactant, will rival the efficacy of natural surfactants, but without the risks of their possible side effects. Administration techniques have also been developed with nasal continuous positive airway pressure (nCPAP) and selective surfactant administration now recommended; multiple surfactant doses have also reported better outcomes. An aerosolised form of surfactant is being trialled in the hope that surfactant can be administered in a non-invasive way. Overall, the advancement, concerning the structure of surfactant and its mode of administration, offers an encouraging future in the management of RDS.

Comparison of poractant alfa and lyophilized lucinactant in a preterm lamb model of acute respiratory distress

INTRODUCTION

A lyophilized formulation of lucinactant has been developed to simplify preparation and dosing. Endotracheal administration of surfactant can be associated with potentially harmful transient hemodynamic changes including decreases in cerebral blood flow and delivery of O2 to the brain. Efficacy and peri-dosing effects of poractant alfa and a lyophilized form of lucinactant were compared in this study.

METHODS

Premature lambs (126-129 d gestation) were delivered by c-section, tracheostomized, ventilated, and instrumented with cerebral laser Doppler flowmetry and tissue PO2 probes. Pulmonary compliance and tidal volumes were monitored continuously and surfactant lung distribution was assessed. Lambs received either poractant alfa or lyophilized lucinactant and were monitored for 3 h after treatment.

RESULTS

Both groups showed significant improvements in arterial pCO2, pH, pulmonary compliance, and tidal volume (all P < 0.01), a similar intra-pulmonary distribution profile, and no significant changes in arterial blood pressure or cerebral blood flow. Administration of poractant alfa was associated with higher mean airway pressures from 75 min post-dosing and transiently decreased heart rate and increased brain tissue PO2 during the first 30 min after treatment.

DISCUSSION

In this newborn lamb model of respiratory distress, lyophilized lucinactant results in improved lung function as compared with poractant alfa.

Myth: all surfactants are alike

There are several surfactant preparations available to the clinician, none of which are alike. They differ in their phospholipid and surfactant protein (SP) composition as well as dosing, yet they all have been shown to be clinically effective as surfactants. Head-to-head randomized clinical trials comparing surfactants have shown some advantages of preparations that contain SP-B and SP-C, primarily in short-term clinical outcomes. A new synthetic surfactant that contains a phospholipid mixture and a peptide resembling SP-B has shown promise as a potential alternative to animal-derived surfactants.

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.

Activity and inhibition resistance of a phospholipase-resistant synthetic surfactant in rat lungs

This study investigates the activity and inhibition resistance in excised rat lungs of a novel synthetic surfactant containing the phospholipase-resistant diether phosphonolipid DEPN-8 plus 1.5% bovine surfactant protein (SP)-B/C compared to calf lung surfactant extract (CLSE). DEPN-8 + 1.5% SP-B/C surpassed CLSE in normalizing surfactant-deficient pressure-volume (P-V) deflation mechanics in lavaged excised lungs in the presence of phospholipase A(2) (PLA(2)) or C18:1 lyso-phosphatidylcholine (LPC). DEPN-8 + 1.5% SP-B/C had activity equal to CLSE in normalizing P-V mechanics in the absence of inhibitors or in the presence of serum albumin. These physiologic activity findings were directly consistent with surface activity measurements on the pulsating bubble surfactometer. In the absence of inhibitors, DEPN-8 + 1.5% SP-B/C and CLSE rapidly reached minimum surface tensions < 1 mN/m (0.5 and 2.5 mg surfactant phospholipid/ml). DEPN-8 + 1.5% SP-B/C maintained its high surface activity in the presence of PLA(2), while the surface activity of CLSE was significantly inhibited by exposure to this enzyme. DEPN-8 + 1.5% SP-B/C also had greater surface activity than CLSE in the presence of LPC, and the two surfactants had equivalent surface activity in the presence of albumin. DEPN-8 + 1.5% SP-B/C also had slightly greater surface activity than CLSE when exposed to peroxynitrite in pulsating bubble studies. These results support the potential of developing highly active and inhibition-resistant synthetic exogenous surfactants containing DEPN-8 + apoprotein/peptide constituents for use in treating direct pulmonary forms of clinical acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS).

Animal-derived surfactants versus past and current synthetic surfactants: current status

In this review, the authors assess major outcomes resulting from head-to-head comparison trials of animal-derived surfactants with previous and newer synthetic surfactants and among them. They also pay special attention to issues of study design and quality of the trials reviewed. Animal-derived surfactants that contain surfactant proteins (Survanta, Infasurf, and Curosurf) perform clinically better than Exosurf, a synthetic surfactant containing only phospholipids, primarily in outcomes related to acute management of respiratory distress syndrome (RDS; faster weaning and pneumothorax) but not in overall mortality or incidence of bronchopulmonary dysplasia (BPD). Trials comparing various animal-derived surfactants that provide different amounts of surface protein B (SP-B) or phospholipids have shown minor differences in outcomes related to the management of RDS or none at all. The exception is the suggestion of better survival using a high initial dose of Curosurf when compared with Survanta. This observation is based on analysis of trials of relatively lesser quality that have included a smaller number of infants than other surfactant comparisons, however. Data from recent trials comparing a new-generation synthetic surfactant that contains a peptide mimicking the action of SP-B, Surfaxin, have shown that it performs better than Exosurf (faster weaning and less BPD) and at least as well as the animal-derived surfactants Survanta and Curosurf. The ideal surfactant comparison trial to demonstrate which surfactant is better has yet to be conducted. Future surfactant comparison trials should pay particular attention to study design, be appropriately sized, and include long-term follow-up.

Observational study to compare the clinical efficacy of the natural surfactants Alveofact and Curosurf in the treatment of respiratory distress syndrome in premature infants

INTRODUCTION

Natural surfactants have been shown to be superior to synthetic surfactants in the treatment of neonatal respiratory distress syndrome (RDS). In Germany, Alveofact (A) and Curosurf (C) are the most frequently used natural surfactant preparations. The aim of this retrospective, observational study was to compare the effects of A and C on gas exchange and outcome in premature infants.

METHODS

During a 5-year period in our neonatal intensive care unit (NICU), 187 premature infants were treated with surfactant, with 82 receiving A and 105 receiving C. We recorded F(I)O(2) and gas exchange (PaO(2)/F(I)O(2) ratio, PaCO(2), SaO(2)) during the first 72h after surfactant application and the incidence of outcome parameters at day 28 (bronchopulmonary dysplasia (BPD), intraventricular hemorrhage (IVH grade III or IV), patent ductus arteriosus (PDA), pneumothorax, necrotizing enterocolites (NEC) and death). The differences between the patient groups were assessed by ANOVA or the calculation of relative risks. Bonferroni correction was used for multiple comparisons.

RESULTS

There were no statistically significant differences between infants treated with A and C in mean gestational age (28.4 vs. 28.4 weeks), birth weight (1210 vs.1258 g) and time of first surfactant application (60 vs. 90 min postnatal). We observed no significant between group differences in course of F(I)O(2) and blood gases, or in incidence at day 28 of BPD (41.7% vs. 42.8%), IVH III/IV (18.3% vs. 14.3%), pneumothorax (9.8% vs. 4.8%), PDA (23.2% vs. 21.9%), PVL (7.3% vs. 9.5%) and death (17% vs. 17.1%). There were also no statistically significant differences in the subgroup of infants <28 weeks. The lower incidence of NEC in A compared with C (1.2% vs. 10.5%, P=0.01) was not statistically significant after Bonferroni correction.

CONCLUSION

Independent of gestational age no significant difference in the clinical efficacy of A and C was observed.

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.

Acute and sustained effects of lucinactant versus poractant-alpha on pulmonary gas exchange and mechanics in premature lambs with respiratory distress syndrome

BACKGROUND

Animal-derived, protein-containing surfactants seem to be superior to protein-free surfactants. Lucinactant, a synthetic surfactant containing a surfactant protein-B peptide analog, has been shown to be effective in animal models and phase II clinical trials. To date, lucinactant has not been compared with an animal-derived surfactant in a premature animal model.

OBJECTIVE

The objective was to compare the acute and sustained effects of lucinactant among premature lambs with respiratory distress syndrome (RDS) with the effects of a natural porcine surfactant (poractant-alpha).

METHODS

After 5 minutes of mechanical ventilation twin premature lambs were assigned randomly to the lucinactant group (30 mg/mL, 5.8 mL/kg) or the poractant-alpha group (80 mg/mL, 2.2 mL/kg). Heart rate, systemic arterial pressure, arterial pH, blood gas values, and lung mechanics were recorded for 12 hours.

RESULTS

Baseline fetal pH values were similar for the 2 groups (pH 7.27). After 5 minutes of mechanical ventilation, severe RDS developed (pH: <7.08; Paco2: >80 mm Hg; Pao2: <40 mm Hg; dynamic compliance: <0.08 mL/cm H2O per kg). After surfactant instillation, similar improvements in gas exchange and lung mechanics were observed for the lucinactant and poractant-alpha groups at 1 hour (pH: 7.3 +/- 0.1 vs 7.4 +/- 0.1; Paco2: 8 +/- 18 mm Hg vs 40 +/- 8 mm Hg; Pao2: 167 +/- 52 mm Hg vs 259 +/- 51 mm Hg; dynamic compliance: 0.3 +/- 0.1 mL/cm H2O per kg vs 0.3 +/- 0.1 mL/cm H2O per kg). The improvements in lung function were sustained, with no differences between groups. Cardiovascular profiles remained stable in both groups.

CONCLUSIONS

Among preterm lambs with severe RDS, lucinactant produced improvements in gas exchange and lung mechanics similar to those observed with a porcine-derived surfactant.

Effects of a recombinant surfactant protein-C-based surfactant on lung function and the pulmonary surfactant system in a model of meconium aspiration syndrome

OBJECTIVE

Meconium aspiration syndrome (MAS) remains a relevant cause of neonatal respiratory failure and is characterized by severe impairment of pulmonary gas exchange, surfactant inactivation, and pronounced inflammatory changes. Surfactant administration has been shown as an effective treatment strategy in MAS. The present study aimed at investigating the impact of a recombinant surfactant protein (SP)-C-based surfactant on pulmonary gas exchange and lung function in this model of neonatal lung injury. Furthermore, SP-B and -C were determined on the transcriptional and protein level.

DESIGN

Laboratory experiment.

SETTING

University laboratory.

SUBJECTS

Twenty three newborn piglets (median age 6 days, weight 1900-2500 g).

INTERVENTIONS

Piglets were intubated and mechanically ventilated and then received 20% sterile meconium (5 mL/kg) for induction of lung injury. After 30 mins, animals were randomized for control (n = 7, MAS controls), recombinant SP-C surfactant (n = 8), or natural surfactant (n = 8). Surfactant preparations were administered as an intratracheal bolus (75 mg/kg), and animals were ventilated for another 330 mins. Nonventilated newborn piglets at term (n = 28; median weight 1484 g, range 720-1990 g) served as a healthy reference group (healthy controls).

MEASUREMENTS AND MAIN RESULTS

Lung function variables, arterial blood gas samples, and lung tissues were obtained. Expression of SP-B and -C messenger RNA was quantified in left lung lobe tissue using real-time polymerase chain reaction. Protein concentrations were determined by enzyme-linked immunosorbent assay. Scanning electron microscopy and transmission electron microscopy were performed in tissue samples of the right lung lobe. Compared with healthy controls, SP-B messenger RNA expression was significantly increased in MAS (p < .02), whereas SP-C messenger RNA expression was found to be significantly reduced (p < .001). SP concentrations, however, were not significantly different. Although a significant improvement of gas exchange and lung function was observed after surfactant administration in both groups, surfactant messenger RNA expression and protein concentrations were not significantly altered. Scanning and transmission electron microscopy showed severe pulmonary ultrastructural changes after meconium aspiration improving after surfactant treatment.

CONCLUSIONS

Impairment of lung function in MAS, associated with marked changes in SP messenger RNA expression, can be sufficiently treated using recombinant SP-C-based or natural surfactant. Despite improved lung function and gas exchange as well as pulmonary ultrastructure after treatment, pulmonary SP messenger RNA expression and concentrations remained significantly affected, giving important insight into the time course following surfactant treatment in MAS.

Surface properties of sulfur- and ether-linked phosphonolipids with and without purified hydrophobic lung surfactant proteins

Two novel C16:0 sulfur-linked phosphonolipids (S-lipid and SO(2)-lipid) and two ether-linked phosphonolipids (C16:0 DEPN-8 and C16:1 UnDEPN-8) were studied for surface behavior alone and in mixtures with purified bovine lung surfactant proteins (SP)-B and/or SP-C. Synthetic C16:0 phosphonolipids all had improved adsorption and film respreading compared to dipalmitoyl phosphatidylcholine, and SO(2)-lipid and DEPN-8 reached maximum surface pressures of 72mN/m (minimum surface tensions of <1mN/m) in compressed films on the Wilhelmy balance (23 degrees C). Dispersions of DEPN-8 (0.5mg/ml) and SO(2)-lipid (2.5mg/ml) also reached minimum surface tensions of <1mN/m on a pulsating bubble surfactometer (37 degrees C, 20cycles/min, 50% area compression). Synthetic lung surfactants containing DEPN-8 or SO(2)-lipid+0.75% SP-B+0.75% SP-C had dynamic surface activity on the bubble equal to that of calf lung surfactant extract (CLSE). Surfactants containing DEPN-8 or SO(2)-lipid plus 1.5% SP-B also had very high surface activity, but less than when both apoproteins were present together. Adding 10wt.% of UnDEPN-8 to synthetic lung surfactants did not improve dynamic surface activity. Surfactants containing DEPN-8 or SO(2)-lipid plus 0.75% SP-B/0.75% SP-C were chemically and biophysically resistant to phospholipase A(2) (PLA(2)), while CLSE was severely inhibited by PLA(2). The high activity and inhibition resistance of synthetic surfactants containing DEPN-8 or SO(2)-lipid plus SP-B/SP-C are promising for future applications in treating surfactant dysfunction in inflammatory lung injury.

Comparison of Infasurf (calfactant) and Survanta (beractant) in the prevention and treatment of respiratory distress syndrome

BACKGROUND

In biophysical and animal testing, Infasurf develops lower surface tension and restores total surfactant activity better than Survanta.

METHODS

We performed 2 prospective, randomized, masked clinical trials; 1 trial used a prophylactic strategy aimed at prevention of respiratory distress syndrome (prophylaxis trial) for infants who were born between 23 weeks, 0 days and 29 weeks, 6 days of gestation, and the second trial used a treatment strategy (treatment trial) for intubated infants with a birth weight of 401 to 2000 g who required fractional inspired oxygen of >0.4 to maintain an arterial oxygen saturation of >90% (or an arterial/alveolar oxygen ratio of <0.2) at any time before 36 hours of age. Our purpose was to determine if Infasurf (calfactant) was more effective than Survanta (beractant) at increasing the proportion of patients alive and not receiving supplemental oxygen at 36 weeks' postmenstrual age. Informed, written, parental consent was required, and protocols were approved by the institutional review boards of all participating institutions. The dose of surfactant was 4 mL/kg (100 mg/kg) for Survanta and 3 mL/kg (105 mg/kg) for Infasurf for both trials. The assigned drug was drawn into 2 masked syringes and administered by a health care professional who, in most cases, was not directly responsible for caring for the patient. A maximum of 3 repeat treatments, at least 6 hours apart, were permitted if the neonate required fractional inspired oxygen of >0.30 to maintain an arterial oxygen saturation of >90% (or an arterial/alveolar oxygen ratio of 0.33) and the infant remained intubated for respiratory distress syndrome.

RESULTS

Both trials were halted for not meeting enrollment targets after a 32-month recruitment period. The decision to end recruitment was made after the interim analysis of the treatment trial. We enrolled 749 infants in the prophylaxis trial and 1361 infants in the treatment trial. The primary outcome (alive and not receiving supplemental oxygen at 36 weeks' postmenstrual age) rate in the prophylaxis trial was 52.1% for group 1 and 52.4% for group 2. In the treatment trial, the primary outcome rate was 58.7% in group 1 and 56.8% in group 2. Based on sample-size requirements for a conclusion of similarity, and the lack of statistical significance to the differences noted in the primary outcome, we have chosen not to break the investigator blind but to report the results as groups 1 and 2.

CONCLUSION

Early trial closure prevents us from either accepting or rejecting our null hypothesis.

Lavage administration of dilute surfactant in a piglet model of meconium aspiration

Maldistribution of exogenous surfactant may preclude any clinical response in acute lung injury associated with surfactant dysfunction. Our previous studies have shown the effectiveness of surfactant lavage after homogenous lung injury. The present study utilizes a histologically confirmed non-homogeneous lung injury model induced by saline lung-lavage followed by meconium injected into a mainstem bronchus. Piglets were then treated with Infasurf or Exosurf by lavage (I-LAVAGE, n = 7; E-LAVAGE, n = 5) or bolus (I-BOLUS, n = 8; E-BOLUS, n = 5), or went untreated (CONTROL, n = 4). Lavage administration utilized a dilute surfactant (35 ml/kg; 4 mg phospholipid/ml) instilled into the lung, followed by gravity drainage. The retained doses of the respective surfactant in the lavage and bolus groups were similar. Results showed that the surfactant distribution was more uniform in the lavage groups compared to the bolus groups. Significant and consistent increases in PaO2 were observed in the lavage groups compared to the bolus groups and the controls. PaO2 (mmHg) at 240 min posttreatment: I-LAVAGE = 297 +/- 54, E-LAVAGE = 280 +/- 57; I-BOLUS = 139 +/- 31; E-BOLUS = 152 +/- 29; C = 119 +/- 73 (mean +/- SEM). Other improved pulmonary function parameters favored lavage administration. We conclude that better surfactant distribution achieved by lavage administration can be more effective than bolus administration in this type of non-homogeneous lung injury.

Modifying calf lung surfactant by hexadecanol

Monolayer properties such as phase behavior, collapse pressure, and surface viscosity are determined by monolayer composition. Learning how to control these properties through simple additives is important to understanding lung surfactant monolayers and to designing optimal replacement surfactants for treatment of disease. The properties of Infasurf, a replacement lung surfactant derived from calf lung lavage organic extract, can be modified in a controlled fashion by adding hexadecanol (HD). Grazing incidence X-ray diffraction shows that the HD preferentially interacts with dipalmitoylphosphatidylcholine (DPPC), the main phospholipid component of Infasurf, in the same way as in binary mixtures of DPPC and HD. HD intercalates between the DPPC chains, which leads to a tighter packing of the two-dimensional lattice and greater stability of the solid phase. This molecular reorganization triggers changes at the macroscopic scale, leading to a greatly increased solid-phase fraction at a given surface pressure and order of magnitude increases in the surface shear viscosity. However, the collapse pressure decreases, and, hence, the minimum surface tension of the film increases.

Surfactant therapy for meconium aspiration syndrome: current status

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.

Immediate changes in lung compliance following natural surfactant administration in premature infants with respiratory distress syndrome: a controlled trial

OBJECTIVE

To compare immediate changes in lung compliance following the administration of two commercially available natural surfactants.

METHOD

We conducted a prospective, randomized study of 40 preterm infants with respiratory distress syndrome requiring surfactant. Infants received either Infasurf or Survanta. The primary outcome measure was the change in compliance assessed by bedside pulmonary monitoring.

RESULTS

There were no significant changes in dynamic lung compliance within or between the two groups 1 hour after surfactant administration. However, infants given Survanta required more doses per patient (4 vs 2, p=0.05) and were more likely to require >2 doses (57 vs 26%, p=0.05). Infants requiring >1 dose of surfactant had a greater change in airway pressure and improved oxygenation just before the second dose when treated with Infasurf.

CONCLUSIONS

We found no significant difference in acute changes in lung compliance. However, treatment with Infasurf seems to be more long lasting than Survanta.

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.

Synthetic and natural surfactant differentially modulate inflammation after meconium aspiration

OBJECTIVE

Meconium aspiration syndrome remains a relevant cause of neonatal respiratory failure and is associated with severe pulmonary changes including surfactant inactivation and pronounced inflammatory changes. The present study investigated the effect of two different surfactant preparations-recombinant surfactant protein C surfactant (rSP-C Surf) and natural bovine surfactant-on pulmonary gas exchange and inflammatory response.

DESIGN AND SUBJECTS

Twenty-three newborn piglets were intubated, mechanically ventilated, received 5 ml/kg 20% sterile meconium for induction of lung injury, and were randomized thereafter for controls ( n=7), rSP-C Surf ( n=8), or natural surfactant ( n=8). Surfactants were given as an intratracheal bolus (75 mg/kg) and animals were further ventilated.

MEASUREMENTS AND RESULTS

Lung function variables, arterial blood gas samples and lung tissues were obtained. Histological evaluation was performed in right lung tissue using an established score. Cytokine mRNA expression (left lung tissue) was quantified using TaqMan real-time PCR (DeltaDeltaCT method, normalized to controls). In addition to significant improvement in gas exchange and lung function, histological evaluation showed significantly lower sum scores in the rSP-C Surf group than in controls). Cytokine mRNA expression of IL-1beta in whole lung tissue was significantly lower after administration of rSP-C Surf than in natural surfactant and controls whereas IL-10 mRNA expression was significantly induced in both surfactant groups.

CONCLUSIONS

Surfactant administration improved both gas exchange and pulmonary inflammatory cytokine transcription. Mechanisms underlying the differential inflammatory response in both surfactant preparations need to be further addressed.

Comparison of three treatment regimens of natural surfactant preparations in neonatal respiratory distress syndrome

The aim of the study was to compare the treatment regimen of three natural surfactants of different extraction and formulation (Alveofact [Surfactant A = SA], Poractant [Surfactant B = SB] and Beractant [Surfactant C = SC]) in neonatal respiratory distress syndrome (RDS). Premature infants of </=32 weeks' gestation with birth weight of </=2,000 g and with established RDS requiring artificial ventilation with a FiO2 >/=0.3 were randomly assigned to receive at least two doses of SA, SB or SC (100 mg/kg per dose). Infants who remained dependent on artificial ventilation with a FiO2 >/=0.3 received up to two additional doses. There were no differences among the groups regarding the necessity for more than two doses. The SA and the SB groups spent fewer days on a ventilator (p-value SA/SB 0.7, SA/SC 0.05, SB/SC 0.043) compared with the SC group, needed fewer days of oxygen administration (p-value SA/SB 0.14, SA/SC 0.05, SB/SC 0.04) and spent fewer days in hospital (p-value SA/SB 0.65, SA/SC 0.04, SB/SC 0.027). There were no statistically significant differences in the incidence of mortality, chronic lung disease, air leaks, necrotising enterocolitis, retinopathy of prematurity and intraventricular haemorrhage among the three groups.

CONCLUSION

The Alveofact and Poractant groups spent fewer days on the ventilator, needed fewer days of oxygen administration and spent fewer days in hospital compared with the Beractant group but no differences were observed among the three groups with regards to mortality and morbidity.

The role of exogenous surfactant in the treatment of acute lung injury

A number of conditions, such as pneumonia, trauma, or systemic sepsis arising from the gut, may result in the acute respiratory distress syndrome (ARDS). Because of its significant morbidity and mortality, ARDS has been the focus of extensive research. One specific area of interest has been the investigation of the role of the surfactant system in the pathophysiology of this disease. Several studies have demonstrated that alterations of surfactant contribute to the lung dysfunction associated with ARDS, which has led to investigations into the use of exogenous surfactant as a therapy for this syndrome. Clinical experience with surfactant therapy has been variable owing to a number of factors including the nature of the injury at the time of treatment, the specific surfactant preparation utilized, the dose and delivery method chosen, the timing of surfactant administration over the course of the disease, and the mode of ventilation used during and after surfactant administration.

Injury responses to different surfactants in ventilated premature lamb lungs

The lung of the preterm infant is easily injured and an initial indication of the injury is an inflammatory response. Surfactant treatment and gentle ventilation will minimize the initiation and progression of injury. We asked if the initial lung injury response differed when preterm ventilated lambs were treated with complete natural sheep surfactant, a lipid extract of sheep surfactant, a surfactant used to treat RDS (Survanta), or a synthetic surfactant containing recombinant SP-C (Venticute). We used a gentle style of ventilation and a positive end expiratory pressure of 4 cmH(2)0 to minimize injury. The surfactants were not distinguishable based on gas exchange, compliance or lung gas volumes over the 6h ventilation period. When compared with unventilated controls the ventilated lambs had increased protein and inflammatory cells in alveolar lavages. The cells from the alveolar lavages produced more H(2)0(2), expressed more surface adhesion antigens and CD-14 receptors, and expressed more mRNA for the pro-inflammatory cytokines IL-1 beta and IL-8 than did cells from unventilated lungs. Lung tissue expressed primarily increased IL-6 mRNA relative to unventilated controls. However, there were no consistent differences in any of the inflammatory indicators between the different surfactant treated groups. Because endotoxin free natural surfactant containing SP-A was not superior to three other surfactants containing differing amounts of the surfactant proteins, additions of these proteins to clinical surfactants may not decrease the indicators of lung inflammation that accompany the initiation of ventilation of the preterm lung.

Lung surfactants for neonatal respiratory distress syndrome: animal-derived or synthetic agents?

Exogenous surfactant therapy is widely used in the management of neonatal respiratory distress syndrome. Two types of surfactants are available: synthetic surfactants, and those derived from animal sources ("natural" surfactants). Both of these surfactants have been shown to be effective. In this article, we review the evidence to compare the two types of surfactants in terms of their physical properties, physiologic effects, and clinical outcomes. Natural surfactants have been shown to have advantages over synthetic surfactants in their physical properties and physiologic effects in animals, as well as in humans. A systematic review of 11 randomized clinical trials comparing natural and synthetic surfactants demonstrated that the use of natural surfactant preparations results in greater clinical benefits compared with synthetic surfactants. These benefits include a more rapid improvement in oxygenation and lung compliance after surfactant therapy, a decrease in the risk of mortality (typical relative risk 0.87; typical risk difference -0.02), and a decrease in the risk of pneumothorax (typical relative risk 0.63; typical risk difference -0.04). Although the use of natural surfactants results in a slightly increased risk of intraventricular hemorrhage (typical relative risk 1.09; typical risk difference 0.03), there is no increase in the risk of grade 3 or 4 intraventricular hemorrhage. There are theoretical but unproven risks of natural surfactants, such as transmission of infectious agents, immunogenicity and impurities in composition. The use of natural surfactants is preferred in most situations. In addition, clinicians should determine the costs of different types of surfactants in their individual practice settings and use this information in decision-making.

Component-specific surface and physiological activity in bovine-derived lung surfactants

Composition, surface activity and effects on pressure-volume (P-V) mechanics are examined for lavaged calf lung surfactant (LS) and the clinical exogenous surfactants Infasurf and Survanta. Lavaged LS and Infasurf had closely-matching compositions of phospholipids and neutral lipids. Survanta had higher levels of free fatty acids and triglycerides consistent with its content of added synthetic palmitic acid and tripalmitin. Infasurf and Survanta both contained less total protein than LS because of extraction with hydrophobic solvents, but the total protein content relative to phospholipid in Survanta was about 45% lower than in Infasurf. This difference was primarily due to surfactant protein (SP)-B, which was present by ELISA at a mean weight percent relative to phospholipid of 1.04% in LS, 0.90% in Infasurf, and 0.044% in Survanta. Studies on component fractions separated by gel permeation chromatography showed that SP-B was a major contributor to the adsorption, dynamic surface activity, and P-V mechanical effects of Infasurf, which approached whole LS in magnitude. Survanta had lower adsorption, higher minimum surface tension, and a smaller effect on surfactant-deficient P-V mechanics consistent with minimal contributions from SP-B. Addition of 0.05% by weight of purified bovine SP-B to Survanta did not improve surface or physiological activity, but added 0.7% SP-B improved adsorption, dynamic surface tension lowering, and P-V activity to levels similar to Infasurf. The SP-B content of lung surfactants appears to be a crucial factor in their surface activity and efficacy in improving surfactant-deficient pulmonary P-V mechanics.

Calfactant

Surfactant administration has proven remarkably effective in the prevention and treatment of infantile respiratory distress syndrome (IRDS) and may also be beneficial in other forms of acute lung injury. Several surfactant products are available commercially along with others in various phases of development and clinical trials. While all of these products share an ability to lower surface tension in vitro, there are substantial compositional differences that appear to affect their in vivo efficacy. At present, the 'modified natural' surfactants containing the hydrophobic surfactant proteins SP-B and SP-C appear most effective. Calfactant may have a particular advantage because of its relatively high content of SP-B and its lack of contamination with non-surfactant lipids and proteins.

Lung salvage and protection ventilatory techniques

Physicians are in the beginning of an era in intensive care medicine in which they finally are starting to see improved outcomes in patients with AHRF. At the same time, intensivists are presented with a bewildering choice of ventilator options and adjunctive therapies. Trying to sort out which are "cosmetic," that is, improve the blood gases as opposed to influencing the outcome, remains a challenge and will be resolved only with additional RCTs. Principles of ventilator management that are driven by mimicking normal physiology are inappropriate and must be rethought.

Animal-derived or synthetic surfactant for the treatment of neonatal respiratory distress syndrome: a review

Animal-derived surfactants containing SP-B and SP-C are more effective in vitro and in animal models than their synthetic counterparts, but are not as effective as unmodified, naturally occurring surfactant. In clinical trials involving newborn babies with respiratory distress syndrome (RDS) these short-term differences are reflected as improvements in gas exchange and lung function. Treatment with animal-derived surfactants results in fewer air leaks and lower neonatal mortality. The evidence is now strong enough to recommend routine use of animal-derived surfactants in very preterm infants with RDS. The newer generation of synthetic surfactants may be important in the future as they have the advantages of currently available animal products with the addition of better resistance to inactivation.

Alveolar metabolism of natural vs. synthetic surfactants in preterm newborn rabbits

We compared the recoveries of four surfactant preparations: two natural [term fetal rabbit surfactant (FRS) and adult rabbit surfactant (ARS)] and two commercially available preparations [apoprotein-based Survanta (S) and synthetic Exosurf (E)] from 27-day gestation rabbit pups treated at birth and ventilated up to 120 min. At 5, 60, and 120 min, we measured the recovery of the heavy-aggregate, metabolically active form (H) and the light-aggregate, nonsurface active metabolic breakdown form (L) of alveolar surfactant and determined the phospholipid content and composition of the intracellularly stored lamellar body (LB) pool. Pups treated with FRS had <15% loss of H by 2 h. ARS-treated pups had a >50% loss of H by 1 h, and E- and S-treated pups had approximately 50% loss by 5 min, with a slower rate of continuing loss of up to 80% by 2 h. The major losses of H phospholipid were not explained by the L-form recovery. LB phospholipid significantly increased only in the E-treated pups and only at 2 h. FRS provides a biologically active form (H) of surfactant that appeared to remain in the airway for a significantly longer time than the other surfactant preparations. The unique properties of FRS merit further study.

Analysis of dynamic surface properties of therapeutic surfactants and lung phospholipids

Exogenous surfactant is a specialized biomaterial used for substitution of the lipoprotein mixture normally present in lungs--pulmonary surfactant. Respiratory Distress Syndrome is a disease of preterm infants mainly caused by a deficiency of mature lung surfactant. Pulmonary surfactant is known to stabilize small alveoli and prevent them from collapsing during expiration due to its unique surface properties. A pulsating bubble surfactometer was used for in vitro analysis of surface parameters of therapeutic surfactants and of test formulations to be used for exogenous therapy in Respiratory Distress Syndrome. Surface parameters that were considered for comparison were minimum surface tension (gamma(min)) at three different frequencies (20, 40 and 60 cpm), adsorption at two extreme bubble radii (Rmin and Rmax), stability index at the three frequencies, recruitment index and the surface viscoelastic parameters. Survanta, ALEC and Exosurf were compared with formulations consisting of the main phospholipids of pulmonary surfactant, namely dipalmitoyl phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) as well as binary mixtures of these phospholipids in the ratio 2:3. Survanta performed much better than the non-protein therapeutic surfactants in all parameters and at all three frequencies. Exosurf had a very low stability index and a very low modulus of surface dilatational elasticity at all three frequencies. The test compounds showed a frequency dependence in their performance. At 20 cpm, PC:PG (2:3) was the best test combination. It achieved a gamma(min) and stability index equivalent to Survanta at this frequency. None of the test compounds were comparable to Survanta at 40 and 60 cpm. These findings may have important therapeutic implications for exogenous surfactants.

High-versus low-threshold surfactant retreatment for neonatal respiratory distress syndrome

Surfactant therapy has become an effective standard therapy for infants with respiratory distress syndrome (RDS). The first dose may be given either as prophylaxis immediately after delivery, or as rescue after an infant has developed RDS. Second and subsequent doses are currently recommended by the manufacturers to be administered at minimal levels of respiratory support.

PURPOSE

This study compared the relative efficacy of administering second and subsequent doses of Infasurf surfactant at a low threshold (FIO(2) >30%, still requiring endotracheal intubation) versus a high threshold (FIO(2) >40%, mean airway pressure >7 cm H(2)O) of respiratory support.

METHODS

A total of 2484 neonates received a first dose of surfactant; 1267 reached conventional retreatment criteria and were randomized to be retreated according to low- or high-threshold criteria. They were then retreated at a minimum of 6-hour intervals each time they reached their assigned threshold until receiving a maximum of 4 total doses. Subjects were stratified by whether they received their first dose by prophylaxis or rescue and by whether their lung disease was considered complicated (evidence of perinatal compromise or sepsis) or uncomplicated.

RESULTS

Among the patients randomized, 33% of prophylaxis and 23% of rescue subjects met criteria for the complicated stratum. Although infants allocated to the high-threshold strategy were receiving slightly more oxygen at 72 hours, there was no difference in the number receiving mechanical ventilation at 72 hours or in the secondary respiratory outcomes (requirement for supplemental oxygen or mechanical ventilation at 28 days, supplemental oxygen at 36 weeks' postconceptional age, inspired oxygen concentration >60% at any time). However, there was a significantly higher mortality for infants with complicated RDS who had received retreatment according to the high-threshold strategy.

CONCLUSIONS

We conclude that equal efficacy can be realized by delaying surfactant retreatment of infants with uncomplicated RDS until they have reached a higher level of respiratory support than is the current standard. We speculate that this would result in a substantial cost-saving from less utilization of drug. Conversely, we believe that infants with complicated RDS should continue to be treated by the low-threshold retreatment strategy, which is currently recommended by the manufacturers of the commercially available surfactants.

Surfactant modulates calcium response of neutrophils to physiologic stimulation via cell membrane depolarization

Pulmonary surfactant (PS) reduces inflammation in the lung by poorly understood mechanisms. We have observed that surfactant-associated proteins (SAP) insert monovalent cation channels in artificial membranes. Neutrophils are primary mediators of acute pulmonary inflammation, and their functions are activated by increases in cytosolic ionized calcium concentration ([Ca2+]) and by changes in membrane potential. We hypothesize that PS inserts SAP-dependent cation channels in neutrophils, causing membrane depolarization, altered [Ca2+] response, and depressed activation. Human neutrophils were isolated, exposed to PS+SAP (1% Survanta), PS-SAP (1% Exosurf), or buffer, and washed before activating with selected stimulants. PS+SAP reduced phorbol ester- and formyl peptide-stimulated adherence and aggregation by 38% (p < 0.05) and 54% (p < 0.02), respectively. PS+SAP also inhibited the formyl peptide-induced [Ca2+] response of neutrophils (p < 0.01), but only in the presence of external Ca2+. Further characterization of this inhibition demonstrated that PS+SAP blocked formyl peptide-induced influx of both Ca2+ and Mn2+, and that this inhibition was present during activation by other neutrophil stimulants (IL-8, immune complexes). Prior depolarization of neutrophils with gramicidin-D similarly inhibited the [Ca2+] response of neutrophils to formyl peptide, and analysis of neutrophil membrane potential by 3,3'-dipentyloxaearbocyanine iodide (diOC5(3)) fluorescence revealed that PS+SAP induced rapid neutrophil depolarization. In contrast, PS-SAP exhibited little effect on neutrophil function, [Ca2+], or membrane potential. We conclude that PS+SAP decreases neutrophil adherence and aggregation responses, blocks Ca2+ influx after physiologic stimulation, and decreases membrane potential. We speculate that these effects are caused by membrane depolarization via SAP-dependent cation channel insertion, and that all of these effects contribute to the antiinflammatory properties of PS+SAP.

Alveolar environment influences the metabolic and biophysical properties of exogenous surfactants

Several factors have been shown to influence the efficacy of exogenous surfactant therapy in the acute respiratory distress syndrome. We investigated the effects of four different alveolar environments (control, saline-lavaged, N-nitroso-N-methylurethane, and hydrochloric acid) on the metabolic and functional properties of two exogenous surfactant preparations: bovine lipid extract surfactant and recombinant surfactant-associated protein (SP) C drug product (rSPC) administered to each of these groups. The main difference between these preparations was the lack of SP-B in the rSPC. Our results demonstrated differences in the large aggregate pool sizes recovered from each of the experimental groups. We also observed differences in SP-A content, surface area cycling characteristics, and biophysical activities of these large aggregate forms after the administration of the two exogenous surfactant preparations. We conclude that the alveolar environment plays a critical role, influencing the overall efficacy of exogenous surfactant therapy. Thus further preclinical studies are warranted to investigate the specific factors within the alveolar environment that lead to the differences observed in this study.

Matrix metalloproteinase inhibitor prevents acute lung injury after cardiopulmonary bypass

BACKGROUND

Acute lung injury (ALI) after cardiopulmonary bypass (CPB) results from sequential priming and activation of neutrophils. Activated neutrophils release neutral serine, elastase, and matrix metalloproteinases (MMPs) and oxygen radical species, which damage alveolar-capillary basement membranes and the extracellular matrix, resulting in an ALI clinically defined as adult respiratory distress syndrome (ARDS). We hypothesized that treatment with a potent MMP and elastase inhibitor, a chemically modified tetracycline (CMT-3), would prevent ALI in our sequential insult model of ALI after CPB.

METHODS AND RESULTS

Anesthetized Yorkshire pigs were randomized to 1 of 5 groups: control (n=3); CPB (n=5), femoral-femoral hypothermic bypass for 1 hour; LPS (n=7), sham bypass followed by infusion of low-dose Escherichia coli lipopolysaccharide (LPS; 1 microgram/kg); CPB+LPS (n=6), both insults; and CPB+LPS+CMT-3 (n=5), both insults plus intravenous CMT-3 dosed to obtain a 25-micromol/L blood concentration. CPB+LPS caused severe lung injury, as demonstrated by a significant fall in PaO(2) and an increase in intrapulmonary shunt compared with all groups (P<0.05). These changes were associated with significant pulmonary infiltration of neutrophils and an increase in elastase and MMP-9 activity.

CONCLUSIONS

All pathological changes typical of ALI after CPB were prevented by CMT-3. Prevention of lung dysfunction followed an attenuation of both elastase and MMP-2 activity. This study suggests that strategies to combat ARDS should target terminal neutrophil effectors.

Calfactant: a review of its use in neonatal respiratory distress syndrome

Calfactant (Infasurt) is a natural bovine surfactant which has been evaluated for intratracheal use in the prevention and rescue treatment of respiratory distress syndrome (RDS) in preterm infants. In 2 randomised, double-blind, multicentre clinical trials of prophylactic use, calfactant 100 or 105 mg phospholipid per kg bodyweight (mg/kg) reduced RDS incidence, RDS severity and mortality rates to a greater extent than colfosceril palmitate (Exosurf Neonatal) 67.5 mg/kg and was generally similar to beractant (Survanta) 100 mg/kg. Although the rate of mortality before discharge from hospital was significantly higher in infants with birthweights <600 g who received calfactant than in those who received beractant, this may not be a typical result. As rescue treatment, calfactant 100 or 105 mg/kg reduced RDS severity, but not mortality rates, significantly more than colfosceril palmitate 67.5 mg/kg or beractant 100 mg/kg in 2 randomised, double-blind, multicentre clinical trials. In addition, the duration of effect of calfactant as prophylaxis or rescue treatment appeared to be longer than that of beractant. In other randomised trials, prophylaxis was more effective than rescue treatment with calfactant, particularly in infants of < or =29 weeks gestational age. The incidence of pulmonary air leak events was lower with calfactant than with colfosceril palmitate (12 vs 22%) but was identical with calfactant and beractant (15% with either agent). The incidence of other complications associated with RDS was usually similar with all 3 agents in clinical trials in preterm infants. The incidence of intraventricular haemorrhage was significantly higher in 1 clinical trial, and that of septicaemia was significantly lower in another, with calfactant versus colfosceril palmitate, but the combined incidences of these complications was similar with the 2 agents when results from different trials were pooled. The incidence of acute adverse events (i.e. those which occurred during administration of the drug) with calfactant was similar to that with beractant and higher than that with colfosceril palmitate; the difference may been related to reduced RDS severity in calfactant versus colfosceril palmitate recipients. Acute adverse events were usually transient and not severe.

CONCLUSIONS

Calfactant is a well tolerated natural bovine surfactant which is effective in the prevention and treatment of RDS in preterm infants. Further investigation is needed to more clearly determine the efficacy and tolerability of calfactant relative to that of other surfactant preparations. When more data are available, it is likely that calfactant will be useful as an alternative to beractant (at least in infants of birthweights >600 g), and calfactant may be preferred over colfosceril palmitate in both the prophylaxis and treatment of RDS.

Soluble tumor necrosis factor receptor prevents post-pump syndrome

Post-pump syndrome is an acute lung injury following cardiopulmonary bypass (CPB) which is indistinguishable from the adult respiratory distress syndrome (ARDS). Tumor necrosis factor (TNF) is central to the inflammatory process and is capable of triggering the entire pathophysiologic response leading to ARDS. We hypothesized that treatment with a soluble TNF receptor-binding protein (TNFbp) would reduce the increase in serum TNF and prevent acute lung injury in our sequential insult model of ARDS following CPB. Anesthetized pigs were randomized to one of three groups: Control (n = 3), surgical preparation only; CPB + LPS (n = 6), femoral-femoral hypothermic bypass for 1 h followed by infusion of low dose Escherichia coli lipopolysaccharide (LPS; 1 microg/kg); and TNFbp + CPB + LPS (n = 4), pretreatment with intravenous TNFbp (2 mg/kg) followed immediately by both insults. CPB + LPS caused severe lung injury demonstrated by a significant fall in PaO2 and an increase in both intrapulmonary shunt and peak airway pressure as compared to all groups (P < 0.05). These changes were associated with a significant increase in plasma TNF level and pulmonary neutrophil sequestration. TNFbp significantly reduced plasma levels of TNF and prevented the lung injury typically observed with this ARDS model, but did not reduce pulmonary neutrophil sequestration. Thus, elevated serum TNF is not responsible for neutrophil sequestration but does play a role in neutrophil activation which causes lung injury. Prophylactic use of TNFbp in CPB patients may prevent neutrophil activation and reduce the incidence of post-pump ARDS.

Comparative trial of artificial and natural surfactants in the treatment of respiratory distress syndrome of prematurity: experiences in a developing country

We conducted a randomized clinical trial to compare the effects of a synthetic (Exosurf) and natural (Survanta) surfactant in infants with neonatal respiratory distress syndrome. Eighty-nine patients were randomly allocated to receive one of the two surfactants. Primary outcome variables were the acute and long-term effects of the surfactant preparations, i.e., ventilatory requirements at 24 h of age as judged by the oxygenation index (OI), and the combined incidence of chronic lung disease or death at 28 days. The OIs in the Exosurf and Survanta groups at 24 h were the same (10.1 and 7, respectively; P > 0.05). The magnitude and rapidity of response, however, were greater for Survanta than for Exosurf. When arterial/alveolar oxygen tension ratios (a/A) were compared, the Exosurf group had a significantly worse a/A ratio at 24 h than the Survanta group (0.21 Exosurf vs. 0.37 Survanta; P < 0.05). The long-term outcome as judged by the combined incidence of death or chronic lung disease was not different in the two groups (18.6% Exosurf vs. 15.2% Survanta; P > 0.05). When the complications of prematurity were compared, there were no statistically significant differences between the two groups. We conclude that both preparations are reasonable choices for the treatment of respiratory distress syndrome of prematurity.

Multiple sequential insults cause post-pump syndrome

BACKGROUND

We hypothesize that post-pump syndrome (PPS) following cardiopulmonary bypass (CPB) can be caused by multiple minor insults and that the mechanism of PPS is a priming and subsequent activation of polymorphonuclear (PMN) leukocytes. In this study extensive pathophysiologic and morphometric assessment was undertaken in a porcine model of sequential insult PPS.

METHODS

Pigs were anesthetized, placed on a ventilator, instrumented for measurements of hemodynamic function, and separated into five groups: (1) Control (n = 4)--surgery only, (2) CPB (n = 4)--placed on femoral-femoral hypothermic (28 degrees C) bypass for 1 h, (3) LPS (n = 6)--underwent sham CPB followed by infusion of low dose endotoxin [E. coli lipopolysaccharide (LPS-1 microg/kg)], (4) Heparin + protamine + LPS (HP + LPS, n = 4)--were heparinized without CPB for 1 h, following which protamine and LPS were infused and (5) CPB + LPS (n = 8)--subjected to both CPB and LPS.

RESULTS

Only CPB + LPS resulted in acute respiratory distress typical of PPS as indicated by a significant decrease in PaO2 and increase in intrapulmonary shunt fraction (p<0.05). CPB + LPS significantly increased tissue density and the number of sequestered monocytes and PMNs (p<0.05) above all other groups. Alveolar macrophages (AM) increased equally in all groups receiving LPS.

CONCLUSIONS

CPB primes the inflammatory system causing pulmonary PMN sequestration without lung injury. Exposure to an otherwise benign dose of endotoxin results in activation of the sequestered PMNs causing PPS. This study confirms that PPS can be caused by multiple minor insults.

Recent developments in inhaled nitric oxide therapy of the newborn

Inhaled nitric oxide therapy improves oxygenation and reduces the need for extracorporeal life support in near-term and term newborns with hypoxemic respiratory failure and persistent pulmonary hypertension of the newborn. Previous studies demonstrated that the efficacy of inhaled nitric oxide therapy is related to the underlying disease associated with persistent pulmonary hypertension and that lung recruitment strategies augment the response to this inhalational vasodilator. This review of recent studies evaluates new insight into important questions regarding the optimal dose of inhaled nitric oxide, potential adverse effects associated with inhaled nitric oxide therapy, and the potential role of inhaled nitric oxide in the premature newborn with hypoxemic respiratory failure.

Surfactant treatment for acute respiratory distress syndrome

OBJECTIVE

To determine prospectively the efficacy of surfactant in acute respiratory distress syndrome.

STUDY DESIGN

Twenty patients, 1 month to 16 years of age, diagnosed with an acute pulmonary disease with severe hypoxaemia (PaO2/FiO2 < 100) (13 with systemic or pulmonary disease and seven with cardiac disease) were treated with one to six doses of 50-200 mg/kg of porcine surfactant administered directly into the trachea. The surfactant was considered to be effective when the PaO2/FiO2 improved by > 20%.

RESULTS

After initial surfactant administration the PaO2/FiO2 increased significantly in patients with systemic or pulmonary disease from 68 to 111, and the oxygenation index (OI) diminished significantly from 36.9 to 27.1. The PaO2/FiO2 and OI did not improve in children with cardiac disease. The improvement of the patients who survived was greater than that of those who died.

CONCLUSIONS

Surfactant moderately improves oxygenation in some children with severe acute respiratory distress syndrome secondary to pulmonary or systemic disease.

Instillation of calf lung surfactant extract (calfactant) is beneficial in pediatric acute hypoxemic respiratory failure. Members of the Mid-Atlantic Pediatric Critical Care Network

OBJECTIVE

Prospective study of the efficacy of calf lung surfactant extract in pediatric respiratory failure.

DESIGN

Multi-institutional, prospective, randomized, controlled, unblinded trial.

SETTING

Eight pediatric intensive care units (ICU) of tertiary medical centers.

PATIENTS

Forty-two children with acute hypoxemic respiratory failure characterized by diffuse, bilateral pulmonary infiltrates, need for ventilatory support, and an oxygenation index of >7.

INTERVENTION

Instillation of intratracheal surfactant (80 mL/m2).

MEASUREMENTS AND MAIN RESULTS

Ventilator parameters, arterial blood gases, and derived oxygenation and ventilation indices were recorded before and at intervals after surfactant administration. Complications and outcome measures, including mortality, duration of mechanical ventilation, and length of pediatric ICU and hospital stay, were also examined. Patients who received surfactant demonstrated rapid improvement in oxygenation and, on average, were extubated 4.2 days (32%) sooner and spent 5 fewer days (30%) in pediatric intensive care than control patients. There was no difference in mortality or overall hospital stay. Surfactant administration was associated with no serious adverse effects.

CONCLUSIONS

Administration of calf lung surfactant extract, calfactant, appears to be safe and is associated with rapid improvement in oxygenation, earlier extubation, and decreased requirement for intensive care in children with acute hypoxemic respiratory failure. Further study is needed, however, before widespread use in pediatric respiratory failure can be recommended.

[Recent developments in the treatment of pediatric acute respiratory distress syndrome]

Acute respiratory distress syndrome (ARDS) is a severe condition with a high mortality rate, despite conventional treatment using mechanical ventilation. Better understanding of the pathophysiology and awareness of important iatrogenic lung injury secondary to mechanical ventilation has led to new therapeutic principles. Mechanical ventilation strategy during ARDS is characterized by positive end-expiratory pressure, increase in the inspiratory time, high inspiratory oxygen concentration and, more recently, use of permissive hypercapnia. High frequency ventilation allows optimal lung recruitment under small tidal volume. The effectiveness of extracorporeal oxygenation techniques is demonstrated, but because of their cost and morbidity these therapies are rational only in patients who seem likely to die. Partial liquid ventilation and inhaled nitric oxide have great potential but require further studies. Intratracheal exogenous surfactant might be beneficial but controlled trials are needed to confirm the usefulness of this expensive therapy. Finally, a number of adjuncts to mechanical ventilation are currently available to minimize iatrogenic lung injury and improve the outcome. The role of these new treatments must be defined with randomized and controlled clinical trials using homogenous inclusion criteria.

Pharmacologic adjuncts to mechanical ventilation in acute respiratory distress syndrome

This article reviews pharmacologic approaches to treating acute respiratory distress syndrome (ARDS). The authors discuss the therapeutic effects of ketoconazole, antioxidants, corticosteroids, surfactant, ketanserin, pentoxifylline, bronchodilators, and almitrine in ARDS. Current animal data and proposed mechanics which may foster future pharmacologic therapies are also examined.

Aerosolized surfactant improves pulmonary function in endotoxin-induced lung injury

Surfactant dysfunction is a primary pathophysiologic component in patients with adult respiratory distress syndrome (ARDS). In this study we tested the efficacy of aerosolized surfactant (Sf ) replacement in a severe lung injury model of endotoxin-induced ARDS. Twenty-one certified healthy pigs were anesthetized, surgically prepared for measurement of hemodynamic and lung function, then randomized into one of four groups: (1) control (n = 5), surgical instrumentation only; (2) lipopolysaccharide (LPS) (n = 6), infused with Escherichia coli LPS (100 microgram/kg) without positive end- expiratory pressure (PEEP) and ventilated with a nonhumidified gas mixture of 50% N2O and 50% O2; (3) LPS + PEEP (n = 4), infused with LPS, placed on PEEP (7.5 cm H2O), and ventilated with a humidified gas mixture; and (4) LPS + PEEP + Sf (n = 6), infused with LPS, placed on PEEP, and ventilated with aerosolized Sf (Infasurf, ONY, Inc.). All animals were studied for 6 h. Arterial PO2 significantly decreased in both the LPS and LPS + PEEP groups (LPS + PEEP = 74 +/- 19 mm Hg; LPS = 74 +/- 19 mm Hg, p < 0.05) while venous admixture (Q S/Q T) increased in these groups (LPS + PEEP = 43.3 +/- 3.9%; LPS = 47.7 +/- 11%, p < 0.05) as compared with the control group. PEEP + Sf reduced the fall in PO2 (142 +/- 20 mm Hg) and rise in Q S/Q T (15.1 +/- 3.6%) caused by LPS. Delayed induction of PEEP (2 h following LPS) did not significantly improve any parameter over the LPS group without PEEP in this ARDS model. LPS without PEEP (3.4 +/- 0.2 cells/6,400 micrometer2) caused a marked increase in the total number of sequestered leukocytes in the pulmonary parenchyma as compared with the control group (1.3 +/- 0.1 cells/6,400 micrometer2). LPS + PEEP + Sf (2.3 +/- 0.2 cells/6,400 micrometer2) significantly decreased while LPS + PEEP significantly increased (4.0 +/- 0.2 cells/6,400 micrometer2) the total number of sequestered leukocytes as compared with the LPS without PEEP group. In summary, aerosolized surfactant replacement decreased leukocyte sequestration and improved oxygenation in our porcine model of endotoxin-induced lung injury.

A risk-benefit assessment of natural and synthetic exogenous surfactants in the management of neonatal respiratory distress syndrome

Alveolar surfactant is central to pulmonary physiology. Quantitative and qualitative surfactant abnormalities appear to be the primary aetiological factors in neonatal respiratory distress syndrome (RDS) and exogenous replacement of surfactant is a rational treatment. Available exogenous surfactants have a natural (mammal-derived lung surfactants) or synthetic origin. Pharmacodynamic and clinical studies have demonstrated that exogenous surfactants immediately improve pulmonary distensibility and gas exchange; however, this is achieved more slowly and with more failures with synthetic surfactants. The ensuing advantageous haemodynamic effects are not so striking and they include an inconvenient increased left to right ductal shunt. Two strategies of administration have been used: prophylactic or rescue therapy to treat declared RDS. All methods of instillation require intubation. In addition to the early benefits (improved gas exchange and reduced ventilatory support) the incidence of classical complications of RDS, especially air leak events, is decreased except for the uncommon problem of pulmonary haemorrhage. The incidence of bronchopulmonary dysplasia is neither uniformly nor significantly reduced although the severity appears to be lessened. The overall incidence of peri-intraventricular haemorrhages is not diminished although separate trials have shown a decreased rate. The most striking beneficial effect of exogenous surfactants is the increased survival (of about 40%) of treated very low birthweight neonates. A small number of adverse effects has been described. The long term outcome of survivor neonates with RDS treated with surfactants versus control neonates with RDS not treated with surfactants is similar in terms of physical growth, at least as good in terms of respiratory status, with a similar or slightly better neurodevelopmental outcome. There is not clear benefit of exogenous surfactant therapy in extremely premature infants (< 26 weeks gestational age, birthweight < 750 g). The potential risks of contamination, inflammatory and immunogenic reaction and the inhalation of platelet activating factor remain a theoretical concern of surfactant therapy which has not been confirmed in clinical practice. The optimal timing of treatment favours prophylaxis over rescue treatment and early rescue treatment rather than delayed therapy. Meta-analyses suggest the clinical superiority of natural surfactant extracts over a synthetic one (colfosceril palmitate). The economic impact of surfactant therapy is favourable and the costs per quality-adjusted life year (QALY) for surviving surfactant treated infants are low. In conclusion, the mid and long term benefit/risk ratio clearly favours the use of exogenous surfactants to prevent or to treat RDS in neonates who have a gestational age of > 26 weeks or a birthweight of > 750 g, especially with the prophylactic strategy using natural surfactant extracts.

Lung disease in premature neonates: impact of new treatments and technologies

Advances in perinatal medicine and neonatology have dramatically changed clinical outcomes for premature neonates and have ushered in a new era of radiological complexity. "Portable" chest radiographs continue to be the mainstay in diagnostic imaging of fragile newborns, but radiologists may be confronted with new and unexpected radiological expressions of once-familiar disease processes. Familiarity with the radiological impact of emerging treatments in premature neonates is essential for accurate film interpretation.

Repeated doses of the perfluorocarbon FC-100 improve lung function of preterm lambs

Intratracheal administration of a single dose of the perfluorocarbon FC-100 improves lung function in surfactant-deficient animals. In this study we compared the response to repeated doses of FC-100 (3 mL/kg 3% solution, n = 5) with that observed after administration of Exosurf (5 mL/kg, n = 5) to mechanically ventilated preterm lambs of 125 d of gestation. The initial dose of FC-100 rapidly increased arterial PO2, decreased arterial PCO2, and improved arterial pH. Also dynamic lung compliance markedly improved with this agent. Administration of an additional dose of FC-100 resulted in relatively similar changes, albeit of lesser magnitude than those observed with the initial dose. In contrast, Exosurf did not improve these variables even after three doses. All lambs treated with FC-100 survived the 6-h study period, whereas one of the five Exosurf-treated lambs survived (p < 0.05). Mean arterial blood pressure and heart rate decreased in those lambs that received FC-100, but not in surviving lambs that received Exosurf. Our data demonstrate that repeated intratracheal administration of the perfluorocarbon FC-100 improves lung function and survival of surfactant-deficient lambs better than the synthetic surfactant Exosurf. We speculate that tensio-active agents with properties different from surfactant, such as FC-100, might improve lung function in preterm neonates with diseases due to surfactant deficiency.