Bronchopulmonary segmental lavage with Surfaxin (KL(4)-surfactant) for acute respiratory distress syndrome

Inhibition of pulmonary surfactant adsorption by serum and the mechanisms of reversal by hydrophilic polymers: theory

A theory based on the Smolukowski analysis of colloid stability shows that the presence of charged, surface-active serum proteins at the alveolar air-liquid interface can severely reduce or eliminate the adsorption of lung surfactant from the subphase to the interface, consistent with the observations reported in the companion article (pages 1769-1779). Adding nonadsorbing, hydrophilic polymers to the subphase provides a depletion attraction between the surfactant aggregates and the interface, which can overcome the steric and electrostatic resistance to adsorption induced by serum. The depletion force increases with polymer concentration as well as with polymer molecular weight. Increasing the surfactant concentration has a much smaller effect than adding polymer, as is observed. Natural hydrophilic polymers, like the SP-A present in native surfactant, or hyaluronan, normally present in the alveolar fluids, can enhance adsorption in the presence of serum to eliminate inactivation.

New Synthetic Surfactants: The Next Generation?

Surfactant preparations have been proven to improve clinical outcome of infants at risk for or having respiratory distress syndrome (RDS). In clinical trials, ani mal-derived surfactant preparations reduce the risk of pneumothorax and mortality when compared to non-protein-containing synthetic surfactant preparations. In part, this is thought to be due to the presence of surfactant proteins in animal-derived surfactant preparations. Four native surfactant proteins have been identified. The hydrophobic surfactant proteins B (SP-B) and C (SP-C) are tightly bound to phospholipids. These proteins have important roles in maintaining the surface tension-lowering properties of pulmonary surfactant. Surfactant protein A (SP-A) and D (SP-D) are extremely hydrophilic and are not retained in the preparation of any commercial animal-derived surfactant products. These proteins are thought to have a role in recycling surfactant and improving host defense. There is concern that animal-derived products may have some batch-to-batch variation regarding the levels of native pulmonary surfactant proteins. In addition, there is concern regarding the hypothetical risk of transmission of viral or unconventional infectious agents from an animal source. New surfactant preparations, composed of synthetic phospholipids and essential hydrophobic surfactant protein analogs, have been developed. These surfactant protein analogs have been produced by peptide synthesis and recombinant technology to provide a new class of synthetic surfactants that may be a suitable alternative to animal-derived surfactants. Preliminary clinical studies have shown that treatment with these novel surfactant preparations can ameliorate RDS and improve clinical outcome. Clinicians will need to further understand any differences in clinical effects between available products.

A multicenter, randomized, controlled trial of lucinactant versus poractant alfa among very premature infants at high risk for respiratory distress syndrome

BACKGROUND

Available therapeutic surfactants are either animal-derived or non-protein-containing synthetic products. Animal-derived surfactants contain variable amounts of surfactant apoproteins, whereas the older-generation synthetic products contain only phospholipids and lack surfactant proteins (SPs). Both decrease morbidity and mortality rates associated with respiratory distress syndrome (RDS) among preterm infants, compared with placebo. However, excess mortality rates have been observed with non-protein-containing synthetic surfactants, compared with the animal-derived products. Evidence suggests that synthetic surfactants consisting solely of phospholipids can be improved with the addition of peptides that are functional analogs of SPs. Lucinactant is a new synthetic peptide-containing surfactant that contains sinapultide, a novel, 21-amino acid peptide (leucine and lysine repeating units, KL4 peptide) designed to mimic human SP-B. It is completely devoid of animal-derived components.

OBJECTIVE

We hypothesized that the outcomes for premature infants treated with lucinactant and poractant alfa would be similar. Therefore, we compared lucinactant (Surfaxin; Discovery Laboratories, Doylestown, PA) with porcine-derived, poractant alfa (Curosurf; Chiesi Farmaceutici, Parma, Italy) in a trial to test for noninferiority.

METHODS

A total of 252 infants born between 24 and 28 weeks of completed gestation, with birth weights between 600 and 1250 g, were assigned randomly in a multicenter, multinational, noninferiority, randomized, controlled study to receive either lucinactant (n = 124) or poractant alfa (n = 128) within 30 minutes of life. The primary outcome was the incidence of being alive without bronchopulmonary dysplasia (BPD) through 28 days of age. Key secondary outcomes included death at day 28 and 36 weeks postmenstrual age (PMA), air leaks, neuroimaging abnormalities, and other complications related to either prematurity or RDS. An independent, international, data and safety monitoring committee monitored the trial.

RESULTS

The treatment difference between lucinactant and poractant alfa for survival without BPD through 28 days was 4.75% (95% confidence interval [CI]: -7.3% to 16.8%) in favor of lucinactant, with the lower boundary of the 95% CI for the difference, ie, -7.3%, being greater than the prespecified noninferiority margin of -14.5%. At 28 days, 45 of 119 infants given lucinactant were alive without BPD (37.8%; 95% CI: 29.1-46.5%), compared with 41 of 124 given poractant alfa (33.1%; 95% CI: 24.8-41.3%); at 36 weeks PMA, the rates were 64.7% and 66.9%, respectively. The corresponding mortality rate through day 28 for the lucinactant group was lower than that for the poractant alfa group (11.8% [95% CI: 6.0-17.6%] vs 16.1% [95% CI: 9.7-22.6%]), as was the rate at 36 weeks PMA (16% and 18.5%, respectively). There were no differences in major dosing complications. In addition, no significant differences were observed in the incidences of common complications of prematurity, including intraventricular hemorrhage (grades 3 and 4) and cystic periventricular leukomalacia (lucinactant: 14.3%; poractant alfa: 16.9%).

CONCLUSIONS

Lucinactant and poractant alfa were similar in terms of efficacy and safety when used for the prevention and treatment of RDS among preterm infants. The ability to enhance the performance of a synthetic surfactant with the addition of a peptide that mimics the action of SP-B, such as sinapultide, brings potential advantages to exogenous surfactant therapy.

Interaction of an artificial surfactant in human pulmonary epithelial cells

Surfaxin (lucinactant), a peptide-based surfactant consisting of dipalmitoylphosphatidylcholine (DPPC) plus KL(4) (sinapultide) (a synthetic peptide modeled after human surfactant protein-B), is effective in treating respiratory distress syndrome in preterm infants. Our goal was to determine the uptake and effects of Surfaxin on human pulmonary type II cells isolated from fetal tissue and other lung cell types. Based on previous published reports, we hypothesized that this exogenous synthetic surfactant would have little effect on type II cell surfactant-related physiological features. Human type II cells and A549 and NCI-H441 adenocarcinoma cells incorporated (3)H-KL(4) and (14)C-DPPC components in Surfaxin, but with different kinetics. Fractionation of NCI-H441 and A549 cellular components indicated that the highest specific activity of (3)H-KL(4) was present in the 18,000g cellular fraction (which contains vesicles and lysosomes). The number of lamellar bodies (LBs) appears to increase in human type II cells incubated in the presence of Surfaxin when visualized by light microscopy, while LB structure (determined by electron microscopy) was not altered. Expression of endogenous surfactant protein (SP-A, SP-B, and SP-C) mRNA levels in human type II cells was not altered by the presence of Surfaxin. We conclude that while human type II cells and other lung cell types can incorporate the components of Surfaxin, the surfactant-related physiological functions of these cells are not altered.

Surfactant Therapy for Meconium Aspiration Syndrome

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

Acute lung injury and acute respiratory distress syndrome in pregnancy

Acute respiratory failure can be the result of a variety of clinical conditions, such as congestive heart failure, pneumonia, pulmonary embolism, exacerbation of obstructive lung diseases, and acute respiratory distress syndrome (ARDS). This article focuses on developments related to acute lung injury and ARDS and reviews epidemiology, pathogenesis and therapeutic advances with an emphasis on the obstetric population. A brief discussion of tocolytic-induced pulmonary edema, preeclampsia, venous air embolism, and aspiration-related ARDS is included. Management of pregnant women with ARDS is outlined.

Surfactant use for neonatal lung injury: beyond respiratory distress syndrome

Surfactant has led to a significant reduction in neonatal mortality for premature infants with lung immaturity and respiratory distress. However, surfactant therapy has been shown to be effective in the treatment of a number of other neonatal respiratory disorders and the evidence for surfactant use in such circumstances is presented. Meconium aspiration is characterised by severe atelectasis, the influx of neutrophils, edema, and hyaline membranes, with decreased levels of SP-A and SP-B and the large aggregate fraction of lung surfactant, and altered surfactant surface morphology. Meconium contains cholesterol, free fatty acids and bilirubin all of which can interfere with surfactant function in a dose-dependent fashion. Providing larger amounts of surfactant can overcome some of this inhibition. Animal models of meconium aspiration treated with surfactant have improved histology, lung mechanics and gas exchange. Studies in human infants with meconium aspiration have found elevated concentrations of total protein, albumin, and membrane-derived phospholipid in lung lavage fluid, and haemorrhagic pulmonary edema. Clinical studies in such neonates have reported improved gas exchange and clinical outcomes following surfactant treatment. More recently surfactant lavage has been shown to be a potentially efficacious therapy for such infants. The inflammatory exudate containing plasma proteins and cytokines which accompanies neonatal pneumonia may inactivate surfactant. Surfactant treatment given to animals following the tracheal instillation of group B Streptococcal resulted in significantly less bacterial growth and improved lung function. Small clinical experiences have demonstrated the benefit of surfactant to infants with pneumonia/sepsis. Pulmonary haemorrhage, which some consider a complication of surfactant therapy, has also been effectively managed using surfactant instillation. The hemoglobin and red blood cell lipids may act to inhibit natural surfactant and treatment with surfactant has been shown to improve outcome for infants with pulmonary haemorrhage. Animal models of congenital diaphragmatic hernia (CDH) have hypoplastic lungs with evidence of decreased lamellar bodies in their type II pneumocytes and resultant surfactant deficiency, and respond to surfactant replacement with improved gas exchange and lung mechanics. The lungs of human infants with CDH contain less phospholipids and phosphatidylcholine per milligram of DNA than control infants. Case reports have reported a benefit of surfactant for infants with CDH. In the near-term infants with severe respiratory distress, surfactant is one of the therapies along with inhaled nitric oxide and high frequency ventilations, that have resulted in improved outcomes. Surfactant treatment may be of significant benefit in newborn infants with respiratory compromise secondary to a number of insults, and further prospective evidence of its efficacy in such disorders is needed.

Surfactant therapy for acute lung injury/acute respiratory distress syndrome

PURPOSE OF REVIEW

Currently, three phase III surfactant replacement trials for acute lung injury (ALI)/acute respiratory distress syndromes (ARDS) patients are underway. Although the efficacy of surfactant replacement therapy will first have to be proved in these phase III trials, recent reports indicate some enticing possibilities for the future of surfactant therapy.

RECENT FINDINGS

Patients requiring mechanical ventilation show alterations in their endogenous surfactant composition. Depending on the type of lung injury or the elapsed time, modifications to surfactant preparations could enhance the efficacy of these preparations. Surfactants that closely resemble natural surfactant, especially those containing surfactant proteins (SP-B/C) and nonphospholipids (cholesterol), are able to restore normal surfactant physiology. Furthermore, lipids that are able to withstand degradation by lipases could further enhance surfactant therapy.

SUMMARY

If surfactant therapy fulfills the promises expected from the ongoing phase III trials, future surfactant preparations may even enhance therapy efficacy and restore the altered endogenous surfactant pool as soon as possible.

A synthetic surfactant based on a poly-Leu SP-C analog and phospholipids: effects on tidal volumes and lung gas volumes in ventilated immature newborn rabbits

Available surfactants for treatment of respiratory distress syndrome in newborn infants are derived from animal lungs, which limits supply and poses a danger of propagating infectious material. Poly-Val-->poly-Leu analogs of surfactant protein (SP)-C can be synthesized in large quantities and exhibit surface activity similar to SP-C. Here, activity of synthetic surfactants containing a poly-Leu SP-C analog (SP-C33) was evaluated in ventilated premature newborn rabbits. Treatment with 2.5 ml/kg body wt of 2% (wt/wt) SP-C33 in 1,2-dipalmitoyl-sn-3-glycero phosphoryl choline (DPPC)-1-palmitoyl-2-oleoyl-sn-3-glycero phosphoryl choline (POPC)-1-palmitoyl-2-oleoyl-sn-3-glycero phosphoryl glycerol (POPG), 68:0:31, 68:11:20, or 68:16:15 (wt/wt/wt) suspended at 80 mg/ml gave tidal volumes (Vt) of 20-25 ml/kg body wt, with an insufflation pressure of 25 cmH2O and no positive end-expiratory pressure (PEEP), comparable to the Vt for animals treated with the porcine surfactant Curosurf. Nontreated littermates had a Vt of approximately 2 ml/kg body wt. The Vt for SP-C33 in DPPC-egg phosphatidylglycerol-palmitic acid [68:22:9 (wt/wt/wt)], DPPC-POPG-palmitic acid [68:22:9 (wt/wt/wt)], and DPPC-POPC-POPG [6:2:2 (wt/wt/wt)] was 15-20 ml/kg body wt. Histological examination of lungs from animals treated with SP-C33-based surfactants showed incomplete, usually patchy air expansion of alveolar spaces associated with only mild airway epithelial damage. Lung gas volume after 30 min of mechanical ventilation were more than threefold larger in animals treated with Curosurf than in those receiving SP-C33 in DPPC-POPC-POPG, 68:11:20. This difference could be largely counterbalanced by ventilation with PEEP (3-4 cmH2O). An artificial surfactant based on SP-C33 improves Vt in immature newborn animals ventilated with standardized peak pressure but requires PEEP to build up adequate lung gas volumes.

Acute respiratory distress syndrome in the septic surgical patient

The acute respiratory distress syndrome (ARDS) is a process of acute inflammatory lung injury that affects a diverse array of surgical and medical patients. The syndrome is mediated by a complex and interacting system of chemical mediators produced by several types of pulmonary cells. Regardless of the predisposing causes, activation of the nuclear factor kappa B seems to be, at the molecular level, a signature event of ARDS, leading to the rapid activation of intracellular signaling pathways, which coordinate the induction of multiple genes encoding inflammatory mediators. There are at least two compelling reasons for promoting an understanding of these interactions and their molecular mediators and second messengers: new therapies intended to modulate these factors continue to be developed, and the levels of some of these molecules, most notably cytokines, may serve as early indicators of the onset of ARDS.

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.

Pulmonary surfactant for neonatal respiratory disorders

Surfactant therapy has revolutionized neonatal care and is used routinely for preterm infants with respiratory distress syndrome. Recent investigation has further elucidated the function of surfactant-associated proteins and their contribution toward surfactant and lung immune defense functions. As the field of neonatology moves away from intubation and mechanical ventilation of preterm infants at birth toward more aggressive use of nasal continuous positive airway pressure, the optimal timing of exogenous surfactant therapy remains unclear. Evidence suggests that preterm neonates with bronchopulmonary dysplasia and prolonged mechanical ventilation also experience surfactant dysfunction; however, exogenous surfactant therapy beyond the first week of life has not been well studied. Surfactant replacement therapy has been studied for use in other respiratory disorders, including meconium aspiration syndrome and pneumonia. Commercial surfactant preparations currently available are not optimal, given the variability of surfactant protein content and their susceptibility to inhibition. Further progress in the treatment of neonatal respiratory disorders may include the development of "designer" surfactant preparations.

Surfactant strengthens the inhibitory effect of C-reactive protein on human lung macrophage cytokine release

In this study we investigated the effect of acute-phase levels of C-reactive protein (CRP) on cytokine production by pulmonary macrophages in the presence or absence of pulmonary surfactant. Both human alveolar and interstitial macrophages as well as human surfactant were obtained from multiple organ donor lungs. Precultured macrophages were stimulated with LPS alone or together with IFN-gamma in the presence or absence of CRP, surfactant, and combinations. Releases of TNF-alpha and of IL-1beta to the medium were determined. We found that CRP could modulate lung inflammation in humans by decreasing the production of proinflammatory cytokines by both alveolar and interstitial macrophages stimulated with LPS alone or together with IFN-gamma. The potential interaction between CRP and surfactant phospholipids did not overcome the effect of either CRP or surfactant on TNF-alpha and IL-1beta release by lung macrophages. On the contrary, CRP and pulmonary surfactant together had a greater inhibitory effect than either alone on the release of proinflammatory cytokines by lung macrophages.

Innovative practices of ventilatory support with pediatric patients

OBJECTIVES

The recognition that alveolar overdistension rather than peak inspiratory airway pressure is the primary determinant of lung injury has shifted our understanding of the pathogenesis of ventilator-induced side effects. In this review, contemporary ventilatory methods, supportive treatments, and future developments relevant to pediatric critical care are reviewed.

DATA SYNTHESIS

A strategy combining recruitment maneuvers, low-tidal volume, and higher positive end-expiratory pressure (PEEP) decreases barotrauma and volutrauma. Given that appropriate tidal volumes are critical in determining adequate alveolar ventilation and avoiding lung injury, volume-control ventilation with high PEEP levels has been proposed as the preferable protective ventilatory mode. Pressure-related volume control ventilation and high-frequency oscillatory ventilation (HFOV) have taken on an important role as protective lung strategies. Further data are required in the treatment of children, confirming the preliminary results in specific lung pathologies. Spontaneous breathing supported artificially during inspiration (pressure support ventilation) is widely used to maintain or reactivate spontaneous breathing and to avoid hemodynamic variation. Volume support ventilation reduces the need for manual adaptation to maintain stable tidal and minute volume and can be useful in weaning. Prone positioning and permissive hypercapnia have taken on an important role in the treatment of patients undergoing artificial ventilation. Surfactant and nitric oxide have been proposed in specific lung pathologies to facilitate ventilation and gas exchange and to reduce inspired oxygen concentration. Investigation of lung ventilation using a liquid instead of gas has opened new vistas on several lung pathologies with high mortality rates.

RESULTS

The conviction emerges that the best ventilatory treatment may be obtained by applying a combination of types of ventilation and supportive treatments as outlined above. Early treatment is important for the overall positive final result. Lung recruitment maneuvers followed by maintaining an open lung favor rapid resolution of pathology and reduce side effects.

CONCLUSIONS

The methods proposed require confirmation through large controlled clinical trials that can assess the efficacy reported in pilot studies and case reports and define the optimal method(s) to treat individual pathologies in the various pediatric age groups.

Inflammation and surfactant

An intact and well-functioning pulmonary surfactant system is critical for normal respiration and protection from lung infection. Surfactant is comprised of phospholipids that reduce surface tension and greatly reduce the work of breathing. The other major component consists of surfactant-associated proteins, which optimise the biophysical function of phospholipids and/or play an important role in host defence by acting as collectins. Alteration of surfactant composition and function occurs with various inflammatory disorders that affect the airways or the lung parenchyma including asthma, infant respiratory distress syndrome/bronchopulmonary dysplasia, cystic fibrosis, acute respiratory distress syndrome and interstitial lung disease. Although surfactant replacement therapy is indicated for infant respiratory distress syndrome, there is no well-proven role for exogenous surfactant in the treatment of inflammatory lung disorders at the present time.

Vascular pharmacology of acute lung injury and acute respiratory distress syndrome

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) following sepsis, major trauma and surgery are leading causes of respiratory insufficiency, warranting artificial ventilation in the intensive care unit. It is caused by an inflammatory reaction in the lung upon exogenous or endogenous etiologies eliciting proinflammatory factors, and results in increased alveolocapillary permeability and protein-rich alveolar edema. The interstitial and alveolar inflammation and edema alter ventilation perfusion matching, gas exchange and mechanical properties of the lung. The current therapy of the condition is supportive, paying careful attention to fluid balance, relieving the increased work of breathing and improving gas exchange by mechanical ventilation, but in vitro, animal and some clinical research is done to evaluate the value of anti-inflammatory therapies on morbidity and outcome, including inflammatory cell-stabilizing corticosteroids, xanthine derivates, prostanoids and inhibitors, O(2) radical scavenging factors such as N-acetylcysteine, surfactant replacement, vasodilators including inhaled nitric oxide, vasoconstrictors such as almitrine, and others. None of these compounds has been proven to benefit survival in patients, however, even though carrying a physiologic benefit, except perhaps for steroids that may improve outcome in the later stage of ARDS. This partly relates to the difficulty to assess the lung injury at the bedside, to the multifactorial pathogenesis and the severity of comorbidity, adversely affecting survival.

The pulmonary physician in critical care - part 9: non-ventilatory strategies in ARDS

Pharmacological approaches to the treatment of ARDS are reviewed. Future treatments should be targeted at elements of the pathological process that produce specific clinical problems.

Pharmacology of acute lung injury

The acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a clinical syndrome that affects both medical and surgical patients. To date, despite improved understanding of the pathogenesis of ALI/ARDS, pharmacological modalities have been unsuccessful in decreasing mortality. However, several pharmacological agents for ARDS are in development and have shown great promise. In addition to the anti-inflammatory category including late corticosteroids, inhaled nitric oxide, alveolar surfactant, and vasodilators are being evaluated. Replacements of anticoagulation mediators have also suggested beneficial effects on the patient outcome. This article provides an overview of pharmacological treatments of ALI/ARDS.

A multicenter, randomized, controlled trial comparing Surfaxin (Lucinactant) lavage with standard care for treatment of meconium aspiration syndrome

OBJECTIVE

Infants with meconium aspiration syndrome (MAS) have marked surfactant dysfunction. Airways and alveoli of affected neonates contain meconium, inflammatory cells, inflammatory mediators, edema fluid, protein, and other debris. The objective of this study was to compare treatment with bronchoalveolar lavage using dilute Surfaxin with standard therapy in a population of newborn infants with MAS.

METHODS

Inclusion criteria were 1) gestational age > or =35 weeks, 2) enrollment within 72 hours of birth, 3) diagnosis of MAS, 4) need for mechanical ventilation, and 5) an oxygenation index > or =8 and < or =25. Subjects were randomized to either lavage with Surfaxin or standard care (2:1 proportion). In lavaged infants, a volume of 8 mL/kg dilute Surfaxin (2.5 mg/mL) was instilled into each lung over approximately 20 seconds followed by suctioning after 5 ventilator breaths. The procedure was repeated twice. The third and final lavage was with a more concentrated solution (10 mg/mL) of Surfaxin.

RESULTS

Twenty-two infants were enrolled (15 Surfaxin and 7 control). Demographic characteristics were similar. There were trends (not significant) for Surfaxin-lavaged infants to be weaned from mechanical ventilation earlier (mean of 6.3 vs 9.9 days, respectively), as well as to have a more rapid decline in their oxygenation indexes compared with control infants, the latter difference persisting for the 96-hour-long study period. The therapy was safe and generally well tolerated by the infants.

CONCLUSIONS

Dilute Surfaxin lavage seems to be a safe and potentially effective therapy in the treatment of MAS. Data from this investigation support future prospective, controlled clinical trials of bronchoalveolar lavage with Surfaxin in neonates with MAS.

Acute respiratory distress syndrome: pharmacological treatment options in development

The acute respiratory distress syndrome (ARDS) is a clinical syndrome with primarily supportive management options. Despite extensive basic and clinical investigations, multiple pharmacological and nonpharmacological modalities have been unsuccessful in decreasing mortality. Nonetheless, these efforts have substantially heightened our understanding of ARDS pathophysiology. Investigators continue to create new and more complex therapeutic strategies that may have significant clinical impact. Several pharmacological agents for ARDS are in development and have shown either great promise or are at most, under phase II evaluation. The order in which therapeutic options are presented in this review highlights therapeutic options other than the anti-inflammatory approach. In addition to the anti-inflammatory category, vasodilators, surfactant therapy, immunonutrition and partial liquid ventilation are all being evaluated. Within the anti-inflammatory category. new mechanistic approaches include the 'anti-inflammatory nature' of interleukin-10, the inhibitory aspects of lysophosphatidic acid on endothelial cell permeability, and the use of recombinant human anti-coagulant proteins (activated protein C and tissue factor pathway inhibitor) to reduce the inflammatory cycle that contributes to microvascular thrombi. Previous work with surfactant in ARDS had its limitations, however, these trials were of sufficient success to spawn 2 new synthetic compounds. These new synthetic surfactants incorporate mixtures of phosphatidylcholine and phosphatidylglycerol (the key phospholipids within endogenous surfactant) and either recombinant surfactant protein C or an analogue of surfactant protein B. Recently, the ARDS Network's low tidal volume study has broken the cycle of decades of negative ARDS trials and demonstrated an improvement in mortality. Through better mechanistic approach and study design, investigator compliance with exclusion criteria, and better understanding of the complexities of patient management, the next pharmacological ARDS trials will hopefully be successful and lead to further reductions in patient mortality.

Clinical developments for treating ARDS

Acute respiratory distress syndrome (ARDS), is characterised by capillary permeability and pulmonary oedema formation and may complicate a variety of medical and surgical illnesses. As a self-perpetuating state of inflammatory derangement, acute lung injury (ALI)/ARDS is manifest clinically as rapid development of radiographic infiltrates, severe hypoxaemia and reduced lung compliance. Over the years, researchers have made significant progress in elucidating the pathophysiology of this complex syndrome. Therapies targeting specific pathophysiologic steps in the development or persistence of this syndrome are in various stages of laboratory and clinical testing. Results to date have shown nitric oxide (NO) to improve oxygenation in the majority of patients but fail to improve mortality. Surfactant replacement has had limited success in adults, but new formulations and delivery methods may prove beneficial. Several inflammatory mediator-targeted therapies have progressed successfully through early clinical evaluation. Among these, neutrophil elastase inhibitors have shown the most promise and are currently undergoing Phase III trials. Other mediator-targeted therapies, such as prostaglandin E1, IL-10 and platelet activating factor antagonists, have not been found efficacious in large clinical trials of ARDS. However, these therapies, along with coagulation modulators, may have a favourable impact on ARDS by improving outcomes in sepsis, the greatest risk factor for developing this condition. In the interim, supportive care through improvements in mechanical ventilation are beneficial, while specific fluid balance and nutrition strategies may prove advantageous.

Surfactant alteration and replacement in acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a frequent, life-threatening disease in which a marked increase in alveolar surface tension has been repeatedly observed. It is caused by factors including a lack of surface-active compounds, changes in the phospholipid, fatty acid, neutral lipid, and surfactant apoprotein composition, imbalance of the extracellular surfactant subtype distribution, inhibition of surfactant function by plasma protein leakage, incorporation of surfactant phospholipids and apoproteins into polymerizing fibrin, and damage/inhibition of surfactant compounds by inflammatory mediators. There is now good evidence that these surfactant abnormalities promote alveolar instability and collapse and, consequently, loss of compliance and the profound gas exchange abnormalities seen in ARDS. An acute improvement of gas exchange properties together with a far-reaching restoration of surfactant properties was encountered in recently performed pilot studies. Here we summarize what is known about the kind and severity of surfactant changes occurring in ARDS, the contribution of these changes to lung failure, and the role of surfactant administration for therapy of ARDS.

Expanded uses of surfactant therapy

There are few therapies for which the cumulative evidence of benefit is as much as that for surfactant therapy for RDS in premature infants. Exogenous surfactant therapy does seem to be beneficial for a number of non-RDS disorders. Although there are some trials supporting its use in MAS and ALI-ARDS, there are only a few small prospective, randomized, controlled trials supporting surfactant use in non-RDS disorders. Use of surfactant therapy for any disorder other than RDS must be considered "off the shelf" and experimental. Much work remains to be done to address the role of surfactant therapy in the myriad disorders discussed. Of import for each of the disorders is addressing the optimum type of surfactant to use, and the appropriate dose, method of delivery, and duration of treatment regimens.

Resistance of different surfactant preparations to inactivation by meconium

A disease similar to acute respiratory distress syndrome may occur in neonates after aspiration of meconium. The aim of the study was to compare the inhibitory effects of human meconium on the following surfactant preparations suspended at a concentration of 2.5 mg/mL: Curosurf, Alveofact, Survanta, Exosurf, Pumactant, rabbit natural surfactant from bronchoalveolar lavage, and two synthetic surfactants based on recombinant surfactant protein-C (Venticute) or a leucine/lysine polypeptide. Minimum surface tension, determined with a pulsating bubble surfactometer, was increased >10 mN/m at meconium concentrations >or=0.04 mg/mL for Curosurf, Alveofact, or Survanta, >or=0.32 mg/mL for recombinant surfactant protein-C, >or=1.25 mg/mL for leucine/lysine polypeptide, and >or=20 mg/mL for rabbit natural surfactant. The protein-free synthetic surfactants Exosurf and Pumactant did not reach minimum surface tension <10 mN/m even in the absence of meconium. We conclude that surfactant activity is inhibited by meconium in a dose-dependent manner. Recombinant surfactant protein-C and leucine/lysine polypeptide surfactant were more resistant to inhibition than the modified natural surfactants Curosurf, Alveofact, or Survanta but less resistant than natural lavage surfactant containing surfactant protein-A. We speculate that recombinant hydrophobic surfactant proteins or synthetic analogs of these proteins can be used for the design of new surfactant preparations that are relatively resistant to inactivation and therefore suitable for treatment of acute respiratory distress syndrome.

Management of the septic patient in the operating room

Sepsis, severe sepsis, and septic shock represent the spectrum of physiological response to a variety of infecting pathogens. Multiple-organ dysfunction may result from widespread activation of inflammatory and antiinflammatory mechanisms. Intensive multiorgan support, effective antibiotic therapy, and eradication of the inciting source remain the cornerstones in the care of septic patients. Perioperative planning and management need to ensure the continuation of such care in addition to providing for the requirements of the given surgical procedure.

Surfactant in respiratory distress syndrome and lung injury

A deficiency in alveolar surfactant due to immaturity of alveolar type II epithelial cells causes respiratory distress syndrome (RDS). In contrast to animals, the fetal maturation of surfactant in human lungs takes place before term, exceptionally large quantities of surfactant accumulating in the amniotic fluid. The antenatal development of surfactant secretion is very variable but corresponds closely to the risk of RDS. The variation in SP-A and SP-B genes, race, sex and perinatal complications influence susceptibility to RDS. Surfactant therapy has improved the prognosis of RDS remarkably. Abnormalities in alveolar or airway surfactant characterize many lung and airway diseases. In the acute respiratory distress syndrome, deficiencies in surfactant components (phospholipids, SP-B, SP-A) are evident, and may be caused by pro-inflammatory cytokines (IL-1, TNF) that decrease surfactant components. The resultant atelectasis localizes the disease, possibly allowing healing (regeneration, increase in surfactant). In the immature fetus, cytokines accelerate the differentiation of surfactant, preventing RDS. After birth, however, persistent inflammation is associated with low SP-A and chronic lung disease. A future challenge is to understand how to inhibit or redirect the inflammatory response from tissue destruction and poor growth towards normal lung development and regeneration.

Mechanisms of repair and remodeling following acute lung injury

At present, we largely lack the ability to correlate the clinical course of ARDS patients with potential factors involved in the biochemical and cellular basis of lung repair. This requires very large patient databases with measurement of many biochemical parameters. Important mechanistic determinants during the repair phase can be sought by correlation with late outcomes, but a large-scale cooperative effort among multiple centers with sharing of follow-up data and patient specimens is essential. We also lack detailed human histologic material from many phases of ARDS and, particularly, know little of the long-term morphologic impact of ARDS in survivors. Establishment of a national registry that follows ARDS survivors and that would seek their cooperation in advance in obtaining autopsy specimens when they die of other causes would be very valuable. Correlating the pathology with their pulmonary function during recovery would give important insights into the reasons for the different patterns of abnormal pulmonary functions. The factors that determine the success of repair are of critical importance in testing new ARDS treatment strategies. Would accelerating the resolution of alveolar edema alter the course of subsequent fibrosis and inflammation? Does surfactant replacement therapy--a costly proposition in adults with ARDS--lead to better long-term outcomes in survivors? How much should we worry about the use of high levels of oxygen for support of arterial partial pressure of oxygen? Is it better to accept hyperoxia to avoid pressure or volume trauma induced by mechanical ventilation with higher minute ventilations? These major management issues all may affect the success of the late repair and recovery process. Intervention trials need to examine the long-term physiologic and functional outcomes.