Pulmonary Surfactant: A Mighty Thin Film

Pulmonary surfactant is a critical component of lung function in healthy individuals. It functions in part by lowering surface tension in the alveoli, thereby allowing for breathing with minimal effort. The prevailing thinking is that low surface tension is attained by a compression-driven squeeze-out of unsaturated phospholipids during exhalation, forming a film enriched in saturated phospholipids that achieves surface tensions close to zero. A thorough review of past and recent literature suggests that the compression-driven squeeze-out mechanism may be erroneous. Here, we posit that a surfactant film enriched in saturated lipids is formed shortly after birth by an adsorption-driven sorting process and that its composition does not change during normal breathing. We provide biophysical evidence for the rapid formation of an enriched film at high surfactant concentrations, facilitated by adsorption structures containing hydrophobic surfactant proteins. We examine biophysical evidence for and against the compression-driven squeeze-out mechanism and propose a new model for surfactant function. The proposed model is tested against existing physiological and pathophysiological evidence in neonatal and adult lungs, leading to ideas for biophysical research, that should be addressed to establish the physiological relevance of this new perspective on the function of the mighty thin film that surfactant provides.

Surfactant status assessment and personalized therapy for surfactant deficiency or dysfunction

Surfactant is a pivotal neonatal drug used both for respiratory distress syndrome due to surfactant deficiency and for more complex surfactant dysfunctions (such as in case of neonatal acute respiratory distress syndrome). Despite its importance, indications for surfactant therapy are often based on oversimplified criteria. Lung biology and modern monitoring provide several diagnostic tools to assess the patient surfactant status and they can be used for a personalized surfactant therapy. This is desirable to improve the efficacy of surfactant treatment and reduce associated costs and side effects. In this review we will discuss these diagnostic tools from a pathophysiological and multi-disciplinary perspective, focusing on the quantitative or qualitative surfactant assays, lung mechanics or aeration measurements, and gas exchange metrics. Their biological and technical characteristics are described with practical information for clinicians. Finally, available evidence-based data are reviewed, and the diagnostic accuracy of the different tools is compared. Lung ultrasound seems the most suitable tool for assessing the surfactant status, while some other promising tests require further research and/or development.

Pulmonary Surfactant in Adult ARDS: Current Perspectives and Future Directions

Acute respiratory distress syndrome (ARDS) is a major cause of hypoxemic respiratory failure in adults, leading to the requirement for mechanical ventilation and poorer outcomes. Dysregulated surfactant metabolism and function are characteristic of ARDS. A combination of alveolar epithelial damage leading to altered surfactant synthesis, secretion, and breakdown with increased functional inhibition from overt alveolar inflammation contributes to the clinical features of poor alveolar compliance and alveolar collapse. Quantitative and qualitative alterations in the bronchoalveolar lavage and tracheal aspirate surfactant composition contribute to ARDS pathogenesis. Compared to neonatal respiratory distress syndrome (nRDS), replacement studies of exogenous surfactants in adult ARDS suggest no survival benefit. However, these studies are limited by disease heterogeneity, variations in surfactant preparations, doses, and delivery methods. More importantly, the lack of mechanistic understanding of the exact reasons for dysregulated surfactant remains a significant issue. Moreover, studies suggest an extremely short half-life of replaced surfactant, implying increased catabolism. Refining surfactant preparations and delivery methods with additional co-interventions to counteract surfactant inhibition and degradation has the potential to enhance the biophysical characteristics of surfactant in vivo.

Epidemiology of Neonatal Acute Respiratory Distress Syndrome: Prospective, Multicenter, International Cohort Study

OBJECTIVES

Age-specific definitions for acute respiratory distress syndrome (ARDS) are available, including a specific definition for neonates (the "Montreux definition"). The epidemiology of neonatal ARDS is unknown. The objective of this study was to describe the epidemiology, clinical course, treatment, and outcomes of neonatal ARDS.

DESIGN

Prospective, international, observational, cohort study.

SETTING

Fifteen academic neonatal ICUs.

PATIENTS

Consecutive sample of neonates of any gestational age admitted to participating sites who met the neonatal ARDS Montreux definition criteria.

MEASUREMENTS AND MAIN RESULTS

Neonatal ARDS was classified as direct or indirect, infectious or noninfectious, and perinatal (≤ 72 hr after birth) or late in onset. Primary outcomes were: 1) survival at 30 days from diagnosis, 2) inhospital survival, and 3) extracorporeal membrane oxygenation (ECMO)-free survival at 30 days from diagnosis. Secondary outcomes included respiratory complications and common neonatal extrapulmonary morbidities. A total of 239 neonates met criteria for the diagnosis of neonatal ARDS. The median prevalence was 1.5% of neonatal ICU admissions with male/female ratio of 1.5. Respiratory treatments were similar across gestational ages. Direct neonatal ARDS (51.5% of neonates) was more common in term neonates and the perinatal period. Indirect neonatal ARDS was often triggered by an infection and was more common in preterm neonates. Thirty-day, inhospital, and 30-day ECMO-free survival were 83.3%, 76.2%, and 79.5%, respectively. Direct neonatal ARDS was associated with better survival outcomes than indirect neonatal ARDS. Direct and noninfectious neonatal ARDS were associated with the poorest respiratory outcomes at 36 and 40 weeks' postmenstrual age. Gestational age was not associated with any primary outcome on multivariate analyses.

CONCLUSIONS

Prevalence and survival of neonatal ARDS are similar to those of pediatric ARDS. The neonatal ARDS subtypes used in the current definition may be associated with distinct clinical outcomes and a different distribution for term and preterm neonates.

Mechanistic Understanding of Lung Inflammation: Recent Advances and Emerging Techniques

Acute respiratory distress syndrome (ARDS) is a life-threatening lung injury characterized by an acute inflammatory response in the lung parenchyma. Hence, it is considered as the most appropriate clinical syndrome to study pathogenic mechanisms of lung inflammation. ARDS is associated with increased morbidity and mortality in the intensive care unit (ICU), while no effective pharmacological treatment exists. It is very important therefore to fully characterize the underlying pathobiology and the related mechanisms, in order to develop novel therapeutic approaches. In vivo and in vitro models are important pre-clinical tools in biological and medical research in the mechanistic and pathological understanding of the majority of diseases. In this review, we will present data from selected experimental models of lung injury/acute lung inflammation, which have been based on clinical disorders that can lead to the development of ARDS and related inflammatory lung processes in humans, including ventilation-induced lung injury (VILI), sepsis, ischemia/reperfusion, smoke, acid aspiration, radiation, transfusion-related acute lung injury (TRALI), influenza, Streptococcus (S.) pneumoniae and coronaviruses infection. Data from the corresponding clinical conditions will also be presented. The mechanisms related to lung inflammation that will be covered are oxidative stress, neutrophil extracellular traps, mitogen-activated protein kinase (MAPK) pathways, surfactant, and water and ion channels. Finally, we will present a brief overview of emerging techniques in the field of omics research that have been applied to ARDS research, encompassing genomics, transcriptomics, proteomics, and metabolomics, which may recognize factors to help stratify ICU patients at risk, predict their prognosis, and possibly, serve as more specific therapeutic targets.

Bile acids-induced lung injury: update of reverse translational biology

The presence of bile acids in lung tissue is associated with some clinical features observed in various medical specialties, but it took time to understand that these are due to a "bile acid-induced lung injury" since specific translational studies and cross-disciplinary awareness were lacking. We used a reverse translational approach to update and summarize the current knowledge about the mechanisms of bile acid-induced lung injury. This has been done in a cross-disciplinary fashion since these conditions may occur in patients of various age and in different medical fields. We here define these clinical conditions, then we review the physiopathology of these conditions and the animal models used to mimic them and, finally, their pathobiology. Mechanisms of bile acid-induced lung injury have been partially clarified overtime and are represented by: 1) the interaction with secretory phospholipase A2 pathway, 2) the effect on surfactant function and structure, 3) the biological effects on inflammation and local immunity, 4) the direct cellular toxicity. These mechanisms are schematically illustrated and histological comparisons between ARDS induced by bile acids and other triggers are also provided. Based on these mechanisms we propose possible direct therapeutic applications and, finally, we discuss further research steps to improve the understanding of processes that generate pathological clinical conditions.

Reduced levels of pulmonary surfactant in COVID-19 ARDS

To provide novel data on surfactant levels in adult COVID-19 patients, we collected bronchoalveolar lavage fluid less than 72 h after intubation and used Fourier Transform Infrared Spectroscopy to measure levels of dipalmitoylphosphatidylcholine (DPPC). A total of eleven COVID-19 patients with moderate-to-severe ARDS (CARDS) and 15 healthy controls were included. CARDS patients had lower DPPC levels than healthy controls. Moreover, a principal component analysis was able to separate patient groups into distinguishable subgroups. Our findings indicate markedly impaired pulmonary surfactant levels in COVID-19 patients, justifying further studies and clinical trials of exogenous surfactant.

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

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

Bovine surfactant in the treatment of pneumonia-induced-neonatal acute respiratory distress syndrome (NARDS) in neonates beyond 34 weeks of gestation: a multicentre, randomized, assessor-blinded, placebo-controlled trial

Neonatal acute respiratory distress syndrome (NARDS) reflects pulmonary surfactant dysfunction, and the usage of bovine surfactant (Calsurf) supplement may therefore be beneficial. To determine whether bovine surfactant given in NARDS can improve oxygenation and survival rate, we conducted a multicenter, randomized trial between January 2018 and June 2019, and we compared Calsurf treatment to controls in neonates with pneumonia accompanied by NARDS. Neonates who met the Montreux criteria definition of NARDS were included, and those with congenital heart and lung malformations were excluded. Primary outcomes were oxygenation index (OI) after Calsurf administration, and secondary outcomes were mortality, and duration of ventilator and oxygen between the two groups, and also other morbidities. Cumulatively, 328 neonates were recruited and analyzed, 162 in the control group, and 166 in the Calsurf group. The results shows that OI in the Calsurf group were significantly lower than that in the control group at 4 h (7.2 ± 2.7 and 11.4 ± 9.1, P = 0.001); similarly, OI in the Calsurf group were significantly lower than in the control group at 12 h ( 7.5 ± 3.1 and 11.2 ± 9.2, P = 0.001). Mortality and duration of ventilator support or oxygen use between the two groups were not significantly different.Conclusion: Calsurf acutely improved OI immediately after administration in pneumonia-induced NARDS; although, we observed no significant decrease in mortality, duration of ventilator or oxygen, or major morbidity. What is known: • The definition proposed as the Monteux criteria for neonatal acute respiratory distress syndrome (NARDS). • Surfactant acutely improved oxygenation and significantly decreased mortality in children and adolescents with acute lung injury. What is new: • This is the first large randomized controlled trail to study on surfactant treatment of neonates with acute respiratory distress syndromes. • Surfactant acutely improved oxygenation immediately after administration in pneumonia-induced NARDS at a gestational age beyond 34 weeks.

The COVID-19 pandemic: a target for surfactant therapy?

INTRODUCTION

The dramatic impact of COVID-19 on humans worldwide has initiated an extraordinary search for effective treatment approaches. One of these is the administration of exogenous surfactant, which is being tested in ongoing clinical trials.

AREAS COVERED

Exogenous surfactant is a life-saving treatment for premature infants with neonatal respiratory distress syndrome. This treatment has also been tested for acute respiratory distress syndrome (ARDS) with limited success possibly due to the complexity of that syndrome. The 60-year history of successes and failures associated with surfactant therapy distinguishes it from many other treatments currently being tested for COVID-19 and provides the opportunity to discuss the factors that may influence the success of this therapy.

EXPERT OPINION

Clinical data provide a strong rationale for using exogenous surfactant in COVID-19 patients. Success of this therapy may be influenced by the mechanical ventilation strategy, the timing of treatment, the doses delivered, the method of delivery and the preparations utilized. In addition, future development of enhanced preparations may improve this treatment approach. Overall, results from ongoing trials may not only provide data to indicate if this therapy is effective for COVID-19 patients, but also lead to further scientific understanding and improved treatment strategies.

[A single-center retrospective study of neonatal acute respiratory distress syndrome based on the Montreux definition]

OBJECTIVE

To investigate the epidemiology, clinical features, treatment, and prognostic factors of neonatal acute respiratory distress syndrome (NARDS) through a retrospective study of NARDS based on the Montreux definition.

METHODS

A retrospective analysis was performed on the medical records of neonates who were hospitalized from January 2017 and July 2018, among whom 314 neonates who met the Montreux definition were enrolled as subjects. According to oxygen index, they were divided into a mild NARDS group with 130 neonates, a moderate NARDS group with 117 neonates, and a severe NARDS group with 67 neonates. The clinical features were compared among the three groups to investigate the influencing factors for the severities of NARDS and the length of hospital stay.

RESULTS

The neonates with NARDS accounted for 2.46% (314/12 789) of the neonates admitted to the neonatal ward during the same period of time and had a mortality rate of 9.6% (30/314). The multivariate ordinal logistic regression analysis showed that the neonates who used pulmonary surfactant (PS) or had a long duration of assisted ventilation tended to have a higher risk of severe NARDS (P < 0.05). The Cox regression analysis showed that the neonates with low birth weight/macrosomia, preterm birth, invasive ventilation, PS therapy, or positive pathogenic detection had a higher risk of prolonged hospital stay (P < 0.05).

CONCLUSIONS

Preterm birth, low birth weight/macrosomia, and perinatal infection may be associated with an increased risk of severe NARDS. The neonates requiring invasive ventilation, prolonged assisted ventilation, or PS therapy tend to have a poor prognosis.

Phosphatidylglycerol and surfactant: A potential treatment for COVID-19?

A hypothesis concerning the potential utility of surfactant supplementation for the treatment of critically ill patients with COVID-19 is proposed, along with a brief summary of the data in the literature supporting this idea. It is thought that surfactant, which is already approved by the Food and Drug Administration for intratracheal administration to treat neonatal respiratory distress syndrome in pre-term infants, could benefit COVID-19-infected individuals by: (1) restoring surfactant damaged by lung infection and/or decreased due to the virus-induced death of the type II pneumocytes that produce it and (2) reducing surface tension to decrease the work of breathing and limit pulmonary edema. In addition, a constituent of surfactant, phosphatidylglycerol, could mitigate COVID-19-induced lung pathology by: (3) decreasing excessive innate immune system stimulation via its inhibition of toll-like receptor-2 and -4 activation by microbial components and cellular proteins released by damaged cells, thereby limiting inflammation and the resultant pulmonary edema, and (4) possibly blocking spread of the viral infection to non-infected cells in the lung. Therefore, it is suggested that surfactant preparations containing phosphatidylglycerol be tested for their ability to improve lung function in critically ill patients with COVID-19.

Stem cell derived exosomes-based therapy for acute lung injury and acute respiratory distress syndrome: A novel therapeutic strategy

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a common critical disease which can be caused by multiple pathological factors in clinic. However, feasible and effective treatment strategies of ALI/ARDS are limited. At present, the beneficial effect of stem cells (SCs)-based therapeutic strategies for ALI/ARDS can be attributed to paracrine. Exosomes, as a paracrine product, are regarded as a critical regulatory mediator. Furthermore, substantial evidence has indicated that exosomes from SCs can transmit bioactive components including genetic material and protein to the recipient cells and provide a protective effect. The protective role is played through a series of process including inflammation modulation, the reconstruction of alveolar epithelium and endothelium, and pulmonary fibrosis prevention. Therefore, SCs derived exosomes have the potential to be used for therapeutic strategies for ALI/ARDS. In this review, we discuss the present understanding of SCs derived exosomes related to ALI/ARDS and provide insights for developing a cell-free strategy for treating ALI/ARDS.

Synthetic surfactant with a recombinant surfactant protein C analogue improves lung function and attenuates inflammation in a model of acute respiratory distress syndrome in adult rabbits

AIM

In acute respiratory distress syndrome (ARDS) damaged alveolar epithelium, leakage of plasma proteins into the alveolar space and inactivation of pulmonary surfactant lead to respiratory dysfunction. Lung function could potentially be restored with exogenous surfactant therapy, but clinical trials have so far been disappointing. These negative results may be explained by inactivation and/or too low doses of the administered surfactant. Surfactant based on a recombinant surfactant protein C analogue (rSP-C33Leu) is easy to produce and in this study we compared its effects on lung function and inflammation with a commercial surfactant preparation in an adult rabbit model of ARDS.

METHODS

ARDS was induced in adult New Zealand rabbits by mild lung-lavages followed by injurious ventilation (V_T 20 m/kg body weight) until P/F ratio < 26.7 kPa. The animals were treated with two intratracheal boluses of 2.5 mL/kg of 2% rSP-C33Leu in DPPC/egg PC/POPG, 50:40:10 or poractant alfa (Curosurf®), both surfactants containing 80 mg phospholipids/mL, or air as control. The animals were subsequently ventilated (V_T 8-9 m/kg body weight) for an additional 3 h and lung function parameters were recorded. Histological appearance of the lungs, degree of lung oedema and levels of the cytokines TNFα IL-6 and IL-8 in lung homogenates were evaluated.

RESULTS

Both surfactant preparations improved lung function vs. the control group and also reduced inflammation scores, production of pro-inflammatory cytokines, and formation of lung oedema to similar degrees. Poractant alfa improved compliance at 1 h, P/F ratio and PaO₂ at 1.5 h compared to rSP-C33Leu surfactant.

CONCLUSION

This study indicates that treatment of experimental ARDS with synthetic lung surfactant based on rSP-C33Leu improves lung function and attenuates inflammation.

An Unsettled Promise: The Newborn Piglet Model of Neonatal Acute Respiratory Distress Syndrome (NARDS). Physiologic Data and Systematic Review

Despite great advances in mechanical ventilation and surfactant administration for the newborn infant with life-threatening respiratory failure no specific therapies are currently established to tackle major pro-inflammatory pathways. The susceptibility of the newborn infant with neonatal acute respiratory distress syndrome (NARDS) to exogenous surfactant is linked with a suppression of most of the immunologic responses by the innate immune system, however, additional corticosteroids applied in any severe pediatric lung disease with inflammatory background do not reduce morbidity or mortality and may even cause harm. Thus, the neonatal piglet model of acute lung injury serves as an excellent model to study respiratory failure and is the preferred animal model for reasons of availability, body size, similarities of porcine and human lung, robustness, and costs. In addition, similarities to the human toll-like receptor 4, the existence of intraalveolar macrophages, the sensitivity to lipopolysaccharide, and the production of nitric oxide make the piglet indispensable in anti-inflammatory research. Here we present the physiologic and immunologic data of newborn piglets from three trials involving acute lung injury secondary to repeated airway lavage (and others), mechanical ventilation, and a specific anti-inflammatory intervention via the intratracheal route using surfactant as a carrier substance. The physiologic data from many organ systems of the newborn piglet—but with preference on the lung—are presented here differentiating between baseline data from the uninjured piglet, the impact of acute lung injury on various parameters (24 h), and the follow up data after 72 h of mechanical ventilation. Data from the control group and the intervention groups are listed separately or combined. A systematic review of the newborn piglet meconium aspiration model and the repeated airway lavage model is finally presented. While many studies assessed lung injury scores, leukocyte infiltration, and protein/cytokine concentrations in bronchoalveolar fluid, a systematic approach to tackle major upstream pro-inflammatory pathways of the innate immune system is still in the fledgling stages. For the sake of newborn infants with life-threatening NARDS the newborn piglet model still is an unsettled promise offering many options to conquer neonatal physiology/immunology and to establish potent treatment modalities.

Acute Respiratory Distress Syndrome: Etiology, Pathogenesis, and Summary on Management

The acute respiratory distress syndrome (ARDS) has multiple causes and is characterized by acute lung inflammation and increased pulmonary vascular permeability, leading to hypoxemic respiratory failure and bilateral pulmonary radiographic opacities. The acute respiratory distress syndrome is associated with substantial morbidity and mortality, and effective treatment strategies are limited. This review presents the current state of the literature regarding the etiology, pathogenesis, and management strategies for ARDS.

Alveolar type 2 progenitor cells for lung injury repair

Alveolar type 2 progenitor cells (AT2) seem closest to clinical translation, specifying the evidence that AT2 may satisfactorily control the immune response to decrease lung injury by stabilizing host immune-competence and a classic and crucial resource for lung regeneration and repair. AT2 establish potential in benefiting injured lungs. However, significant discrepancies linger in our understanding vis-à-vis the mechanisms for AT2 as a regime for stem cell therapy as well as essential guiding information for clinical trials, including effectiveness in appropriate pre-clinical models, safety, mostly specifications for divergent lung injury patients. These important gaps shall be systematically investigated prior to the vast therapeutic perspective of AT2 cells for pulmonary diseases can be considered. This review focused on AT2 cells homeostasis, pathophysiological changes in the pathogenesis of lung injury, physiological function of AT2 cells, apoptosis of AT2 cells in lung diseases, the role of AT2 cells in repairing processes after lung injury, mechanism of AT2 cells activation promote repairing processes after lung injury, and potential therapy of lung disease by utilizing the AT2 progenitor cells. The advancement remains to causally connect the molecular and cellular alteration of AT2 cells to lung injury and repair. Conclusively, it is identified that AT2 cells can convert into AT1 cells; but, the comprehensive cellular mechanisms involved in this transition are unrevealed. Further investigation is mandatory to determine new strategies to prevent lung injury.

Surfactant protein C dampens inflammation by decreasing JAK/STAT activation during lung repair

Surfactant protein C (SPC), a key component of pulmonary surfactant, also plays a role in regulating inflammation. SPC deficiency in patients and mouse models is associated with increased inflammation and delayed repair, but the key drivers of SPC-regulated inflammation in response to injury are largely unknown. This study focuses on a new mechanism of SPC as an anti-inflammatory molecule using SPC-TK/SPC-KO (surfactant protein C-thymidine kinase/surfactant protein C knockout) mice, which represent a novel sterile injury model that mimics clinical acute respiratory distress syndrome (ARDS). SPC-TK mice express the inducible suicide gene thymidine kinase from by the SPC promoter, which targets alveolar type 2 (AT2) cells for depletion in response to ganciclovir (GCV). We compared GCV-induced injury and repair in SPC-TK mice that have normal endogenous SPC expression with SPC-TK/SPC-KO mice lacking SPC expression. In contrast to SPC-TK mice, SPC-TK/SPC-KO mice treated with GCV exhibited more severe inflammation, resulting in over 90% mortality; there was only 8% mortality of SPC-TK animals. SPC-TK/SPC-KO mice had highly elevated inflammatory cytokines and granulocyte infiltration in the bronchoalveolar lavage (BAL) fluid. Consistent with a proinflammatory phenotype, immunofluorescence revealed increased phosphorylated signal transduction and activation of transcription 3 (pSTAT3), suggesting enhanced Janus kinase (JAK)/STAT activation in inflammatory and AT2 cells of SPC-TK/SPC-KO mice. The level of suppressor of cytokine signaling 3, an anti-inflammatory mediator that decreases pSTAT3 signaling, was significantly decreased in the BAL fluid of SPC-TK/SPC-KO mice. Hyperactivation of pSTAT3 and inflammation were rescued by AZD1480, a JAK1/2 inhibitor. Our findings showing a novel role for SPC in regulating inflammation via JAK/STAT may have clinical applications.

Pathophysiology and Management of Acute Respiratory Distress Syndrome in Children

Acute respiratory distress syndrome (ARDS) is a syndrome of noncardiogenic pulmonary edema and hypoxia that accompanies up to 30% of deaths in pediatric intensive care units. Pediatric ARDS (PARDS) is diagnosed by the presence of hypoxia, defined by oxygenation index or Pao₂/Fio₂ ratio cutoffs, and new chest infiltrate occurring within 7 days of a known insult. Hallmarks of ARDS include hypoxemia and decreased lung compliance, increased work of breathing, and impaired gas exchange. Mortality is often accompanied by multiple organ failure. Although many modalities to treat PARDS have been investigated, supportive therapies and lung protective ventilator support remain the mainstay.

Efficacy study of pulmonary surfactant combined with assisted ventilation for acute respiratory distress syndrome management of term neonates

The clinical efficacy of pulmonary surfactant (PS) combined with assisted ventilation was assessed for acute respiratory distress syndrome (RDS) management of term neonates. The total sample size was of 60 subjects. Group I: Experimental group, 30 cases were treated with standard of care with tracheal intubation, mechanical ventilation and PS (100-200 mg/kg). In case of hypoxaemia present even after 12 h standard of care was administered again, up to 4 times. Group II: Control group, 30 cases treated with conventional tracheal intubation and mechanical ventilation. PaO₂, PaO₂/FiO₂ and X-ray were compared between the two groups after 24-h treatment. Analysis of the results indicate that the PS combined with ventilation can improve the clinical symptoms and blood gas analysis index of ARDS neonates. The PaO₂, PaCO₂, PaO₂/FiO₂ levels were improved in the two groups after treatment, the improvement effect of the experimental group was better than in the control group, P<0.05. The surfactant therapy is proved to be effective as preventive and rescue treatment of NRDS in term neonates. This result is supported by conventional concepts and clinical confirmation in patients with lung injury-associated respiratory failure.

In vitro and in vivo comparison between poractant alfa and the new generation synthetic surfactant CHF5633

BACKGROUND

CHF5633 is a new generation synthetic surfactant containing both SP-B and SP-C analogues developed for the treatment of respiratory distress syndrome. Here, the optimal dose and its performance in comparison to the animal-derived surfactant poractant alfa were investigated.

METHODS

In vitro surfactant activity was determined by means of the Wilhelmy balance and the capillary surfactometer. The dose-finding study was performed in preterm rabbits with severe surfactant deficiency. CHF5633 doses ranging from 50 to 300 mg/kg were used. Untreated animals and animals treated with 200 mg/kg of poractant alfa were included for comparison.

RESULTS

In vitro, minimum surface tension (γ_min) was decreased from values above 70 to 0 mN/m by both surfactants, and they formed rapidly a film at the air-liquid interface. In vivo studies showed a clear dose-dependent improvement of lung function for CHF5633. The pulmonary effect of CHF5633 200 mg/kg dose was comparable to the pulmonary response elicited by 200 mg/kg of poractant alfa in preterm rabbits.

CONCLUSION

CHF5633 is as efficient as poractant alfa in our in vitro and in vivo settings. A clear dose-dependent improvement of lung function could be observed for CHF5633, with the dose of 200 mg/kg being the most efficient one.

The evolving potential for pediatric ex vivo lung perfusion

Despite the rise in the number of adult lung transplantations performed, rates of pediatric lung transplantation remain low. Lung transplantation is an accepted therapy for pediatric end-stage lung disease; however, it is limited by a shortage of donor organs. EVLP has emerged as a platform for assessment and preservation of donor lung function. EVLP has been adopted in adult lung transplantation and has successfully led to increased adult lung transplantations and donor lung utilization. We discuss the future implications of EVLP utilization, specifically, its potential evolving role in overcoming donor shortages in smaller children and adolescents to improve the quality and outcomes of lung transplantation in pediatric patients.

[Critically ill pediatric hemato-oncology patient: What we do is what we should do?]

OBJECTIVE

Primary objective, to describe the management and monitorization of critically ill pediatric hemato-oncology patient (CIPHO) in the Spanish pediatric intensive care units (PICU). Secondary objective, through a literature review, to identify possible areas of improvement.

MATERIAL AND METHODS

Observational transversal descriptive study. An anonymous web-based survey was sent to 324 Spanish pediatric intensivists from April 2011 to May 2011. None of them were pediatric residents.

RESULTS

The survey was answered by 105 intensivists, 59/105 always agreed their treatment with the oncologist. In case of hemodynamic instability, non-invasive blood pressure monitoring is always done by 85/105 and almost always optimized by intra-arterial measuring (85/105) and central venous pressure (70/105). If respiratory failure the use of non-invasive ventilation (NIPPV) is always (36/105) or frequently (60/105) established prior to conventional mechanical ventilation. To replace or withdraw non-invasive ventilation only 44/96 of the respondents to this question use a clinical protocol. Before the instauration of conventional mechanical ventilation the oncological prognosis is considered by 72/105. In case of acute oliguric renal failure the renal replacement techniques are widely used (74/105). The withdrawal of sustaining life support is frequently discussed (75/103) and agreed with the oncologist (91/103) and caregivers (81/103).

CONCLUSIONS

In our study, despite there is not a defined standard-of-care, the respondents showed similar therapeutics and monitorization choices. The use of NIPPV as first respiratory assistance is extended. Prospective, observational and multicenter studies should be developed to establish the results of this management in this population.

Stem cells for respiratory failure

PURPOSE OF REVIEW

The prognosis of patients with respiratory failure in the ICU remains poor, while current therapeutic approaches are aimed at minimizing ventilator-induced lung injury. Stem cell-based therapies have the potential to transform respiratory failure treatment by achieving lung repair. The purpose of this article is to critically review the large body of clinical and experimental work performed with respect to the use of stem/progenitor cells in respiratory failure, and to discuss current challenges and future directions.

RECENT FINDINGS

Since the initial report of cell therapy for lung injury in 2005, numerous preclinical and clinical studies have been performed that support the ability of various stem cell populations to improve physiologic lung function and reduce inflammation in both infective and sterile acute respiratory distress syndrome. Nevertheless, many important issues (e.g., mechanism of action, long-term engraftment, optimal cell type, dose, route of administration) remain to be resolved.

SUMMARY

Cell-based therapeutics hold promise, particularly for acute respiratory distress syndrome, and early preclinical testing has been encouraging. To advance clinical testing of cell therapies in respiratory failure, and to help ensure that this approach will facilitate bench-to-bedside and bedside-to-bench discoveries, parallel paths of basic and clinical research are needed, including measures of cell therapy effectiveness in vivo and in vitro.

Acute respiratory distress syndrome on the intensive care unit

Acute respiratory distress syndrome is a life-threatening condition that is common in critically ill patients. Historically, diagnosis has been difficult and prognosis has been poor, but the Berlin definition and developments in medical therapies provide promise that we can improve outcomes for these patients in the future.

Pharmacological therapies for acute respiratory distress syndrome

PURPOSE OF REVIEW

Despite recent advances in the management of patients with acute respiratory distress syndrome (ARDS) by using protective ventilator strategies, the mortality rate of ARDS remains high. The complexity of the pathogenesis and the heterogeneity of coexisting diseases in patients with ARDS require critical care physicians and researchers to search for multiple therapeutic approaches in order to further improve patient outcome. This review article therefore focuses on the recent studies in the field of pharmacological intervention in ARDS.

RECENT FINDINGS

A number of approaches for pharmacological intervention have been evaluated in patients with ARDS, but most of them failed to reduce mortality or improve outcomes despite some promising observations seen in preclinical studies. Prior methods such as nitric oxide inhalation, neuromuscular blocking agents and corticosteroids may still have a place in the treatment, while novel therapeutic approaches including the use of angiotensin-converting enzyme inhibitors, statins and stem cells are currently under investigation.

SUMMARY

Overall, there is no proven pharmacological therapy in ARDS, but some pharmacological interventions were associated with beneficial effects in certain subgroups of patients depending on the cause, underlying diseases, the concurrent supportive therapies and timing. Further clinical trials are warranted to assess multiple outcome measurement of the promising pharmacological interventions in selected patients with ARDS.

Adjunctive treatments in pediatric acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a devastating process that involves pulmonary inflammation, alveolar damage and hypoxemic respiratory failure. Although advances in management approaches over the past two decades have resulted in significantly improved outcomes, death from pediatric ARDS may still occur in up to 35% of patients. While invasive mechanical ventilation is an essential component of ARDS management, various adjuncts have been utilized as treatment for these patients. However, evidence-based data in infants and children in this area are lacking. In this article, the authors review the available evidence supporting (or not supporting) the use of non-ventilatory adjunctive strategies in the management of pediatric ARDS, including prone positioning, pulmonary vasodilators, β-agonists, steroids and surfactant.

Structure-function relationships in pulmonary surfactant membranes: from biophysics to therapy

Pulmonary surfactant is an essential lipid-protein complex to maintain an operative respiratory surface at the mammalian lungs. It reduces surface tension at the alveolar air-liquid interface to stabilise the lungs against physical forces operating along the compression-expansion breathing cycles. At the same time, surfactant integrates elements establishing a primary barrier against the entry of pathogens. Lack or deficiencies of the surfactant system are associated with respiratory pathologies, which treatment often includes supplementation with exogenous materials. The present review summarises current models on the molecular mechanisms of surfactant function, with particular emphasis in its biophysical properties to stabilise the lungs and the molecular alterations connecting impaired surfactant with diseased organs. It also provides a perspective on the current surfactant-based strategies to treat respiratory pathologies. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

Therapeutic effect of intravenous infusion of perfluorocarbon emulsion on LPS-induced acute lung injury in rats

Acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome (ARDS) are the leading causes of death in critical care. Despite extensive efforts in research and clinical medicine, mortality remains high in these diseases. Perfluorocarbon (PFC), a chemical compound known as liquid ventilation medium, is capable of dissolving large amounts of physiologically important gases (mainly oxygen and carbon dioxide). In this study we aimed to investigate the effect of intravenous infusion of PFC emulsion on lipopolysaccharide (LPS) induced ALI in rats and elucidate its mechanism of action. Forty two Wistar rats were randomly divided into three groups: 6 rats were treated with saline solution by intratracheal instillation (control group), 18 rats were treated with LPS by intratracheal instillation (LPS group) and the other 18 rats received PFC through femoral vein prior to LPS instillation (LPS+PFC group). The rats in the control group were sacrificed 6 hours later after saline instillation. At 2, 4 and 6 hours of exposure to LPS, 6 rats in the LPS group and 6 rats in LPS+PFC group were sacrificed at each time point. By analyzing pulmonary pathology, partial pressure of oxygen in the blood (PaO2) and lung wet-dry weight ratio (W/D) of each rat, we found that intravenous infusion of PFC significantly alleviated acute lung injury induced by LPS. Moreover, we showed that the expression of pulmonary myeloperoxidase (MPO), intercellular adhesion molecule-1 (ICAM-1) of endothelial cells and CD11b of polymorphonuclear neutrophils (PMN) induced by LPS were significantly decreased by PFC treatment in vivo. Our results indicate that intravenous infusion of PFC inhibits the infiltration of PMNs into lung tissue, which has been shown as the core pathogenesis of ALI/ARDS. Thus, our study provides a theoretical foundation for using intravenous infusion of PFC to prevent and treat ALI/ARDS in clinical practice.

Mechanisms of acute respiratory distress syndrome in children and adults: a review and suggestions for future research

OBJECTIVES

To provide a current overview of the epidemiology and pathophysiology of acute respiratory distress syndrome in adults and children, and to identify research questions that will address the differences between adults and children with acute respiratory distress syndrome.

DATA SOURCES

Narrative literature review and author-generated data.

DATA SELECTION

The epidemiology of acute respiratory distress syndrome in adults and children, lung morphogenesis, and postnatal lung growth and development are reviewed. The pathophysiology of acute respiratory distress syndrome is divided into eight categories: alveolar fluid transport, surfactant, innate immunity, apoptosis, coagulation, direct alveolar epithelial injury by bacterial products, ventilator-associated lung injury, and repair.

DATA EXTRACTION AND SYNTHESIS

Epidemiologic data suggest significant differences in the prevalence and mortality of acute respiratory distress syndrome between children and adults. Postnatal lung development continues through attainment of adult height, and there is overlap between the regulation of postnatal lung development and inflammatory, apoptotic, alveolar fluid clearance, and repair mechanisms. Therefore, there is a different biological baseline network of gene and protein expression in children as compared with adults.

CONCLUSIONS

There are significant obstacles to performing research on children with acute respiratory distress syndrome. However, epidemiologic, clinical, and animal studies suggest age-dependent differences in the pathophysiology of acute respiratory distress syndrome. In order to reduce the prevalence and improve the outcome of patients with acute respiratory distress syndrome, translational studies of inflammatory, apoptotic, alveolar fluid clearance, and repair mechanisms are needed. Understanding the differences in pathophysiologic mechanisms in acute respiratory distress syndrome between children and adults should facilitate identification of novel therapeutic interventions to prevent or modulate lung injury and improve lung repair.

Risk factors for the development of acute lung injury in patients with infectious pneumonia

INTRODUCTION

Although pneumonia has been identified as the single most common risk factor for acute lung injury (ALI), we have a limited knowledge as to why ALI develops in some patients with pneumonia and not in others. The objective of this study was to determine frequency, risk factors, and outcome of ALI in patients with infectious pneumonia.

METHODS

A retrospective cohort study of adult patients with microbiologically positive pneumonia, hospitalized at two Mayo Clinic Rochester hospitals between January 1, 2005, and December 31, 2007. In a subsequent nested case-control analysis, we evaluated the differences in prehospital and intrahospital exposures between patients with and without ALI/acute respiratory distress syndrome (ARDS) matched by specific pathogen, isolation site, gender, and closest age in a 1:1 manner.

RESULTS

The study included 596 patients; 365 (61.2%) were men. The median age was 65 (IQR, 53 to 75) years. In total, 171 patients (28.7%) were diagnosed with ALI. The occurrence of ALI was less frequent in bacterial (n = 99 of 412, 24%) compared with viral (n = 19 of 55, 35%), fungal (n = 39 of 95, 41%), and mixed isolates pneumonias (n = 14 of 34, 41%; P = 0.002). After adjusting for baseline severity of illness and comorbidities, patients in whom ALI developed had a markedly increased risk of hospital death (ORadj 9.7; 95% CI, 6.0 to 15.9). In a nested case-control study, presence of shock (OR, 8.9; 95% CI, 2.8 to 45.9), inappropriate initial antimicrobial treatment (OR, 3.2; 95% CI, 1.3 to 8.5), and transfusions (OR, 4.8; 95% CI, 1.5 to 19.6) independently predicted ALI development.

CONCLUSIONS

The development of ALI among patients hospitalized with infectious pneumonia varied among pulmonary pathogens and was associated with increased mortality. Inappropriate initial antimicrobial treatment and transfusion predict the development of ALI independent of pathogen.

Clinical review: Stem cell therapies for acute lung injury/acute respiratory distress syndrome - hope or hype?

A growing understanding of the complexity of the pathophysiology of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), coupled with advances in stem cell biology, has led to a renewed interest in the therapeutic potential of stem cells for this devastating disease. Mesenchymal stem cells appear closest to clinical translation, given the evidence that they may favourably modulate the immune response to reduce lung injury, while maintaining host immune-competence and also facilitating lung regeneration and repair. The demonstration that human mesenchymal stem cells exert benefit in the endotoxin-injured human lung is particularly persuasive. Endothelial progenitor cells also demonstrate promise in reducing endothelial damage, which is a key pathophysiological feature of ALI. Embryonic and induced pluripotent stem cells are at an earlier stage in the translational process, but offer the hope of directly replacing injured lung tissue. The lung itself also contains endogenous stem cells, which may ultimately offer the greatest hope for lung diseases, given their physiologic role in replacing and regenerating native lung tissues. However, significant deficits remain in our knowledge regarding the mechanisms of action of stem cells, their efficacy in relevant pre-clinical models, and their safety, particularly in critically ill patients. These gaps need to be addressed before the enormous therapeutic potential of stem cells for ALI/ARDS can be realised.

Potential clinical application of KGF-2 (FGF-10) for acute lung injury/acute respiratory distress syndrome

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is an acute life-threatening form of hypoxemic respiratory failure with a high mortality rate, and there is still a great need for more effective therapies for such a severe and lethal disease. Dysfunction of endothelial and epithelial barriers is one of the most important mechanisms in hypoxia-associated ALI/ARDS. The acceleration of the epithelial repair process in the injured lung may provide an effective therapeutic target. KGF-2, a potent alveolar epithelial cell mitogen, plays an important role in organ morphogenesis and epithelial differentiation, and modulates a variety of mechanisms recognized to be important in alveolar repair and resolution in ALI/ARDS. Preclinical and clinical studies have suggested that KGF-2 may be the candidate of novel therapies for alveolar epithelial damage during ALI/ARDS.

Exogenous surfactant may improve oxygenation but not mortality in adult patients with acute lung injury/acute respiratory distress syndrome: a meta-analysis of 9 clinical trials

OBJECTIVE

To evaluate whether exogenous surfactant therapy may be useful in adult patients with acute lung injury or acute respiratory distress syndrome, using a meta-analysis of published clinical trials.

DESIGN

A comprehensive literature search was performed to identify all randomized clinical trials examining the effects of the treatment of acute lung injury/acute respiratory distress syndrome with exogenous surfactant in adults. The primary outcome measurement was mortality 28 or 30 days after randomization. Secondary outcome measurements included a change in the ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen in the first 24 hours or after 120 hours, the number of ventilation-free days, and any adverse effects. The meta-analysis was performed using the Review Manager 5.0.0 system.

PARTICIPANTS

Randomized clinical trials.

INTERVENTION

Meta-analysis of 9 trials.

MEASUREMENTS AND MAIN RESULTS

Nine trials involving 2,575 patients were included in the meta-analysis. The analysis showed that treatment with exogenous pulmonary surfactant does not decrease mortality significantly. There was a significant effect of exogenous surfactant treatment on the change in the partial pressure of arterial oxygen/fraction of inspired oxygen ratio in the first 24 hours but this was lost by 120 hours. The duration of ventilation trended lower in surfactant-treated patients but this was not significant. In addition, surfactant-treated patients had a significantly higher risk of adverse effects.

CONCLUSIONS

An exogenous surfactant may improve oxygenation over the first 24 hours after administration. However, treatment does not improve mortality and oxygenation over ≥120 hours after administration and results in a high rate of adverse effects. Therefore, the present data suggest that an exogenous surfactant cannot be considered an effective adjunctive therapy in patients with acute lung injury/acute respiratory distress syndrome.

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.

Nonconventional support of respiration

PURPOSE OF REVIEW

Several alternative treatments have been proposed to decrease mortality of patients with acute respiratory distress syndrome (ARDS). We will discuss most recent trials and meta-analysis studies on nonconventional ventilatory and pharmacological treatments of ARDS patients.

RECENT FINDINGS

Nonconventional ventilatory treatments such as prone positioning, high frequency oscillatory ventilation (HFOV), and extracorporeal membrane oxygenation (ECMO) aim to restore gas exchange while further decreasing ventilator induced lung injury. Though randomized trials failed to prove survival benefits with the use of prone positioning or HFOV, recent meta-analyses have shown, for both treatments, a decrease in mortality in the subpopulation of more severe ARDS patients. In a randomized controlled trial, referral of ARDS patients in a center with experience on ECMO was associated with an improved survival rate. Promising results come from new miniaturized extracorporeal techniques optimized for effective CO(2) removal from low blood flow. These techniques should allow early application of superprotective ventilator strategies. Pharmacological treatments such as neuromuscular blocking and intravenous β2 agonist may be effective in specific times and subsets of patients.

SUMMARY

Existing data suggest that some of the available nonconventional treatments may be effective in more severe ARDS patients. New techniques and drugs that should facilitate prevention or healing of lung injury are under investigation.

Mesenchymal stem cells - a promising therapy for Acute Respiratory Distress Syndrome

Acute Respiratory Distress Syndrome (ARDS) constitutes a spectrum of severe acute respiratory failure in response to a variety of inciting stimuli that is the leading cause of death and disability in the critically ill. Despite decades of research, there are no therapies for ARDS, and management remains supportive. A growing understanding of the complexity of the pathophysiology of ARDS, coupled with advances in stem cell biology, has lead to a renewed interest in the therapeutic potential of mesenchymal stem cells for ARDS. Recent evidence suggests that mesenchymal stem cells can modulate the immune response to reduce injury and also increase resistance to infection, while also facilitating regeneration and repair of the injured lung. This unique combination of effects has generated considerable excitement. We review the biological characteristics of mesenchymal stem cells that underlie their therapeutic potential for ARDS. We also summarise existing pre-clinical evidence, evaluate the potential and pitfalls of using mesenchymal stem cells for treatment, and examine the likely future directions for mesenchymal stem cells in ARDS.

A comprehensive review of predictive and prognostic composite factors implicated in the heterogeneity of treatment response and outcome across disease areas

AIM

To assess and present the current body of evidence regarding composite measures associated with differential treatment response or outcome as a result of patient heterogeneity and to evaluate their consistency across disease areas.

METHODS

A comprehensive review of the literature from the last 10 years was performed using three databases (PubMed, Embase and Cochrane). All articles that met the inclusion/exclusion criteria were selected, abstracted and assessed using the NICE level-of-evidence criteria.

RESULTS

Forty-nine studies were identified in the data abstraction. Approximately one-third focused on existing composite measures, and the rest investigated emerging composite factors. The majority of studies targeted patients with cancer, cardiovascular disease or psychological disorders. As a whole, the composite measures were found to be disease-specific, but some composite elements, including age, gender, comorbidities and health status, showed consistency across disease areas. To complement these findings, common individual factors found in five previous independent disease-specific literature assessments were also summarised, including age, gender, treatment adherence and satisfaction, healthcare resource utilisation and health status.

CONCLUSIONS

Composite measures can play an important role in characterising heterogeneity of treatment response and outcome in patients suffering from various medical conditions. These measures can help clinicians to better distinguish between patients with high likelihood to respond well to treatment and patients with minimal chances of positive therapeutic outcomes. Herein, the individual factors identified can be used to develop novel predictive or prognostic composite measures that can be applicable across disease areas. Reflecting these cross-disease measures in clinical and public health decisions has the distinctive appeal to enable targeted treatment for patients suffering from multiple medical conditions, which may ultimately yield significant gains in individual outcomes, population health and cost-effective resource allocation.

Acute respiratory distress syndrome

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a common diagnosis among children admitted to pediatric intensive care units. This heterogeneous disorder has numerous pulmonary and non-pulmonary causes and is associated with a significant risk of mortality. Many supportive therapies exist for ARDS. SEARCH: Literature search was performed by using the key words ARDS and related topics on the Pubmed search engine maintained by the National Heart, Lung, Blood Institute. Pediatric randomized controlled trials that have been published in the last 10 years were included. Emphasis was placed on pediatric literature, although sentinel adult studies have been included. Most of the evidence presented is of levels I and II.

RESULTS

Low tidal volume is the only strategy that has consistently improved outcome in ARDS. A tidal volume of ≤ 6 mL/kg predicted body weight should be used. Ventilator induced lung injury may result in systemic effects with multi-system organ failure, and all efforts should be made to minimize this. Positive end-expiratory pressure should be used to judiciously maintain lung recruitment. There is insufficient evidence to routinely use high frequency ventilation, prone positioning, or inhaled nitric oxide. Calfactant therapy is promising and may be considered in children with direct lung injury and ARDS. Current literature does not support routine use of corticosteroids for non-resolving ARDS.

Influence of genetic variability at the surfactant proteins A and D in community-acquired pneumonia: a prospective, observational, genetic study

INTRODUCTION

Genetic variability of the pulmonary surfactant proteins A and D may affect clearance of microorganisms and the extent of the inflammatory response. The genes of these collectins (SFTPA1, SFTPA2 and SFTPD) are located in a cluster at 10q21-24. The objective of this study was to evaluate the existence of linkage disequilibrium (LD) among these genes, and the association of variability at these genes with susceptibility and outcome of community-acquired pneumonia (CAP). We also studied the effect of genetic variability on SP-D serum levels.

METHODS

Seven non-synonymous polymorphisms of SFTPA1, SFTPA2 and SFTPD were analyzed. For susceptibility, 682 CAP patients and 769 controls were studied in a case-control study. Severity and outcome were evaluated in a prospective study. Haplotypes were inferred and LD was characterized. SP-D serum levels were measured in healthy controls.

RESULTS

The SFTPD aa11-C allele was significantly associated with lower SP-D serum levels, in a dose-dependent manner. We observed the existence of LD among the studied genes. Haplotypes SFTPA1 6A(2) (P = 0.0009, odds ration (OR) = 0.78), SFTPA(2) 1A(0) (P = 0.002, OR = 0.79), SFTPA1-SFTPA2 6A2-1A(0) (P = 0.0005, OR = 0.77), and SFTPD-SFTPA1-SFTPA(2)C-6A2-1A(0) (P = 0.00001, OR = 0.62) were underrepresented in patients, whereas haplotypes SFTPA2 1A(10) (P = 0.00007, OR = 6.58) and SFTPA1-SFTPA2 6A(3)-1A (P = 0.0007, OR = 3.92) were overrepresented. Similar results were observed in CAP due to pneumococcus, though no significant differences were now observed after Bonferroni corrections. 1A(10) and 6A-1A were associated with higher 28-day and 90-day mortality, and with multi-organ dysfunction syndrome (MODS) and acute respiratory distress syndrome (ARDS) respectively. SFTPD aa11-C allele was associated with development of MODS and ARDS.

CONCLUSIONS

Our study indicates that missense single nucleotide polymorphisms and haplotypes of SFTPA1, SFTPA2 and SFTPD are associated with susceptibility to CAP, and that several haplotypes also influence severity and outcome of CAP.