FiftyYears ofResearch inARDS.Insight into Acute Respiratory Distress Syndrome. From Models to Patients

Elastic static power, its correlation with acute respiratory distress syndrome severity: A Bayesian post-hoc analysis of the Mechanical Power Day cross-sectional trial

OBJECTIVE

The relationship between different power equations and the severity of acute respiratory distress syndrome (ARDS) remains unclear. This study aimed to evaluate various power equations: total mechanical power, total elastic power (comprising elastic static and elastic dynamic power), and resistive power, in a cohort of mechanically ventilated patients with and without ARDS. Bayesian analysis was employed to refine estimates and quantify uncertainty by incorporating a priori distributions.

DESIGN

A Bayesian post-hoc analysis was conducted on data from the Mechanical Power Day study.

SETTING

113 intensive care units across 15 countries and 4 continents.

PATIENTS

Adults who received invasive mechanical ventilation in volume-controlled mode, with (mild and moderate/severe ARDS) and without ARDS.

INTERVENTIONS

None.

MAIN VARIABLES OF INTEREST

ARDS, Elastic static power.

RESULTS

Elastic static power was 5.8 J/min (BF: 0.3) in patients with mild ARDS and 7.4 J/min (BF: 0.9) in moderate/severe ARDS patients. Bayesian regression and modeling analysis revealed that elastic static power was independently correlated with mild (a posteriori Mean: 1.3; 95% Credible Interval [Cred. Interval]: 0.2-2.2) and moderate/severe ARDS (a posteriori Mean: 2.8; 95% Cred. Interval: 1.7-3.8) more strongly than other power equations.

CONCLUSIONS

Elastic static power was found to have the strongest correlation with ARDS severity among the power equations studied. Prospective studies are needed to further validate these findings.

Gαq/11 aggravates acute lung injury in mice by promoting endoplasmic reticulum stress-mediated NETosis

BACKGROUND

Acute lung injury (ALI) is distinguished by exaggerated neutrophil extracellular traps (NETs), elevated clinical mortality rates, and a paucity of targeted therapeutic interventions. The Gαq/11 protein, a member of the G protein subfamily, is an effective intervention target for a variety of diseases, but little is known about its role in ALI.

METHODS

In this study, a murine model of ALI induced by lipopolysaccharide (LPS) was utilized, employing myeloid cell-specific Gna11 knockout mice. The pulmonary pathology of mice was assessed and the lung samples were collected for immunofluorescence staining and RNA-sequencing analysis to elucidate the impact and underlying mechanisms of Gαq/11 in ALI. Mouse bone marrow-derived neutrophils were isolated and cultured for live-cell imaging to investigate the in vitro effects of Gαq/11.

RESULTS

The expression of Gαq/11 was found to be upregulated in the lung tissues of mice with ALI, coinciding with the increased expression of inflammatory genes. Myeloid cell-specific Gna11 deficience attenuated LPS-induced lung injury and the formation of NETs in mice. Mechanistically, Gαq/11 facilitates NETosis by promoting the activation of the endoplasmic reticulum (ER) stress sensor IRE1α in neutrophils and mediating the production of mitochondrial reactive oxygen species (mitoROS). Pharmacological inhibition of Gαq/11 using YM-254,890 was shown to reduce NETs formation and lung injury in mice.

CONCLUSIONS

The upregulation of Gαq/11 exacerbates ALI through the promotion of ER stress-mediated NETosis. Consequently, Gαq/11 represents a potential therapeutic target for the treatment of ALI.

Association of dynamic changes in arterial partial pressure of carbon dioxide with neurological outcomes in aneurysmal subarachnoid hemorrhage

Background

Cerebral blood flow (CBF) is closely regulated by carbon dioxide (CO2). In patients with aneurysmal subarachnoid hemorrhage (aSAH), abnormal arterial partial pressure of CO2 (PaCO2) might deteriorate brain injuries. Nevertheless, the impact of dynamic PaCO2 fluctuations on neurological outcomes in aSAH patients has not been extensively studied. Our study aimed to investigate the association between dynamic PaCO2 levels and unfavorable neurological outcomes in aSAH patients.

Methods

In this retrospective observational study, we consecutively enrolled 159 aSAH patients from December 2019 to July 2021. Arterial blood gas measurements within 10 days after intensive care unit (ICU) admission for each patient were recorded to calculate the time-weighted average (TWA)-PaCO2, an indicator representing the dynamic changes in PaCO2 levels. For the association between TWA-PaCO2 levels and unfavorable neurological outcomes in aSAH patients, multivariable logistic analysis was used to explore TWA-PaCO2 levels as categorical variables, and restricted cubic spline (RCS) was used to explore TWA-PaCO2 levels as continuous variables.

Results

In multivariable logistic analysis, after adjusting confounders, when TWA-PaCO2 35-45 mmHg was as a reference, TWA-PaCO2 < 35 mmHg (odds ratio [OR] 2.15, 95 % confidence interval [CI] 0.83-5.55, P = 0.113) and TWA-PaCO2 > 45 mmHg (OR 8.31, 95 % CI 0.72-96.14, P = 0.090) were not independently associated with unfavorable neurological outcomes (modified Rankin score of 3-6). The RCS shows a "U" shape curve between TWA-PaCO2 levels and unfavorable neurological outcomes, with a nonlinear P-value of 0.023. The lowest ORs of unfavorable neurological outcomes were within PaCO2 32.8-38.1 mmHg.

Conclusions

Both lower and higher PaCO2 levels are harmful to aSAH patients. PaCO2 in the range of 32.8-38.1 mmHg is associated with lowest unfavorable neurological outcomes.

Regional distribution of mechanical strain and macrophage-associated lung inflammation after ventilator-induced lung injury: an experimental study

BACKGROUND

Alveolar macrophages activation to the pro-inflammatory phenotype M1 is pivotal in the pathophysiology of Ventilator-Induced Lung Injury (VILI). Increased lung strain is a known determinant of VILI, but a direct correspondence between regional lung strain and macrophagic activation remains unestablished. [68Ga]Ga-DOTA-TATE is a Positron Emission Tomography (PET) radiopharmaceutical with a high affinity for somatostatin receptor subtype 2 (SSTR2), which is overexpressed by pro-inflammatory-activated macrophages. Aim of the study was to determine, in a porcine model of VILI, whether mechanical strain correlates topographically with distribution of activated macrophages detected by [68Ga]Ga-DOTA-TATE uptake.

METHODS

Seven anesthetized pigs underwent VILI, while three served as control. Lung CT scans were acquired at incremental tidal volumes, simultaneously recording lung mechanics. [68Ga]Ga-DOTA-TATE was administered, followed by dynamic PET scans. Custom MatLab scripts generated voxel-by-voxel gas volume and strain maps from CT slices at para-diaphragmatic (Para-D) and mid-thoracic (Mid-T) levels. Analysis of regional Voxel-associated Normal Strain (VoStrain) and [68Ga]Ga-DOTA-TATE uptake was performed and a measure of the statistical correlation between these two variables was quantified using the linear mutual information (LMI) method.

RESULTS

Compared to controls, the VILI group exhibited statistically significant higher VoStrain and Standardized Uptake Value Ratios (SUVR) both at Para-D and Mid-T levels. Both VoStrain and SUVR increased along the gravitational axis with an increment described by statistically different regression lines between VILI and healthy controls and reaching the peak in the dependent regions of the lung (for strain in VILI vs. control was at Para-D: 760 ± 210 vs. 449 ± 106; at Mid-T level 497 ± 373 vs. 193 ± 160; for SUVR, in VILI vs. control was at Para-D: 2.2 ± 1.3 vs. 1.3 ± 0.1; at Mid-T level 1.3 ± 1.0 vs. 0.6 ± 0.03). LMI in both Para-D and Mid-T was statistically significantly higher in VILI than in controls.

CONCLUSIONS

In this porcine model of VILI, we found a topographical correlation between lung strain and [68Ga]Ga-DOTA-TATE uptake at voxel level, suggesting that mechanical alteration and specific activation of inflammatory cells are strongly linked in VILI. This study represents the first voxel-by-voxel examination of this relationship in a multi-modal imaging analysis.

Endotoxin-Induced Sepsis on Ceftriaxone-Treated Rats' Ventilatory Mechanics and Pharmacokinetics

Sepsis can trigger acute respiratory distress syndrome (ARDS), which can lead to a series of physiological changes, modifying the effectiveness of therapy and culminating in death. For all experiments, male Wistar rats (200-250 g) were split into the following groups: control and sepsis-induced by endotoxin lipopolysaccharide (LPS); the control group received only intraperitoneal saline or saline + CEF while the treated groups received ceftriaxone (CEF) (100 mg/kg) IP; previously or not with sepsis induction by LPS (1 mg/kg) IP. We evaluated respiratory mechanics, and alveolar bronchial lavage was collected for nitrite and vascular endothelial growth factor (VEGF) quantification and cell evaluation. For pharmacokinetic evaluation, two groups received ceftriaxone, one already exposed to LPS. Respiratory mechanics shows a decrease in total airway resistance, dissipation of viscous energy, and elastance of lung tissues in all sepsis-induced groups compared to the control group. VEGF and NOx values were higher in sepsis animals compared to the control group, and ceftriaxone was able to reduce both parameters. The pharmacokinetic parameters for ceftriaxone, such as bioavailability, absorption, and terminal half-life, were smaller in the sepsis-induced group than in the control group since clearance was higher in septic animals. Despite the pharmacokinetic changes, ceftriaxone showed a reduction in resistance in the airways. In addition, CEF lowers nitrite levels in the lungs and acts on their adverse effects, reflecting pharmacological therapy of the disease.

Blocking P2Y2 purinergic receptor prevents the development of lipopolysaccharide-induced acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is associated with high morbidity and mortality resulting from a direct or indirect injury of the lung. It is characterized by a rapid alveolar injury, lung inflammation with neutrophil accumulation, elevated permeability of the microvascular-barrier leading to an aggregation of protein-rich fluid in the lungs, followed by impaired oxygenation in the arteries and eventual respiratory failure. Very recently, we have shown an involvement of the Gq-coupled P2Y2 purinergic receptor (P2RY2) in allergic airway inflammation (AAI). In the current study, we aimed to elucidate the contribution of the P2RY2 in lipopolysaccharide (LPS)-induced ARDS mouse model. We found that the expression of P2ry2 in neutrophils, macrophages and lung tissue from animals with LPS-induced ARDS was strongly upregulated at mRNA level. In addition, ATP-neutralization by apyrase in vivo markedly attenuated inflammation and blocking of P2RY2 by non-selective antagonist suramin partially decreased inflammation. This was indicated by a reduction in the number of neutrophils, concentration of proinflammatory cytokines in the BALF, microvascular plasma leakage and reduced features of inflammation in histological analysis of the lung. P2RY2 blocking has also attenuated polymorphonuclear neutrophil (PMN) migration into the interstitium of the lungs in ARDS mouse model. Consistently, treatment of P2ry2 deficient mice with LPS lead to an amelioration of the inflammatory response showed by reduced number of neutrophils and concentrations of proinflammatory cytokines. In attempts to identify the cell type specific role of P2RY2, a series of experiments with conditional P2ry2 knockout animals were performed. We observed that P2ry2 expression in neutrophils, but not in the airway epithelial cells or CD4+ cells, was associated with the inflammatory features caused by ARDS. Altogether, our findings imply for the first time that increased endogenous ATP concentration via activation of P2RY2 is related to the pathogenesis of LPS-induced lung inflammation and may represent a potential therapeutic target for the treatment of ARDS and predictably assess new treatments in ARDS.

A key role for platelet GPVI in neutrophil recruitment, migration, and NETosis in the early stages of acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are associated with high morbidity and mortality. Excessive neutrophil infiltration into the pulmonary airspace is the main cause for the acute inflammation and lung injury. Platelets have been implicated in the pathogenesis of ALI/ARDS, but the underlying mechanisms are not fully understood. Here, we show that the immunoreceptor tyrosine-based activation motif-coupled immunoglobulin-like platelet receptor, glycoprotein VI (GPVI), plays a key role in the early phase of pulmonary thrombo-inflammation in a model of lipopolysaccharide (LPS)-induced ALI in mice. In wild-type (WT) control mice, intranasal LPS application triggered severe pulmonary and blood neutrophilia, hypothermia, and increased blood lactate levels. In contrast, GPVI-deficient mice as well as anti-GPVI-treated WT mice were markedly protected from pulmonary and systemic compromises and showed no increased pulmonary bleeding. High-resolution multicolor microscopy of lung sections and intravital confocal microcopy of the ventilated lung revealed that anti-GPVI treatment resulted in less stable platelet interactions with neutrophils and overall reduced platelet-neutrophil complex (PNC) formation. Anti-GPVI treatment also reduced neutrophil crawling and adhesion on endothelial cells, resulting in reduced neutrophil transmigration and alveolar infiltrates. Remarkably, neutrophil activation was also diminished in anti-GPVI-treated animals, associated with strongly reduced formation of PNC clusters and neutrophil extracellular traps (NETs) compared with that in control mice. These results establish GPVI as a key mediator of neutrophil recruitment, PNC formation, and NET formation (ie, NETosis) in experimental ALI. Thus, GPVI inhibition might be a promising strategy to reduce the acute pulmonary inflammation that causes ALI/ARDS.

Knockdown of versican 1 in lung fibroblasts aggravates Lipopolysaccharide-induced acute inflammation through up-regulation of the SP1-Toll-like Receptor 2-NF-κB Axis: a potential barrier to promising Versican-targeted therapy

OBJECTIVE

Versican participates in various pathological processes like inflammation and fibrosis and is a potential therapeutic target for inflammatory diseases. Versican 1 (V1) has increased expression in inflammatory diseases, but its role is unclear. We explored the effects of V1 on acute lung inflammation to determine whether targeting V1 had therapeutic potential.

METHODS

Human fetal lung fibroblast (HFL1) was transfected with or without V1-inhibiting lentivirus and treated with LPS. The expression levels of inflammatory cytokines, V1, cellular signaling pathway and Toll-like receptors (TLRs) were detected by qPCR, ELISA and western blot. The migration and adhesion of neutrophils and monocytes to HFL1s were performed. The activity of transcriptional factors was determined by dual-luciferase reporter assay.

RESULTS

Inflammatory factors increased dramatically and continuously with V1 knockdown and LPS stimulation (P < 0.01), orchestrating migration of inflammatory cells and an enhanced inflammatory reaction. V1-knockdown increased TLR2 (P < 0.01) and activated the NF-κB pathway, which was partially reversed with a TLR2 neutralizing antibody and an NF-κB inhibitor. Explosion of LPS-induced inflammation was induced by knockdown of V1 via the SP1-TLR2-NF-κB axis.

CONCLUSION

Increased expression of V1 might be protective in acute inflammation, and an infection-induced cytokine storm might be a severe complication of V1-targeted interventions.

Linking Acute Physiology to Outcomes in the ICU: Challenges and Solutions for Research

ICU clinicians rely on bedside physiological measurements to inform many routine clinical decisions. Because deranged physiology is usually associated with poor clinical outcomes, it is tempting to hypothesize that manipulating and intervening on physiological parameters might improve outcomes for patients. However, testing these hypotheses through mathematical models of the relationship between physiology and outcomes presents a number of important methodological challenges. These models reflect the theories of the researcher and can therefore be heavily influenced by one's assumptions and background beliefs. Model building must therefore be approached with great care and forethought, because failure to consider relevant sources of measurement error, confounding, coupling, and time dependency or failure to assess the direction of causality for associations of interest before modeling may give rise to spurious results. This paper outlines the main challenges in analyzing and interpreting these models and offers potential solutions to address these challenges.

Immune Modulation in Sepsis, ARDS, and Covid-19 - The Road Traveled and the Road Ahead

Immune Modulation in Sepsis, ARDS, and Covid-19Leligdowicz et al. consider the history and future of immunomodulating therapies in sepsis and ARDS, including ARDS due to Covid-19, and remark on the larger challenge of clinical research on therapies for syndromes with profound clinical and biologic heterogeneity.

Mesenchymal stem cell therapy on top of triple therapy with remdesivir, dexamethasone, and tocilizumab improves PaO2/FiO2 in severe COVID-19 pneumonia

Background

Despite patients with severe coronavirus disease (COVID-19) receiving standard triple therapy, including steroids, antiviral agents, and anticytokine therapy, health condition of certain patients continue to deteriorate. In Taiwan, the COVID-19 mortality has been high since the emergence of previous variants of this disease (such as alpha, beta, or delta). We aimed to evaluate whether adjunctive infusion of human umbilical cord mesenchymal stem cells (MSCs) (hUC-MSCs) on top of dexamethasone, remdesivir, and tocilizumab improves pulmonary oxygenation and suppresses inflammatory cytokines in patients with severe COVID-19.

Methods

Hospitalized patients with severe or critical COVID-19 pneumonia under standard triple therapy were separated into adjuvant hUC-MSC and non-hUC-MSC groups to compare the changes in the arterial partial pressure of oxygen (PaO₂)/fraction of inspired oxygen (FiO₂) ratio and biological variables.

Results

Four out of eight patients with severe or critical COVID-19 received either one (n = 2) or two (n = 2) doses of intravenous infusions of hUC-MSCs using a uniform cell dose of 1.0 × 10⁸. Both high-sensitivity C-reactive protein (hs-CRP) level and monocyte distribution width (MDW) were significantly reduced, with a reduction in the levels of interleukin (IL)-6, IL-13, IL-12p70 and vascular endothelial growth factor following hUC-MSC transplantation. The PaO₂/FiO₂ ratio increased from 83.68 (64.34–126.75) to 227.50 (185.25–237.50) and then 349.56 (293.03–367.92) within 7 days after hUC-MSC infusion (P < 0.001), while the change of PaO₂/FiO₂ ratio was insignificant in non-hUC-MSC patients (admission day: 165.00 [102.50–237.61]; day 3: 100.00 [72.00–232.68]; day 7: 250.00 [71.00–251.43], P = 0.923).

Conclusion

Transplantation of hUC-MSCs as adjunctive therapy improves pulmonary oxygenation in patients with severe or critical COVID-19. The beneficial effects of hUC-MSCs were presumably mediated by the mitigation of inflammatory cytokines, characterized by the reduction in both hs-CRP and MDW.

Failed clinical trials on COVID-19 acute respiratory distress syndrome in hospitalized patients: common oversights and streamlining the development of clinically effective therapeutics

INTRODUCTION

The coronavirus disease 2019 (COVID-19) pandemic has put a strain on global healthcare systems. Despite admirable efforts to develop rapidly new pharmacotherapies, supportive treatments remain the standard of care. Multiple clinical trials have failed due to design issues, biased patient enrollment, small sample sizes, inadequate control groups, and lack of long-term outcomes monitoring.

AREAS COVERED

This narrative review depicts the current situation around failed and success COVID-19 clinical trials and recommendations in hospitalized patients with COVID-19, oversights and streamlining of clinically effective therapeutics. PubMed, EBSCO, Cochrane Library, and WHO and NIH guidelines were searched for relevant literature up to 5 August 2022.

EXPERT OPINION

The WHO, NIH, and IDSA have issued recommendations to better clarify which drugs should be used during the different phases of the disease. Given the biases and high heterogeneity of published studies, interpretation of the current literature is difficult. Future clinical trials should be designed to standardize clinical approaches, with appropriate organization, patient selection, addition of control groups, and careful identification of disease phase to reduce heterogeneity and bias and should rely on the integration of scientific societies to promote a consensus on interpretation of the data and recommendations for optimal COVID-19 therapies.

Treatment for acute respiratory distress syndrome in adults: A narrative review of phase 2 and 3 trials

INTRODUCTION

Ventilatory management and general supportive care of acute respiratory distress syndrome (ARDS) in the adult population have led to significant clinical improvements, but morbidity and mortality remain high. Pharmacologic strategies acting on the coagulation cascade, inflammation, oxidative stress, and endothelial cell injury have been targeted in the last decade for patients with ARDS, but only a few of these have shown potential benefits with a meaningful clinical response and improved patient outcomes. The lack of availability of specific pharmacologic treatments for ARDS can be attributed to its complex pathophysiology, different risk factors, huge heterogeneity, and difficult classification into specific biological phenotypes and genotypes.

AREAS COVERED

In this narrative review, we briefly discuss the relevance and current advances in pharmacologic treatments for ARDS in adults and the need for the development of new pharmacological strategies.

EXPERT OPINION

Identification of ARDS phenotypes, risk factors, heterogeneity, and pathophysiology may help to design clinical trials personalized according to ARDS-specific features, thus hopefully decreasing the rate of failed clinical pharmacologic trials. This concept is still under clinical investigation and needs further development.

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.

The Impact of Sample Size Misestimations on the Interpretation of ARDS Trials: Systematic Review and Meta-analysis

BACKGROUND

Indeterminate randomized controlled trials (RCTs) in ARDS may arise from sample size misspecification, leading to abandonment of efficacious therapies.

RESEARCH QUESTIONS

If evidence exists for sample size misspecification in ARDS RCTs, has this led to rejection of potentially beneficial therapies? Does evidence exist for prognostic enrichment in RCTs using mortality as a primary outcome?

STUDY DESIGN AND METHODS

We identified 150 ARDS RCTs commencing recruitment after the 1994 American European Consensus Conference ARDS definition and published before October 31, 2020. We examined predicted-observed sample size, predicted-observed control event rate (CER), predicted-observed average treatment effect (ATE), and the relationship between observed CER and observed ATE for RCTs with mortality and nonmortality primary outcome measures. To quantify the strength of evidence, we used Bayesian-averaged meta-analysis, trial sequential analysis, and Bayes factors.

RESULTS

Only 84 of 150 RCTs (56.0%) reported sample size estimations. In RCTs with mortality as the primary outcome, CER was overestimated in 16 of 28 RCTs (57.1%). To achieve predicted ATE, interventions needed to prevent 40.8% of all deaths, compared with the original prediction of 29.3%. Absolute reduction in mortality ≥ 10% was observed in 5 of 28 RCTs (17.9%), but predicted in 21 of 28 RCTs (75%). For RCTs with mortality as the primary outcome, no association was found between observed CER and observed ATE (pooled OR: β = -0.04; 95% credible interval, -0.18 to 0.09). We identified three interventions that are not currently standard of care with a Bayesian-averaged effect size of > 0.20 and moderate strength of existing evidence: corticosteroids, airway pressure release ventilation, and noninvasive ventilation.

INTERPRETATION

Reporting of sample size estimations was inconsistent in ARDS RCTs, and misspecification of CER and ATE was common. Prognostic enrichment strategies in ARDS RCTs based on all-cause mortality are unlikely to be successful. Bayesian methods can be used to prioritize interventions for future effectiveness RCTs.

Vaping and Lung Inflammation and Injury

The use of electronic (e)-cigarettes was initially considered a beneficial solution to conventional cigarette smoking cessation. However, paradoxically, e-cigarette use is rapidly growing among nonsmokers, including youth and young adults. In 2019, this rapid growth resulted in an epidemic of hospitalizations and deaths of e-cigarette users (vapers) due to acute lung injury; this novel disease was termed e-cigarette or vaping use-associated lung injury (EVALI). Pathophysiologic mechanisms of EVALI likely involve cytotoxicity and neutrophilic inflammation caused by inhaled chemicals, but further details remain unknown. The undiscovered mechanisms of EVALI are a barrier to identifying biomarkers and developing therapeutics. Furthermore, adverse effects of e-cigarette use have been linked to chronic lung diseases and systemic effects on multiple organs. In this comprehensive review, we discuss the diverse spectrum of vaping exposures, epidemiological and clinical reports, and experimental findings to provide a better understanding of EVALI and the adverse health effects of chronic e-cigarette exposure.

Update on the Features and Measurements of Experimental Acute Lung Injury in Animals: An Official American Thoracic Society Workshop Report

Advancements in methods, technology, and our understanding of the pathobiology of lung injury have created the need to update the definition of experimental acute lung injury (ALI). We queried 50 participants with expertise in ALI and acute respiratory distress syndrome using a Delphi method composed of a series of electronic surveys and a virtual workshop. We propose that ALI presents as a "multidimensional entity" characterized by four "domains" that reflect the key pathophysiologic features and underlying biology of human acute respiratory distress syndrome. These domains are 1) histological evidence of tissue injury, 2) alteration of the alveolar-capillary barrier, 3) presence of an inflammatory response, and 4) physiologic dysfunction. For each domain, we present "relevant measurements," defined as those proposed by at least 30% of respondents. We propose that experimental ALI encompasses a continuum of models ranging from those focusing on gaining specific mechanistic insights to those primarily concerned with preclinical testing of novel therapeutics or interventions. We suggest that mechanistic studies may justifiably focus on a single domain of lung injury, but models must document alterations of at least three of the four domains to qualify as "experimental ALI." Finally, we propose that a time criterion defining "acute" in ALI remains relevant, but the actual time may vary based on the specific model and the aspect of injury being modeled. The continuum concept of ALI increases the flexibility and applicability of the definition to multiple models while increasing the likelihood of translating preclinical findings to critically ill patients.

Pulmonary surfactant as a versatile biomaterial to fight COVID-19

The COVID-19 pandemic has wielded an enormous pressure on global health care systems, economics and politics. Ongoing vaccination campaigns effectively attenuate viral spreading, leading to a reduction of infected individuals, hospitalizations and mortality. Nevertheless, the development of safe and effective vaccines as well as their global deployment is time-consuming and challenging. In addition, such preventive measures have no effect on already infected individuals and can show reduced efficacy against SARS-CoV-2 variants that escape vaccine-induced host immune responses. Therefore, it is crucial to continue the development of specific COVID-19 targeting therapeutics, including small molecular drugs, antibodies and nucleic acids. However, despite clear advantages of local drug delivery to the lung, inhalation therapy of such antivirals remains difficult. This review aims to highlight the potential of pulmonary surfactant (PS) in the treatment of COVID-19. Since SARS-CoV-2 infection can progress to COVID-19-related acute respiratory distress syndrome (CARDS), which is associated with PS deficiency and inflammation, replacement therapy with exogenous surfactant can be considered to counter lung dysfunction. In addition, due to its surface-active properties and membrane-interacting potential, PS can be repurposed to enhance drug spreading along the respiratory epithelium and to promote intracellular drug delivery. By merging these beneficial features, PS can be regarded as a versatile biomaterial to combat respiratory infections, in particular COVID-19.

Spontaneous Versus Controlled Mechanical Ventilation in Patients with Acute Respiratory Distress Syndrome

Purpose of Review

To review clinical evidence on whether or not to allow mechanically ventilated patients with acute respiratory distress syndrome (ARDS) to breathe spontaneously.

Recent Findings

Observational data (LUNG SAFE study) indicate that mechanical ventilation allowing for spontaneous breathing (SB) is associated with more ventilator-free days and a shorter stay in the intensive care unit without any effect on hospital mortality. A paediatric trial, comparing airway pressure release ventilation (APRV) and low-tidal volume ventilation, showed an increase in mortality in the APRV group. Conversely, in an unpublished trial comparing SB and controlled ventilation (NCT01862016), the authors concluded that SB is feasible but did not improve outcomes in ARDS patients.

Summary

A paucity of clinical trial data continues to prevent firm guidance on if or when to allow SB during mechanical ventilation in patients with ARDS. No published large randomised controlled trial exists to inform practice about the benefits and harms of either mode.

Precision medicine in acute respiratory distress syndrome: workshop report and recommendations for future research

Acute respiratory distress syndrome (ARDS) is a devastating critical illness that can be triggered by a wide range of insults and remains associated with a high mortality of around 40%. The search for targeted treatment for ARDS has been disappointing, possibly due to the enormous heterogeneity within the syndrome. In this perspective from the European Respiratory Society research seminar on "Precision medicine in ARDS", we will summarise the current evidence for heterogeneity, explore the evidence in favour of precision medicine and provide a roadmap for further research in ARDS. There is evident variation in the presentation of ARDS on three distinct levels: 1) aetiological; 2) physiological and 3) biological, which leads us to the conclusion that there is no typical ARDS. The lack of a common presentation implies that intervention studies in patients with ARDS need to be phenotype aware and apply a precision medicine approach in order to avoid the lack of success in therapeutic trials that we faced in recent decades. Deeper phenotyping and integrative analysis of the sources of variation might result in identification of additional treatable traits that represent specific pathobiological mechanisms, or so-called endotypes.

NAVA and PAV+ for lung and diaphragm protection

PURPOSE OF REVIEW

Complications of mechanical ventilation, such as ventilator-induced lung injury (VILI) and ventilator-induced diaphragmatic dysfunction (VIDD), adversely affect the outcome of critically ill patients. Although mostly studied during control ventilation, it is increasingly appreciated that VILI and VIDD also occur during assisted ventilation. Hence, current research focuses on identifying ways to monitor and deliver protective ventilation in assisted modes. This review describes the operating principles of proportional modes of assist, their implications for lung and diaphragm protective ventilation, and the supporting clinical data.

RECENT FINDINGS

Proportional modes of assist, proportional assist ventilation, PAV, and neurally adjusted ventilatory assist, NAVA, deliver a pressure assist that is proportional to the patient's effort, enabling ventilation to be better controlled by the patient's brain. This control underlies the potential of proportional modes to avoid over-assist and under-assist, improve patient--ventilator interaction, and provide protective ventilation. Indeed, in clinical studies, proportional modes have been associated with reduced asynchronies, enhanced diaphragmatic recovery, and limitation of excessive tidal volume. Additionally, proportional modes facilitate better monitoring of the delivery of protective assisted ventilation.

SUMMARY

Physiological rationale and clinical data suggest a potential role for proportional modes of assist in providing and monitoring lung and diaphragm protective ventilation.

Plasma Insulin-like Growth Factor Binding Protein 7 Contributes Causally to ARDS 28-Day Mortality: Evidence From Multistage Mendelian Randomization

BACKGROUND

ARDS is a devastating syndrome with heterogeneous subtypes, but few causal biomarkers have been identified.

RESEARCH QUESTION

Would multistage Mendelian randomization identify new causal protein biomarkers for ARDS 28-day mortality?

STUDY DESIGN AND METHODS

Three hundred moderate to severe ARDS patients were selected randomly from the Molecular Epidemiology of ARDS cohort for proteomics analysis. Orthogonal projections to latent structures discriminant analysis was applied to detect the association between proteins and ARDS 28-day mortality. Candidate proteins were analyzed using generalized summary data-based Mendelian randomization (GSMR). Protein quantitative trait summary statistics were retrieved from the Efficiency and safety of varying the frequency of whole blood donation (INTERVAL) study (n = 2,504), and a genome-wide association study for ARDS was conducted from the Identification of SNPs Predisposing to Altered Acute Lung Injury Risk (iSPAAR) consortium study (n = 534). Causal mediation analysis detected the role of platelet count in mediating the effect of protein on ARDS prognosis.

RESULTS

Plasma insulin-like growth factor binding protein 7 (IGFBP7) moderately increased ARDS 28-day mortality (OR, 1.11; 95% CI, 1.04-1.19; P = .002) per log2 increase. GSMR analysis coupled with four other Mendelian randomization methods revealed IGFBP7 as a causal biomarker for ARDS 28-day mortality (OR, 2.61; 95% CI, 1.33-5.13; P = .005). Causal mediation analysis indicated that the association between IGFBP7 and ARDS 28-day mortality is mediated by platelet count (OR, 1.03; 95% CI, 1.02-1.04; P = .01).

INTERPRETATION

We identified plasma IGFBP7 as a novel causal protein involved in the pathogenesis of ARDS 28-day mortality and platelet function in ARDS, a topic for further experimental and clinical investigation.

Time Course of Evolving Ventilator-Induced Lung Injury: The "Shrinking Baby Lung"

OBJECTIVES

To examine the potentially modifiable drivers that injure and heal the "baby lung" of acute respiratory distress syndrome and describe a rational clinical approach to favor benefit.

DATA SOURCES

Published experimental studies and clinical papers that address varied aspects of ventilator-induced lung injury pathogenesis and its consequences.

STUDY SELECTION

Published information relevant to the novel hypothesis of progressive lung vulnerability and to the biophysical responses of lung injury and repair.

DATA EXTRACTION

None.

DATA SYNTHESIS

In acute respiratory distress syndrome, the reduced size and capacity for gas exchange of the functioning "baby lung" imply loss of ventilatory capability that dwindles in proportion to severity of lung injury. Concentrating the entire ventilation workload and increasing perfusion to these already overtaxed units accentuates their potential for progressive injury. Unlike static airspace pressures, which, in theory, apply universally to aerated structures of all dimensions, the components of tidal inflation that relate to power (which include frequency and flow) progressively intensify their tissue-stressing effects on parenchyma and microvasculature as the ventilated compartment shrinks further, especially during the first phase of the evolving injury. This "ventilator-induced lung injury vortex" of the shrinking baby lung is opposed by reactive, adaptive, and reparative processes. In this context, relatively little attention has been paid to the evolving interactions between lung injury and response and to the timing of interventions that worsen, limit or reverse a potentially accelerating ventilator-induced lung injury process. Although universal and modifiable drivers hold the potential to progressively injure the functional lung units of acute respiratory distress syndrome in a positive feedback cycle, measures can be taken to interrupt that process and encourage growth and healing of the "baby lung" of severe acute respiratory distress syndrome.

Pulmonary and systemic hemodynamics are associated with myocardial injury in the acute respiratory distress syndrome

Background

Whether right and left heart hemodynamics are associated with myocardial injury in the acute respiratory distress syndrome (ARDS) is not known.

Methods

We performed a retrospective cohort study of subjects who had right heart catheterization within the ALVEOLI trial and Fluid and Catheter Treatment Trial. Myocardial injury was assessed using a highly sensitive troponin assay (hsTn; Abbot ARCHITECT). Hemodynamic variables included right atrial pressure, pulmonary artery wedge pressure, cardiac index and stroke volume, pulmonary vascular resistance, pulmonary arterial compliance, and pulmonary effective arterial elastance. We performed linear, logistic, and Cox regression to determine the association of hemodynamic variables with myocardial injury and to determine if hemodynamics mediated the association between myocardial injury and death.

Results

Among 252 ARDS patients, median day 0 troponin was 65.4 (13.8–397.8) ng/L. Lower cardiac index (β −0.23 SE 0.10; P < 0.001) and stroke volume (β −0.26 SE 0.005; P < 0.001), higher pulmonary vascular resistance (β 0.22 SE 0.11; P < 0.001), lower pulmonary arterial compliance (β −0.24 SE 0.06; P < 0.001), and higher arterial elastance (β 0.27 SE 0.43; P < 0.001) were associated with greater myocardial injury in univariable and adjusted models. Changes in stroke volume, cardiac index, pulmonary arterial compliance, pulmonary vascular resistance, and arterial elastance were all associated with progressive myocardial injury over three days. hsTn levels were associated with mortality; however, the association was attenuated after adjustment for each of stroke volume, pulmonary vascular resistance, pulmonary arterial compliance, and arterial elastance.

Conclusion

Pulmonary vascular hemodynamics are associated with myocardial injury in ARDS, while filling pressures are not. Pulmonary vascular disease may represent a treatable contributor to myocardial injury in ARDS.

Spontaneous versus controlled mechanical ventilation in patients with acute respiratory distress syndrome - Protocol for a scoping review

BACKGROUND

In caring for mechanically ventilated adults with acute respiratory distress syndrome (ARDS), clinicians are faced with an uncertain choice between controlled or spontaneous breathing modes. Observational data indicate considerable practice variation which may be driven by differences in sedation and mobilisation practices. The benefits and harms of either strategy are largely unknown.

METHODS

A scoping review will be prepared according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) extension for scoping reviews. We will review the clinical literature on controlled vs spontaneous breathing in mechanically ventilated patients with ARDS of any severity. Studies reporting on qualitative and/or quantitative data from any world region will be considered. For inclusion, studies must include data on mechanically ventilated patients with ARDS who are allowed spontaneous (triggered ventilation). Searches will be conducted in four electronic databases without any limitation on publication date and language. We will assess the quality of evidence according to the Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology, where appropriate.

CONCLUSION

We will perform a scoping review of the clinical literature on controlled vs spontaneously breathing in mechanically ventilated patients who fulfil ARDS criteria (including acute lung injury). This is to elucidate if a pragmatic clinical trial comparing controlled and spontaneous mechanical ventilation is warranted and will allow us to formulate relevant research questions.

Static and Dynamic Contributors to Ventilator-induced Lung Injury in Clinical Practice. Pressure, Energy, and Power

Ventilation is inherently a dynamic process. The present-day clinical practice of concentrating on the static inflation characteristics of the individual tidal cycle (plateau pressure, positive end-expiratory pressure, and their difference [driving pressure, the ratio of Vt to compliance]) does not take into account key factors shown experimentally to influence ventilator-induced lung injury (VILI). These include rate of airway pressure change (influenced by flow amplitude, inspiratory time fraction, and inspiratory inflation contour) and cycling frequency. Energy must be expended to cause injury, and the product of applied stress and resulting strain determines the energy delivered to the lungs per breathing cycle. Understanding the principles of VILI energetics may provide valuable insights and guidance to intensivists for safer clinical practice. In this interpretive review, we highlight that the injuring potential of the inflation pattern depends upon tissue vulnerability, the number of intolerable high-energy cycles applied in unit time (mechanical power), and the duration of that exposure. Yet, as attractive as this energy/power hypothesis for encapsulating the drivers of VILI may be for clinical applications, we acknowledge that even these all-inclusive and measurable ergonomic parameters (energy per cycle and power) are still too bluntly defined to pinpoint the precise biophysical link between ventilation strategy and tissue injury.

Acute respiratory distress syndrome subphenotypes and therapy responsive traits among preclinical models: protocol for a systematic review and meta-analysis

BACKGROUND

Subphenotypes were recently reported within clinical acute respiratory distress syndrome (ARDS), with distinct outcomes and therapeutic responses. Experimental models have long been used to mimic features of ARDS pathophysiology, but the presence of distinct subphenotypes among preclinical ARDS remains unknown. This review will investigate whether: 1) subphenotypes can be identified among preclinical ARDS models; 2) such subphenotypes can identify some responsive traits.

METHODS

We will include comparative preclinical (in vivo and ex vivo) ARDS studies published between 2009 and 2019 in which pre-specified therapies were assessed (interleukin (IL)-10, IL-2, stem cells, beta-agonists, corticosteroids, fibroblast growth factors, modulators of the receptor for advanced glycation end-products pathway, anticoagulants, and halogenated agents) and outcomes compared to a control condition. The primary outcome will be a composite of the four key features of preclinical ARDS as per the American Thoracic Society consensus conference (histologic evidence of lung injury, altered alveolar-capillary barrier, lung inflammatory response, and physiological dysfunction). Secondary outcomes will include the single components of the primary composite outcome, net alveolar fluid clearance, and death. MEDLINE, Embase, and Cochrane databases will be searched electronically and data from eligible studies will be extracted, pooled, and analyzed using random-effects models. Individual study reporting will be assessed according to the Animal Research: Reporting of In Vivo Experiments guidelines. Meta-regressions will be performed to identify subphenotypes prior to comparing outcomes across subphenotypes and treatment effects.

DISCUSSION

This study will inform on the presence and underlying pathophysiological features of subphenotypes among preclinical models of ARDS and should help to determine whether sufficient evidence exists to perform preclinical trials of subphenotype-targeted therapies, prior to potential clinical translation.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO (ID: CRD42019157236).

Fraxin Alleviates LPS-Induced ARDS by Downregulating Inflammatory Responses and Oxidative Damages and Reducing Pulmonary Vascular Permeability

Acute respiratory distress syndrome (ARDS) is a severe acute disease that threatens human health, and few drugs that can effectively treat this disease are available. Fraxin, one of the main active ingredients of Cortex Fraxini, a Chinese herbal medicine, has presented various pharmacological and biological activities. However, the effects of fraxin on ARDS have yet to be reported. In the present study, the protective effect of fraxin in lipopolysaccharide (LPS)-induced ARDS in a mouse model was analyzed. Results from the hematoxylin and eosin staining showed that fraxin might alleviate pathological changes in the lung tissues of mice with ARDS. ELISA and Western blot results revealed that fraxin might inhibit the production of inflammatory factors, namely, IL-6, TNF-α, and IL-1β, and the activation of NF-κB and MAPK signaling pathways in the lungs. Thus, the inflammatory responses were reduced. Fraxin might inhibit the increase in reactive oxygen species (ROS) and malondialdehyde (MDA), a product of lipid peroxidation in lung tissues. Fraxin might increase the superoxide dismutase (SOD) activity to avoid oxidative damage. Vascular permeability was also assessed through Evans blue dye tissue extravasation and fluorescein isothiocyanate-labeled albumin (FITC-albumin) leakage. Fraxin might inhibit the increase in pulmonary vascular permeability and relieve pulmonary edema. Fraxin was also related to the inhibition of the increase in matrix metalloproteinase-9, which is a glycocalyx-degrading enzyme, and the relief of damages to the endothelial glycocalyx. Thus, fraxin elicited protective effects on mice with LPS-induced ARDS and might be used as a drug to cure ARDS induced by Gram-negative bacterial infection.

An NMR based panorama of the heterogeneous biology of acute respiratory distress syndrome (ARDS) from the standpoint of metabolic biomarkers

Acute respiratory distress syndrome (ARDS), manifested by intricate etiology and pathophysiology, demands careful clinical surveillance due to its high mortality and imminent life support measures. NMR based metabolomics provides an approach for ARDS which culminates from a wide spectrum of illness thereby confounding early manifestation and prognosis predictors. ¹ H NMR with its manifold applications in critical disease settings can unravel the biomarker of ARDS thus holding potent implications by providing surrogate endpoints of clinical utility. NMR metabolomics which is the current apogee platform of omics trilogy is contributing towards the possible panacea of ARDS by subsequent validation of biomarker credential on larger datasets. In the present review, the physiological derangements that jeopardize the whole metabolic functioning in ARDS are exploited and the biomarkers involved in progression are addressed and substantiated. The following sections of the review also outline the clinical spectrum of ARDS from the standpoint of NMR based metabolomics which is an emerging element of systems biology. ARDS is the main premise of intensivists textbook, which has been thoroughly reviewed along with its incidence, progressive stages of severity, new proposed diagnostic definition, and the preventive measures and the current pitfalls of clinical management. The advent of new therapies, the need for biomarkers, the methodology and the contemporary promising approaches needed to improve survival and address heterogeneity have also been evaluated. The review has been stepwise illustrated with potent biometrics employed to selectively pool out differential metabolites as diagnostic markers and outcome predictors. The following sections have been drafted with an objective to better understand ARDS mechanisms with predictive and precise biomarkers detected so far on the basis of underlying physiological parameters having close proximity to diseased phenotype. The aim of this review is to stimulate interest in conducting more studies to help resolve the complex heterogeneity of ARDS with biomarkers of clinical utility and relevance.

Microphysiological systems modeling acute respiratory distress syndrome that capture mechanical force-induced injury-inflammation-repair

Complex in vitro models of the tissue microenvironment, termed microphysiological systems, have enormous potential to transform the process of discovering drugs and disease mechanisms. Such a paradigm shift is urgently needed in acute respiratory distress syndrome (ARDS), an acute lung condition with no successful therapies and a 40% mortality rate. Here, we consider how microphysiological systems could improve understanding of biological mechanisms driving ARDS and ultimately improve the success of therapies in clinical trials. We first discuss how microphysiological systems could explain the biological mechanisms underlying the segregation of ARDS patients into two clinically distinct phenotypes. Then, we contend that ARDS-mimetic microphysiological systems should recapitulate three critical aspects of the distal airway microenvironment, namely, mechanical force, inflammation, and fibrosis, and we review models that incorporate each of these aspects. Finally, we recognize the substantial challenges associated with combining inflammation, fibrosis, and/or mechanical force in microphysiological systems. Nevertheless, complex in vitro models are a novel paradigm for studying ARDS, and they could ultimately improve patient care.

Genomic and Genetic Approaches to Deciphering Acute Respiratory Distress Syndrome Risk and Mortality

Significance: Acute respiratory distress syndrome (ARDS) is a severe, highly heterogeneous critical illness with staggering mortality that is influenced by environmental factors, such as mechanical ventilation, and genetic factors. Significant unmet needs in ARDS are addressing the paucity of validated predictive biomarkers for ARDS risk and susceptibility that hamper the conduct of successful clinical trials in ARDS and the complete absence of novel disease-modifying therapeutic strategies. Recent Advances: The current ARDS definition relies on clinical characteristics that fail to capture the diversity of disease pathology, severity, and mortality risk. We undertook a comprehensive survey of the available ARDS literature to identify genes and genetic variants (candidate gene and limited genome-wide association study approaches) implicated in susceptibility to developing ARDS in hopes of uncovering novel biomarkers for ARDS risk and mortality and potentially novel therapeutic targets in ARDS. We further attempted to address the well-known health disparities that exist in susceptibility to and mortality from ARDS. Critical Issues: Bioinformatic analyses identified 201 ARDS candidate genes with pathway analysis indicating a strong predominance in key evolutionarily conserved inflammatory pathways, including reactive oxygen species, innate immunity-related inflammation, and endothelial vascular signaling pathways. Future Directions: Future studies employing a system biology approach that combines clinical characteristics, genomics, transcriptomics, and proteomics may allow for a better definition of biologically relevant pathways and genotype-phenotype connections and result in improved strategies for the sub-phenotyping of diverse ARDS patients via molecular signatures. These efforts should facilitate the potential for successful clinical trials in ARDS and yield a better fundamental understanding of ARDS pathobiology.

Imaging the Injured Lung: Mechanisms of Action and Clinical Use

Acute respiratory distress syndrome (ARDS) consists of acute hypoxemic respiratory failure characterized by massive and heterogeneously distributed loss of lung aeration caused by diffuse inflammation and edema present in interstitial and alveolar spaces. It is defined by consensus criteria, which include diffuse infiltrates on chest imaging-either plain radiography or computed tomography. This review will summarize how imaging sciences can inform modern respiratory management of ARDS and continue to increase the understanding of the acutely injured lung. This review also describes newer imaging methodologies that are likely to inform future clinical decision-making and potentially improve outcome. For each imaging modality, this review systematically describes the underlying principles, technology involved, measurements obtained, insights gained by the technique, emerging approaches, limitations, and future developments. Finally, integrated approaches are considered whereby multimodal imaging may impact management of ARDS.

Endothelial Hypoxia-Inducible Factor-1α Is Required for Vascular Repair and Resolution of Inflammatory Lung Injury through Forkhead Box Protein M1

Endothelial barrier dysfunction is a central factor in the pathogenesis of persistent lung inflammation and protein-rich edema formation, the hallmarks of acute respiratory distress syndrome. However, little is known about the molecular mechanisms that are responsible for vascular repair and resolution of inflammatory injury after sepsis challenge. Herein, we show that hypoxia-inducible factor-1α (HIF-1α), expressed in endothelial cells (ECs), is the critical transcriptional factor mediating vascular repair and resolution of inflammatory lung injury. After sepsis challenge, HIF-1α but not HIF-2α expression was rapidly induced in lung vascular ECs, and mice with EC-restricted disruption of Hif1α (Hif1af/f/Tie2Cre+) exhibited defective vascular repair, persistent inflammation, and increased mortality in contrast with the wild-type littermates after polymicrobial sepsis or endotoxemia challenge. Hif1af/f/Tie2Cre+ lungs exhibited marked decrease of EC proliferation during recovery after sepsis challenge, which was associated with inhibited expression of forkhead box protein M1 (Foxm1), a reparative transcription factor. Therapeutic restoration of endothelial Foxm1 expression, via liposomal delivery of Foxm1 plasmid DNA to Hif1af/f/Tie2Cre+ mice, resulted in reactivation of the vascular repair program and improved survival. Together, our studies, for the first time, delineate the essential role of endothelial HIF-1α in driving the vascular repair program. Thus, therapeutic activation of HIF-1α-dependent vascular repair may represent a novel and effective therapy to treat inflammatory vascular diseases, such as sepsis and acute respiratory distress syndrome.

Preclinical septic shock research: why we need an animal ICU

Animal experiments are widely used in preclinical medical research with the goal of disease modeling and exploration of novel therapeutic approaches. In the context of sepsis and septic shock, the translation into clinical practice has been disappointing. Classical animal models of septic shock usually involve one-sex-one-age animal models, mostly in mice or rats, contrasting with the heterogeneous population of septic shock patients. Many other factors limit the reliability of preclinical models and may contribute to preclinical research failure in critical care, including the host specificity of several pathogens, the fact that laboratory animals are raised in pathogen-free facilities and that organ support techniques are either absent or minimal. Advanced animal models have been developed with the aim of improving the clinical translatability of experimental findings. So-called animal ICUs refer to the preclinical investigation of adult or even aged animals of either sex, using—in case of rats and mice—miniaturized equipment allowing for reproducing an ICU environment at a small animal scale and integrating chronic comorbidities to more closely reflect the clinical conditions studied. Strength and limitations of preclinical animal models designed to decipher the mechanisms involved in septic cardiomyopathy are discussed. This article reviews the current status and the challenges of setting up an animal ICU.

Pulmonary Endothelial Mechanical Sensing and Signaling, a Story of Focal Adhesions and Integrins in Ventilator Induced Lung Injury

Patients with critical illness such as acute lung injury often undergo mechanical ventilation in the intensive care unit. Though lifesaving in many instances, mechanical ventilation often results in ventilator induced lung injury (VILI), characterized by overdistension of lung tissue leading to release of edemagenic agents, which further damage the lung and contribute to the mortality and progression of pulmonary inflammation. The endothelium is particularly sensitive, as VILI associated mechanical stress results in endothelial cytoskeletal rearrangement, stress fiber formation, and integrity loss. At the heart of these changes are integrin tethered focal adhesions (FAs) which participate in mechanosensing, structure, and signaling. Here, we present the known roles of FA proteins including c-Src, talin, FAK, paxillin, vinculin, and integrins in the sensing and response to cyclic stretch and VILI associated stress. Attention is given to how stretch is propagated from the extracellular matrix through integrins to talin and other FA proteins, as well as signaling cascades that include FA proteins, leading to stress fiber formation and other cellular responses. This unifying picture of FAs aids our understanding in an effort to prevent and treat VILI.

Synthetic surfactants with SP-B and SP-C analogues to enable worldwide treatment of neonatal respiratory distress syndrome and other lung diseases

Treatment of neonatal respiratory distress syndrome (RDS) using animal-derived lung surfactant preparations has reduced the mortality of handling premature infants with RDS to a 50th of that in the 1960s. The supply of animal-derived lung surfactants is limited and only a part of the preterm babies is treated. Thus, there is a need to develop well-defined synthetic replicas based on key components of natural surfactant. A synthetic product that equals natural-derived surfactants would enable cost-efficient production and could also facilitate the development of the treatments of other lung diseases than neonatal RDS. Recently the first synthetic surfactant that contains analogues of the two hydrophobic surfactant proteins B (SP-B) and SP-C entered clinical trials for the treatment of neonatal RDS. The development of functional synthetic analogues of SP-B and SP-C, however, is considerably more challenging than anticipated 30 years ago when the first structural information of the native proteins became available. For SP-B, a complex three-dimensional dimeric structure stabilized by several disulphides has necessitated the design of miniaturized analogues. The main challenge for SP-C has been the pronounced amyloid aggregation propensity of its transmembrane region. The development of a functional non-aggregating SP-C analogue that can be produced synthetically was achieved by designing the amyloidogenic native sequence so that it spontaneously forms a stable transmembrane α-helix.

Syndecan-2-positive, Bone Marrow-derived Human Mesenchymal Stromal Cells Attenuate Bacterial-induced Acute Lung Injury and Enhance Resolution of Ventilator-induced Lung Injury in Rats

WHAT WE ALREADY KNOW ABOUT THIS TOPIC

WHAT THIS ARTICLE TELLS US THAT IS NEW: BACKGROUND:: Human mesenchymal stromal cells demonstrate promise for acute respiratory distress syndrome, but current studies use highly heterogenous cell populations. We hypothesized that a syndecan 2 (CD362)-expressing human mesenchymal stromal cell subpopulation would attenuate Escherichia coli-induced lung injury and enhance resolution after ventilator-induced lung injury.

METHODS

In vitro studies determined whether CD362 human mesenchymal stromal cells could modulate pulmonary epithelial inflammation, wound healing, and macrophage phagocytosis. Two in vivo rodent studies determined whether CD362 human mesenchymal stromal cells attenuated Escherichia coli-induced lung injury (n = 10/group) and enhanced resolution of ventilation-induced injury (n = 10/group).

RESULTS

CD362 human mesenchymal stromal cells attenuated cytokine-induced epithelial nuclear factor kappa B activation, increased epithelial wound closure, and increased macrophage phagocytosis in vitro. CD362 human mesenchymal stromal cells attenuated Escherichia coli-induced injury in rodents, improving arterial oxygenation (mean ± SD, 83 ± 9 vs. 60 ± 8 mmHg, P < 0.05), improving lung compliance (mean ± SD: 0.66 ± 0.08 vs. 0.53 ± 0.09 ml · cm H2O, P < 0.05), reducing bacterial load (median [interquartile range], 1,895 [100-3,300] vs. 8,195 [4,260-8,690] colony-forming units, P < 0.05), and decreasing structural injury compared with vehicle. CD362 human mesenchymal stromal cells were more effective than CD362 human mesenchymal stromal cells and comparable to heterogenous human mesenchymal stromal cells. CD362 human mesenchymal stromal cells enhanced resolution after ventilator-induced lung injury in rodents, restoring arterial oxygenation (mean ± SD: 113 ± 11 vs. 89 ± 11 mmHg, P < 0.05) and lung static compliance (mean ± SD: 0.74 ± 0.07 vs. 0.45 ± 0.07 ml · cm H2O, P < 0.05), resolving lung inflammation, and restoring histologic structure compared with vehicle. CD362 human mesenchymal stromal cells efficacy was at least comparable to heterogenous human mesenchymal stromal cells.

CONCLUSIONS

A CD362 human mesenchymal stromal cell population decreased Escherichia coli-induced pneumonia severity and enhanced recovery after ventilator-induced lung injury.

Dissipation of energy during the respiratory cycle: conditional importance of ergotrauma to structural lung damage

PURPOSE OF REVIEW

To describe and put into context recent conceptual advances regarding the relationship of energy load and power to ventilator-induced lung injury (VILI).

RECENT FINDINGS

Investigative emphasis regarding VILI has almost exclusively centered on the static characteristics of the individual tidal cycle - tidal volume, plateau pressure, positive end-expiratory pressure, and driving pressure. Although those static characteristics of the tidal cycle are undeniably important, the 'dynamic' characteristics of ventilation must not be ignored. To inflict the nonrupturing damage we identify as VILI, work must be performed and energy expended by high stress cycles applied at rates that exceed the capacity of endogenous repair. Machine power, the pace at which the work performing energy load is applied by the ventilator, has received increasing scrutiny as a candidate for the proximate and integrative cause of VILI.

SUMMARY

Although the unmodified values of machine-delivered energy or power (which are based on airway pressures and tidal volumes) cannot serve unconditionally as a rigid and quantitative guide to ventilator adjustment for lung protection, bedside consideration of the dynamics of ventilation and potential for ergotrauma represents a clear conceptual advance that complements the static parameters of the individual tidal cycle that with few exceptions have held our scientific attention.

Lung injury does not aggravate mechanical ventilation-induced early cerebral inflammation or apoptosis in an animal model

Introduction

The acute respiratory distress syndrome is not only associated with a high mortality, but also goes along with cognitive impairment in survivors. The cause for this cognitive impairment is still not clear. One possible mechanism could be cerebral inflammation as result of a “lung-brain-crosstalk”. Even mechanical ventilation itself can induce cerebral inflammation. We hypothesized, that an acute lung injury aggravates the cerebral inflammation induced by mechanical ventilation itself and leads to neuronal damage.

Methods

After approval of the institutional and state animal care committee 20 pigs were randomized to one of three groups: lung injury by central venous injection of oleic acid (n = 8), lung injury by bronchoalveolar lavage in combination with one hour of injurious ventilation (n = 8) or control (n = 6). Brain tissue of four native animals from a different study served as native group. For six hours all animals were ventilated with a tidal volume of 7 ml kg^-1 and a scheme for positive end-expiratory pressure and inspired oxygen fraction, which was adapted from the ARDS network tables. Afterwards the animals were killed and the brains were harvested for histological (number of neurons and microglia) and molecular biologic (TNFalpha, IL-1beta, and IL-6) examinations.

Results

There was no difference in the number of neurons or microglia cells between the groups. TNFalpha was significantly higher in all groups compared to native (p < 0.05), IL-6 was only increased in the lavage group compared to native (p < 0.05), IL-1beta showed no difference between the groups.

Discussion

With our data we can confirm earlier results, that mechanical ventilation itself seems to trigger cerebral inflammation. This is not aggravated by acute lung injury, at least not within the first 6 hours after onset. Nevertheless, it seems too early to dismiss the idea of lung-injury induced cerebral inflammation, as 6 hours might be just not enough time to see any profound effect.

The Role of Pulmonary and Systemic Immunosenescence in Acute Lung Injury

Acute lung injury (ALI) is associated with increased morbidity and mortality in the elderly (> 65 years), but the knowledge about origin and effects of immunosenescence in ALI is limited. Here, we investigated the immune response at pulmonary, systemic and cellular level in young (2-3 months) and old (18-19 months) C57BL/6J mice to localize and characterize effects of immunosenescence in ALI. ALI was induced by intranasal lipopolysaccharide (LPS) application and the animals were sacrificed 24 or 72 h later. Pulmonary inflammation was investigated by analyzing histopathology, bronchoalveolar lavage fluid (BALF) cytometry and cytokine expression. Systemic serum cytokine expression, spleen lymphocyte populations and the gut microbiome were analyzed, as well as activation of alveolar and bone marrow derived macrophages (BMDM) in vitro. Pulmonary pathology of ALI was more severe in old compared with young mice. Old mice showed significantly more inflammatory cells and pro-inflammatory cyto- or chemokines (TNFα, IL-6, MCP-1, CXCL1, MIP-1α) in the BALF, but a delayed expression of cytokines associated with activation of adaptive immunity and microbial elimination (IL-12 and IFNγ). Alveolar macrophages, but not BMDM, of old mice showed greater activation after in vivo and in vitro stimulation with LPS. No systemic enhanced pro-inflammatory cytokine response was detected in old animals after LPS exposure, but a delayed expression of IL-12 and IFNγ. Furthermore, old mice had less CD8⁺ T-cells and NK cells and more regulatory T-cells in the spleen compared with young mice and a distinct gut microbiome structure. The results of our study show an increased alveolar macrophage activation and pro-inflammatory signaling in the lungs, but not systemically, suggesting a key role of senescent alveolar macrophages in ALI. A decrease in stimulators of adaptive immunity with advancing age might further promote the susceptibility to a worse prognosis in ALI in elderly.

Optimising experimental research in respiratory diseases: an ERS statement

Experimental models are critical for the understanding of lung health and disease and are indispensable for drug development. However, the pathogenetic and clinical relevance of the models is often unclear. Further, the use of animals in biomedical research is controversial from an ethical perspective.The objective of this task force was to issue a statement with research recommendations about lung disease models by facilitating in-depth discussions between respiratory scientists, and to provide an overview of the literature on the available models. Focus was put on their specific benefits and limitations. This will result in more efficient use of resources and greater reduction in the numbers of animals employed, thereby enhancing the ethical standards and translational capacity of experimental research.The task force statement addresses general issues of experimental research (ethics, species, sex, age, ex vivo and in vitro models, gene editing). The statement also includes research recommendations on modelling asthma, chronic obstructive pulmonary disease, pulmonary fibrosis, lung infections, acute lung injury and pulmonary hypertension.The task force stressed the importance of using multiple models to strengthen validity of results, the need to increase the availability of human tissues and the importance of standard operating procedures and data quality.

Alternative and Natural Therapies for Acute Lung Injury and Acute Respiratory Distress Syndrome

Introduction

Acute respiratory distress syndrome (ARDS) is a complex clinical syndrome characterized by acute inflammation, microvascular damage, and increased pulmonary vascular and epithelial permeability, frequently resulting in acute respiratory failure and death. Current best practice for ARDS involves “lung-protective ventilation,” which entails low tidal volumes and limiting the plateau pressures in mechanically ventilated patients. Although considerable progress has been made in understanding the pathogenesis of ARDS, little progress has been made in the development of specific therapies to combat injury and inflammation.

Areas Covered

In recent years, several natural products have been studied in experimental models and have been shown to inhibit multiple inflammatory pathways associated with acute lung injury and ARDS at a molecular level. Because of the pleiotropic effects of these agents, many of them also activate antioxidant pathways through nuclear factor erythroid-related factor 2, thereby targeting multiple pathways. Several of these agents are prescribed for treatment of inflammatory conditions in the Asian subcontinent and have shown to be relatively safe.

Expert Commentary

Here we review natural remedies shown to attenuate lung injury and inflammation in experimental models. Translational human studies in patients with ARDS may facilitate treatment of this devastating disease.