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The understanding of acute respiratory distress syndrome (ARDS) has evolved greatly since it was first described in a 1967 case series, with several subsequent updates to the definition of the syndrome. Basic science advances and clinical trials have provided insight into the mechanisms of lung injury in ARDS and led to reduced mortality through comprehensive critical care interventions. This review summarizes the current understanding of the epidemiology, pathophysiology, and management of ARDS. Key highlights include a recommended new global definition of ARDS and updated guidelines for managing ARDS on a backbone of established interventions such as low tidal volume ventilation, prone positioning, and a conservative fluid strategy. Future priorities for investigation of ARDS are also highlighted., Competing Interests: Competing interests: We have read and understood the BMJ policy on declaration of interests and declare the following interests: LBW and MAM’s institutions receive funding from the National Institutes of Health; MAM’s institution receives funding from the Department of Defense, Roche-Genentech, and Quantum Therapeutics; LBW received funding from Arrowhead, Akebia, Santhera, Global Blood Therapeutics, and Boehringer Ingelheim; she is a stockholder of Virtuoso Surgical, a company that is not related to the topic of this review; MAM received funding from Gilead Pharmaceuticals, Novartis, Johnson and Johnson, Citius Pharmaceuticals, Pliant Therapeutics, Gen1ELifesciences, and Calcimedica., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.)

Biomarkers are an important tool aiding researchers in the study of acute respiratory distress syndrome (ARDS). Mechanisms involving injury to the alveolar-capillary membrane, endothelium and epithelium resulting in lung inflammation and alterations in coagulation pathways have been validated in human trials and have been used to discover promising phenotypes that share similar characteristics and differential treatment responses. The emergence of powerful point-of-care technologies will enable the prospective study of biomarkers for future enrichment trials with the goal of transforming biomarkers into the clinical realm to inform delivery of personalized medicine at the bedside., Competing Interests: Disclosure A A. Zalucky declares no competing interests., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Background: Hypoinflammatory and hyperinflammatory phenotypes have been identified in both Acute Respiratory Distress Syndrome (ARDS) and sepsis. Attributable mortality of ARDS in each phenotype of sepsis is yet to be determined. We aimed to estimate the population attributable fraction of death from ARDS (PAF ARDS ) in hypoinflammatory and hyperinflammatory sepsis, and to determine the primary cause of death within each phenotype., Methods: We studied 1737 patients with sepsis from two prospective cohorts. Patients were previously assigned to the hyperinflammatory or hypoinflammatory phenotype using latent class analysis. The PAF ARDS in patients with sepsis was estimated separately in the hypo and hyperinflammatory phenotypes. Organ dysfunction, severe comorbidities, and withdrawal of life support were abstracted from the medical record in a subset of patients from the EARLI cohort who died (n = 130/179). Primary cause of death was defined as the organ system that most directly contributed to death or withdrawal of life support., Results: The PAF ARDS was 19% (95%CI 10,28%) in hypoinflammatory sepsis and, 14% (95%CI 6,20%) in hyperinflammatory sepsis. Cause of death differed between the two phenotypes (p < 0.001). Respiratory failure was the most common cause of death in hypoinflammatory sepsis, whereas circulatory shock was the most common cause in hyperinflammatory sepsis. Death with severe underlying comorbidities was more frequent in hypoinflammatory sepsis (81% vs. 67%, p = 0.004)., Conclusions: The PAF ARDS is modest in both phenotypes whereas primary cause of death among patients with sepsis differed substantially by phenotype. This study identifies challenges in powering future clinical trials to detect changes in mortality outcomes among patients with sepsis and ARDS., (© 2024. The Author(s).)

Cell-free hemoglobin (CFH) is elevated in the airspace of patients with acute respiratory distress syndrome (ARDS) and is sufficient to cause acute lung injury in a murine model. However, the pathways through which CFH causes lung injury are not well understood. Toll-like receptor 4 (TLR4) is a mediator of inflammation after detection of damage- and pathogen-associated molecular patterns. We hypothesized that TLR4 signaling mediates the proinflammatory effects of CFH in the airspace. After intratracheal CFH, BALBc mice deficient in TLR4 had reduced inflammatory cell influx into the airspace [bronchoalveolar lavage (BAL) cell counts, median TLR4 knockout (KO): 0.8 × 10 4 /mL [IQR 0.4-1.2 × 10 4 /mL], wild-type (WT): 3.0 × 10 4 /mL [2.2-4.0 × 10 4 /mL], P < 0.001] and attenuated lung permeability (BAL protein, TLR4KO: 289 µg/mL [236-320], WT: 488 µg/mL [422-536], P < 0.001). These mice also had attenuated production of interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α in the airspace. C57Bl/6 mice lacking TLR4 on myeloid cells only (LysM.Cre +/- TLR4 fl/fl ) had reduced cytokine production in the airspace after CFH, without attenuation of lung permeability. In vitro studies confirm that WT primary murine alveolar macrophages exposed to CFH (0.01-1 mg/mL) had dose-dependent increases in IL-6, IL-1 β, CXC motif chemokine ligand 1 (CXCL-1), TNF-α, and IL-10 ( P < 0.001). Murine MH-S alveolar-like macrophages show TLR4-dependent expression of IL-1β, IL-6, and CXCL-1 in response to CFH. Primary alveolar macrophages from mice lacking TLR4 adaptor proteins myeloid differentiation primary response 88 (MyD88) or TIR-domain-containing adapter-inducing interferon-β (TRIF) revealed that MyD88KO macrophages had 71-96% reduction in CFH-dependent proinflammatory cytokine production ( P < 0.001), whereas macrophages from TRIFKO mice had variable changes in cytokine responses. These data demonstrate that myeloid TLR4 signaling through MyD88 is a key regulator of airspace inflammation in response to CFH. NEW & NOTEWORTHY Cell-free hemoglobin (CFH) is elevated in the airspace of most patients with acute respiratory distress syndrome and causes severe inflammation. Here, we identify that CFH contributes to macrophage-induced cytokine production via Toll-like receptor 4 (TLR4) and myeloid differentiation primary response 88 (MyD88) signaling. These data increase our knowledge of the mechanisms through which CFH contributes to lung injury and may inform development of targeted therapeutics to attenuate inflammation.

Background: Since publication of the 2012 Berlin definition of acute respiratory distress syndrome (ARDS), several developments have supported the need for an expansion of the definition, including the use of high-flow nasal oxygen, the expansion of the use of pulse oximetry in place of arterial blood gases, the use of ultrasound for chest imaging, and the need for applicability in resource-limited settings. Methods: A consensus conference of 32 critical care ARDS experts was convened, had six virtual meetings (June 2021 to March 2022), and subsequently obtained input from members of several critical care societies. The goal was to develop a definition that would 1 ) identify patients with the currently accepted conceptual framework for ARDS, 2 ) facilitate rapid ARDS diagnosis for clinical care and research, 3 ) be applicable in resource-limited settings, 4 ) be useful for testing specific therapies, and 5 ) be practical for communication to patients and caregivers. Results: The committee made four main recommendations: 1 ) include high-flow nasal oxygen with a minimum flow rate of ⩾30 L/min; 2 ) use Pa O 2 :Fi O 2  ⩽ 300 mm Hg or oxygen saturation as measured by pulse oximetry Sp O 2 :Fi O 2  ⩽ 315 (if oxygen saturation as measured by pulse oximetry is ⩽97%) to identify hypoxemia; 3 ) retain bilateral opacities for imaging criteria but add ultrasound as an imaging modality, especially in resource-limited areas; and 4 ) in resource-limited settings, do not require positive end-expiratory pressure, oxygen flow rate, or specific respiratory support devices. Conclusions: We propose a new global definition of ARDS that builds on the Berlin definition. The recommendations also identify areas for future research, including the need for prospective assessments of the feasibility, reliability, and prognostic validity of the proposed global definition.

Background: In sepsis and acute respiratory distress syndrome (ARDS), heterogeneity has contributed to difficulty identifying effective pharmacotherapies. In ARDS, two molecular phenotypes (hypoinflammatory and hyperinflammatory) have consistently been identified, with divergent outcomes and treatment responses. In this study, we sought to derive molecular phenotypes in critically ill adults with sepsis, determine their overlap with previous ARDS phenotypes, and evaluate whether they respond differently to treatment in completed sepsis trials., Methods: We used clinical data and plasma biomarkers from two prospective sepsis cohorts, the Validating Acute Lung Injury biomarkers for Diagnosis (VALID) study (N=1140) and the Early Assessment of Renal and Lung Injury (EARLI) study (N=818), in latent class analysis (LCA) to identify the optimal number of classes in each cohort independently. We used validated models trained to classify ARDS phenotypes to evaluate concordance of sepsis and ARDS phenotypes. We applied these models retrospectively to the previously published Prospective Recombinant Human Activated Protein C Worldwide Evaluation in Severe Sepsis and Septic Shock (PROWESS-SHOCK) trial and Vasopressin and Septic Shock Trial (VASST) to assign phenotypes and evaluate heterogeneity of treatment effect., Findings: A two-class model best fit both VALID and EARLI (p<0·0001). In VALID, 804 (70·5%) of the 1140 patients were classified as hypoinflammatory and 336 (29·5%) as hyperinflammatory; in EARLI, 530 (64·8%) of 818 were hypoinflammatory and 288 (35·2%) hyperinflammatory. We observed higher plasma pro-inflammatory cytokines, more vasopressor use, more bacteraemia, lower protein C, and higher mortality in the hyperinflammatory than in the hypoinflammatory phenotype (p<0·0001 for all). Classifier models indicated strong concordance between sepsis phenotypes and previously identified ARDS phenotypes (area under the curve 0·87-0·96, depending on the model). Findings were similar excluding participants with both sepsis and ARDS. In PROWESS-SHOCK, 1142 (68·0%) of 1680 patients had the hypoinflammatory phenotype and 538 (32·0%) had the hyperinflammatory phenotype, and response to activated protein C differed by phenotype (p=0·0043). In VASST, phenotype proportions were similar to other cohorts; however, no treatment interaction with the type of vasopressor was observed (p=0·72)., Interpretation: Molecular phenotypes previously identified in ARDS are also identifiable in multiple sepsis cohorts and respond differently to activated protein C. Molecular phenotypes could represent a treatable trait in critical illness beyond the patient's syndromic diagnosis., Funding: US National Institutes of Health., Competing Interests: Declaration of interests PS reports funding from the US National Institutes of Health (NIH) and National Institute of General Medical Sciences; and consulting fees from AstraZeneca. LBW reports funding from NIH, Department of Defense (DoD), Genentech, Boehringer Ingelheim, and CSL Behring; consulting fees from Akebia Therapeutics, Santhera, Global Blood Therapeutics, and Boehringer Ingelheim; and stock options in Virtuoso Surgical. CSC reports funding from NIH; research grants from Roche Genentech and Quantum Leap Healthcare Collaborative; consulting fees from Vasomune Therapeutics, GEn1E Lifesciences, NGM Bio, Cellenkos, and Janssen; and a patent on metagenomic sequencing for sepsis diagnosis (co-recipient). MAM reports funding from Roche Genentech, Quantum Therapeutics, NIH/National Heart, Lung, and Blood Institute/National Institute of Allergy and Infectious Diseases, DoD, and California Institute for Regenerative Medicine; and consulting fees from Johnson & Johnson, Gilead Sciences, and Novartis. MMC reports funding from NIH and DoD; and intellectual property royalties from an issued patent (#11 410 777). JAR reports an investigator-initiated grant from Grifols provided to and administered by the University of British Columbia, Canadian Institutes of Health Research; three grants from the St Paul's Foundation; patents owned by the University of British Columbia related to the use of PCSK9 inhibitor(s) in sepsis and the use of vasopressin in septic shock, and by Ferring Pharmaceuticals for use of selepressin in septic shock; formerly being a founder, Director, and shareholder in Cyon Therapeutics (now closed); being a shareholder in Molecular You; receiving consulting fees in the last 3 years from SIB, Ferring Pharmaceuticals, and Par Pharmaceutical; and having been a funded member of the Data and Safety Monitoring Board of an NIH-sponsored trial of plasma in COVID-19 (PASS-IT-ON). KDL reports grants from NIH: National Institute of Diabetes and Digestive and Kidney Diseases; consulting fees from bioMérieux, UpToDate, SeaStar Medical, AM-Pharma, and Baxter; and stock or stock options in Amgen. All other authors declare no competing interests., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

There are no effective targeted therapies to treat acute respiratory distress syndrome (ARDS). Recently, the commonly used diabetes and obesity medications, glucagon-like peptide-1 (GLP-1) receptor agonists, have been found to have anti-inflammatory properties. We, therefore, hypothesized that liraglutide pretreatment would attenuate murine sepsis-induced acute lung injury (ALI). We used a two-hit model of ALI (sepsis+hyperoxia). Sepsis was induced by intraperitoneal injection of cecal slurry (CS; 2.4 mg/g) or 5% dextrose (control) followed by hyperoxia [HO; fraction of inspired oxygen ([Formula: see text]) = 0.95] or room air (control; [Formula: see text] = 0.21). Mice were pretreated twice daily with subcutaneous injections of liraglutide (0.1 mg/kg) or saline for 3 days before initiation of CS+HO. At 24-h post CS+HO, physiological dysfunction was measured by weight loss, severity of illness score, and survival. Animals were euthanized, and bronchoalveolar lavage (BAL) fluid, lung, and spleen tissues were collected. Bacterial burden was assessed in the lung and spleen. Lung inflammation was assessed by BAL inflammatory cell numbers, cytokine concentrations, lung tissue myeloperoxidase activity, and cytokine expression. Disruption of the alveolar-capillary barrier was measured by lung wet-to-dry weight ratios, BAL protein, and epithelial injury markers (receptor for advanced glycation end products and sulfated glycosaminoglycans). Histological evidence of lung injury was quantified using a five-point score with four parameters: inflammation, edema, septal thickening, and red blood cells (RBCs) in the alveolar space. Compared with saline treatment, liraglutide improved sepsis-induced physiological dysfunction and reduced lung inflammation, alveolar-capillary barrier disruption, and lung injury. GLP-1 receptor activation may hold promise as a novel treatment strategy for sepsis-induced ARDS. Additional studies are needed to better elucidate its mechanism of action. NEW & NOTEWORTHY In this study, pretreatment with liraglutide, a commonly used diabetes medication and glucagon-like peptide-1 (GLP-1) receptor agonist, attenuated sepsis-induced acute lung injury in a two-hit mouse model (sepsis + hyperoxia). Septic mice who received the drug were less sick, lived longer, and displayed reduced lung inflammation, edema, and injury. These therapeutic effects were not dependent on weight loss. GLP-1 receptor activation may hold promise as a new treatment strategy for sepsis-induced acute respiratory distress syndrome.

Purpose: Exposures to ambient air pollutants may prime the lung enhancing risk of acute respiratory distress syndrome (ARDS) in sepsis. Our objective was to determine the association of short-, medium-, and long-term pollutant exposures and ARDS risk in critically ill sepsis patients., Methods: We analyzed a prospective cohort of 1858 critically ill patients with sepsis, and estimated short- (3 days), medium- (6 weeks), and long- (5 years) term exposures to ozone, nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2 ), carbon monoxide (CO), particulate matter < 2.5 μm (PM 2.5 ), and PM < 10 μm (PM 10 ) using weighted averages of daily levels from monitors within 50 km of subjects' residences. Subjects were followed for 6 days for ARDS by the Berlin Criteria. The association between each pollutant and ARDS was determined using multivariable logistic regression adjusting for preselected confounders. In 764 subjects, we measured plasma concentrations of inflammatory proteins at presentation and tested for an association between pollutant exposure and protein concentration via linear regression., Results: ARDS developed in 754 (41%) subjects. Short- and long-term exposures to SO 2 , NO 2 , and PM 2.5 were associated with ARDS risk (SO 2 : odds ratio (OR) for the comparison of the 75-25th long-term exposure percentile 1.43 (95% confidence interval (CI) 1.16, 1.77); p < 0.01; NO 2 : 1.36 (1.06, 1.74); p = 0.04, PM 2.5 : 1.21 (1.04, 1.41); p = 0.03). Long-term exposures to these three pollutants were also associated with plasma interleukin-1 receptor antagonist and soluble tumor necrosis factor receptor-1 concentrations., Conclusion: Short and long-term exposures to ambient SO 2 , PM 2.5 , and NO 2 are associated with increased ARDS risk in sepsis, representing potentially modifiable environmental risk factors for sepsis-associated ARDS., (© 2023. Springer-Verlag GmbH Germany, part of Springer Nature.)

Background: Despite the availability of COVID-19 vaccinations, there remains a need to investigate treatments to reduce the risk or severity of potentially fatal complications of COVID-19, such as acute respiratory distress syndrome (ARDS). This study evaluated the efficacy and safety of the transient receptor potential channel C6 (TRPC6) inhibitor, BI 764198, in reducing the risk and/or severity of ARDS in patients hospitalised for COVID-19 and requiring non-invasive, supplemental oxygen support (oxygen by mask or nasal prongs, oxygen by non-invasive ventilation or high-flow nasal oxygen)., Methods: Multicentre, double-blind, randomised phase II trial comparing once-daily oral BI 764198 (n=65) with placebo (n=64) for 28 days (+2-month follow-up)., Primary Endpoint: proportion of patients alive and free of mechanical ventilation at day 29. Secondary endpoints: proportion of patients alive and discharged without oxygen (day 29); occurrence of either in-hospital mortality, intensive care unit admission or mechanical ventilation (day 29); time to first response (clinical improvement/recovery); ventilator-free days (day 29); and mortality (days 15, 29, 60 and 90)., Results: No difference was observed for the primary endpoint: BI 764198 (83.1%) versus placebo (87.5%) (estimated risk difference -5.39%; 95% CI -16.08 to 5.30; p=0.323). For secondary endpoints, a longer time to first response (rate ratio 0.67; 95% CI 0.46 to 0.99; p=0.045) and longer hospitalisation (+3.41 days; 95% CI 0.49 to 6.34; p=0.023) for BI 764198 versus placebo was observed; no other significant differences were observed. On-treatment adverse events were similar between trial arms and more fatal events were reported for BI 764198 (n=7) versus placebo (n=2). Treatment was stopped early based on an interim observation of a lack of efficacy and an imbalance of fatal events (Data Monitoring Committee recommendation)., Conclusions: TRPC6 inhibition was not effective in reducing the risk and/or severity of ARDS in patients with COVID-19 requiring non-invasive, supplemental oxygen support., Trial Registration Number: NCT04604184., Competing Interests: Competing interests: LW reports receipt of research support from Boehringer Ingelheim, Genentech and CSL Behring and consulting fees from Merck, Citius, Foresee and Quark. NS, WC and AG are employees of Boehringer Ingelheim. DFM reports personal fees from consultancy for GlaxoSmithKline, Boehringer Ingelheim, Bayer, Novartis, SOBI and Eli Lilly, and from sitting on Data Monitoring and Ethics Committees for trials undertaken by Vir Biotechnology and Faron Pharmaceuticals. DFM’s institution has received funds from grants from the NIHR Wellcome Trust, MRC, Innovate UK and NIHSC R&D, and others for studies in patients with ARDS and COVID-19; he also has a patent (US8962032) issued to his institution for a treatment for inflammatory disease. DFM is the MRC/NIHR EME Programme Director; DFM’s spouse is joint Editor-in-Chief for Thorax. VE reports clinical trial support and consulting fees from Gilead. GAD reports receipt of clinical trial research support from Boehringer Ingelheim, Edesa Biotech, Gilead Sciences, Regeneron and Roche, and scientific advisory board membership for Safeology., (© Author(s) (or their employer(s)) 2023. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

The aim of these guidelines is to update the 2017 clinical practice guideline (CPG) of the European Society of Intensive Care Medicine (ESICM). The scope of this CPG is limited to adult patients and to non-pharmacological respiratory support strategies across different aspects of acute respiratory distress syndrome (ARDS), including ARDS due to coronavirus disease 2019 (COVID-19). These guidelines were formulated by an international panel of clinical experts, one methodologist and patients' representatives on behalf of the ESICM. The review was conducted in compliance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement recommendations. We followed the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach to assess the certainty of evidence and grade recommendations and the quality of reporting of each study based on the EQUATOR (Enhancing the QUAlity and Transparency Of health Research) network guidelines. The CPG addressed 21 questions and formulates 21 recommendations on the following domains: (1) definition; (2) phenotyping, and respiratory support strategies including (3) high-flow nasal cannula oxygen (HFNO); (4) non-invasive ventilation (NIV); (5) tidal volume setting; (6) positive end-expiratory pressure (PEEP) and recruitment maneuvers (RM); (7) prone positioning; (8) neuromuscular blockade, and (9) extracorporeal life support (ECLS). In addition, the CPG includes expert opinion on clinical practice and identifies the areas of future research., (© 2023. The Author(s).)

The diagnosis of acute respiratory distress syndrome (ARDS) traditionally requires calculation of the ratio of partial pressure of arterial oxygen to fraction of inspired oxygen (PaO 2 /FiO 2 ) using arterial blood, which can be costly and is not possible in many resource-limited settings. By contrast, pulse oximetry is continuously available, accurate, inexpensive, and non-invasive. Pulse oximetry-based indices, such as the ratio of pulse-oximetric oxygen saturation to FiO 2 (SpO 2 /FiO 2 ), have been validated in clinical studies for the diagnosis and risk stratification of patients with ARDS. Limitations of the SpO 2 /FiO 2 ratio include reduced accuracy in poor perfusion states or above oxygen saturations of 97%, and the potential for reduced accuracy in patients with darker skin pigmentation. Application of pulse oximetry to the diagnosis and management of ARDS, including formal adoption of the SpO 2 /FiO 2 ratio as an alternative to PaO 2 /FiO 2 to meet the diagnostic criterion for hypoxaemia in ARDS, could facilitate increased and earlier recognition of ARDS worldwide to advance both clinical practice and research., Competing Interests: Declaration of interests KDW has received research grant support from the US National Institutes of Health (NIH; 5T32GM008440-24). MAM has received research grant support from the NIH (HL134828, HL126456, HL140026, and 143896), the US Department of Defense, and Roche-Genentech for observational studies on acute respiratory distress syndrome; he reports consultancy fees from Citius Pharmaceuticals, Johnson & Johnson, Gilead Pharmaceuticals, Plant Therapeutics, and Novartis pharmaceuticals, outside of the submitted work. LBW has received research grant support from the NIH (HL103836, HL126176, HL158906) and the US Department of Defense, and grants or contracts from Genentech, Boehringer Ingelheim, and CSL Behring; she reports consultancy fees from Foresee, Merck, Citius Pharmaceuticals, Quark, and Boehringer Ingelheim, outside of the submitted work., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Acute respiratory distress syndrome (ARDS) is a common clinical syndrome of acute respiratory failure as a result of diffuse lung inflammation and oedema. ARDS can be precipitated by a variety of causes. The pathophysiology of ARDS is complex and involves the activation and dysregulation of multiple overlapping and interacting pathways of injury, inflammation, and coagulation, both in the lung and systemically. Mechanical ventilation can contribute to a cycle of lung injury and inflammation. Resolution of inflammation is a coordinated process that requires downregulation of proinflammatory pathways and upregulation of anti-inflammatory pathways. The heterogeneity of the clinical syndrome, along with its biology, physiology, and radiology, has increasingly been recognised and incorporated into identification of phenotypes. A precision-medicine approach that improves the identification of more homogeneous ARDS phenotypes should lead to an improved understanding of its pathophysiological mechanisms and how they differ from patient to patient., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Clinical and molecular heterogeneity are common features of human disease. Understanding the basis for heterogeneity has led to major advances in therapy for many cancers and pulmonary diseases such as cystic fibrosis and asthma. Although heterogeneity of risk factors, disease severity, and outcomes in survivors are common features of the acute respiratory distress syndrome (ARDS), many challenges exist in understanding the clinical and molecular basis for disease heterogeneity and using heterogeneity to tailor therapy for individual patients. This report summarizes the proceedings of the 2021 Aspen Lung Conference, which was organized to review key issues related to understanding clinical and molecular heterogeneity in ARDS. The goals were to review new information about ARDS phenotypes, to explore multicellular and multisystem mechanisms responsible for heterogeneity, and to review how best to account for clinical and molecular heterogeneity in clinical trial design and assessment of outcomes. The report concludes with recommendations for future research to understand the clinical and basic mechanisms underlying heterogeneity in ARDS to advance the development of new treatments for this life-threatening critical illness.

The acute respiratory distress syndrome (ARDS) is a common critical illness syndrome with high morbidity and mortality. There are no proven pharmacological therapies for ARDS. The current definition of ARDS is based on shared clinical characteristics but does not capture the heterogeneity in clinical risk factors, imaging characteristics, physiology, timing of onset and trajectory, and biology of the syndrome. There is increasing interest within the ARDS clinical trialist community to design clinical trials that reduce heterogeneity in the trial population. This effort must be balanced with ongoing work to craft an inclusive, global definition of ARDS, with important implications for trial design. Ultimately, the two aims-to design trials that are applicable to the diverse global ARDS population while also advancing opportunities to identify targetable traits-should coexist. In this Personal View, we recommend two primary strategies to improve future ARDS trials: the development of new methods to target treatable traits in clinical trial populations, and improvements in the representativeness of ARDS trials, with the inclusion of global populations. We emphasise that these two strategies are complementary. We also discuss how a proposed expansion of the definition of ARDS could affect the future of clinical trials., Competing Interests: Declaration of interests SJ receives consulting fees from Drager, Fisher-Paykel, Medtronic, Mindray, and Baxter. NL receives grant funding from Guerbet. GL receives consulting fees from Abbott, Abiomed, and Baxter; and speaking fees from LivaNova. AM receives grants from 4TEEN4, Abbott, Roche, and Sphyngotec; and consulting fees from Orion, Roche, Adrenomed, and Fire1. AM participates on the data and safety monitoring board for Roche. LBW declares grants from Genentech, Boehringer Ingelheim, and CSL Behring, outside the submitted work; and consulting fees from Foresee, Merck, Citius Pharmaceuticals, Quark, and Boehringer Ingelheim. MAM declares grant support from Roche-Genentech for ARDS observational studies; and consulting income from Citius Pharmaceuticals, Johnson & Johnson, Gilead Pharmaceuticals, Plant Therapeutics, and Novartis Pharmaceuticals, outside the submitted work. All other authors declare no competing interests., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Background: Two acute respiratory distress syndrome (ARDS) subphenotypes (hyperinflammatory and hypoinflammatory) with distinct clinical and biological features and differential treatment responses have been identified using latent class analysis (LCA) in seven individual cohorts. To facilitate bedside identification of subphenotypes, clinical classifier models using readily available clinical variables have been described in four randomised controlled trials. We aimed to assess the performance of these models in observational cohorts of ARDS., Methods: In this observational, multicohort, retrospective study, we validated two machine-learning clinical classifier models for assigning ARDS subphenotypes in two observational cohorts of patients with ARDS: Early Assessment of Renal and Lung Injury (EARLI; n=335) and Validating Acute Lung Injury Markers for Diagnosis (VALID; n=452), with LCA-derived subphenotypes as the gold standard. The primary model comprised only vital signs and laboratory variables, and the secondary model comprised all predictors in the primary model, with the addition of ventilatory variables and demographics. Model performance was assessed by calculating the area under the receiver operating characteristic curve (AUC) and calibration plots, and assigning subphenotypes using a probability cutoff value of 0·5 to determine sensitivity, specificity, and accuracy of the assignments. We also assessed the performance of the primary model in EARLI using data automatically extracted from an electronic health record (EHR; EHR-derived EARLI cohort). In Large Observational Study to Understand the Global Impact of Severe Acute Respiratory Failure (LUNG SAFE; n=2813), a multinational, observational ARDS cohort, we applied a custom classifier model (with fewer variables than the primary model) to determine the prognostic value of the subphenotypes and tested their interaction with the positive end-expiratory pressure (PEEP) strategy, with 90-day mortality as the dependent variable., Findings: The primary clinical classifier model had an area under receiver operating characteristic curve (AUC) of 0·92 (95% CI 0·90-0·95) in EARLI and 0·88 (0·84-0·91) in VALID. Performance of the primary model was similar when using exclusively EHR-derived predictors compared with manually curated predictors (AUC=0·88 [95% CI 0·81-0·94] vs 0·92 [0·88-0·97]). In LUNG SAFE, 90-day mortality was higher in patients assigned the hyperinflammatory subphenotype than in those with the hypoinflammatory phenotype (414 [57%] of 725 vs 694 [33%] of 2088; p<0·0001). There was a significant treatment interaction with PEEP strategy and ARDS subphenotype (p=0·041), with lower 90-day mortality in the high PEEP group of patients with the hyperinflammatory subphenotype (hyperinflammatory subphenotype: 169 [54%] of 313 patients in the high PEEP group vs 127 [62%] of 205 patients in the low PEEP group; hypoinflammatory subphenotype: 231 [34%] of 675 patients in the high PEEP group vs 233 [32%] of 734 patients in the low PEEP group)., Interpretation: Classifier models using clinical variables alone can accurately assign ARDS subphenotypes in observational cohorts. Application of these models can provide valuable prognostic information and could inform management strategies for personalised treatment, including application of PEEP, once prospectively validated., Funding: US National Institutes of Health and European Society of Intensive Care Medicine., Competing Interests: Declaration of interests MC has a patent (ARCD P0535US.P2) pending to the University of Chicago (IL, USA) related to clinical deterioration risk prediction algorithms for patients admitted to hospital. MAM reports grants from Roche/Genentech, and personal fees from Johnson and Johnson, Novartis Pharmaceuticals, Gilead Pharmaceuticals, and Pliant Therapeutics, outside the submitted work. LBW reports grants and personal fees from Boehringer Ingelheim, outside the submitted work; grants from Genentech and CSL Behring, outside the submitted work; and personal fees from Merck, Citius, Quark, and Foresee, outside the submitted work. JGL reports personal fees from GlaxoSmithKline and Baxter, outside of the submitted work. GB reports grants and personal fees from Draeger Medical, and personal fees from Ge Healthcare, Hamilton Medical, and Flowmeter SPA, outside the submitted work. CSC reports grants and personal fees from Roche/Genentech and Bayer, outside the submitted work; personal fees from Quark Pharmaceuticals, Gen1e Life Sciences, and Vasomune, outside the submitted work; and grants from Quantum Leap Healthcare Collaborative, outside the submitted work. All other authors declare no competing interests., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Acute respiratory distress syndrome (ARDS) is a common cause of respiratory failure yet has few pharmacologic therapies, reflecting the mechanistic heterogeneity of lung injury. We hypothesized that damage to the alveolar epithelial glycocalyx, a layer of glycosaminoglycans interposed between the epithelium and surfactant, contributes to lung injury in patients with ARDS. Using mass spectrometry of airspace fluid noninvasively collected from mechanically ventilated patients, we found that airspace glycosaminoglycan shedding (an index of glycocalyx degradation) occurred predominantly in patients with direct lung injury and was associated with duration of mechanical ventilation. Male patients had increased shedding, which correlated with airspace concentrations of matrix metalloproteinases. Selective epithelial glycocalyx degradation in mice was sufficient to induce surfactant dysfunction, a key characteristic of ARDS, leading to microatelectasis and decreased lung compliance. Rapid colorimetric quantification of airspace glycosaminoglycans was feasible and could provide point-of-care prognostic information to clinicians and/or be used for predictive enrichment in clinical trials.

Acute respiratory distress syndrome (ARDS) is a heterogeneous clinical syndrome. Understanding of the complex pathways involved in lung injury pathogenesis, resolution, and repair has grown considerably in recent decades. Nevertheless, to date, only therapies targeting ventilation-induced lung injury have consistently proven beneficial, and despite these gains, ARDS morbidity and mortality remain high. Many candidate therapies with promise in preclinical studies have been ineffective in human trials, probably at least in part due to clinical and biological heterogeneity that modifies treatment responsiveness in human ARDS. A precision medicine approach to ARDS seeks to better account for this heterogeneity by matching therapies to subgroups of patients that are anticipated to be most likely to benefit, which initially might be identified in part by assessing for heterogeneity of treatment effect in clinical trials. In October 2019, the US National Heart, Lung, and Blood Institute convened a workshop of multidisciplinary experts to explore research opportunities and challenges for accelerating precision medicine in ARDS. Topics of discussion included the rationale and challenges for a precision medicine approach in ARDS, the roles of preclinical ARDS models in precision medicine, essential features of cohort studies to advance precision medicine, and novel approaches to clinical trials to support development and validation of a precision medicine strategy. In this Position Paper, we summarise workshop discussions, recommendations, and unresolved questions for advancing precision medicine in ARDS. Although the workshop took place before the COVID-19 pandemic began, the pandemic has highlighted the urgent need for precision therapies for ARDS as the global scientific community grapples with many of the key concepts, innovations, and challenges discussed at this workshop., Competing Interests: Declaration of interests JRB reports grants from the US National Institutes of Health (NIH) and Quantum Leap Healthcare Collaborative and personal fees from Sedana Medical and Hamilton Medical, outside of the submitted work. BTT reports grants from NIH and personal fees from Bayer, Novartis, and Thetis, outside of the submitted work. RMB reports grants from NIH and personal fees from Merck and Genentech, outside of the submitted work. JAB reports grants from NIH, outside of the submitted work. LCD reports grants from NIH, grants and personal fees from AstraZeneca, and personal fees from Sanofi-Regeneron, outside of the submitted work. LE reports being an uncompensated board member of Quantum Leap Healthcare Collaborative. MNG reports grants from NIH and the Agency for Healthcare Research and Quality, outside of the submitted work. RJL is the senior medical scientist at Berry Consultants, a statistical consulting firm that specialises in innovative clinical trial design, including Bayesian adaptive and platform trial designs. JCM is chair of the International Forum for Acute Care Trialists, and reports personal fees from AM Pharma, Gilead Pharmaceuticals, and the Society of Critical Care Medicine, outside of the submitted work. TRM reports personal fees from Novartis Pharmaceuticals, Translate Bio, NIH, the Gates Foundation, and TVM Capital Life Science, outside of the submitted work. DFM reports personal fees for consultancy from GlaxoSmithKline, Boehringer Ingelheim, Bayer, and Novartis, and he holds a patent issued to his institution for a treatment for acute respiratory distress syndrome (ARDS), outside of the submitted work. NJM reports grants from NIH, Athersys, the Marcus Foundation, BioMarck, and Quantum Leap Healthcare Collaborative, outside of the submitted work. MM reports grants from NIH, outside of the submitted work. ER is the president of the ARDS Foundation. EPS reports grants from NIH and equity interest in IHP Therapeutics, outside of the submitted work. LBW reports personal fees from Merck, Bayer, Boehringer Ingelheim, CSL Behring, Quark, Foresee Pharmaceuticals, and Citius, and grants from CSL Behring and Genentech, outside of the submitted work. HRW reports grants from NIH and holds a patent for sepsis biomarkers for prognostic and predictive enrichment. CSC reports grants from NIH and Quantum Leap Healthcare Collaborative, grants and personal fees from Genentech and Bayer, and personal fees from Quark Pharmaceuticals, Prometric, Gen1e Life Sciences, and Vasomune, outside of the submitted work. The other authors declared no conflicts of interest., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Rationale: Using latent class analysis (LCA), two subphenotypes of acute respiratory distress syndrome (ARDS) have consistently been identified in five randomised controlled trials (RCTs), with distinct biological characteristics, divergent outcomes and differential treatment responses to randomised interventions. Their existence in unselected populations of ARDS remains unknown. We sought to identify subphenotypes in observational cohorts of ARDS using LCA., Methods: LCA was independently applied to patients with ARDS from two prospective observational cohorts of patients admitted to the intensive care unit, derived from the Validating Acute Lung Injury markers for Diagnosis (VALID) (n=624) and Early Assessment of Renal and Lung Injury (EARLI) (n=335) studies. Clinical and biological data were used as class-defining variables. To test for concordance with prior ARDS subphenotypes, the performance metrics of parsimonious classifier models (interleukin 8, bicarbonate, protein C and vasopressor-use), previously developed in RCTs, were evaluated in EARLI and VALID with LCA-derived subphenotypes as the gold-standard., Results: A 2-class model best fit the population in VALID (p=0.0010) and in EARLI (p<0.0001). Class 2 comprised 27% and 37% of the populations in VALID and EARLI, respectively. Consistent with the previously described 'hyperinflammatory' subphenotype, Class 2 was characterised by higher proinflammatory biomarkers, acidosis and increased shock and worse clinical outcomes. The similarities between these and prior RCT-derived subphenotypes were further substantiated by the performance of the parsimonious classifier models in both cohorts (area under the curves 0.92-0.94). The hyperinflammatory subphenotype was associated with increased prevalence of chronic liver disease and neutropenia and reduced incidence of chronic obstructive pulmonary disease. Measurement of novel biomarkers showed significantly higher levels of matrix metalloproteinase-8 and markers of endothelial injury in the hyperinflammatory subphenotype, whereas, matrix metalloproteinase-9 was significantly lower., Conclusion: Previously described subphenotypes are generalisable to unselected populations of non-trauma ARDS., Competing Interests: Competing interests: PS declares no competing interests. CSC has received grant funding from the NIH, US Food and Drug Administration, Roche-Genentech, Quantum Leap Healthcare Collaborative, and Bayer Pharmaceuticals and has served as a consultant to Vasomune, Quark, and Gen1e Life Sciences., (© Author(s) (or their employer(s)) 2022. No commercial re-use. See rights and permissions. Published by BMJ.)

BACKGROUNDWhether airspace biomarkers add value to plasma biomarkers in studying acute respiratory distress syndrome (ARDS) is not well understood. Mesenchymal stromal cells (MSCs) are an investigational therapy for ARDS, and airspace biomarkers may provide mechanistic evidence for MSCs' impact in patients with ARDS.METHODSWe carried out a nested cohort study within a phase 2a safety trial of treatment with allogeneic MSCs for moderate-to-severe ARDS. Nonbronchoscopic bronchoalveolar lavage and plasma samples were collected 48 hours after study drug infusion. Airspace and plasma biomarker concentrations were compared between the MSC (n = 17) and placebo (n = 10) treatment arms, and correlation between the two compartments was tested. Airspace biomarkers were also tested for associations with clinical and radiographic outcomes.RESULTSCompared with placebo, MSC treatment significantly reduced airspace total protein, angiopoietin-2 (Ang-2), IL-6, and soluble TNF receptor-1 concentrations. Plasma biomarkers did not differ between groups. Each 10-fold increase in airspace Ang-2 was independently associated with 6.7 fewer days alive and free of mechanical ventilation (95% CI, -12.3 to -1.0, P = 0.023), and each 10-fold increase in airspace receptor for advanced glycation end-products (RAGE) was independently associated with a 6.6-point increase in day 3 radiographic assessment of lung edema score (95% CI, 2.4 to 10.8, P = 0.004).CONCLUSIONMSCs reduced biological evidence of lung injury in patients with ARDS. Biomarkers from the airspaces provide additional value for studying pathogenesis, treatment effects, and outcomes in ARDS.TRIAL REGISTRATIONClinicalTrials.gov NCT02097641.FUNDINGNational Heart, Lung, and Blood Institute.

Noninvasive sampling of the distal airspace in patients with acute respiratory distress syndrome (ARDS) has long eluded clinical and translational researchers. We recently reported that fluid collected from heat moisture exchange (HME) filters closely mirrors fluid directly aspirated from the distal airspace. In the current study, we sought to determine fluid yield from different HME types, optimal HME circuit dwell time, and reliability of HME fluid in reflecting the distal airspace. We studied fluid yield from four different filter types by loading increasing volumes of saline and measuring volumes of fluid recovered. We collected filters after 1, 2, and 4 h of dwell time for measurement of fluid volume and total protein from 13 subjects. After identifying 4 h as the optimal dwell time, we measured total protein and IgM in HME fluid from 42 subjects with ARDS and nine with hydrostatic pulmonary edema (HYDRO). We found that the fluid yield varies greatly by filter type. With timed sample collection, fluid recovery increased with increasing circuit dwell time with a median volume of 2.0 mL [interquartile range (IQR) 1.2-2.7] after 4 h. Total protein was higher in the 42 subjects with ARDS compared with nine with HYDRO [median 708 µg/mL (IQR 244-2017) vs. 364 µg/mL (IQR 136-578), P = 0.047], confirming that total protein concentration in HME is higher in ARDS compared with hydrostatic edema. These studies establish a standardized HME fluid collection protocol and confirm that HME fluid analysis is a novel noninvasive tool for the study of the distal airspace in ARDS.

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., Competing Interests: Conflict of interest: L.D.J. Bos reports grants from the Dutch Lung Foundation (Young investigator grant), the Dutch Lung Foundation and Health Holland (Public–Private Partnership grant) and the Dutch Lung Foundation (Dirkje Postma Award), and grants from IMI COVID19 imitative and Amsterdam UMC Fellowship, outside the submitted work. Conflict of interest: A. Artigas reports grants from Grifols and Fisher & Paykel, and personal fees from Grifols, outside the submitted work. Conflict of interest: J-M. Constantin has nothing to disclose. Conflict of interest: L.A. Hagens has nothing to disclose. Conflict of interest: N. Heijnen has nothing to disclose. Conflict of interest: J.G. Laffey reports grants from Science Foundation Ireland and Health Research Board Ireland, outside the submitted work. Conflict of interest: N. Meyer reports grants from National Institutes of Health, outside the submitted work. Conflict of interest: L. Papazian has nothing to disclose. Conflict of interest: L. Pisani reports personal fees from Fisher & Paykel, outside the submitted work. Conflict of interest: M.J. Schultz has nothing to disclose. Conflict of interest: M. Shankar-Hari has nothing to disclose. Conflict of interest: M.R. Smit has nothing to disclose. Conflict of interest: C. Summers reports grants from GlaxoSmithKline and AstraZeneca, outside the submitted work. Conflict of interest: L.B. Ware reports grants from National Institutes of Health, during the conduct of the study; other funding from CSL Behring, Genentech and Global Blood Therapeutics, and personal fees from Merck, Bayer and Quark, outside the submitted work. Conflict of interest: R. Scala has nothing to disclose. Conflict of interest: C. Calfee reports grants from NIH, during the conduct of the study; grants and personal fees from Roche/Genentech and Bayer, personal fees from Quark Pharmaceuticals, Prometic, Gen1e Life Sciences and Vasomune, outside the submitted work., (Copyright ©ERS 2021.)

Purpose of Review: This article provides an overview of protein biomarkers for acute respiratory distress syndrome (ARDS) and their potential use in future clinical trials., Recent Findings: The protein biomarkers studied as indices of biological processes involved in the pathogenesis of ARDS may have diagnostic and/or prognostic value. Recently, they also proved useful for identifying ARDS phenotypes and assessing heterogeneity of treatment effect in retrospective analyses of completed clinical trials., Summary: This article summarizes the current research on ARDS biomarkers and provides insights into how they should be integrated as prognostic and predictive enrichment tools in future clinical trials., (Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.)

A history of chronic cigarette smoking is known to increase risk for acute respiratory distress syndrome (ARDS), but the corresponding risks associated with chronic e-cigarette use are largely unknown. The chromosomal fragile site gene, WWOX, is highly susceptible to genotoxic stress from environmental exposures and thus an interesting candidate gene for the study of exposure-related lung disease. Lungs harvested from current versus former/never-smokers exhibited a 47% decrease in WWOX mRNA levels. Exposure to nicotine-containing e-cigarette vapor resulted in an average 57% decrease in WWOX mRNA levels relative to vehicle-treated controls. In separate studies, endothelial (EC)-specific WWOX knockout (KO) versus WWOX flox control mice were examined under ARDS-producing conditions. EC WWOX KO mice exhibited significantly greater levels of vascular leak and histologic lung injury. ECs were isolated from digested lungs of untreated EC WWOX KO mice using sorting by flow cytometry for CD31 + CD45 - cells. These were grown in culture, confirmed to be WWOX deficient by RT-PCR and Western blotting, and analyzed by electric cell impedance sensing as well as an FITC dextran transwell assay for their barrier properties during methicillin-resistant Staphylococcus aureus or LPS exposure. WWOX KO ECs demonstrated significantly greater declines in barrier function relative to cells from WWOX flox controls during either methicillin-resistant S. aureus or LPS treatment as measured by both electric cell impedance sensing and the transwell assay. The increased risk for ARDS observed in chronic smokers may be mechanistically linked, at least in part, to lung WWOX downregulation, and this phenomenon may also manifest in the near future in chronic users of e-cigarettes.

Although the acute respiratory distress syndrome (ARDS) is well defined by the development of acute hypoxemia, bilateral infiltrates and non-cardiogenic pulmonary edema, ARDS is heterogeneous in terms of clinical risk factors, physiology of lung injury, microbiology, and biology, potentially explaining why pharmacologic therapies have been mostly unsuccessful in treating ARDS. Identifying phenotypes of ARDS and integrating this information into patient selection for clinical trials may increase the chance for efficacy with new treatments. In this review, we focus on classifying ARDS by the associated clinical disorders, physiological data, and radiographic imaging. We consider biologic phenotypes, including plasma protein biomarkers, gene expression, and common causative microbiologic pathogens. We will also discuss the issue of focusing clinical trials on the patient's phase of lung injury, including prevention, administration of therapy during early acute lung injury, and treatment of established ARDS. A more in depth understanding of the interplay of these variables in ARDS should provide more success in designing and conducting clinical trials and achieving the goal of personalized medicine.

Background: The Radiographic Assessment of Lung Edema (RALE) score is associated with the severity of ARDS, and treatments targeted at reducing pulmonary edema such as conservative fluid management cause a reduction in RALE score over time., Research Question: Are early changes in RALE score over time associated with survival in patients with ARDS?, Study Design and Methods: Data from patients enrolled in three centers in the Lung Imaging for Ventilation sEtting in ARDS (LIVE) trial with available chest radiographs at baseline (day 0) and days 2 or 3 were used. The RALE was scored by two independent reviewers. The primary end point was death by day 90, considering RALE score both at baseline and as a time-varying covariate in a marginal Cox survival model., Results: RALE was scored from 135, 64, and 88 radiographs on days 0, 2, and 3, respectively. Both baseline RALE (hazard ratio [HR] for each one-point increment, 1.04; 95% CI, 1.01-1.08; P = .006) and the change in RALE over time (HR for each one-point decrease per unit of time, 0.99; 95% CI, 0.99-0.99; P = .03) were associated with death by day 90, even after adjustment for age, sex, BMI, Simplified Acute Physiology Score II, vasopressor use, and total volume of fluids received since study entry., Interpretation: The change in RALE during the first days after ARDS onset is independently associated with survival and may be useful as a surrogate end point in future clinical trials of new therapeutics in ARDS., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

With the exception of a few successes in trials of supportive care, the majority of interventional clinical trials for acute respiratory distress syndrome (ARDS) have not led to new therapies. To improve the likelihood of benefit from clinical trial interventions in ARDS, clinical trial design must be improved. To optimize trial design, many factors need to be considered including the type of therapy to be tested, the type of trial (phase 2 or 3), how patients will be selected, primary and secondary end-points, and strategy for conduct of the trial, including potential newer trial designs such as platform or adaptive trials. Of these, optimization of patient selection is central to the likelihood of success and is particularly relevant in ARDS, which is a heterogeneous clinical syndrome, not a homogeneous disease. Recent advances including improved understanding of pathophysiologic mechanisms and better tools for outcome prediction in ARDS should facilitate both predictive and prognostic enrichment. This commentary focuses on new information and novel methods for prognostic and predictive enrichment that may be useful to optimize patient selection and increase the likelihood of positive clinical trials in ARDS.

Introduction : Acute respiratory distress syndrome (ARDS) is a severe form of acute lung injury common in critically ill patients and characterized by significant morbidity and mortality. It frequently manifests long-lasting effects beyond hospitalization, from cognitive impairment to physical weakness. Areas covered : Several complications of ARDS have been identified in patients after hospital discharge. The authors conducted literature searches to identify observational studies, randomized clinical trials, systematic reviews, and guidelines. A summary of is presented here to outline the sequelae of ARDS and their risk factors with a focus on the limited but growing research into possible therapies. Long term sequelae of ARDS commonly identified in the literature include long-term cognitive impairment, psychological morbidities, neuromuscular weakness, pulmonary dysfunction, and ongoing healthcare utilization with reduced quality of life. Expert opinion : Given the public health significance of long-term complications following ARDS, the development of new therapies for prevention and treatment is of vital importance. Furthering knowledge of the pathophysiology of these impairments will provide a framework to develop new therapeutic targets to fuel future clinical trials in this area of critical care medicine.

Purpose: Previous studies assessing impact of acute respiratory distress syndrome (ARDS) on mortality have shown conflicting results. We sought to assess the independent association of ARDS with in-hospital mortality among intensive care unit (ICU) patients with sepsis., Methods: We studied two prospective sepsis cohorts drawn from the Early Assessment of Renal and Lung Injury (EARLI; n = 474) and Validating Acute Lung Injury markers for Diagnosis (VALID; n = 337) cohorts. ARDS was defined by Berlin criteria. We used logistic regression to compare in-hospital mortality in patients with and without ARDS, controlling for baseline severity of illness. We also estimated attributable mortality, adjusted for illness severity by stratification., Results: ARDS occurred in 195 EARLI patients (41%) and 99 VALID patients (29%). ARDS was independently associated with risk of hospital death in multivariate analysis, even after controlling for severity of illness, as measured by APACHE II (odds ratio [OR] 1.65 (95% confidence interval [CI] 1.02, 2.67), p = 0.04 in EARLI; OR 2.12 (CI 1.16, 3.92), p = 0.02 in VALID). Patients with severe ARDS (P/F < 100) primarily drove this relationship. The attributable mortality of ARDS was 27% (CI 14%, 37%) in EARLI and 37% (CI 10%, 51%) in VALID. ARDS was independently associated with ICU mortality, hospital length of stay (LOS), ICU LOS, and ventilator-free days., Conclusions: Development of ARDS among ICU patients with sepsis confers increased risk of ICU and in-hospital mortality in addition to other important outcomes. Clinical trials targeting patients with severe ARDS will be best poised to detect measurable differences in these outcomes.

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).

Critical illness syndromes, including sepsis and the acute respiratory distress syndrome (ARDS), are identified using consensus definitions that are based on broad, clinically available criteria and include patients with heterogeneous biology. This heterogeneity is a barrier to developing and testing effective therapies for these syndromes. Biomarkers identify clinically distinct molecular phenotypes of ARDS and sepsis. These molecular phenotypes are associated with differences in mortality and predict response to several treatments in retrospective analyses of clinical trials. Biomarkers can be used for prognostic and predictive enrichment of clinical trials in critical illness to incorporate precision medicine in critical care., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Rationale: Acute respiratory distress syndrome (ARDS) lacks known causal biomarkers. Plasma concentrations of sRAGE (soluble receptor for advanced glycation end products) strongly associate with ARDS risk. However, whether plasma sRAGE contributes causally to ARDS remains unknown. Objectives: Evaluate plasma sRAGE as a causal intermediate in ARDS by Mendelian randomization (MR), a statistical method to infer causality using observational data. Methods: We measured early plasma sRAGE in two critically ill populations with sepsis. The cohorts were whole-genome genotyped and phenotyped for ARDS. To select validated genetic instruments for MR, we regressed plasma sRAGE on genome-wide genotypes in both cohorts. The causal effect of plasma sRAGE on ARDS was inferred using the top variants with significant associations in both populations ( P  < 0.01, R 2  > 0.02). We applied the inverse variance-weighted method to obtain consistent estimates of the causal effect of plasma sRAGE on ARDS risk. Measurements and Main Results: There were 393 European and 266 African ancestry patients in the first cohort and 843 European ancestry patients in the second cohort. Plasma sRAGE was strongly associated with ARDS risk in both populations (odds ratio, 1.86; 95% confidence interval [1.54-2.25]; 2.56 [2.14-3.06] per log increase). Using genetic instruments common to both populations, plasma sRAGE had a consistent causal effect on ARDS risk with a β estimate of 0.50 (95% confidence interval [0.09-0.91] per log increase). Conclusions: Plasma sRAGE is genetically regulated during sepsis, and MR analysis indicates that increased plasma sRAGE leads to increased ARDS risk, suggesting plasma sRAGE acts as a causal intermediate in sepsis-related ARDS.

Acute respiratory distress syndrome (ARDS) is an inflammatory lung disorder that frequently complicates critical illness and commonly occurs in sepsis. Although numerous clinical and environmental risk factors exist, not all patients with risk factors develop ARDS, raising the possibility of genetic underpinnings for ARDS susceptibility. We have previously reported that circulating cell-free hemoglobin (CFH) is elevated during sepsis, and higher levels predict worse outcomes. Excess CFH is rapidly scavenged by haptoglobin (Hp). A common HP genetic variant, HP2, is unique to humans and is common in many populations worldwide. HP2 haptoglobin has reduced ability to inhibit CFH-mediated inflammation and oxidative stress compared with the alternative HP1. We hypothesized that HP2 increases ARDS susceptibility during sepsis when plasma CFH levels are elevated. In a murine model of sepsis with elevated CFH, transgenic mice homozygous for Hp2 had increased lung inflammation, pulmonary vascular permeability, lung apoptosis, and mortality compared with wild-type mice. We then tested the clinical relevance of our findings in 496 septic critically ill adults, finding that HP2 increased ARDS susceptibility after controlling for clinical risk factors and plasma CFH. These observations identify HP2 as a potentially novel genetic ARDS risk factor during sepsis and may have important implications in the study and treatment of ARDS.

Introduction: Automated electronic sniffers may be useful for early detection of acute respiratory distress syndrome (ARDS) for institution of treatment or clinical trial screening., Methods: In a prospective cohort of 2929 critically ill patients, we retrospectively applied published sniffer algorithms for automated detection of acute lung injury to assess their utility in diagnosis of ARDS in the first 4 ICU days. Radiographic full-text reports were searched for "edema" OR ("bilateral" AND "infiltrate") and a more detailed algorithm for descriptions consistent with ARDS. Patients were flagged as possible ARDS if a radiograph met search criteria and had a PaO 2 /FiO 2 or SpO 2 /FiO 2 of 300 or 315, respectively. Test characteristics of the electronic sniffers and clinical suspicion of ARDS were compared to a gold standard of 2-physician adjudicated ARDS., Results: Thirty percent of 2841 patients included in the analysis had gold standard diagnosis of ARDS. The simpler algorithm had sensitivity for ARDS of 78.9%, specificity of 52%, positive predictive value (PPV) of 41%, and negative predictive value (NPV) of 85.3% over the 4-day study period. The more detailed algorithm had sensitivity of 88.2%, specificity of 55.4%, PPV of 45.6%, and NPV of 91.7%. Both algorithms were more sensitive but less specific than clinician suspicion, which had sensitivity of 40.7%, specificity of 94.8%, PPV of 78.2%, and NPV of 77.7%., Conclusions: Published electronic sniffer algorithms for ARDS may be useful automated screening tools for ARDS and improve on clinical recognition, but they are limited to screening rather than diagnosis because their specificity is poor.

Purpose: Bronchoalveolar fluid (BALF) and plasma biomarkers are often endpoints in early phase randomized trials (RCTs) in acute respiratory distress syndrome (ARDS). With ARDS mortality decreasing, we analyzed baseline biomarkers in samples from contemporary ARDS patients participating in a prior RCT and compared these to historical controls. Materials and methods: Ninety ARDS adult patients enrolled in the parent trial. BALF and blood were collected at baseline, day 4 ± 1, and day 8 ± 1. Interleukins-8/-6/-1β/-1 receptor antagonist/-10; granulocyte colony stimulating factor; monocyte chemotactic protein-1; tumour necrosis factor-α; surfactant protein-D; von Willebrand factor; leukotriene B 4 ; receptor for advanced glycosylation end products; soluble Fas ligand; and neutrophil counts were measured. Results: Compared to historical measurements, our values were generally substantially lower, despite our participants being similar to historical controls. For example, our BALF IL-8 and plasma IL-6 were notably lower than in a 1999 RCT of low tidal volume ventilation and a 2007 biomarker study, respectively. Conclusions: Baseline biomarker levels in current ARDS patients are substantially lower than 6-20 years before collection of these samples. These findings, whether from ICU care changes resulting in less inflammation or from variation in assay techniques over time, have important implications for design of future RCTs with biomarkers as endpoints.

Acute respiratory distress syndrome (ARDS) is a syndrome of acute respiratory failure caused by noncardiogenic pulmonary edema. Despite five decades of basic and clinical research, there is still no effective pharmacotherapy for this condition and the treatment remains primarily supportive. It is critical to study the molecular and physiologic mechanisms that cause ARDS to improve our understanding of this syndrome and reduce mortality. The goal of this review is to describe our current understanding of the pathogenesis and pathophysiology of ARDS. First, we will describe how pulmonary edema fluid accumulates in ARDS due to lung inflammation and increased alveolar endothelial and epithelial permeabilities. Next, we will review how pulmonary edema fluid is normally cleared in the uninjured lung, and describe how these pathways are disrupted in ARDS. Finally, we will explain how clinical trials and preclinical studies of novel therapeutic agents have further refined our understanding of this condition, highlighting, in particular, the study of mesenchymal stromal cells in the treatment of ARDS., Competing Interests: This work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.)

Rationale: Exposure to air pollution has molecular and physiologic effects on the lung that may increase the risk of acute respiratory distress syndrome (ARDS) after injury., Objectives: To determine the association of short- and long-term air pollutant exposures and ARDS risk after severe trauma., Methods: We analyzed data from a prospective cohort of 996 critically ill patients presenting with acute trauma and an injury severity score greater than 15. Exposures to ozone, nitrogen dioxide, sulfur dioxide, carbon monoxide, and particulate matter less than 2.5 μm were assessed by weighted averages of daily levels from all monitors within 50 km of the geocoded location of a patient's residence. Patients were followed for 6 days for the development of ARDS according to Berlin Criteria. The association between each exposure and ARDS was determined via multivariable logistic regression adjusting for potential confounders., Measurements and Main Results: ARDS developed in 243 (24%) patients. None of the short-term exposures averaged over the 3 days before presentation was associated with ARDS, except sulfur dioxide, which demonstrated a nonlinear association. Nitrogen dioxide, sulfur dioxide, and particulate matter less than or equal to 2.5 μm in aerodynamic diameter exposure over the 6 weeks before presentation was significantly associated with ARDS (P < 0.05). All long-term exposures (3 yr) were associated with ARDS (P < 0.01) in adjusted models, despite exposure levels largely below U.S. and European Union air quality standards., Conclusions: Long-term low- to moderate-level air pollutant exposure is associated with a greater risk of developing ARDS after severe trauma and represents a novel and potentially modifiable environmental risk factor for ARDS.

Background: There is no accurate, non-invasive measurement to estimate the degree of pulmonary oedema in acute respiratory distress syndrome (ARDS). We developed the Radiographic Assessment of Lung Oedema (RALE) score to evaluate the extent and density of alveolar opacities on chest radiographs. After first comparing the RALE score to gravimetric assessment of pulmonary oedema in organ donors, we then evaluated the RALE score in patients with ARDS for its relationship to oxygenation and clinical outcomes., Methods: We compared radiographs with excised lung weights from 72 organ donors (derivation cohort) and radiographs with clinical data from 174 patients with ARDS in the ARDSNet Fluid and Catheter Treatment Trial (validation cohort). To calculate RALE, each radiographic quadrant was scored for extent of consolidation (0-4) and density of opacification (1-3). The product of the consolidation and density scores for each of the four quadrants was summed (maximum score=48)., Results: Agreement between two independent reviewers for RALE score was excellent (intraclass correlation coefficient=0.93, 95% CI 0.91 to 0.95). In donors, pre-procurement RALE score correlated with height-adjusted total lung weight (ρ=0.59, p<0.001). In patients with ARDS, higher RALE scores were independently associated with lower PaO 2 /fractional inspired oxygen and worse survival. Conservative fluid management significantly decreased RALE score over 3 days compared with liberal fluid management., Conclusions: The RALE score can be used to assess both the extent of pulmonary oedema and the severity of ARDS, by utilising information that is already obtained routinely, safely and inexpensively in every patient with ARDS. This novel non-invasive measure should be useful for assessing ARDS severity and monitoring response to therapy., Competing Interests: Competing interests: JAB has received research funding from the National Institutes of Health and Global Blood Therapeutics. TWR has received consulting fees from Avisa Pharma and Cumberland Pharmaceuticals. CSC has received research funding from the National Institutes of Health, the Food and Drug Administration (FDA), the Department of Defense, Bayer and GlaxoSmithKline. She has received consulting fees from GlaxoSmithKline, Boehringer Ingelheim, Bayer, Prometic, CSL Behring and Roche/Genentech. MAM has received research grants from Amgen and GlaxoSmithKline and has a current research grant from Bayer Pharmaceuticals for ARDS studies. He has received consultation fees from CSL Behring, Boehinger Ingelheim, Cerus Therapeutics, Quark Pharmaceuticals, Thesan Pharmaceuticals and Bayer Pharmaceuticals. He was Chair of a DSMB for Asthma trials for Roche-Genentech (2013-2017). He also receives grant support for research and clinical trials from the NHLBI, FDA and the Department of Defense. LBW has received research funding from the National Institutes of Health, Boehringer Ingelheim and Global Blood Therapeutics and consultant fees from CSL Behring., (© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)

Rationale: Two distinct acute respiratory distress syndrome (ARDS) subphenotypes have been identified using data obtained at time of enrolment in clinical trials; it remains unknown if these subphenotypes are durable over time., Objective: To determine the stability of ARDS subphenotypes over time., Methods: Secondary analysis of data from two randomised controlled trials in ARDS, the ARMA trial of lung protective ventilation (n=473; patients randomised to low tidal volumes only) and the ALVEOLI trial of low versus high positive end-expiratory pressure (n=549). Latent class analysis (LCA) and latent transition analysis (LTA) were applied to data from day 0 and day 3, independent of clinical outcomes., Measurements and Main Results: In ALVEOLI, LCA indicated strong evidence of two ARDS latent classes at days 0 and 3; in ARMA, evidence of two classes was stronger at day 0 than at day 3. The clinical and biological features of these two classes were similar to those in our prior work and were largely stable over time, though class 2 demonstrated evidence of progressive organ failures by day 3, compared with class 1. In both LCA and LTA models, the majority of patients (>94%) stayed in the same class from day 0 to day 3. Clinical outcomes were statistically significantly worse in class 2 than class 1 and were more strongly associated with day 3 class assignment., Conclusions: ARDS subphenotypes are largely stable over the first 3 days of enrolment in two ARDS Network trials, suggesting that subphenotype identification may be feasible in the context of clinical trials., Competing Interests: Competing interests: CSC has ongoing grant funding from Bayer, prior grant funding from GlaxoSmithKline and consulting for GlaxoSmithKline, Bayer and Boehringer Ingelheim. Other authors have no competing interests to declare., (© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)

Rationale: A major barrier to a more complete understanding of acute respiratory distress syndrome (ARDS) pathophysiology is the inability to sample the distal airspace of patients with ARDS. The heat moisture exchanger (HME) filter is an inline bacteriostatic sponge that collects exhaled moisture from the lungs of mechanically ventilated patients., Objectives: To test the hypothesis that HME filter fluid (HMEF) represents the distal airspace fluid in patients with ARDS., Methods: Samples of HMEF were collected from 37 patients with acute pulmonary edema (either from ARDS or hydrostatic causes [HYDRO; control subjects]). Concurrent undiluted pulmonary edema fluid (EF) and HMEF were collected from six patients. HMEF from 11 patients (8 ARDS and 3 HYDRO) were analyzed by liquid chromatography-coupled tandem mass spectometry. Total protein (bicinchoninic acid assay), MMP-9 (matrix metalloproteinase-9), and MPO (myeloperoxidase) (ELISA) were measured in 29 subjects with ARDS and 5 subjects with HYDRO. SP-D (surfactant protein-D), RAGE (receptor for advanced glycation end-products) (ELISA), and cytokines (IL-1β, IL-6, IL-8, and tumor necrosis factor-α) (electrochemiluminescent assays) were measured in six concurrent HMEF and EF samples., Measurements and Main Results: Liquid chromatography-coupled tandem mass spectrometry on concurrent EF and HMEF samples from four patients revealed similar base peak intensities and m/z values indicating similar protein composition. There were 21 significantly elevated proteins in HMEF from patients with ARDS versus HYDRO. Eight proteins measured in concurrent EF and HMEF from six patients were highly correlated. In HMEF, total protein and MMP-9 were significantly higher in ARDS than in HYDRO., Conclusions: These data suggest that HMEF is a novel, noninvasive method to accurately sample the distal airspace in patients with ARDS.

Background: Traditional measures of ARDS severity such as Pao 2 /Fio 2 may not reliably predict clinical outcomes. The oxygenation index (OI [Fio 2  × mean airway pressure × 100)/Pao 2 ]) may more accurately reflect ARDS severity but requires arterial blood gas measurement. We hypothesized that the oxygenation saturation index (OSI [Fio 2  × mean airway pressure × 100)/oxygen saturation by pulse oximetry (Spo 2 )]) is a reliable noninvasive surrogate for the OI that is associated with hospital mortality and ventilator-free days (VFDs) in patients with ARDS., Methods: Critically ill patients enrolled in a prospective cohort study were eligible if they developed ARDS (Berlin criteria) during the first 4 ICU days and had mean airway pressure, Spo 2 /Fio 2 , and Pao 2 /Fio 2 values recorded on the first day of ARDS (N = 329). The highest mean airway pressure and lowest Spo 2 /Fio 2 and Pao 2 /Fio 2 values were used to calculate OI and OSI. The association between OI or OSI and hospital mortality or VFD was analyzed by using logistic regression and linear regression, respectively. The area under the receiver-operating characteristic curve (AUC) for mortality was compared among OI, OSI, Spo 2 /Fio 2 , Pao 2 /Fio 2 , and Acute Physiology and Chronic Health Evaluation II scores., Results: OI and OSI were strongly correlated (rho = 0.862; P < .001). OSI was independently associated with hospital mortality (OR per 5-point increase in OSI, 1.228 [95% CI, 1.056-1.429]; P = .008). OI and OSI were each associated with a reduction in VFD (OI, P = .023; OSI, P = .005). The AUC for mortality prediction was greatest for Acute Physiology and Chronic Health Evaluation II scores (AUC, 0.695; P < .005) and OSI (AUC, 0.602; P = .007). The AUC for OSI was substantially better in patients aged < 40 years (AUC, 0.779; P < .001)., Conclusions: In patients with ARDS, the OSI was correlated with the OI. The OSI on the day of ARDS diagnosis was significantly associated with increased mortality and fewer VFDs. The findings suggest that OSI is a reliable surrogate for OI that can noninvasively provide prognostic information and assessment of ARDS severity., (Copyright © 2017 American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.)

Purpose: Mortality prediction in ARDS is important for prognostication and risk stratification. However, no prediction models have been independently validated. A combination of two biomarkers with age and APACHE III was superior in predicting mortality in the NHLBI ARDSNet ALVEOLI trial. We validated this prediction tool in two clinical trials and an observational cohort., Methods: The validation cohorts included 849 patients from the NHLBI ARDSNet Fluid and Catheter Treatment Trial (FACTT), 144 patients from a clinical trial of sivelestat for ARDS (STRIVE), and 545 ARDS patients from the VALID observational cohort study. To evaluate the performance of the prediction model, the area under the receiver operating characteristic curve (AUC), model discrimination, and calibration were assessed, and recalibration methods were applied., Results: The biomarker/clinical prediction model performed well in all cohorts. Performance was better in the clinical trials with an AUC of 0.74 (95% CI 0.70-0.79) in FACTT, compared to 0.72 (95% CI 0.67-0.77) in VALID, a more heterogeneous observational cohort. The AUC was 0.73 (95% CI 0.70-0.76) when FACTT and VALID were combined., Conclusion: We validated a mortality prediction model for ARDS that includes age, APACHE III, surfactant protein D, and interleukin-8 in a variety of clinical settings. Although the model performance as measured by AUC was lower than in the original model derivation cohort, the biomarker/clinical model still performed well and may be useful for risk assessment for clinical trial enrollment, an issue of increasing importance as ARDS mortality declines, and better methods are needed for selection of the most severely ill patients for inclusion.

This year is the 50th anniversary of the first description of acute respiratory distress syndrome (ARDS). Since then, much has been learned about the pathogenesis of lung injury in ARDS, with an emphasis on the mechanisms of injury to the lung endothelium and the alveolar epithelium. In terms of treatment, major progress has been made in reducing mortality from ARDS with lung-protective ventilation, using a tidal volume of 6 mL per kg of predicted bodyweight and a plateau airway pressure of less than 30 cm H 2 O. In more severely hypoxaemic patients with ARDS, neuromuscular blockade and prone positioning have further reduced mortality, probably by extending the therapeutic effects of lung protective ventilation. Fluid-conservative therapy has also increased ventilator-free days in patients with ARDS. The lack of success of pharmacological therapies for ARDS, however, presents a continued challenge in the field. In addition to presenting a brief summary of previous experience with clinical trials in ARDS, we focus in this Review on future opportunities to improve clinical trial design to maximise the likelihood of identifying beneficial pharmacological therapies. In view of the heterogeneity in ARDS, both prognostic and predictive enrichment strategies are needed that target therapies toward specific subgroups of patients with ARDS on the basis of both severity and biology. Approaches to reducing heterogeneity in ARDS clinical trials include using physiological, radiographic, and biological criteria to select patients for both phase 2 and 3 trials. Additionally, interest is growing in the design of preventive clinical trials in ARDS and to initiate early treatment of patients with acute lung injury before the need for endotracheal intubation. We also present promising new approaches to treating ARDS, including combination therapies, cell-based therapies, and generic pharmacological compounds with low-risk profiles that are already in routine clinical use for other clinical indications., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Background: It is unclear how to identify which patients at risk for acute respiratory distress syndrome (ARDS) will develop this condition during critical illness. Elevated microparticle (MP) concentrations in the airspace during ARDS are associated with activation of coagulation and in vitro studies have demonstrated that MPs contribute to acute lung injury, but the significance of MPs in the circulation during ARDS has not been well studied. The goal of the present study was to test the hypothesis that elevated levels of circulating MPs could prospectively identify critically ill patients who will develop ARDS and that elevated circulating MPs are associated with poor clinical outcomes., Methods: A total of 280 patients with platelet-poor plasma samples from the prospective Validating Acute Lung Injury biomarkers for Diagnosis (VALID) cohort study were selected for this analysis. Demographics and clinical data were obtained by chart review. MP concentrations in plasma were measured at study enrollment on intensive care unit (ICU) day 2 and on ICU day 4 by MP capture assay. Activation of coagulation was measured by plasma recalcification (clot) times., Results: ARDS developed in 90 of 280 patients (32%) in the study. Elevated plasma MP concentrations were associated with reduced risk of developing ARDS (odds ratio (OR) 0.70 per 10 μM increase in MP concentration, 95% CI 0.50-0.98, p = 0.042), but had no significant effect on hospital mortality. MP concentration was greatest in patients with sepsis, pneumonia, or aspiration as compared with those with trauma or receiving multiple blood transfusions. MP levels did not significantly change over time. The inverse association of MP levels with ARDS development was most striking in patients with sepsis. After controlling for age, presence of sepsis, and severity of illness, higher MP concentrations were independently associated with a reduced risk of developing ARDS (OR 0.69, 95% CI 0.49-0.98, p = 0.038). MP concentration was associated with reduced plasma recalcification time., Conclusions: Elevated levels of circulating MPs are independently associated with a reduced risk of ARDS in critically ill patients. Whether this is due to MP effects on systemic coagulation warrants further investigation.

Objectives: To determine the association between preadmission oral corticosteroid receipt and the development of acute respiratory distress syndrome in critically ill patients with sepsis., Design: Retrospective observational study., Setting: Medical, surgical, trauma, and cardiovascular ICUs of an academic medical center., Patients: A total of 1,080 critically ill patients with sepsis., Interventions: None., Measurements and Main Results: The unadjusted occurrence rate of acute respiratory distress syndrome within 96 hours of ICU admission was 35% among patients who had received oral corticosteroids compared with 42% among those who had not (p = 0.107). In a multivariable analysis controlling for prespecified confounders, preadmission oral corticosteroids were associated with a lower incidence of acute respiratory distress syndrome in the 96 hours after ICU admission (odds ratio, 0.53; 95% CI, 0.33-0.84; p = 0.008), a finding that persisted in multiple sensitivity analyses. The median daily dose of oral corticosteroids among the 165 patients receiving oral corticosteroids, in prednisone equivalents, was 10 mg (interquartile range, 5-30 mg). Higher doses of preadmission oral corticosteroids were associated with a lower incidence of acute respiratory distress syndrome (odds ratio for 30 mg of prednisone compared with 5 mg 0.53; 95% CI, 0.32-0.86). In multivariable analyses, preadmission oral corticosteroids were not associated with in-hospital mortality (odds ratio, 1.41; 95% CI, 0.87-2.28; p = 0.164), ICU length of stay (odds ratio, 0.90; 95% CI, 0.63-1.30; p = 0.585), or ventilator-free days (odds ratio, 1.06; 95% CI, 0.71-1.57; p = 0.783)., Conclusions: Among ICU patients with sepsis, preadmission oral corticosteroids were independently associated with a lower incidence of early acute respiratory distress syndrome.