Rethinking Acute Respiratory Distress Syndrome after COVID-19: If a "Better" Definition Is the Answer, What Is the Question?

Defining and subphenotyping ARDS: insights from an international Delphi expert panel

Although the definition of acute respiratory distress syndrome (ARDS) has undergone numerous revisions aimed at enhancing its diagnostic accuracy and clinical practicality, the usefulness and precision of these definitions remain matters of ongoing discussion. In this Position Paper, we report on a Delphi study to reach a consensus on the conceptual model of ARDS, specifically identifying its defining components within clinical, research, and educational contexts as well as exploring the potential role of subphenotyping. We did a four-round Delphi study, involving experts in ARDS research and management from a diverse range of geoeconomic regions and professional backgrounds. Consensus was achieved for the conceptual model of ARDS; key components to be included for an ARDS definition in the context of research, education, and patient management; and the need for further research in subphenotyping ARDS. Additionally, we highlight knowledge gaps and research priorities that could guide future investigations in this area. Our study builds on previous non-Delphi-based consensus processes (eg, the new global definition of ARDS and recent society-based guidelines) by using a rigorous Delphi method that ensured panellist anonymity and used clear quantitative criteria to mitigate potential peer pressure and group conformity. The findings underscore the need to refine the ARDS definition to better account for the heterogeneity of clinical presentations and underlying pathophysiology, and to improve diagnostic precision, including the use of subphenotyping where appropriate.

Acute respiratory distress syndrome

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.

Highlights from the Respiratory Failure and Mechanical Ventilation Conference 2024

The Respiratory Intensive Care Assembly of the European Respiratory Society gathered in Berlin to organise the third Respiratory Failure and Mechanical Ventilation Conference in February 2024. The conference covered key points of acute and chronic respiratory failure in adults. During the 3-day conference ventilatory strategies, patient selection, diagnostic approaches, treatment and health-related quality of life topics were addressed by a panel of international experts. In this article, lectures delivered during the event have been summarised by early career members of the Assembly and take-home messages highlighted.

Glucocorticoid therapy for acute respiratory distress syndrome: Current concepts

Acute respiratory distress syndrome (ARDS), a fatal critical disease, is induced by various insults. ARDS represents a major global public health burden, and the management of ARDS continues to challenge healthcare systems globally, especially during the pandemic of the coronavirus disease 2019 (COVID-19). There remains no confirmed specific pharmacotherapy for ARDS, despite advances in understanding its pathophysiology. Debate continues about the potential role of glucocorticoids (GCs) as a promising ARDS clinical therapy. Questions regarding GC agent, dose, and duration in patients with ARDS need to be answered, because of substantial variations in GC administration regimens across studies. ARDS heterogeneity likely affects the therapeutic actions of exogenous GCs. This review includes progress in determining the GC mechanisms of action and clinical applications in ARDS, especially during the COVID-19 pandemic.

Comparing the impact of targeting limited driving pressure to low tidal volume ventilation on mortality in mechanically ventilated adults with COVID-19 ARDS: an exploratory target trial emulation

BACKGROUND

An association between driving pressure (∆P) and the outcomes of invasive mechanical ventilation (IMV) may exist. However, the effect of a sustained limitation of ∆P on mortality in patients with acute respiratory distress syndrome (ARDS), including patients with COVID-19 (COVID-19-related acute respiratory distress syndrome (C-ARDS)) undergoing IMV, has not been rigorously evaluated. The use of emulations of a target trial in intensive care unit research remains in its infancy. To inform future, large ARDS target trials, we explored using a target trial emulation approach to analyse data from a cohort of IMV adults with C-ARDS to determine whether maintaining daily ∆p<15 cm H2O (in addition to traditional low tidal volume ventilation (LTVV) (tidal volume 5-7 cc/PBW+plateau pressure (Pplat) ≤30 cm H2O), compared with LTVV alone, affects the 28-day mortality.

METHODS

To emulate a target trial, adults with C-ARDS requiring >24 hours of IMV were considered to be assigned to limited ∆P or LTVV. Lung mechanics were measured twice daily after ventilator setting adjustments were made. To evaluate the effect of each lung-protective ventilation (LPV) strategy on the 28-day mortality, we fit a stabilised inverse probability weighted marginal structural model that adjusted for baseline and time-varying confounders known to affect protection strategy use/adherence or survival.

RESULTS

Among the 92 patients included, 27 (29.3%) followed limited ∆P ventilation, 23 (25.0%) the LTVV strategy and 42 (45.7%) received no LPV strategy. The adjusted estimated 28-day survival was 47.0% (95% CI 23%, 76%) in the limited ∆P group, 70.3% in the LTVV group (95% CI 37.6%, 100%) and 37.6% (95% CI 20.8%, 58.0%) in the no LPV strategy group.

INTERPRETATION

Limiting ∆P may not provide additional survival benefits for patients with C-ARDS over LTVV. Our results help inform the development of future target trial emulations focused on evaluating LPV strategies, including reduced ∆P, in adults with ARDS.

A bibliometric analysis of respiratory mechanics research related to acute respiratory distress syndrome from 1985 to 2023

Background

Acute respiratory distress syndrome (ARDS) is a severe condition characterized by lung stiffness and compromised gas exchange, often requiring mechanical ventilation for treatment. In addition to its clinical significance, understanding the publication trends and research patterns in respiratory mechanics related to ARDS can provide insights into the evolution of this field from a bibliometric perspective, aiding in strategic planning and resource allocation for future research endeavors.

Objective

This study aimed to explore the trends and identify the hotspots in respiratory mechanics research related to ARDS.

Methods

All relevant studies on respiratory mechanics of ARDS published between 1985 and 2023 were retrieved from the Web of Science Core Collection (WoSCC), and the retrieval strategy was topic search "TS = respiratory mechanics OR lung mechanics AND TS = ARDS OR acute respiratory distress syndrome." Annual trends, citation patterns, and contributions from countries, institutions, authors, and journals were analyzed using Bibliometrix Biblioshiny. Networks and overlay of authors, institutions, countries, journals, co-citations, and keywords were analyzed and visualized using VOSviewer.

Results

Our analysis included 1,248 articles published between 1985 and 2023, revealing fluctuations in publication output over time. The United States emerged as the leading contributor, with Critical Care Medicine being the most prominent journal. Key research themes included mechanical ventilation, acute lung injury, and protective ventilation strategies. International collaboration was evident, facilitating knowledge exchange and interdisciplinary cooperation.

Conclusion

Our study sheds light on the evolving landscape of respiratory mechanics research in ARDS. International collaboration is pivotal in advancing the field, while researchers increasingly focus on personalized approaches to address the complexities of ARDS respiratory mechanics.

End-expiratory lung volumes as a potential indicator for COVID-19 associated acute respiratory distress syndrome: a retrospective study

BACKGROUND

End-expiratory lung volume (EELV) has been observed to decrease in acute respiratory distress syndrome (ARDS). Yet, research investigating EELV in patients with COVID-19 associated ARDS (CARDS) remains limited. It is unclear whether EELV could serve as a potential metric for monitoring disease progression and identifying patients with ARDS at increased risk of adverse outcomes.

STUDY DESIGN AND METHODS

This retrospective study included mechanically ventilated patients diagnosed with CARDS during the initial phase of epidemic control in Shanghai. EELV was measured using the nitrogen washout-washin technique within 48 h post-intubation, followed by regular assessments every 3-4 days. Chest CT scans, performed within a 24-hour window around each EELV measurement, were analyzed using AI software. Differences in patient demographics, clinical data, respiratory mechanics, EELV, and chest CT findings were assessed using linear mixed models (LMM).

RESULTS

Out of the 38 patients enrolled, 26.3% survived until discharge from the ICU. In the survivor group, EELV, EELV/predicted body weight (EELV/PBW) and EELV/predicted functional residual capacity (EELV/preFRC) were significantly higher than those in the non-survivor group (survivor group vs. non-survivor group: EELV: 1455 vs. 1162 ml, P = 0.049; EELV/PBW: 24.1 vs. 18.5 ml/kg, P = 0.011; EELV/preFRC: 0.45 vs. 0.34, P = 0.005). Follow-up assessments showed a sustained elevation of EELV/PBW and EELV/preFRC among the survivors. Additionally, EELV exhibited a positive correlation with total lung volume and residual lung volume, while demonstrating a negative correlation with lesion volume determined through chest CT scans analyzed using AI software.

CONCLUSION

EELV is a useful indicator for assessing disease severity and monitoring the prognosis of patients with CARDS.

ARDS in solid organ transplant recipients hospitalized for COVID-19 based on the 2023 new definition

BACKGROUND

Solid organ transplant recipients (SOTRs) are more likely to suffer complications after being infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

OBJECTIVES

We aimed to describe the clinical features of SOTRs infected with SARS-CoV-2 and to assess independent risk factors associated with the development of acute respiratory distress syndrome (ARDS) following COVID-19 infection in SOTRs based on the new ARDS definition.

METHODS

358 SOTRs infected with SARS-CoV-2 were recruited and divided into two groups, patients with ARDS (n = 81) and patients without ARDS (n = 277). Demographic data, initial laboratory findings, therapeutic measures, and outcome indicators were compared between the two groups. The association between the onset of ARDS and related factors was analyzed using a logistic regression model. A nomogram was created to estimate the probability of developing ARDS.

RESULTS

Approximately 22.6 % (81/358) of hospitalized SOTRs infected with SARS-CoV-2 developed ARDS. In comparison to patients without ARDS, those with ARDS presented with more underlying conditions, decreased lymphocyte counts and serum albumin levels, but increased levels of leukocytes, serum creatinine, nitrogen urea, uric acid, and inflammatory markers. Cerebrovascular disease, leukocyte counts, albumin levels, and IL-6 levels were independent risk factors for the development of ARDS in this population. Furthermore, a nomogram prediction model was created utilizing the aforementioned factors to facilitate early prediction of ARDS, exhibiting an AUC (area under curve) of 0.81.

CONCLUSIONS

Cerebrovascular disease, leukocyte counts, albumin levels, and IL-6 levels were independent risk factors for the development of ARDS following COVID-19 infection in SOTRs.

Post-pandemic acute respiratory distress syndrome: A New Global Definition with extension to lower-resource regions

Acute respiratory distress syndrome (ARDS), first described in 1967, is characterized by acute respiratory failure causing profound hypoxemia, decreased pulmonary compliance, and bilateral CXR infiltrates. After several descriptions, the Berlin definition was adopted in 2012, which established three categories of severity according to hypoxemia (mild, moderate and severe), specified temporal aspects for diagnosis, and incorporated the use of non-invasive ventilation. The COVID-19 pandemic led to changes in ARDS management, focusing on continuous monitoring of oxygenation and on utilization of high-flow oxygen therapy and lung ultrasound. In 2021, a New Global Definition based on the Berlin definition of ARDS was proposed, which included a category for non-intubated patients, considered the use of SpO2, and established no particular requirement for oxygenation support in regions with limited resources. Although debates persist, the continuous evolution seeks to adapt to clinical and epidemiological needs, and to the search of personalized treatments.

Consensus statements on the utility of defining ARDS and the utility of past and current definitions of ARDS-protocol for a Delphi study

INTRODUCTION

Acute respiratory distress syndrome (ARDS), marked by acute hypoxemia and bilateral pulmonary infiltrates, has been defined in multiple ways since its first description. This Delphi study aims to collect global opinions on the conceptual framework of ARDS, assess the usefulness of components within current and past definitions and investigate the role of subphenotyping. The varied expertise of the panel will provide valuable insights for refining future ARDS definitions and improving clinical management.

METHODS

A diverse panel of 35-40 experts will be selected based on predefined criteria. Multiple choice questions (MCQs) or 7-point Likert-scale statements will be used in the iterative Delphi rounds to achieve consensus on key aspects related to the utility of definitions and subphenotyping. The Delphi rounds will be continued until a stable agreement or disagreement is achieved for all statements.

ANALYSIS

Consensus will be considered as reached when a choice in MCQs or Likert-scale statement achieved ≥80% of votes for agreement or disagreement. The stability will be checked by non-parametric χ2 tests or Kruskal Wallis test starting from the second round of Delphi process. A p-value ≥0.05 will be used to define stability.

ETHICS AND DISSEMINATION

The study will be conducted in full concordance with the principles of the Declaration of Helsinki and will be reported according to CREDES guidance. This study has been granted an ethical approval waiver by the NMC Healthcare Regional Research Ethics Committee, Dubai (NMCHC/CR/DXB/REC/APP/002), owing to the nature of the research. Informed consent will be obtained from all panellists before the start of the Delphi process. The study will be published in a peer-review journal with the authorship agreed as per ICMJE requirements.

TRIAL REGISTRATION NUMBER

NCT06159465.

Prone position in the mechanical ventilation of acute respiratory distress syndrome children: a systematic review and meta-analysis

Background

Prone position has been well recognized for the treatment of adult acute respiratory distress syndrome (ARDS). We aimed to evaluate the role of prone position in the mechanical ventilation in children with ARDS, to provide evidence to the treatment and care of children with ARDS.

Methods

We searched the Pubmed et al. databases by computer until January 23, 2024 for randomized controlled trials (RCTs) on the role of prone position in the mechanical ventilation in children with ARDS. We evaluated the quality of included studies according to the quality evaluation criteria recommended by the Cochrane library. RevMan 5.3 software was used for meta-analysis.

Results

7 RCTs involving 433 children with ARDS were included. Meta-analysis indicated that prone position is beneficial to improve the arterial oxygenation pressure [MD = 4.27 mmHg, 95% CI (3.49, 5.06)], PaO2/FiO2 [MD = 26.97, 95% CI (19.17, 34.77)], reduced the oxygenation index [MD = -3.52, 95% CI (-5.41, -1.64)], mean airway pressure [MD = -1.91 cmH2O, 95% CI (-2.27, -1.55)] and mortality [OR = 0.33, 95% CI (0.15, 0.73), all P < 0.05]. There were no statistical differences in the duration of mechanical ventilation between the prone position group and control group [MD = -17.01, 97.27, 95% CI (-38.28, 4.26), P = 0.12]. Egger test results showed that no significant publication bias was found (all P > 0.05).

Conclusions

Prone position ventilation has obvious advantages in improving oxygenation, but there is no significant improvement in the time of mechanical ventilation in the treatment of children with ARDS. In the future, more large-sample, high-quality RCTs are still needed to further analyze the role of prone position in the mechanical ventilation in children with ARDS.

A New Global Definition of Acute Respiratory Distress Syndrome

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 PaO2:FiO2 ⩽ 300 mm Hg or oxygen saturation as measured by pulse oximetry SpO2:FiO2 ⩽ 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.

Hypoxemia Trajectory of Non-COVID-19 Acute Respiratory Distress Syndrome Patients. An Observational Study Focusing on Hypoxemia Resolver Status

IMPORTANCE

Most studies on acute respiratory distress syndrome (ARDS) group patients by severity based on their initial degree of hypoxemia. However, this grouping has limitations, including inconsistent hypoxemia trajectories and outcomes.

OBJECTIVES

This study explores the benefits of grouping patients by resolver status based on their hypoxemia progression over the first 7 days.

DESIGN SETTING AND PARTICIPANTS

This is an observational study from a large single-center database. Medical Information Mart for Intensive Care (MIMIC)-IV and MIMIC Chest X-ray JPEG databases were used. Mechanically ventilated patients that met the Berlin ARDS criteria were included.

MAIN OUTCOMES AND MEASURES

The primary outcome was the proportion of hypoxemia resolvers vs. nonresolvers in non-COVID-19 ARDS patients. Nonresolvers were defined as those whose hypoxemia worsened or remained moderate or severe over the first 7 days. Secondary outcomes included baseline admission characteristics, initial blood gases and ventilation settings, length of invasive mechanical ventilation, length of ICU stay, and ICU survival rates across resolver groups.

RESULTS

A total of 894 ICU admissions were included in the study. Of these, 33.9% were hypoxemia nonresolvers. The resolver groups showed no significant difference in age, body mass index, comorbidities, or Charlson score. There was no significant difference in the percentage of those with initial severe hypoxemia between the two groups (8.1% vs. 9.2%; p = 0.126). The initial Pao2/Fio2 ratio did not significantly increase the odds ratio (OR) of being a nonresolver (OR, 0.84; 95% CI, 0.65-1.10). Nonresolver mortality was 61.4%, comparable to the survival rates seen in nonresolvers in a previous large COVID-19 ARDS study.

CONCLUSIONS AND RELEVANCE

Our study shows that resolver status is a valuable grouping in ARDS. It has significant advantages over grouping by initial degree of hypoxemia, including better mapping of trajectory and comparable outcomes across other studies. While it may offer insights into disease-specific associations, future studies should include resolver status analysis for more definitive conclusions.

Evaluating construct validity of computable acute respiratory distress syndrome definitions in adults hospitalized with COVID-19: an electronic health records based approach

BACKGROUND

Evolving ARDS epidemiology and management during COVID-19 have prompted calls to reexamine the construct validity of Berlin criteria, which have been rarely evaluated in real-world data. We developed a Berlin ARDS definition (EHR-Berlin) computable in electronic health records (EHR) to (1) assess its construct validity, and (2) assess how expanding its criteria affected validity.

METHODS

We performed a retrospective cohort study at two tertiary care hospitals with one EHR, among adults hospitalized with COVID-19 February 2020-March 2021. We assessed five candidate definitions for ARDS: the EHR-Berlin definition modeled on Berlin criteria, and four alternatives informed by recent proposals to expand criteria and include patients on high-flow oxygen (EHR-Alternative 1), relax imaging criteria (EHR-Alternatives 2-3), and extend timing windows (EHR-Alternative 4). We evaluated two aspects of construct validity for the EHR-Berlin definition: (1) criterion validity: agreement with manual ARDS classification by experts, available in 175 patients; (2) predictive validity: relationships with hospital mortality, assessed by Pearson r and by area under the receiver operating curve (AUROC). We assessed predictive validity and timing of identification of EHR-Berlin definition compared to alternative definitions.

RESULTS

Among 765 patients, mean (SD) age was 57 (18) years and 471 (62%) were male. The EHR-Berlin definition classified 171 (22%) patients as ARDS, which had high agreement with manual classification (kappa 0.85), and was associated with mortality (Pearson r = 0.39; AUROC 0.72, 95% CI 0.68, 0.77). In comparison, EHR-Alternative 1 classified 219 (29%) patients as ARDS, maintained similar relationships to mortality (r = 0.40; AUROC 0.74, 95% CI 0.70, 0.79, Delong test P = 0.14), and identified patients earlier in their hospitalization (median 13 vs. 15 h from admission, Wilcoxon signed-rank test P < 0.001). EHR-Alternative 3, which removed imaging criteria, had similar correlation (r = 0.41) but better discrimination for mortality (AUROC 0.76, 95% CI 0.72, 0.80; P = 0.036), and identified patients median 2 h (P < 0.001) from admission.

CONCLUSIONS

The EHR-Berlin definition can enable ARDS identification with high criterion validity, supporting large-scale study and surveillance. There are opportunities to expand the Berlin criteria that preserve predictive validity and facilitate earlier identification.

ESICM guidelines on acute respiratory distress syndrome: definition, phenotyping and respiratory support strategies

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.

Caring for Patients With Acute Respiratory Distress Syndrome: Summary of the 2023 ESICM Practice Guidelines

This article summarizes the 2023 updated ARDS guidelines from the European Society of Intensive Care Medicine, including the guidelines’ methods, findings, and implications, along with reflections on next steps.

ARDS: hidden perils of an overburdened diagnosis

A diagnosis of ARDS serves as a pretext for several perilous clinical practices. Clinical trials demonstrated that tidal volume 12 ml/kg increases patient mortality, but 6 ml/kg has not proven superior to 11 ml/kg or anything in between. Present guidelines recommend 4 ml/kg, which foments severe air hunger, leading to prescription of hazardous (yet ineffective) sedatives, narcotics and paralytic agents. Inappropriate lowering of tidal volume also fosters double triggering, which promotes alveolar overdistention and lung injury. Successive panels have devoted considerable energy to developing a more precise definition of ARDS to homogenize the recruitment of patients into clinical trials. Each of three pillars of the prevailing Berlin definition is extremely flimsy and the source of confusion and unscientific practices. For doctors at the bedside, none of the revisions have enhanced patient care over that using the original 1967 description of Ashbaugh and colleagues. Bedside doctors are better advised to diagnose ARDS on the basis of pattern recognition and instead concentrate their vigilance on resolving the numerous hidden dangers that follow inevitably once a diagnosis has been made.