Interobserver variability in applying a radiographic definition for ARDS

Global and Regional Diagnostic Accuracy of Lung Ultrasound Compared to CT in Patients With Acute Respiratory Distress Syndrome

OBJECTIVES

Lung CT is the reference imaging technique for acute respiratory distress syndrome, but requires transportation outside the intensive care and x-ray exposure. Lung ultrasound is a promising, inexpensive, radiation-free, tool for bedside imaging. Aim of the present study was to compare the global and regional diagnostic accuracy of lung ultrasound and CT scan.

DESIGN

A prospective, observational study.

SETTING

Intensive care and radiology departments of a University hospital.

PATIENTS

Thirty-two sedated, paralyzed acute respiratory distress syndrome patients (age 65 ± 14 yr, body mass index 25.9 ± 6.5 kg/m, and PaO2/FIO2 139 ± 47).

INTERVENTIONS

Lung CT scan and lung ultrasound were performed at positive end-expiratory pressure 5 cm H2O. A standardized assessment of six regions per hemithorax was used; each region was classified for the presence of normal aeration, alveolar-interstitial syndrome, consolidation, and pleural effusion. Agreement between the two techniques was calculated, and diagnostic variables were assessed for lung ultrasound using lung CT as a reference.

MEASUREMENTS AND MAIN RESULTS

Global agreement between lung ultrasound and CT ranged from 0.640 (0.391-0.889) to 0.934 (0.605-1.000) and was on average 0.775 (0.577-0.973). The overall sensitivity and specificity of lung ultrasound ranged from 82.7% to 92.3% and from 90.2% to 98.6%, respectively. Similar results were found with regional analysis. The diagnostic accuracy of lung ultrasound was significantly higher when those patterns not reaching the pleural surface were excluded (area under the receiver operating characteristic curve: alveolar-interstitial syndrome 0.854 [0.821-0.887] vs 0.903 [0.852-0.954]; p = 0.049 and consolidation 0.851 [0.818-0.884] vs 0.896 [0.862-0.929]; p = 0.044).

CONCLUSIONS

Lung ultrasound is a reproducible, sensitive, and specific tool, which allows for bedside detections of the morphologic patterns in acute respiratory distress syndrome. The presence of deep lung alterations may impact the diagnostic performance of this technique.

Prognostic relevance and inter-observer reliability of chest-imaging in pediatric ARDS: a pediatric acute respiratory distress incidence and epidemiology (PARDIE) study

Purpose

Definitions of acute respiratory distress syndrome (ARDS) include radiographic criteria, but there are concerns about reliability and prognostic relevance. This study aimed to evaluate the independent relationship between chest imaging and mortality and examine the inter-rater variability of interpretations of chest radiographs (CXR) in pediatric ARDS (PARDS).

Methods

Prospective, international observational study in children meeting Pediatric Acute Lung Injury Consensus Conference (PALICC) criteria for PARDS, which requires new infiltrate(s) consistent with pulmonary parenchymal disease, without mandating bilateral infiltrates. Mortality analysis focused on the entire cohort, whereas inter-observer variability used a subset of patients with blinded, simultaneous interpretation of CXRs by intensivists and radiologists.

Results

Bilateral infiltrates and four quadrants of alveolar consolidation were associated with mortality on a univariable basis, using CXRs from 708 patients with PARDS. For patients on either invasive (IMV) or non-invasive ventilation (NIV) with PaO₂/FiO₂ (PF) ratios (or SpO₂/FiO₂ (SF) ratio equivalent) > 100, neither bilateral infiltrates (OR 1.3 (95% CI 0.68, 2.5), p = 0.43), nor 4 quadrants of alveolar consolidation (OR 1.6 (0.85, 3), p = 0.14) were associated with mortality. For patients with PF ≤ 100, bilateral infiltrates (OR 3.6 (1.4, 9.4), p = 0.01) and four quadrants of consolidation (OR 2.0 (1.14, 3.5), p = 0.02) were associated with higher mortality. A subset of 702 CXRs from 233 patients had simultaneous interpretations. Interobserver agreement for bilateral infiltrates and quadrants was “slight” (kappa 0.31 and 0.33). Subgroup analysis showed agreement did not differ when stratified by PARDS severity but was slightly higher for children with chronic respiratory support (kappa 0.62), NIV at PARDS diagnosis (kappa 0.53), age > 10 years (kappa 0.43) and fluid balance > 40 ml/kg (kappa 0.48).

Conclusion

Bilateral infiltrates and quadrants of alveolar consolidation are associated with mortality only for those with PF ratio ≤ 100, although there is high- inter-rater variability in these chest-x ray parameters.

Electronic supplementary material

The online version of this article (10.1007/s00134-020-06074-7) contains supplementary material, which is available to authorized users.

Systems Biology ARDS Research with a Focus on Metabolomics

Acute respiratory distress syndrome (ARDS) is a clinical syndrome that inflicts a considerably heavy toll in terms of morbidity and mortality. While there are multitudes of conditions that can lead to ARDS, the vast majority of ARDS cases are caused by a relatively small number of diseases, especially sepsis and pneumonia. Currently, there is no clinically agreed upon reliable diagnostic test for ARDS, and the detection or diagnosis of ARDS is based on a constellation of laboratory and radiological tests in the absence of evidence of left ventricular dysfunction, as specified by the Berlin definition of ARDS. Virtually all the ARDS biomarkers to date have been proven to be of very limited clinical utility. Given the heterogeneity of ARDS due to the wide variation in etiology, clinical and molecular manifestations, there is a current scientific consensus agreement that ARDS is not just a single entity but rather a spectrum of conditions that need further study for proper classification, the identification of reliable biomarkers and the adequate institution of therapeutic targets. This scoping review aims to elucidate ARDS omics research, focusing on metabolomics and how metabolomics can boost the study of ARDS biomarkers and help to facilitate the identification of ARDS subpopulations.

Using lung ultrasound to quantitatively evaluate pulmonary water content

BACKGROUND

Increases in extravascular lung water (EVLW) can lead to respiratory failure. This study aimed to investigate whether the B-line score (BLS) was correlated with the EVLW content determined by the lung wet/dry ratio in a rabbit model.

METHODS

A total of 45 New Zealand rabbits were randomly assigned to nine groups. Among the animals, models of various lung water content levels were induced by the infusion of different volumes of warm sterile normal saline (NS) via the endotracheal tube. The arterial blood gas, spontaneous respiratory rate, and PaO₂ /FiO₂ ratio were detected before and after infusion. In addition, the B-lines were determined before and immediately after infusion in each group. Finally, both lungs were resected to determine the wet/dry ratio. In addition, all lung specimens were analyzed histologically, and EVLW was quantified using the BLS based on the number and confluence of B-lines in the intercostal space.

RESULTS

The BLS increased with increasing infusion volume. The BLS was statistically correlated with the wet/dry ratio (r² = .946) and with the PaO₂ /FiO₂ ratio (r² = .916). Furthermore, a repeatability study was performed for the lung ultrasound (LUS) technology (Bland-Altman plots), and the results suggest that LUS had favorable intraobserver and interobserver reproducibility.

CONCLUSIONS

This study is the first to suggest that the BLS can serve as a sensitive, quantitative, noninvasive, and real-time indicator of EVLW in a rabbit model of lung water accumulation. Notably, the BLS displayed an obvious correlation with the experimental gravimetry results and could also be used to predict the pulmonary oxygenation status.

Effect of Intravenous Interferon β-1a on Death and Days Free From Mechanical Ventilation Among Patients With Moderate to Severe Acute Respiratory Distress Syndrome: A Randomized Clinical Trial

IMPORTANCE

Acute respiratory distress syndrome (ARDS) is associated with high mortality. Interferon (IFN) β-1a may prevent the underlying event of vascular leakage.

OBJECTIVE

To determine the efficacy and adverse events of IFN-β-1a in patients with moderate to severe ARDS.

DESIGN, SETTING, AND PARTICIPANTS

Multicenter, randomized, double-blind, parallel-group trial conducted at 74 intensive care units in 8 European countries (December 2015-December 2017) that included 301 adults with moderate to severe ARDS according to the Berlin definition. The radiological and partial pressure of oxygen, arterial (Pao2)/fraction of inspired oxygen (Fio2) criteria for ARDS had to be met within a 24-hour period, and the administration of the first dose of the study drug had to occur within 48 hours of the diagnosis of ARDS. The last patient visit was on March 6, 2018.

INTERVENTIONS

Patients were randomized to receive an intravenous injection of 10 μg of IFN-β-1a (144 patients) or placebo (152 patients) once daily for 6 days.

MAIN OUTCOMES AND MEASURES

The primary outcome was a score combining death and number of ventilator-free days at day 28 (score ranged from -1 for death to 27 if the patient was off ventilator on the first day). There were 16 secondary outcomes, including 28-day mortality, which were tested hierarchically to control type I error.

RESULTS

Among 301 patients who were randomized (mean age, 58 years; 103 women [34.2%]), 296 (98.3%) completed the trial and were included in the primary analysis. At 28 days, the median composite score of death and number of ventilator-free days at day 28 was 10 days (interquartile range, -1 to 20) in the IFN-β-1a group and 8.5 days (interquartile range, 0 to 20) in the placebo group (P = .82). There was no significant difference in 28-day mortality between the IFN-β-1a vs placebo groups (26.4% vs 23.0%; difference, 3.4% [95% CI, -8.1% to 14.8%]; P = .53). Seventy-four patients (25.0%) experienced adverse events considered to be related to treatment during the study (41 patients [28.5%] in the IFN-β-1a group and 33 [21.7%] in the placebo group).

CONCLUSIONS AND RELEVANCE

Among adults with moderate or severe ARDS, intravenous IFN-β-1a administered for 6 days, compared with placebo, resulted in no significant difference in a composite score that included death and number of ventilator-free days over 28 days. These results do not support the use of IFN-β-1a in the management of ARDS.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02622724.

Time to stop randomized and large pragmatic trials for intensive care medicine syndromes: the case of sepsis and acute respiratory distress syndrome

In this paper we discuss the limitations of large randomized controlled trials with mortality endpoints in patients with critical illness associated diagnoses such as sepsis. When patients with the same syndrome diagnosis do not share the pathways that lead to death (the attributable risk), any therapy can only lead to small effects in these populations. Using Monte Carlo simulations, we show how the syndrome-attributable risks of critical illness-associated diagnoses are likely overestimated using common statistical methods. This overestimation of syndrome-attributable risks leads to a corresponding overestimation of attainable treatment effects and an underestimation of required sample sizes. We demonstrate that larger and more 'pragmatic' randomized trials are not the solution because they decrease therapeutic and diagnostic precision, the therapeutic effect size and the probability of finding a beneficial effect. Finally, we argue that the most logical solution is a renewed focus on mechanistic research into the complexities of critical illness syndromes.

Imaging of Diffuse Lung Disease in the Intensive Care Unit Patient

There is a wide variety of causes of diffuse lung disease in the intensive care unit patient, of which adult respiratory distress syndrome is the commonest clinical consideration. Plain radiography, computed tomography, and ultrasound can be used synergistically to evaluate patients with diffuse lung disease and respiratory impairment. Imaging is not limited to characterization of the cause of diffuse lung disease but also aids in monitoring its evolution and in ventilator setting management.

ERS statement on chest imaging in acute respiratory failure

Chest imaging in patients with acute respiratory failure plays an important role in diagnosing, monitoring and assessing the underlying disease. The available modalities range from plain chest X-ray to computed tomography, lung ultrasound, electrical impedance tomography and positron emission tomography. Surprisingly, there are presently no clear-cut recommendations for critical care physicians regarding indications for and limitations of these different techniques.The purpose of the present European Respiratory Society (ERS) statement is to provide physicians with a comprehensive clinical review of chest imaging techniques for the assessment of patients with acute respiratory failure, based on the scientific evidence as identified by systematic searches. For each of these imaging techniques, the panel evaluated the following items: possible indications, technical aspects, qualitative and quantitative analysis of lung morphology and the potential interplay with mechanical ventilation. A systematic search of the literature was performed from inception to September 2018. A first search provided 1833 references. After evaluating the full text and discussion among the committee, 135 references were used to prepare the current statement.These chest imaging techniques allow a better assessment and understanding of the pathogenesis and pathophysiology of patients with acute respiratory failure, but have different indications and can provide additional information to each other.

Imaging the Injured Lung: Mechanisms of Action and Clinical Use

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

Acute Respiratory Distress Syndrome Phenotypes

The acute respiratory distress syndrome (ARDS) phenotype was first described over 50 years ago and since that time significant progress has been made in understanding the biologic processes underlying the syndrome. Despite this improved understanding, no pharmacologic therapies aimed at the underlying biology have been proven effective in ARDS. Increasingly, ARDS has been recognized as a heterogeneous syndrome characterized by subphenotypes with distinct clinical, radiographic, and biologic differences, distinct outcomes, and potentially distinct responses to therapy. The Berlin Definition of ARDS specifies three severity classifications: mild, moderate, and severe based on the PaO₂ to FiO₂ ratio. Two randomized controlled trials have demonstrated a potential benefit to prone positioning and neuromuscular blockade in moderate to severe phenotypes of ARDS only. Precipitating risk factor, direct versus indirect lung injury, and timing of ARDS onset can determine other clinical phenotypes of ARDS after admission. Radiographic phenotypes of ARDS have been described based on a diffuse versus focal pattern of infiltrates on chest imaging. Finally and most promisingly, biologic subphenotypes or endotypes have increasingly been identified using plasma biomarkers, genetics, and unbiased approaches such as latent class analysis. The potential of precision medicine lies in identifying novel therapeutics aimed at ARDS biology and the subpopulation within ARDS most likely to respond. In this review, we discuss the challenges and approaches to subphenotype ARDS into clinical, radiologic, severity, and biologic phenotypes with an eye toward the future of precision medicine in critical care.

Lung injury prediction scores: Clinical validation and C-reactive protein involvement in high risk patients

OBJECTIVE

A study was made to validate two previously derived lung injury prediction scores (LIPS) for the prediction of acute respiratory distress syndrome (ARDS) in high risk intensive care patients, with the incorporation of C-reactive protein (CRP) for improving score accuracy.

DESIGN

A prospective, observational cohort study was carried out.

PATIENTS

A total of 200 patients with APACHE II score ≥15 and at least one ARDS risk factor upon ICU admission were included.

INTERVENTIONS

Calculation of LIPS using formulas developed by Cartin-Ceba et al. (2009) and Trillo-Alvarez et al. (2011) (LIPS-2009 and LIPS-2011). C-reactive protein was measured upon admission (CRP-0) and after 48h (CRP-48).

MAIN VARIABLES OF INTEREST

Independent variables: LIPS-2009, LIPS-2011 and CRP values. Dependent variable: development of ARDS.

RESULTS

Eighty-eight patients (44%) developed ARDS after a median (Q₁-Q₃) of 2.5 (1.3-6.8) days. The LIPS-2009 and LIPS-2011 scores were 4 (3-6) and 5 (3.6-6.5) in ARDS patients compared to 2 (1-4) and 3.5 (1.5-4.5) in non-ARDS patients (p<0.001). CRP-48 was 96 (67.5-150.3)mg/L and 48 (24-96)mg/L in the two groups, respectively (p<0.001). ΔCRP (i.e., CRP-48 minus CRP-0) was significantly higher in the ARDS patients (p<0.001). The AUC was 0.740 and 0.738 for LIPS-2011 and LIPS-2009, respectively - the difference being nonsignificant (p=0.9, 0.9 and 0.8 for pairwise comparison of the different ROC curves). Integrating ΔCRP with LIPS-2011 using binary logistic regression analysis identified a new score (LIPS-N) with AUC 0.803, which was significantly higher than the AUC of LIPS-2011 (p=0.01).

CONCLUSIONS

Both LIPS scores are equally effective in predicting ARDS in high risk ICU patients. Integrating the change in CRP within the score might improve its accuracy.

Differences between Patients in Whom Physicians Agree and Disagree about the Diagnosis of Acute Respiratory Distress Syndrome

RATIONALE

Because the Berlin definition of acute respiratory distress syndrome (ARDS) has only moderate reliability, physicians disagree about the diagnosis of ARDS in some patients. Understanding the clinical differences between patients with agreement and disagreement about the diagnosis of ARDS may provide insight into the epidemiology and pathophysiology of this syndrome, and inform strategies to improve the reliability of ARDS diagnosis.

OBJECTIVES

To characterize patients with diagnostic disagreement about ARDS among critical-care-trained physicians and compare them with patients with a consensus that ARDS developed.

METHODS

Patients with acute hypoxemic respiratory failure (arterial oxygen tension/pressure [PaO2]/fraction of inspired oxygen [FiO2] < 300 during invasive mechanical ventilation) were independently reviewed for ARDS by multiple critical-care physicians and categorized as consensus-ARDS, disagreement about the diagnosis, or no ARDS.

RESULTS

Among 738 patients reviewed, 110 (15%) had consensus-ARDS, 100 (14%) had disagreement, and 528 (72%) did not have ARDS. ARDS diagnosis rates ranged from 9% to 47% across clinicians. Patients with disagreement had baseline comorbidity rates similar to those of patients with consensus-ARDS, but lower rates of ARDS risk factors and less severe measures of lung injury. Mean days of severe hypoxemia (PaO2/FiO2 < 100) were 3.2 (95% confidence interval [CI], 2.6-3.9), 2.0 (95% CI, 1.5-2.4), and 0.8 (95% CI, 0.7-0.9) among patients with consensus-ARDS, disagreement, and no ARDS, respectively. Hospital mortality was 37% (95% CI, 28-46%), 35% (95% CI, 26-44%), and 19% (95% CI, 15-22%) across groups. Simple combinations of specific ARDS risk factors and lowest PaO2/FiO2 value could effectively discriminate patients (area under the receiver operating characteristic curve = 0.90; 95% CI, 0.88-0.92). For example, 63% of patients with pneumonia, shock, and PaO2/FiO2 < 110 had consensus-ARDS, whereas 100% of patients without pneumonia or shock and PaO2/FiO2 > 180 did not have ARDS.

CONCLUSIONS

Disagreement about the diagnosis of ARDS is common and can be partly explained by the difficulty of dichotomizing patients along a continuous spectrum of ARDS manifestations. Considering both the presence of key ARDS risk factors and hypoxemia severity can help guide clinicians in identifying patients with diagnosis of ARDS agreed upon by a consensus of physicians.

Acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a common cause of respiratory failure in critically ill patients and is defined by the acute onset of noncardiogenic pulmonary oedema, hypoxaemia and the need for mechanical ventilation. ARDS occurs most often in the setting of pneumonia, sepsis, aspiration of gastric contents or severe trauma and is present in ~10% of all patients in intensive care units worldwide. Despite some improvements, mortality remains high at 30-40% in most studies. Pathological specimens from patients with ARDS frequently reveal diffuse alveolar damage, and laboratory studies have demonstrated both alveolar epithelial and lung endothelial injury, resulting in accumulation of protein-rich inflammatory oedematous fluid in the alveolar space. Diagnosis is based on consensus syndromic criteria, with modifications for under-resourced settings and in paediatric patients. Treatment focuses on lung-protective ventilation; no specific pharmacotherapies have been identified. Long-term outcomes of patients with ARDS are increasingly recognized as important research targets, as many patients survive ARDS only to have ongoing functional and/or psychological sequelae. Future directions include efforts to facilitate earlier recognition of ARDS, identifying responsive subsets of patients and ongoing efforts to understand fundamental mechanisms of lung injury to design specific treatments.

Paediatric acute respiratory distress syndrome incidence and epidemiology (PARDIE): an international, observational study

BACKGROUND

Paediatric acute respiratory distress syndrome (PARDS) is associated with high mortality in children, but until recently no paediatric-specific diagnostic criteria existed. The Pediatric Acute Lung Injury Consensus Conference (PALICC) definition was developed to overcome limitations of the Berlin definition, which was designed and validated for adults. We aimed to determine the incidence and outcomes of children who meet the PALICC definition of PARDS.

METHODS

In this international, prospective, cross-sectional, observational study, 145 paediatric intensive care units (PICUs) from 27 countries were recruited, and over a continuous 5 day period across 10 weeks all patients were screened for enrolment. Patients were included if they had a new diagnosis of PARDS that met PALICC criteria during the study week. Exclusion criteria included meeting PARDS criteria more than 24 h before screening, cyanotic heart disease, active perinatal lung disease, and preparation or recovery from a cardiac intervention. Data were collected on the PICU characteristics, patient demographics, and elements of PARDS (ie, PARDS risk factors, hypoxaemia severity metrics, type of ventilation), comorbidities, chest imaging, arterial blood gas measurements, and pulse oximetry. The primary outcome was PICU mortality. Secondary outcomes included 90 day mortality, duration of invasive mechanical and non-invasive ventilation, and cause of death.

FINDINGS

Between May 9, 2016, and June 16, 2017, during the 10 study weeks, 23 280 patients were admitted to participating PICUs, of whom 744 (3·2%) were identified as having PARDS. 95% (708 of 744) of patients had complete data for analysis, with 17% (121 of 708; 95% CI 14-20) mortality, whereas only 32% (230 of 708) of patients met Berlin criteria with 27% (61 of 230) mortality. Based on hypoxaemia severity at PARDS diagnosis, mortality was similar among those who were non-invasively ventilated and with mild or moderate PARDS (10-15%), but higher for those with severe PARDS (33% [54 of 165; 95% CI 26-41]). 50% (80 of 160) of non-invasively ventilated patients with PARDS were subsequently intubated, with 25% (20 of 80; 95% CI 16-36) mortality. By use of PALICC PARDS definition, severity of PARDS at 6 h after initial diagnosis (area under the curve [AUC] 0·69, 95% CI 0·62-0·76) discriminates PICU mortality better than severity at PARDS diagnosis (AUC 0·64, 0·58-0·71), and outperforms Berlin severity groups at 6 h (0·64, 0·58-0·70; p=0·01).

INTERPRETATION

The PALICC definition identified more children as having PARDS than the Berlin definition, and PALICC PARDS severity groupings improved the stratification of mortality risk, particularly when applied 6 h after PARDS diagnosis. The PALICC PARDS framework should be considered for use in future epidemiological and therapeutic research among children with PARDS.

FUNDING

University of Southern California Clinical Translational Science Institute, Sainte Justine Children's Hospital, University of Montreal, Canada, Réseau en Santé Respiratoire du Fonds de Recherche Quebec-Santé, and Children's Hospital Los Angeles, Department of Anesthesiology and Critical Care Medicine.

Chest radiography versus lung ultrasound for identification of acute respiratory distress syndrome: a retrospective observational study

Background

Lung ultrasound may be a reasonable alternative to chest radiography for the identification of acute respiratory distress syndrome (ARDS), but the diagnostic performance of lung ultrasound for ARDS is uncertain. We therefore analyzed the clinical outcomes of ARDS diagnosed according to the Berlin Definition, using either chest radiography (Berlin-CXR) or lung ultrasound (Berlin-LUS) as an alternative imaging method.

Methods

This was a retrospective observational study in a 20-bed medical intensive care unit (ICU). Patients who required noninvasive ventilation or invasive ventilation for hypoxemic respiratory failure on ICU admission from August 2014 to March 2017 were included. Both chest radiography and lung ultrasound were performed routinely upon ICU admission. Comparisons were made using either the Berlin-CXR or Berlin-LUS definitions to diagnose ARDS with respect to the patient characteristics and clinical outcomes for each definition. ICU and hospital mortality were the main outcome measures for both definitions.

Results

The first admissions of 456 distinct patients were analyzed. Compared with the 216 patients who met the Berlin-CXR definition (ICU mortality 19.4%, hospital mortality 36.1%), 229 patients who met the Berlin-LUS definition (ICU mortality 22.7%, hospital mortality 34.5%) and 79 patients who met the Berlin-LUS but not the Berlin-CXR definition (ICU mortality 21.5%, hospital mortality 29.1%) had similar outcomes. In contrast, the 295 patients who met either definition had higher mortality than the 161 patients who did not meet either definition (ICU mortality 20.0% versus 12.4%, P = 0.041; hospital mortality 34.2% versus 24.2%, P = 0.027). Compared with Berlin-CXR, Berlin-LUS had a positive predictive value of 0.66 (95% confidence interval 0.59–0.72) and a negative predictive value of 0.71 (0.65–0.77). Among the 216 Berlin-CXR ARDS patients, 150 patients (69.4%) also fulfilled Berlin-LUS definition.

Conclusions

For the identification of ARDS using the Berlin definition, both chest radiography and lung ultrasound were equally related to mortality. The Berlin definition using lung ultrasound helped identify patients at higher risk of death, even if these patients did not fulfill the conventional Berlin definition using chest radiography. However, the moderate overlap of patients when chest imaging modalities differed suggests that chest radiography and lung ultrasound should be complementary rather than used interchangeably.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2105-y) contains supplementary material, which is available to authorized users.

Mild to Moderate to Severe: What Drives the Severity of ARDS in Trauma Patients?

Acute respiratory distress syndrome (ARDS) is a complex inflammatory process with multifactorial etiologies. Risk factors for its development have been extensively studied, but factors associated with worsening severity of disease, as defined by the Berlin criteria, are poorly understood. A retrospective chart and trauma registry review identified trauma patients in our surgical intensive care unit who developed ARDS, defined according to the Berlin definition, between 2010 and 2015. The primary outcome was development of mild, moderate, or severe ARDS. A logistic regression model identified risk factors associated with developing ARDS and with worsening severity of disease. Of 2704 total patients, 432 (16%) developed ARDS. Of those, 100 (23%) were categorized as mild, 176 (41%) as moderate, and 156 (36%) as severe. Two thousand two hundred and seventy-two patients who did not develop ARDS served as controls. Male gender, blunt trauma, severe head and chest injuries, and red blood cell as well as total blood product transfusions are independent risk factors associated with ARDS. Worsening severity of disease is associated with severe chest trauma and volume of plasma transfusion. Novel findings in our study include the association between plasma transfusions and specifically severe chest trauma with worsening severity of ARDS in trauma patients.

Continued under-recognition of acute respiratory distress syndrome after the Berlin definition: what is the solution?

PURPOSE OF REVIEW

Timely recognition of acute respiratory distress syndrome (ARDS) may allow for more prompt management and less exacerbation of lung injury. However, the absence of a diagnostic test for ARDS means that the diagnosis of ARDS requires clinician recognition in what is usually a complicated and evolving illness. We review data concerning the extent of recognition of ARDS in the era of the Berlin definition of ARDS.

RECENT FINDINGS

ARDS continues to be under-recognized - even in the era of the more recent 'Berlin' definition, and significant delay in its recognition is common. Factors contributing to under-recognition may include the complexity of ARDS biology, low specificity of the consensus (diagnostic) criteria, and concerns about reliable interpretation of the chest radiograph. Understandably, 'external' factors are also at play: ICU occupancy and higher patient to clinician ratio impair recognition of ARDS. Timely recognition of ARDS appears important, as it is associated with the use of higher PEEP, prone positioning and neuromuscular blockade which can lower mortality. Computer-aided decision tools seem diagnostically useful, and together with the integration of reliable biomarkers, may further enhance and speed recognition of this syndrome.

SUMMARY

Significant numbers of patients with ARDS are still unrecognized by clinicians in the era of the Berlin definition of ARDS, with potentially important consequences for patient management and outcome.

Accounting for Label Uncertainty in Machine Learning for Detection of Acute Respiratory Distress Syndrome

When training a machine learning algorithm for a supervised-learning task in some clinical applications, uncertainty in the correct labels of some patients may adversely affect the performance of the algorithm. For example, even clinical experts may have less confidence when assigning a medical diagnosis to some patients because of ambiguity in the patient's case or imperfect reliability of the diagnostic criteria. As a result, some cases used in algorithm training may be mislabeled, adversely affecting the algorithm's performance. However, experts may also be able to quantify their diagnostic uncertainty in these cases. We present a robust method implemented with support vector machines (SVM) to account for such clinical diagnostic uncertainty when training an algorithm to detect patients who develop the acute respiratory distress syndrome (ARDS). ARDS is a syndrome of the critically ill that is diagnosed using clinical criteria known to be imperfect. We represent uncertainty in the diagnosis of ARDS as a graded weight of confidence associated with each training label. We also performed a novel time-series sampling method to address the problem of intercorrelation among the longitudinal clinical data from each patient used in model training to limit overfitting. Preliminary results show that we can achieve meaningful improvement in the performance of algorithm to detect patients with ARDS on a hold-out sample, when we compare our method that accounts for the uncertainty of training labels with a conventional SVM algorithm.

X-Ray Dark-field Imaging to Depict Acute Lung Inflammation in Mice

The aim of this study was to evaluate the feasibility of early stage imaging of acute lung inflammation in mice using grating-based X-ray dark-field imaging in vivo. Acute lung inflammation was induced in mice by orotracheal instillation of porcine pancreatic elastase. Control mice received orotracheal instillation of PBS. Mice were imaged immediately before and 1 day after the application of elastase or PBS to assess acute changes in pulmonary structure due to lung inflammation. Subsequently, 6 mice from each group were sacrificed and their lungs were lavaged and explanted for histological analysis. A further 7, 14 and 21 days later the remaining mice were imaged again. All images were acquired with a prototype grating-based small-animal scanner to generate dark-field and transmission radiographs. Lavage confirmed that mice in the experimental group had developed acute lung inflammation one day after administration of elastase. Acute lung inflammation was visible as a striking decrease in signal intensity of the pulmonary parenchyma on dark-field images at day 1. Quantitative analysis confirmed that dark-field signal intensity at day 1 was significantly lower than signal intensities measured at the remaining timepoints, confirming that acute lung inflammation can be depicted in vivo with dark-field radiography.

Interobserver Reliability of the Berlin ARDS Definition and Strategies to Improve the Reliability of ARDS Diagnosis

BACKGROUND

Failure to reliably diagnose ARDS may be a major driver of negative clinical trials and underrecognition and treatment in clinical practice. We sought to examine the interobserver reliability of the Berlin ARDS definition and examine strategies for improving the reliability of ARDS diagnosis.

METHODS

Two hundred five patients with hypoxic respiratory failure from four ICUs were reviewed independently by three clinicians, who evaluated whether patients had ARDS, the diagnostic confidence of the reviewers, whether patients met individual ARDS criteria, and the time when criteria were met.

RESULTS

Interobserver reliability of an ARDS diagnosis was "moderate" (kappa = 0.50; 95% CI, 0.40-0.59). Sixty-seven percent of diagnostic disagreements between clinicians reviewing the same patient was explained by differences in how chest imaging studies were interpreted, with other ARDS criteria contributing less (identification of ARDS risk factor, 15%; cardiac edema/volume overload exclusion, 7%). Combining the independent reviews of three clinicians can increase reliability to "substantial" (kappa = 0.75; 95% CI, 0.68-0.80). When a clinician diagnosed ARDS with "high confidence," all other clinicians agreed with the diagnosis in 72% of reviews. There was close agreement between clinicians about the time when a patient met all ARDS criteria if ARDS developed within the first 48 hours of hospitalization (median difference, 5 hours).

CONCLUSIONS

The reliability of the Berlin ARDS definition is moderate, driven primarily by differences in chest imaging interpretation. Combining independent reviews by multiple clinicians or improving methods to identify bilateral infiltrates on chest imaging are important strategies for improving the reliability of ARDS diagnosis.

Fifty Years of Research in ARDS. Genomic Contributions and Opportunities

Clinical factors alone poorly explain acute respiratory distress syndrome (ARDS) risk and ARDS outcome. In the search for individual factors that may influence ARDS risk, the past 20 years have witnessed the identification of numerous genes and genetic variants that are associated with ARDS. The field of ARDS genomics has cycled from candidate gene association studies to bias-free approaches that identify new candidates, and increasing effort is made to understand the functional consequences that may underlie significant associations. More recently, methodologies of causal inference are being applied to maximize the information gained from genetic associations. Although challenges of sample size, both recognized and unrecognized phenotypic heterogeneity, and the paucity of early ARDS lung tissue limit some applications of the rapidly evolving field of genomic investigation, ongoing genetic research offers unique contributions to elucidating ARDS pathogenesis and the paradigm of precision ARDS medicine.

Predictors of diffuse alveolar damage in patients with acute respiratory distress syndrome: a retrospective analysis of clinical autopsies

Background

Although diffuse alveolar damage (DAD) is considered the typical histological pattern of acute respiratory distress syndrome (ARDS), only half of patients exhibit this morphological hallmark. Patients with DAD may have higher mortality than those without DAD. Therefore, we aimed to identify the factors associated with DAD in patients with ARDS.

Methods

We analyzed autopsy samples of 356 patients who had ARDS at the time of death. DAD was assessed by two pathologists, and ARDS criteria were evaluated by two intensivists. Criteria for severe ARDS included the degree of hypoxemia and the ancillary variables of the current Berlin definition assessed within 48 h before death: radiographic severity, high positive end-expiratory pressure (PEEP) level, and physiological variables (i.e., altered respiratory system compliance and large anatomic dead space).

Results

After multivariable analysis, high PEEP levels, physiological variables, and opacities involving only three quadrants on chest radiographs were not associated with DAD. The four markers independently associated with DAD were (1) duration of evolution (OR 3.29 [1.95–5.55] for patients with ARDS ≥ 3 days, p < 0.001), (2) degree of hypoxemia (OR 3.92 [1.48–10.3] for moderate ARDS and 6.18 [2.34–16.3] for severe ARDS, p < 0.01 for both), (3) increased dynamic driving pressure (OR 1.06 [1.04–1.09], p = 0.007), and (4) radiographic severity (OR 2.91 [1.47–5.75] for patients with diffuse opacities involving the four quadrants, p = 0.002). DAD was found in two-thirds of patients with a ratio of partial pressure of arterial oxygen to fraction of inspired oxygen ≤ 100 mmHg and opacities involving the four quadrants.

Conclusions

In addition to severe hypoxemia, diffuse opacities involving the four quadrants were a strong marker of DAD.

Low tidal volume ventilation use remains low in patients with acute respiratory distress syndrome at a single center

PURPOSE

Low tidal volume ventilation (LTVV) reduces mortality in acute respiratory distress syndrome (ARDS) patients. Understanding local barriers to LTVV use at a former ARDS Network hospital may provide new insight to improve LTVV implementation.

METHODS

A cohort of 214 randomly selected adults met the Berlin definition of ARDS at Harborview Medical Center between 2008 and 2012. The primary outcome was the receipt of LTVV (tidal volume of ≤6.5mL/kg predicted body weight) within 48h of ARDS onset. We constructed a multivariable logistic regression model to identify factors associated with the outcome.

RESULTS

Only 27% of patients received tidal volumes of ≤6.5mL/kg PBW within 48h of ARDS onset. Increasing plateau pressure (OR 1.11; 95% CI 1.03 to 1.19; p-value<0.01) was positively associated with LTVV use while increasing PaO₂:F_IO₂ ratio was negatively associated (OR 0.75; 95% CI 0.57 to 0.98; p-value 0.03). Physicians documented an ARDS diagnosis in only 21% of the cohort. Neither patient height nor gender was associated with LTVV use.

CONCLUSIONS

Most ARDS patients did not receive LTVV despite implementation of a protocol. ARDS was also recognized in a minority of patients, suggesting an opportunity for improvement of care.

Driving Pressure and Hospital Mortality in Patients Without ARDS: A Cohort Study

BACKGROUND

Driving pressure (ΔP) is associated with mortality in patients with ARDS and with pulmonary complications in patients undergoing general anesthesia. Whether ΔP is associated with outcomes of patients without ARDS who undergo ventilation in the ICU is unknown. Our objective was to determine the independent association between ΔP and outcomes in mechanically ventilated patients without ARDS on day 1 of mechanical ventilation.

METHODS

This was a retrospective analysis of a cohort of 622 mechanically ventilated adult patients without ARDS on day 1 of mechanical ventilation from five ICUs in a tertiary center in the United States. The primary outcome was hospital mortality. The presence of ARDS was determined using the minimum daily Pao₂ to Fio₂ (PF) ratio and an automated text search of chest radiography reports. The data set was validated by first testing the model in 543 patients with ARDS.

RESULTS

In patients without ARDS on day 1 of mechanical ventilation, ΔP was not independently associated with hospital mortality (OR, 1.01; 95% CI, 0.97-1.05). The results of the primary analysis were confirmed in a series of preplanned sensitivity analyses.

CONCLUSIONS

In this cohort of patients without ARDS on day 1 of mechanical ventilation and within the limits of ventilatory settings normally used by clinicians, ΔP was not associated with hospital mortality. This study also confirms the association between ΔP and mortality in patients with ARDS not enrolled in a trial and in hypoxemic patients without ARDS.

Assessment of Pulmonary Edema: Principles and Practice

Pulmonary edema increasingly is recognized as a perioperative complication affecting outcome. Several risk factors have been identified, including those of cardiogenic origin, such as heart failure or excessive fluid administration, and those related to increased pulmonary capillary permeability secondary to inflammatory mediators. Effective treatment requires prompt diagnosis and early intervention. Consequently, over the past 2 centuries a concentrated effort to develop clinical tools to rapidly diagnose pulmonary edema and track response to treatment has occurred. The ideal properties of such a tool would include high sensitivity and specificity, easy availability, and the ability to diagnose early accumulation of lung water before the development of the full clinical presentation. In addition, clinicians highly value the ability to precisely quantify extravascular lung water accumulation and differentiate hydrostatic from high permeability etiologies of pulmonary edema. In this review, advances in understanding the physiology of extravascular lung water accumulation in health and in disease and the various mechanisms that protect against the development of pulmonary edema under physiologic conditions are discussed. In addition, the various bedside modalities available to diagnose early accumulation of extravascular lung water and pulmonary edema, including chest auscultation, chest roentgenography, lung ultrasonography, and transpulmonary thermodilution, are examined. Furthermore, advantages and limitations of these methods for the operating room and intensive care unit that are critical for proper modality selection in each individual case are explored.

External Validity of Electronic Sniffers for Automated Recognition of Acute Respiratory Distress Syndrome

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 PaO₂/FiO₂ or SpO₂/FiO₂ 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.

Fifty Years of Research in ARDS. The Epidemiology of Acute Respiratory Distress Syndrome. A 50th Birthday Review

Since its first description 50 years ago, no other intensive care syndrome has been as extensively studied as acute respiratory distress syndrome (ARDS). Despite this extensive body of research, many basic epidemiologic questions remain unsolved. The lack of gold standard tests jeopardizes accurate diagnosis and translational research. Wide variation in the population incidence has been reported, making even simple estimates of the burden of disease problematic. Despite these limitations, there has been an increase in the understanding of pathophysiology and important risk factors both for the development of ARDS and for important patient-centered outcomes like mortality. In this Critical Care Perspective, we discuss the historical context of ARDS description and attempts at its definition. We highlight the epidemiologic challenges of studying ARDS, as well as other intensive care syndromes, and propose solutions to address them. We update the current knowledge of ARDS trends in incidence and mortality, risk factors, and recently described endotypes.

Definition and epidemiology of acute respiratory distress syndrome

Fifty years ago, Ashbaugh and colleagues defined for the first time the acute respiratory distress syndrome (ARDS), one among the most challenging clinical condition of the critical care medicine. The scientific community worked over the years to generate a unified definition of ARDS, which saw its revisited version in the Berlin definition, in 2014. Epidemiologic information about ARDS is limited in the era of the new Berlin definition, and wide differences are reported among countries all over the world. Despite decades of study in the field of lung injury, ARDS is still so far under-recognized, with 2 out of 5 cases missed by clinicians. Furthermore, although advances of ventilator strategies in the management of ARDS associated with outcome improvements-such as protective mechanical ventilation, lower driving pressure, higher PEEP levels and prone positioning-ARDS appears to be undertreated and mortality remains elevated up to 40%. In this review, we cover the history that led to the current worldwide accepted Berlin definition of ARDS and we summarize the recent data regarding ARDS epidemiology.

National survey of outcomes and practices in acute respiratory distress syndrome in Singapore

INTRODUCTION

In the past 20 years, our understanding of acute respiratory distress syndrome (ARDS) management has improved, but the worldwide incidence and current outcomes are unclear. The reported incidence is highly variable, and no studies specifically characterise ARDS epidemiology in Asia. This observation study aims to determine the incidence, mortality and management practices of ARDS in a high income South East Asian country.

METHODS

We conducted a prospective, population based observational study in 6 public hospitals. During a one month period, we identified all ARDS patients admitted to public hospital intensive care units (ICU) in Singapore, according to the Berlin definition. Demographic information, clinical management data and ICU outcome data was collected.

RESULTS

A total of 904 adult patients were admitted to ICU during the study period and 15 patients met ARDS criteria. The unadjusted incidence of ARDS was 4.5 cases per 100,000 population, accounting for 1.25% of all ICU patients. Most patients were male (75%), Chinese (62%), had pneumonia (73%), and were admitted to a Medical ICU (56%). Management strategies varied across all ICUs. In-hospital mortality was 40% and median length of ICU stay was 7 days.

CONCLUSION

The incidence of ARDS in a developed S.E Asia country is comparable to reported rates in European studies.

Epigenetic contribution of the myosin light chain kinase gene to the risk for acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a devastating clinical syndrome with a considerable case fatality rate (∼30%-40%). Health disparities exist with African descent (AD) subjects exhibiting greater mortality than European descent (ED) individuals. Myosin light chain kinase is encoded by MYLK, whose genetic variants are implicated in ARDS pathogenesis and may influence ARDS mortality. As baseline population-specific epigenetic changes, that is, cytosine modifications, have been observed between AD and ED individuals, epigenetic variations in MYLK may provide insights into ARDS disparities. We compared methylation levels of MYLK cytosine-guanine dinucleotides (CpGs) between ARDS patients and intensive care unit (ICU) controls overall and by ethnicity in a nested case-control study of 39 ARDS cases and 75 non-ARDS ICU controls. Two MYLK CpG sites (cg03892735 and cg23344121) were differentially modified between ARDS subjects and controls (P < 0.05; q < 0.25) in a logistic regression model, where no effect modification by ethnicity or age was found. One CpG site was associated with ARDS in patients aged <58 years, cg19611163 (intron 19, 20). Two CpG sites were associated with ARDS in EDs only, gene body CpG (cg01894985, intron 2, 3) and CpG (cg16212219, intron 31, 32), with higher modification levels exhibited in ARDS subjects than controls. Cis-acting modified cytosine quantitative trait loci (mQTL) were identified using linear regression between local genetic variants and modification levels for 2 ARDS-associated CpGs (cg23344121 and cg16212219). In summary, these ARDS-associated MYLK CpGs with effect modification by ethnicity and local mQTL suggest that MYLK epigenetic variation and local genetic background may contribute to health disparities observed in ARDS.

Does training improve diagnostic accuracy and inter-rater agreement in applying the Berlin radiographic definition of acute respiratory distress syndrome? A multicenter prospective study

BACKGROUND

Poor inter-rater reliability in chest radiograph interpretation has been reported in the context of acute respiratory distress syndrome (ARDS), although not for the Berlin definition of ARDS. We sought to examine the effect of training material on the accuracy and consistency of intensivists' chest radiograph interpretations for ARDS diagnosis.

METHODS

We conducted a rater agreement study in which 286 intensivists (residents 41.3%, junior attending physicians 35.3%, and senior attending physician 23.4%) independently reviewed the same 12 chest radiographs developed by the ARDS Definition Task Force ("the panel") before and after training. Radiographic diagnoses by the panel were classified into the consistent (n = 4), equivocal (n = 4), and inconsistent (n = 4) categories and were used as a reference. The 1.5-hour training course attended by all 286 intensivists included introduction of the diagnostic rationale, and a subsequent in-depth discussion to reach consensus for all 12 radiographs.

RESULTS

Overall diagnostic accuracy, which was defined as the percentage of chest radiographs that were interpreted correctly, improved but remained poor after training (42.0 ± 14.8% before training vs. 55.3 ± 23.4% after training, p < 0.001). Diagnostic sensitivity and specificity improved after training for all diagnostic categories (p < 0.001), with the exception of specificity for the equivocal category (p = 0.883). Diagnostic accuracy was higher for the consistent category than for the inconsistent and equivocal categories (p < 0.001). Comparisons of pre-training and post-training results revealed that inter-rater agreement was poor and did not improve after training, as assessed by overall agreement (0.450 ± 0.406 vs. 0.461 ± 0.575, p = 0.792), Fleiss's kappa (0.133 ± 0.575 vs. 0.178 ± 0.710, p = 0.405), and intraclass correlation coefficient (ICC; 0.219 vs. 0.276, p = 0.470).

CONCLUSIONS

The radiographic diagnostic accuracy and inter-rater agreement were poor when the Berlin radiographic definition was used, and were not significantly improved by the training set of chest radiographs developed by the ARDS Definition Task Force.

TRIAL REGISTRATION

The study was registered at ClinicalTrials.gov (registration number NCT01704066 ) on 6 October 2012.

Acute respiratory distress syndrome

Acute respiratory distress syndrome presents as hypoxia and bilateral pulmonary infiltrates on chest imaging in the absence of heart failure sufficient to account for this clinical state. Management is largely supportive, and is focused on protective mechanical ventilation and the avoidance of fluid overload. Patients with severe hypoxaemia can be managed with early short-term use of neuromuscular blockade, prone position ventilation, or extracorporeal membrane oxygenation. The use of inhaled nitric oxide is rarely indicated and both β2 agonists and late corticosteroids should be avoided. Mortality remains at approximately 30%.

Imaging of Acute Lung Injury

Acute lung injury (ALI) is the clinical syndrome associated with histopathologic diffuse alveolar damage. It is a common cause of acute respiratory symptoms and admission to the intensive care unit. Diagnosis of ALI is typically based on clinical and radiographic criteria; however, because these criteria can be nonspecific, diagnostic uncertainty is common. A multidisciplinary approach that synthesizes clinical, imaging, and pathologic data can ensure an accurate diagnosis. Radiologists must be aware of the radiographic and computed tomographic findings of ALI and its mimics. This article discusses the multidisciplinary diagnosis of ALI from the perspective of the imager.

Acute Respiratory Distress Syndrome Measurement Error. Potential Effect on Clinical Study Results

RATIONALE

Identifying patients with acute respiratory distress syndrome (ARDS) is a recognized challenge. Experts often have only moderate agreement when applying the clinical definition of ARDS to patients. However, no study has fully examined the implications of low reliability measurement of ARDS on clinical studies.

OBJECTIVES

To investigate how the degree of variability in ARDS measurement commonly reported in clinical studies affects study power, the accuracy of treatment effect estimates, and the measured strength of risk factor associations.

METHODS

We examined the effect of ARDS measurement error in randomized clinical trials (RCTs) of ARDS-specific treatments and cohort studies using simulations. We varied the reliability of ARDS diagnosis, quantified as the interobserver reliability (κ-statistic) between two reviewers. In RCT simulations, patients identified as having ARDS were enrolled, and when measurement error was present, patients without ARDS could be enrolled. In cohort studies, risk factors as potential predictors were analyzed using reviewer-identified ARDS as the outcome variable.

MEASUREMENTS AND MAIN RESULTS

Lower reliability measurement of ARDS during patient enrollment in RCTs seriously degraded study power. Holding effect size constant, the sample size necessary to attain adequate statistical power increased by more than 50% as reliability declined, although the result was sensitive to ARDS prevalence. In a 1,400-patient clinical trial, the sample size necessary to maintain similar statistical power increased to over 1,900 when reliability declined from perfect to substantial (κ = 0.72). Lower reliability measurement diminished the apparent effectiveness of an ARDS-specific treatment from a 15.2% (95% confidence interval, 9.4-20.9%) absolute risk reduction in mortality to 10.9% (95% confidence interval, 4.7-16.2%) when reliability declined to moderate (κ = 0.51). In cohort studies, the effect on risk factor associations was similar.

CONCLUSIONS

ARDS measurement error can seriously degrade statistical power and effect size estimates of clinical studies. The reliability of ARDS measurement warrants careful attention in future ARDS clinical studies.

The Epidemiology of Transfusion-related Acute Lung Injury Varies According to the Applied Definition of Lung Injury Onset Time

RATIONALE

Research that applies an unreliable definition for transfusion-related acute lung injury (TRALI) may draw false conclusions about its risk factors and biology. The effectiveness of preventive strategies may decrease as a consequence. However, the reliability of the consensus TRALI definition is unknown.

OBJECTIVES

To prospectively study the effect of applying two plausible definitions of acute respiratory distress syndrome onset time on TRALI epidemiology.

METHODS

We studied 316 adults admitted to the intensive care unit and transfused red blood cells within 24 hours of blunt trauma. We identified patients with acute respiratory distress syndrome, and defined acute respiratory distress syndrome onset time two ways: (1) the time at which the first radiographic or oxygenation criterion was met, and (2) the time both criteria were met. We categorized two corresponding groups of TRALI cases transfused in the 6 hours before acute respiratory distress syndrome onset. We used Cohen's kappa to measure agreement between the TRALI cases and implicated blood components identified by the two acute respiratory distress syndrome onset time definitions. In a nested case-control study, we examined potential risk factors for each group of TRALI cases, including demographics, injury severity, and characteristics of blood components transfused in the 6 hours before acute respiratory distress syndrome onset.

MEASUREMENTS AND MAIN RESULTS

Forty-two of 113 patients with acute respiratory distress syndrome were TRALI cases per the first acute respiratory distress syndrome onset time definition and 63 per the second definition. There was slight agreement between the two groups of TRALI cases (κ = 0.16; 95% confidence interval, -0.01 to 0.33) and between the implicated blood components (κ = 0.15, 95% confidence interval, 0.11-0.20). Age, Injury Severity Score, high plasma-volume components, and transfused plasma volume were risk factors for TRALI when applying the second acute respiratory distress syndrome onset time definition but not when applying the first definition.

CONCLUSIONS

The epidemiology of TRALI varies when applying two plausible definitions of acute respiratory distress syndrome onset time to severely injured trauma patients. A TRALI definition that standardizes acute respiratory distress syndrome onset time might improve reliability and align efforts to understand epidemiology, biology, and prevention.

Effect of Picture Archiving and Communication System Image Manipulation on the Agreement of Chest Radiograph Interpretation in the Neonatal Intensive Care Unit

OBJECTIVE

Variability in image interpretation has been attributed to differences in the interpreters' knowledge base, experience level, and access to the clinical scenario. Picture archiving and communication system (PACS) has allowed the user to manipulate the images while developing their impression of the radiograph. The aim of this study was to determine the agreement of chest radiograph (CXR) impressions among radiologists and neonatologists and help determine the effect of image manipulation with PACS on report impression.

MATERIALS AND METHODS

Prospective cohort study included 60 patients from the Neonatal Intensive Care Unit undergoing CXRs. Three radiologists and three neonatologists reviewed two consecutive frontal CXRs of each patient. Each physician was allowed manipulation of images as needed to provide a decision of "improved," "unchanged," or "disease progression" lung disease for each patient. Each physician repeated the process once more; this time, they were not allowed to individually manipulate the images, but an independent radiologist presets the image brightness and contrast to best optimize the CXR appearance. Percent agreement and opposing reporting views were calculated between all six physicians for each of the two methods (allowing and not allowing image manipulation).

RESULTS

One hundred percent agreement in image impression between all six observers was only seen in 5% of cases when allowing image manipulation; 100% agreement was seen in 13% of the cases when there was no manipulation of the images.

CONCLUSION

Agreement in CXR interpretation is poor; the ability to manipulate the images on PACS results in a decrease in agreement in the interpretation of these studies. New methods to standardize image appearance and allow improved comparison with previous studies should be sought to improve clinician agreement in interpretation consistency and advance patient care.

Personalized medicine for ARDS: the 2035 research agenda

In the last 20 years, survival among patients with acute respiratory distress syndrome (ARDS) has increased substantially with advances in lung-protective ventilation and resuscitation. Building on this success, personalizing mechanical ventilation to patient-specific physiology for enhanced lung protection will be a top research priority for the years ahead. However, the ARDS research agenda must be broader in scope. Further understanding of the heterogeneous biology, from molecular to mechanical, underlying early ARDS pathogenesis is essential to inform therapeutic discovery and tailor treatment and prevention strategies to the individual patient. The ARDSne(x)t research agenda for the next 20 years calls for bringing personalized medicine to ARDS, asking simultaneously both whether a treatment affords clinically meaningful benefit and for whom. This expanded scope necessitates standard acquisition of highly granular biological, physiological, and clinical data across studies to identify biologically distinct subgroups that may respond differently to a given intervention. Clinical trials will need to consider enrichment strategies and incorporate long-term functional outcomes. Tremendous investment in research infrastructure and global collaboration will be vital to fulfilling this agenda.

Application of a Framework to Assess the Usefulness of Alternative Sepsis Criteria

The current definition of sepsis is life-threatening, acute organ dysfunction secondary to a dysregulated host response to infection. Criteria to operationalize this definition can be judged by six domains of usefulness (reliability, content, construct and criterion validity, measurement burden, and timeliness). The relative importance of these six domains depends on the intended purpose for the criteria (clinical care, basic and clinical research, surveillance, or quality improvement [QI] and audit). For example, criteria for clinical care should have high content and construct validity, timeliness, and low measurement burden to facilitate prompt care. Criteria for surveillance or QI/audit place greater emphasis on reliability across individuals and sites and lower emphasis on timeliness. Criteria for clinical trials require timeliness to ensure prompt enrollment and reasonable reliability but can tolerate high measurement burden. Basic research also tolerates high measurement burden and may not need stability over time. In an illustrative case study, we compared examples of criteria designed for clinical care, surveillance and QI/audit among 396,241 patients admitted to 12 academic and community hospitals in an integrated health system. Case rates differed four-fold and mortality three-fold. Predictably, clinical care criteria, which emphasized timeliness and low burden and therefore used vital signs and routine laboratory tests, had the greater case identification with lowest mortality. QI/audit criteria, which emphasized reliability and criterion validity, used discharge information and had the lowest case identification with highest mortality. Using this framework to identify the purpose and apply domains of usefulness can help with the evaluation of existing sepsis diagnostic criteria and provide a roadmap for future work.

Non-infectious Parenchymal Lung Disease

Acute dyspnea is a common presenting complaint in the emergency room, emergency medicine and intensive care. It may have a cardiovascular or a non-cardiovascular origin, the latter including pulmonary parenchymal diseases. Depending on the cause, it may be associated with fever, cough, hemoptysis, and/or chest pain, with a duration of symptoms that can range from hours to days.

Prompt identification of the underlying cause of acute dyspnea is essential in guiding appropriate therapy and management, as patients may rapidly progress to acute respiratory failure. Evaluation with chest radiography is vital for initial assessment and may reveal diffuse parenchymal abnormalities, which may require further assessment with computed tomography (HRCT).

Acute non-infectious parenchymal lung diseases are often overlooked and may be under-diagnosed. Their diagnosis requires the evaluation, along with the HRCT pattern, of the clinical and laboratory features and of the bronchoalveolar lavage. Biopsy may be necessary in more complex cases.

Although the most frequent cause of diffuse non-infectious parenchymal lung involvement is acute hydrostatic pulmonary edema, there is a wide variety of diseases that may be encountered, including acute drug toxicity, hypersensitivity pneumonitis (HP), acute respiratory distress syndrome (ARDS) and diffuse alveolar hemorrhage (DAH). In trauma patients, fat embolism syndrome (FES) must be taken into account. Acute respiratory failure is an eventuality that can occur during the course of chronic lung diseases (UIP for example), which may have been unknown until then.

Misclassification of acute respiratory distress syndrome after traumatic injury: The cost of less rigorous approaches

BACKGROUND

Adherence to rigorous research protocols for identifying adult respiratory distress syndrome (ARDS) after trauma is variable. To examine how misclassification of ARDS may bias observational studies in trauma populations, we evaluated the agreement of two methods for adjudicating ARDS after trauma: the current gold standard, direct review of chest radiographs and review of dictated radiology reports, a commonly used alternative.

METHODS

This nested cohort study included 123 mechanically ventilated patients between 2005 and 2008, with at least one PaO2/FIO2 less than 300 within the first 8 days of admission. Two blinded physician investigators adjudicated ARDS by two methods. The investigators directly reviewed all chest radiographs to evaluate for bilateral infiltrates. Several months later, blinded to their previous assessments, they adjudicated ARDS using a standardized rubric to classify radiology reports. A κ statistics was calculated. Regression analyses quantified the association between established risk factors as well as important clinical outcomes and ARDS determined by the aforementioned methods as well as hypoxemia as a surrogate marker.

RESULTS

The κ was 0.47 for the observed agreement between ARDS adjudicated by direct review of chest radiographs and ARDS adjudicated by review of radiology reports. Both the magnitude and direction of bias on the estimates of association between ARDS and established risk factors as well as clinical outcomes varied by method of adjudication.

CONCLUSION

Classification of ARDS by review of dictated radiology reports had only moderate agreement with the current gold standard, ARDS adjudicated by direct review of chest radiographs. While the misclassification of ARDS had varied effects on the estimates of associations with established risk factors, it tended to weaken the association of ARDS with important clinical outcomes. A standardized approach to ARDS adjudication after trauma by direct review of chest radiographs will minimize misclassification bias in future observational studies.

LEVEL OF EVIDENCE

Diagnostic study, level II.