Respiratory drive heterogeneity associated with systemic inflammation and vascular permeability in acute respiratory distress syndrome

BACKGROUND

In acute respiratory distress syndrome (ARDS), respiratory drive often differs among patients with similar clinical characteristics. Readily observable factors like acid-base state, oxygenation, mechanics, and sedation depth do not fully explain drive heterogeneity. This study evaluated the relationship of systemic inflammation and vascular permeability markers with respiratory drive and clinical outcomes in ARDS.

METHODS

ARDS patients enrolled in the multicenter EPVent-2 trial with requisite data and plasma biomarkers were included. Neuromuscular blockade recipients were excluded. Respiratory drive was measured as PES0.1, the change in esophageal pressure during the first 0.1 s of inspiratory effort. Plasma angiopoietin-2, interleukin-6, and interleukin-8 were measured concomitantly, and 60-day clinical outcomes evaluated.

RESULTS

54.8% of 124 included patients had detectable respiratory drive (PES0.1 range of 0-5.1 cm H2O). Angiopoietin-2 and interleukin-8, but not interleukin-6, were associated with respiratory drive independently of acid-base, oxygenation, respiratory mechanics, and sedation depth. Sedation depth was not significantly associated with PES0.1 in an unadjusted model, or after adjusting for mechanics and chemoreceptor input. However, upon adding angiopoietin-2, interleukin-6, or interleukin-8 to models, lighter sedation was significantly associated with higher PES0.1. Risk of death was less with moderate drive (PES0.1 of 0.5-2.9 cm H2O) compared to either lower drive (hazard ratio 1.58, 95% CI 0.82-3.05) or higher drive (2.63, 95% CI 1.21-5.70) (p = 0.049).

CONCLUSIONS

Among patients with ARDS, systemic inflammatory and vascular permeability markers were independently associated with higher respiratory drive. The heterogeneous response of respiratory drive to varying sedation depth may be explained in part by differences in inflammation and vascular permeability.

Frequency of screening and SBT Technique Trial-North American Weaning Collaboration (FAST-NAWC): an update to the protocol and statistical analysis plan

BACKGROUND

This update summarizes key changes made to the protocol for the Frequency of Screening and Spontaneous Breathing Trial (SBT) Technique Trial-North American Weaning Collaborative (FAST-NAWC) trial since the publication of the original protocol. This multicenter, factorial design randomized controlled trial with concealed allocation, will compare the effect of both screening frequency (once vs. at least twice daily) to identify candidates to undergo a SBT and SBT technique [pressure support + positive end-expiratory pressure vs. T-piece] on the time to successful extubation (primary outcome) in 760 critically ill adults who are invasively ventilated for at least 24 h in 20 North American intensive care units.

METHODS/DESIGN

Protocols for the pilot, factorial design trial and the full trial were previously published in J Clin Trials ( https://doi.org/10.4172/2167-0870.1000284 ) and Trials (https://doi: 10.1186/s13063-019-3641-8). As planned, participants enrolled in the FAST pilot trial will be included in the report of the full FAST-NAWC trial. In response to the onset of the coronavirus disease of 2019 (COVID-19) pandemic when approximately two thirds of enrollment was complete, we revised the protocol and consent form to include critically ill invasively ventilated patients with COVID-19. We also refined the statistical analysis plan (SAP) to reflect inclusion and reporting of participants with and without COVID-19. This update summarizes the changes made and their rationale and provides a refined SAP for the FAST-NAWC trial. These changes have been finalized before completion of trial follow-up and the commencement of data analysis.

TRIAL REGISTRATION

Clinical Trials.gov NCT02399267.

Intravenous aviptadil and remdesivir for treatment of COVID-19-associated hypoxaemic respiratory failure in the USA (TESICO): a randomised, placebo-controlled trial

BACKGROUND

There is a clinical need for therapeutics for COVID-19 patients with acute hypoxemic respiratory failure whose 60-day mortality remains at 30-50%. Aviptadil, a lung-protective neuropeptide, and remdesivir, a nucleotide prodrug of an adenosine analog, were compared with placebo among patients with COVID-19 acute hypoxaemic respiratory failure.

METHODS

TESICO was a randomised trial of aviptadil and remdesivir versus placebo at 28 sites in the USA. Hospitalised adult patients were eligible for the study if they had acute hypoxaemic respiratory failure due to confirmed SARS-CoV-2 infection and were within 4 days of the onset of respiratory failure. Participants could be randomly assigned to both study treatments in a 2 × 2 factorial design or to just one of the agents. Participants were randomly assigned with a web-based application. For each site, randomisation was stratified by disease severity (high-flow nasal oxygen or non-invasive ventilation vs invasive mechanical ventilation or extracorporeal membrane oxygenation [ECMO]), and four strata were defined by remdesivir and aviptadil eligibility, as follows: (1) eligible for randomisation to aviptadil and remdesivir in the 2 × 2 factorial design; participants were equally randomly assigned (1:1:1:1) to intravenous aviptadil plus remdesivir, aviptadil plus remdesivir matched placebo, aviptadil matched placebo plus remdesvir, or aviptadil placebo plus remdesivir placebo; (2) eligible for randomisation to aviptadil only because remdesivir was started before randomisation; (3) eligible for randomisation to aviptadil only because remdesivir was contraindicated; and (4) eligible for randomisation to remdesivir only because aviptadil was contraindicated. For participants in strata 2-4, randomisation was 1:1 to the active agent or matched placebo. Aviptadil was administered as a daily 12-h infusion for 3 days, targeting 600 pmol/kg on infusion day 1, 1200 pmol/kg on day 2, and 1800 pmol/kg on day 3. Remdesivir was administered as a 200 mg loading dose, followed by 100 mg daily maintenance doses for up to a 10-day total course. For participants assigned to placebo for either agent, matched saline placebo was administered in identical volumes. For both treatment comparisons, the primary outcome, assessed at day 90, was a six-category ordinal outcome: (1) at home (defined as the type of residence before hospitalisation) and off oxygen (recovered) for at least 77 days, (2) at home and off oxygen for 49-76 days, (3) at home and off oxygen for 1-48 days, (4) not hospitalised but either on supplemental oxygen or not at home, (5) hospitalised or in hospice care, or (6) dead. Mortality up to day 90 was a key secondary outcome. The independent data and safety monitoring board recommended stopping the aviptadil trial on May 25, 2022, for futility. On June 9, 2022, the sponsor stopped the trial of remdesivir due to slow enrolment. The trial is registered with ClinicalTrials.gov, NCT04843761.

FINDINGS

Between April 21, 2021, and May 24, 2022, we enrolled 473 participants in the study. For the aviptadil comparison, 471 participants were randomly assigned to aviptadil or matched placebo. The modified intention-to-treat population comprised 461 participants who received at least a partial infusion of aviptadil (231 participants) or aviptadil matched placebo (230 participants). For the remdesivir comparison, 87 participants were randomly assigned to remdesivir or matched placebo and all received some infusion of remdesivir (44 participants) or remdesivir matched placebo (43 participants). 85 participants were included in the modified intention-to-treat analyses for both agents (ie, those enrolled in the 2 x 2 factorial). For the aviptadil versus placebo comparison, the median age was 57 years (IQR 46-66), 178 (39%) of 461 participants were female, and 246 (53%) were Black, Hispanic, Asian or other (vs 215 [47%] White participants). 431 (94%) of 461 participants were in an intensive care unit at baseline, with 271 (59%) receiving high-flow nasal oxygen or non-invasive ventiliation, 185 (40%) receiving invasive mechanical ventilation, and five (1%) receiving ECMO. The odds ratio (OR) for being in a better category of the primary efficacy endpoint for aviptadil versus placebo at day 90, from a model stratified by baseline disease severity, was 1·11 (95% CI 0·80-1·55; p=0·54). Up to day 90, 86 participants in the aviptadil group and 83 in the placebo group died. The cumulative percentage who died up to day 90 was 38% in the aviptadil group and 36% in the placebo group (hazard ratio 1·04, 95% CI 0·77-1·41; p=0·78). The primary safety outcome of death, serious adverse events, organ failure, serious infection, or grade 3 or 4 adverse events up to day 5 occurred in 146 (63%) of 231 patients in the aviptadil group compared with 129 (56%) of 230 participants in the placebo group (OR 1·40, 95% CI 0·94-2·08; p=0·10).

INTERPRETATION

Among patients with COVID-19-associated acute hypoxaemic respiratory failure, aviptadil did not significantly improve clinical outcomes up to day 90 when compared with placebo. The smaller than planned sample size for the remdesivir trial did not permit definitive conclusions regarding safety or efficacy.

FUNDING

National Institutes of Health.

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.

I-SPY COVID adaptive platform trial for COVID-19 acute respiratory failure: rationale, design and operations

INTRODUCTION

The COVID-19 pandemic brought an urgent need to discover novel effective therapeutics for patients hospitalised with severe COVID-19. The Investigation of Serial studies to Predict Your Therapeutic Response with Imaging And moLecular Analysis (ISPY COVID-19 trial) was designed and implemented in early 2020 to evaluate investigational agents rapidly and simultaneously on a phase 2 adaptive platform. This manuscript outlines the design, rationale, implementation and challenges of the ISPY COVID-19 trial during the first phase of trial activity from April 2020 until December 2021.

METHODS AND ANALYSIS

The ISPY COVID-19 Trial is a multicentre open-label phase 2 platform trial in the USA designed to evaluate therapeutics that may have a large effect on improving outcomes from severe COVID-19. The ISPY COVID-19 Trial network includes academic and community hospitals with significant geographical diversity across the country. Enrolled patients are randomised to receive one of up to four investigational agents or a control and are evaluated for a family of two primary outcomes-time to recovery and mortality. The statistical design uses a Bayesian model with 'stopping' and 'graduation' criteria designed to efficiently discard ineffective therapies and graduate promising agents for definitive efficacy trials. Each investigational agent arm enrols to a maximum of 125 patients per arm and is compared with concurrent controls. As of December 2021, 11 investigational agent arms had been activated, and 8 arms were complete. Enrolment and adaptation of the trial design are ongoing.

ETHICS AND DISSEMINATION

ISPY COVID-19 operates under a central institutional review board via Wake Forest School of Medicine IRB00066805. Data generated from this trial will be reported in peer-reviewed medical journals.

TRIAL REGISTRATION NUMBER

NCT04488081.

Association of PEEP and Lung Recruitment Selection Strategies with Mortality in Acute Respiratory Distress Syndrome: A Systematic Review and Network Meta-Analysis

RATIONALE

The most beneficial positive end-expiratory pressure (PEEP) selection strategy in patients with acute respiratory distress syndrome (ARDS) is unknown and current practice is variable.

OBJECTIVES

To compare the relative effects of different PEEP selection strategies on mortality in adults with moderate to severe ARDS.

METHODS

We conducted a network meta-analysis using a Bayesian framework. Certainty of evidence was evaluated using GRADE methodology.

RESULTS

We included 18 randomized trials (4646 participants). In comparison to a lower PEEP strategy, the posterior probability of mortality benefit from a higher PEEP without lung recruitment maneuver (LRM) strategy was 99% (RR 0.77, 95% Crl 0.60-0.96, high certainty), the posterior probability of benefit of the Pes-guided strategy was 87% (RR 0.77, 95% CrI 0.48-1.22, moderate certainty), the posterior probability of benefit of a higher PEEP with brief LRM strategy was 96% (RR 0.83, 95% CrI 0.67-1.02, moderate certainty), and the posterior probability of increased mortality from a higher PEEP with prolonged LRM strategy was 77% (RR 1.06, 95% Crl 0.89-1.22, low certainty). In comparison to a higher PEEP without LRM strategy, the posterior probability of increased mortality from a higher PEEP with prolonged LRM strategy was 99% (RR 1.37, 95% CrI 1.04-1.81, moderate certainty).

CONCLUSIONS AND RELEVANCE

In patients with moderate to severe ARDS, higher PEEP without LRM is associated with a lower risk of death as compared to lower PEEP. A higher PEEP with prolonged LRM strategy is associated with increased risk of death when compared to higher PEEP without LRM.

Geoeconomic variations in epidemiology, ventilation management, and outcomes in invasively ventilated intensive care unit patients without acute respiratory distress syndrome: a pooled analysis of four observational studies

Background

Geoeconomic variations in epidemiology, the practice of ventilation, and outcome in invasively ventilated intensive care unit (ICU) patients without acute respiratory distress syndrome (ARDS) remain unexplored. In this analysis we aim to address these gaps using individual patient data of four large observational studies.

Methods

In this pooled analysis we harmonised individual patient data from the ERICC, LUNG SAFE, PRoVENT, and PRoVENT-iMiC prospective observational studies, which were conducted from June, 2011, to December, 2018, in 534 ICUs in 54 countries. We used the 2016 World Bank classification to define two geoeconomic regions: middle-income countries (MICs) and high-income countries (HICs). ARDS was defined according to the Berlin criteria. Descriptive statistics were used to compare patients in MICs versus HICs. The primary outcome was the use of low tidal volume ventilation (LTVV) for the first 3 days of mechanical ventilation. Secondary outcomes were key ventilation parameters (tidal volume size, positive end-expiratory pressure, fraction of inspired oxygen, peak pressure, plateau pressure, driving pressure, and respiratory rate), patient characteristics, the risk for and actual development of acute respiratory distress syndrome after the first day of ventilation, duration of ventilation, ICU length of stay, and ICU mortality.

Findings

Of the 7608 patients included in the original studies, this analysis included 3852 patients without ARDS, of whom 2345 were from MICs and 1507 were from HICs. Patients in MICs were younger, shorter and with a slightly lower body-mass index, more often had diabetes and active cancer, but less often chronic obstructive pulmonary disease and heart failure than patients from HICs. Sequential organ failure assessment scores were similar in MICs and HICs. Use of LTVV in MICs and HICs was comparable (42·4% vs 44·2%; absolute difference –1·69 [–9·58 to 6·11] p=0·67; data available in 3174 [82%] of 3852 patients). The median applied positive end expiratory pressure was lower in MICs than in HICs (5 [IQR 5–8] vs 6 [5–8] cm H₂O; p=0·0011). ICU mortality was higher in MICs than in HICs (30·5% vs 19·9%; p=0·0004; adjusted effect 16·41% [95% CI 9·52–23·52]; p<0·0001) and was inversely associated with gross domestic product (adjusted odds ratio for a US$10 000 increase per capita 0·80 [95% CI 0·75–0·86]; p<0·0001).

Interpretation

Despite similar disease severity and ventilation management, ICU mortality in patients without ARDS is higher in MICs than in HICs, with a strong association with country-level economic status.

Funding

No funding.

Risks and Benefits of Ultra-Lung-Protective Invasive Mechanical Ventilation Strategies with a Focus on Extracorporeal Support

Lung-protective ventilation strategies are the current standard of care for patients with acute respiratory distress syndrome (ARDS) in an effort to provide adequate ventilatory requirements while minimizing ventilator-induced lung injury. Some patients may benefit from ultra-lung-protective ventilation, a strategy that achieves lower airway pressures and tidal volumes than the current standard. Specific physiological parameters beyond severity of hypoxemia, such as driving pressure and respiratory system elastance, may be predictive of those most likely to benefit. Since application of ultra-lung-protective ventilation is often limited by respiratory acidosis, extracorporeal membrane oxygenation (ECMO) or extracorporeal carbon dioxide removal (ECCO2R), which remove carbon dioxide from blood, are attractive options. These strategies are associated with hematological complications, especially when applied at low blood flow rates with devices designed for higher blood flows, and a recent large randomized, controlled trial failed to show a benefit from an ECCO2R-facilitated ultra-lung-protective ventilation strategy. Only in patients with very severe forms of ARDS has the use of an ultra-lung-protective ventilation strategy - accomplished with ECMO - been suggested to have a favorable risk-to-benefit profile. In this Critical Care Perspective, we address key areas of controversy related to ultra-lung-protective ventilation, including the trade-offs between minimizing ventilator-induced lung injury and the risks from strategies to achieve this added protection. In addition, we suggest which patients might benefit most from an ultra-lung-protective strategy and propose areas of future research.

Advancing precision medicine for acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a heterogeneous clinical syndrome. Understanding of the complex pathways involved in lung injury pathogenesis, resolution, and repair has grown considerably in recent decades. Nevertheless, to date, only therapies targeting ventilation-induced lung injury have consistently proven beneficial, and despite these gains, ARDS morbidity and mortality remain high. Many candidate therapies with promise in preclinical studies have been ineffective in human trials, probably at least in part due to clinical and biological heterogeneity that modifies treatment responsiveness in human ARDS. A precision medicine approach to ARDS seeks to better account for this heterogeneity by matching therapies to subgroups of patients that are anticipated to be most likely to benefit, which initially might be identified in part by assessing for heterogeneity of treatment effect in clinical trials. In October 2019, the US National Heart, Lung, and Blood Institute convened a workshop of multidisciplinary experts to explore research opportunities and challenges for accelerating precision medicine in ARDS. Topics of discussion included the rationale and challenges for a precision medicine approach in ARDS, the roles of preclinical ARDS models in precision medicine, essential features of cohort studies to advance precision medicine, and novel approaches to clinical trials to support development and validation of a precision medicine strategy. In this Position Paper, we summarise workshop discussions, recommendations, and unresolved questions for advancing precision medicine in ARDS. Although the workshop took place before the COVID-19 pandemic began, the pandemic has highlighted the urgent need for precision therapies for ARDS as the global scientific community grapples with many of the key concepts, innovations, and challenges discussed at this workshop.

Latent Class Analysis Reveals COVID-19-related Acute Respiratory Distress Syndrome Subgroups with Differential Responses to Corticosteroids

Rationale

Two distinct subphenotypes have been identified in acute respiratory distress syndrome (ARDS), but the presence of subgroups in ARDS associated with coronavirus disease (COVID-19) is unknown.

Objectives

To identify clinically relevant, novel subgroups in COVID-19–related ARDS and compare them with previously described ARDS subphenotypes.

Methods

Eligible participants were adults with COVID-19 and ARDS at Columbia University Irving Medical Center. Latent class analysis was used to identify subgroups with baseline clinical, respiratory, and laboratory data serving as partitioning variables. A previously developed machine learning model was used to classify patients as the hypoinflammatory and hyperinflammatory subphenotypes. Baseline characteristics and clinical outcomes were compared between subgroups. Heterogeneity of treatment effect for corticosteroid use in subgroups was tested.

Measurements and Main Results

From March 2, 2020, to April 30, 2020, 483 patients with COVID-19–related ARDS met study criteria. A two-class latent class analysis model best fit the population (P = 0.0075). Class 2 (23%) had higher proinflammatory markers, troponin, creatinine, and lactate, lower bicarbonate, and lower blood pressure than class 1 (77%). Ninety-day mortality was higher in class 2 versus class 1 (75% vs. 48%; P < 0.0001). Considerable overlap was observed between these subgroups and ARDS subphenotypes. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RT-PCR cycle threshold was associated with mortality in the hypoinflammatory but not the hyperinflammatory phenotype. Heterogeneity of treatment effect to corticosteroids was observed (P = 0.0295), with improved mortality in the hyperinflammatory phenotype and worse mortality in the hypoinflammatory phenotype, with the caveat that corticosteroid treatment was not randomized.

Conclusions

We identified two COVID-19–related ARDS subgroups with differential outcomes, similar to previously described ARDS subphenotypes. SARS-CoV-2 PCR cycle threshold had differential value for predicting mortality in the subphenotypes. The subphenotypes had differential treatment responses to corticosteroids.

Promises and challenges of personalized medicine to guide ARDS therapy

Identifying new effective treatments for the acute respiratory distress syndrome (ARDS), including COVID-19 ARDS, remains a challenge. The field of ARDS investigation is moving increasingly toward innovative approaches such as the personalization of therapy to biological and clinical sub-phenotypes. Additionally, there is growing recognition of the importance of the global context to identify effective ARDS treatments. This review highlights emerging opportunities and continued challenges for personalizing therapy for ARDS, from identifying treatable traits to innovative clinical trial design and recognition of patient-level factors as the field of critical care investigation moves forward into the twenty-first century.

Effect of Esophageal Pressure-Guided Positive End-Expiratory Pressure on Survival from Acute Respiratory Distress Syndrome: A Risk-Based and Mechanistic Reanalysis of the EPVent-2 Trial

RATIONALE

In acute respiratory distress syndrome (ARDS), the effect of positive end-expiratory pressure (PEEP) may depend on the extent to which multiorgan dysfunction contributes to risk of death, and the precision with which PEEP is titrated to attenuate atelectrauma without exacerbating overdistension.

OBJECTIVE

To evaluate whether multiorgan dysfunction and lung mechanics modified treatment effect in EPVent-2, a multicenter trial of esophageal pressure (P_ES)-guided PEEP versus empirical high PEEP in moderate-to-severe ARDS.

METHODS

This post-hoc reanalysis of EPVent-2 evaluated for heterogeneity of treatment effect on mortality by baseline multiorgan dysfunction, determined via Acute Physiology and Chronic Health Evaluation-II (APACHE-II). It also evaluated whether PEEP titrated to end-expiratory transpulmonary pressure near 0 cmH₂O was associated with survival.

MEASUREMENTS AND MAIN RESULTS

All 200 trial participants were included. Treatment effect on 60-day mortality differed by multiorgan dysfunction severity (p=0.03 for interaction). P_ES-guided PEEP was associated with lower mortality among patients with lower APACHE-II (HR 0.43, 95% CI 0.20-0.92 for APACHE-II less than median) and may have had the opposite effect in patients with higher APACHE-II (HR 1.69; 95% CI 0.93-3.05). Independent of treatment group or multiorgan dysfunction severity, mortality was lowest when PEEP titration achieved end-expiratory transpulmonary pressure near 0 cmH₂O.

CONCLUSIONS

The effect on survival of P_ES-guided PEEP, compared to empirical high PEEP, differed by multiorgan dysfunction severity. Independent of multiorgan dysfunction, PEEP titrated to end-expiratory transpulmonary pressure closer to 0 cmH₂O was associated with greater survival than more positive or negative values. These findings warrant prospective testing in a future trial.

Use of N-Acetylcysteine for Clozapine-Induced Acute Liver Injury: A Case Report and Literature Review

Purpose: To report a case of clozapine-induced hepatotoxicity managed with intravenous (IV) N-acetylcysteine (NAC) and summarize the available literature. Summary: A 46-year-old woman with history of bipolar disorder with psychotic features presented to the intensive care unit with asterixis and elevations in liver enzymes. The patient had been initiated on risperidone, clozapine, and lithium approximately 1 month prior to admission. After ruling out other possible non-drug etiologies, clozapine was suspected as the likeliest cause of the acute liver injury. Her acute liver injury was managed with the discontinuation of all antipsychotics, administration of IV NAC, and other standard of care supportive measures. Conclusion: Although clozapine has been associated with hepatitis and acute liver failure, there are no reports of NAC used in the management of clozapine-induced hepatotoxicity. NAC was used in our patient after considering the potential benefit and limited adverse effects. The role of NAC in non-acetaminophen-induced acute liver failure remains promising, but more research is warranted.

Esophageal Manometry

The estimation of pleural pressure with esophageal manometry has been used for decades, and it has been a fertile area of physiology research in healthy subject as well as during mechanical ventilation in patients with lung injury. However, its scarce adoption in clinical practice takes its roots from the (false) ideas that it requires expertise with years of training, that the values obtained are not reliable due to technical challenges or discrepant methods of calculation, and that measurement of esophageal pressure has not proved to benefit patient outcomes. Despites these criticisms, esophageal manometry could contribute to better monitoring, optimization, and personalization of mechanical ventilation from the acute initial phase to the weaning period. This review aims to provide a comprehensive but comprehensible guide addressing the technical aspects of esophageal catheter use, its application in different clinical situations and conditions, and an update on the state of the art with recent studies on this topic and on remaining questions and ways for improvement.

Phenotypes and personalized medicine in the acute respiratory distress syndrome

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

Lung- and Diaphragm-Protective Ventilation

Mechanical ventilation can cause acute diaphragm atrophy and injury, and this is associated with poor clinical outcomes. Although the importance and impact of lung-protective ventilation is widely appreciated and well established, the concept of diaphragm-protective ventilation has recently emerged as a potential complementary therapeutic strategy. This Perspective, developed from discussions at a meeting of international experts convened by PLUG (the Pleural Pressure Working Group) of the European Society of Intensive Care Medicine, outlines a conceptual framework for an integrated lung- and diaphragm-protective approach to mechanical ventilation on the basis of growing evidence about mechanisms of injury. We propose targets for diaphragm protection based on respiratory effort and patient-ventilator synchrony. The potential for conflict between diaphragm protection and lung protection under certain conditions is discussed; we emphasize that when conflicts arise, lung protection must be prioritized over diaphragm protection. Monitoring respiratory effort is essential to concomitantly protect both the diaphragm and the lung during mechanical ventilation. To implement lung- and diaphragm-protective ventilation, new approaches to monitoring, to setting the ventilator, and to titrating sedation will be required. Adjunctive interventions, including extracorporeal life support techniques, phrenic nerve stimulation, and clinical decision-support systems, may also play an important role in selected patients in the future. Evaluating the clinical impact of this new paradigm will be challenging, owing to the complexity of the intervention. The concept of lung- and diaphragm-protective ventilation presents a new opportunity to potentially improve clinical outcomes for critically ill patients.

Clinical strategies for implementing lung and diaphragm-protective ventilation: avoiding insufficient and excessive effort

Mechanical ventilation may have adverse effects on both the lung and the diaphragm. Injury to the lung is mediated by excessive mechanical stress and strain, whereas the diaphragm develops atrophy as a consequence of low respiratory effort and injury in case of excessive effort. The lung and diaphragm-protective mechanical ventilation approach aims to protect both organs simultaneously whenever possible. This review summarizes practical strategies for achieving lung and diaphragm-protective targets at the bedside, focusing on inspiratory and expiratory ventilator settings, monitoring of inspiratory effort or respiratory drive, management of dyssynchrony, and sedation considerations. A number of potential future adjunctive strategies including extracorporeal CO₂ removal, partial neuromuscular blockade, and neuromuscular stimulation are also discussed. While clinical trials to confirm the benefit of these approaches are awaited, clinicians should become familiar with assessing and managing patients’ respiratory effort, based on existing physiological principles. To protect the lung and the diaphragm, ventilation and sedation might be applied to avoid excessively weak or very strong respiratory efforts and patient-ventilator dysynchrony.

COVID-19-associated acute respiratory distress syndrome: is a different approach to management warranted?

The COVID-19 pandemic has seen a surge of patients with acute respiratory distress syndrome (ARDS) in intensive care units across the globe. As experience of managing patients with COVID-19-associated ARDS has grown, so too have efforts to classify patients according to respiratory system mechanics, with a view to optimising ventilatory management. Personalised lung-protective mechanical ventilation reduces mortality and has become the mainstay of treatment in ARDS. In this Viewpoint, we address ventilatory strategies in the context of recent discussions on phenotypic heterogeneity in patients with COVID-19-associated ARDS. Although early reports suggested that COVID-19-associated ARDS has distinctive features that set it apart from historical ARDS, emerging evidence indicates that the respiratory system mechanics of patients with ARDS, with or without COVID-19, are broadly similar. In the absence of evidence to support a shift away from the current paradigm of ventilatory management, we strongly recommend adherence to evidence-based management, informed by bedside physiology, as resources permit.

Emerging concepts in ventilation-induced lung injury

Ventilation-induced lung injury results from mechanical stress and strain that occur during tidal ventilation in the susceptible lung. Classical descriptions of ventilation-induced lung injury have focused on harm from positive pressure ventilation. However, injurious forces also can be generated by patient effort and patient–ventilator interactions. While the role of global mechanics has long been recognized, regional mechanical heterogeneity within the lungs also appears to be an important factor propagating clinically significant lung injury. The resulting clinical phenotype includes worsening lung injury and a systemic inflammatory response that drives extrapulmonary organ failures. Bedside recognition of ventilation-induced lung injury requires a high degree of clinical acuity given its indistinct presentation and lack of definitive diagnostics. Yet the clinical importance of ventilation-induced lung injury is clear. Preventing such biophysical injury remains the most effective management strategy to decrease morbidity and mortality in patients with acute respiratory distress syndrome and likely benefits others at risk.

Respiratory drive in the acute respiratory distress syndrome: pathophysiology, monitoring, and therapeutic interventions

Neural respiratory drive, i.e., the activity of respiratory centres controlling breathing, is an overlooked physiologic variable which affects the pathophysiology and the clinical outcome of acute respiratory distress syndrome (ARDS). Spontaneous breathing may offer multiple physiologic benefits in these patients, including decreased need for sedation, preserved diaphragm activity and improved cardiovascular function. However, excessive effort to breathe due to high respiratory drive may lead to patient self-inflicted lung injury (P-SILI), even in the absence of mechanical ventilation. In the present review, we focus on the physiological and clinical implications of control of respiratory drive in ARDS patients. We summarize the main determinants of neural respiratory drive and the mechanisms involved in its potentiation, in health and ARDS. We also describe potential and pitfalls of the available bedside methods for drive assessment and explore classical and more “futuristic” interventions to control drive in ARDS patients.

Alive and Ventilator Free: A Hierarchical, Composite Outcome for Clinical Trials in the Acute Respiratory Distress Syndrome

OBJECTIVES

Survival from acute respiratory distress syndrome is improving, and outcomes beyond mortality may be important for testing new treatments. The "ventilator-free days" score, is an established composite that equates ventilation on day 28 to death. A hierarchical outcome treating death as a worse than prolonged ventilation would enhance face validity, but performance characteristics and reporting of such an outcome are unknown. We therefore evaluated the performance of a novel hierarchical composite endpoint, the Alive and Ventilator Free score.

DESIGN

Using data from four Acute Respiratory Distress Syndrome Network clinical trials, we compared Alive and Ventilator Free to the ventilator-free days score. Alive and Ventilator Free compares each patient with every other patient in a win-lose-tie for each comparison. Duration of mechanical ventilation is only compared if both patients survived. We evaluated power of Alive and Ventilator Free versus ventilator-free days score under various circumstances.

SETTING

ICUs within the Acute Respiratory Distress Syndrome Network.

PATIENTS

Individuals enrolled in four Acute Respiratory Distress Syndrome Network trials.

INTERVENTIONS

None for this analysis.

MEASUREMENTS AND MAIN RESULTS

Within the four trials (n = 2,410 patients), Alive and Ventilator Free and ventilator-free days score had similar power, with Alive and Ventilator Free slightly more powerful when a mortality difference was present, and ventilator-free days score slightly more powerful with a difference in duration of mechanical ventilation. Alive and Ventilator Free less often found in favor of treatments that increased mortality and increased days free of ventilation among survivors.

CONCLUSIONS

A hierarchical composite endpoint, Alive and Ventilator Free, preserves statistical power while improving face validity. Alive and Ventilator Free is less prone to favor a treatment with discordant effects on survival and days free of ventilation. This general approach can support complex outcome hierarchies with multiple constituent outcomes. Approaches to interpretation of differences in Alive and Ventilator Free are also presented.

Physiologic Analysis and Clinical Performance of the Ventilatory Ratio in Acute Respiratory Distress Syndrome

RATIONALE

Pulmonary dead space fraction (Vd/Vt) is an independent predictor of mortality in acute respiratory distress syndrome (ARDS). Yet, it is seldom used in practice. The ventilatory ratio is a simple bedside index that can be calculated using routinely measured respiratory variables and is a measure of impaired ventilation. Ventilatory ratio is defined as [minute ventilation (ml/min) × Pa_CO2 (mm Hg)]/(predicted body weight × 100 × 37.5).

OBJECTIVES

To determine the relation of ventilatory ratio with Vd/Vt in ARDS.

METHODS

First, in a single-center, prospective observational study of ARDS, we tested the association of Vd/Vt with ventilatory ratio. With in-hospital mortality as the primary outcome and ventilator-free days as the secondary outcome, we tested the role of ventilatory ratio as an outcome predictor. The findings from this study were further verified in secondary analyses of two NHLBI ARDS Network randomized controlled trials.

MEASUREMENTS AND MAIN RESULTS

Ventilatory ratio positively correlated with Vd/Vt. Ordinal groups of ventilatory ratio had significantly higher Vd/Vt. Ventilatory ratio was independently associated with increased risk of mortality after adjusting for Pa_O2/Fi_O2, and positive end-expiratory pressure (odds ratio, 1.51; P = 0.024) and after adjusting for Acute Physiologic Assessment and Chronic Health Evaluation II score (odds ratio, 1.59; P = 0.04). These findings were further replicated in secondary analyses of two separate NHLBI randomized controlled trials.

CONCLUSIONS

Ventilatory ratio correlates well with Vd/Vt in ARDS, and higher values at baseline are associated with increased risk of adverse outcomes. These results are promising for the use of ventilatory ratio as a simple bedside index of impaired ventilation in ARDS.

Equipoise in Appropriate Initial Volume Resuscitation for Patients in Septic Shock With Heart Failure: Results of a Multicenter Clinician Survey

PURPOSE

International clinical practice guidelines call for initial volume resuscitation of at least 30 mL/kg body weight for patients with sepsis-induced hypotension or shock. Although not considered in the guidelines, preexisting cardiac dysfunction may be an important factor clinicians weigh in deciding the quantity of volume resuscitation for patients with septic shock.

METHODS

We conducted a multicenter survey of clinicians who routinely treat patients with sepsis to evaluate their beliefs, behaviors, knowledge, and perceived structural barriers regarding initial volume resuscitation for patients with sepsis and concomitant heart failure with reduced ejection fraction (HFrEF) <40%. Initial volume resuscitation preferences were captured as ordinal values, and additional testing for volume resuscitation preferences was performed using McNemar and Wilcoxon signed rank tests as indicated. Univariable logistic regression models were used to identify significant predictors of ≥30 mL/kg fluid administration.

RESULTS

A total of 317 clinicians at 9 US hospitals completed the survey (response rate 47.3%). Most respondents were specialists in either internal medicine or emergency medicine. Substantial heterogeneity was found regarding sepsis resuscitation preferences for patients with concomitant HFrEF. The belief that patients with septic shock and HFrEF should be exempt from current sepsis bundle initiatives was shared by 39.4% of respondents. A minimum fluid challenge of ∼30 mL/kg or more was deemed appropriate in septic shock by only 56.4% of respondents for patients with concomitant HFrEF, compared to 89.1% of respondents for patients without HFrEF (P < .01). Emergency medicine physicians were most likely to feel that <30 mL/kg was most appropriate in patients with septic shock and HFrEF.

CONCLUSIONS

Clinical equipoise exists regarding initial volume resuscitation for patients with sepsis-induced hypotension or shock and concomitant HFrEF. Future studies and clinical practice guidelines should explicitly address resuscitation in this subpopulation.

Incorporating baseline functional status to improve validity of neurological outcome assessments following cardiac arrest

BACKGROUND

Neurological status at hospital discharge is routinely used to assess patient outcome after cardiac arrest. However, attribution of impairment to the arrest is valid only if baseline neurological status is known. This study evaluated whether incorporating baseline neurological status improves performance of a widely employed neurological outcome scale for quantifying arrest-attributable morbidity.

METHODS

Retrospective cohort study of two U.S. hospitals. Neurological function was assessed via Cerebral performance category (CPC), an ordinal five-point scale with 1 indicating sufficient cognition to lead an independent life and 5 representing brain death. Hospitalized adult patients who suffered in-hospital cardiac arrest for which cardiopulmonary resuscitation was attempted between 2011-2015 were included. Patients were identified through a quality improvement registry that captures all inpatient arrests in the two hospitals.

RESULTS

Of 486 patients who suffered in-hospital cardiac arrest, 124 (25.5%) had baseline abnormal neurological function (pre-hospitalization CPC>1). Although 54 patients had a normal discharge CPC of 1, 80 patients had no change in CPC from their prior baseline (11.1% vs. 16.5% met criterion for "normal" outcome defined as CPC of 1 vs. change-in-CPC of 0; McNemar p < .01; kappa for agreement: .78, 95% CI .69-.86). Across several formulations of criteria for "good" neurological outcome, similar discordance existed between conventional definitions considering only discharge CPC and modified definitions that included change-in-CPC from baseline.

CONCLUSIONS

Incorporating change-in-CPC into criteria for "good" neurological outcome post-arrest yields discordant results from traditional approaches that consider discharge CPC only and increases face validity of reporting arrest-related morbidity.

Optimal Ventilator Strategies in Acute Respiratory Distress Syndrome

Mechanical ventilation practices in patients with acute respiratory distress syndrome (ARDS) have progressed with a growing understanding of the disease pathophysiology. Paramount to the care of affected patients is the delivery of lung-protective mechanical ventilation which prioritizes tidal volume and plateau pressure limitation. Lung protection can probably be further enhanced by scaling target tidal volumes to the specific respiratory mechanics of individual patients. The best procedure for selecting optimal positive end-expiratory pressure (PEEP) in ARDS remains uncertain; several relevant issues must be considered when selecting PEEP, particularly lung recruitability. Noninvasive ventilation must be used with caution in ARDS as excessively high respiratory drive can further exacerbate lung injury; newer modes of delivery offer promising approaches in hypoxemic respiratory failure. Airway pressure release ventilation offers an alternative approach to maximize lung recruitment and oxygenation, but clinical trials have not demonstrated a survival benefit of this mode over conventional ventilation strategies. Rescue therapy with high-frequency oscillatory ventilation is an important option in refractory hypoxemia. Despite a disappointing lack of benefit (and possible harm) in patients with moderate or severe ARDS, possibly due to lung hyperdistention and right ventricular dysfunction, high-frequency oscillation may improve outcome in patients with very severe hypoxemia.

Effect of Titrating Positive End-Expiratory Pressure (PEEP) With an Esophageal Pressure-Guided Strategy vs an Empirical High PEEP-Fio2 Strategy on Death and Days Free From Mechanical Ventilation Among Patients With Acute Respiratory Distress Syndrome: A Randomized Clinical Trial

IMPORTANCE

Adjusting positive end-expiratory pressure (PEEP) to offset pleural pressure might attenuate lung injury and improve patient outcomes in acute respiratory distress syndrome (ARDS).

OBJECTIVE

To determine whether PEEP titration guided by esophageal pressure (PES), an estimate of pleural pressure, was more effective than empirical high PEEP-fraction of inspired oxygen (Fio2) in moderate to severe ARDS.

DESIGN, SETTING, AND PARTICIPANTS

Phase 2 randomized clinical trial conducted at 14 hospitals in North America. Two hundred mechanically ventilated patients aged 16 years and older with moderate to severe ARDS (Pao2:Fio2 ≤200 mm Hg) were enrolled between October 31, 2012, and September 14, 2017; long-term follow-up was completed July 30, 2018.

INTERVENTIONS

Participants were randomized to PES-guided PEEP (n = 102) or empirical high PEEP-Fio2 (n = 98). All participants received low tidal volumes.

MAIN OUTCOMES AND MEASURES

The primary outcome was a ranked composite score incorporating death and days free from mechanical ventilation among survivors through day 28. Prespecified secondary outcomes included 28-day mortality, days free from mechanical ventilation among survivors, and need for rescue therapy.

RESULTS

Two hundred patients were enrolled (mean [SD] age, 56 [16] years; 46% female) and completed 28-day follow-up. The primary composite end point was not significantly different between treatment groups (probability of more favorable outcome with PES-guided PEEP: 49.6% [95% CI, 41.7% to 57.5%]; P = .92). At 28 days, 33 of 102 patients (32.4%) assigned to PES-guided PEEP and 30 of 98 patients (30.6%) assigned to empirical PEEP-Fio2 died (risk difference, 1.7% [95% CI, -11.1% to 14.6%]; P = .88). Days free from mechanical ventilation among survivors was not significantly different (median [interquartile range]: 22 [15-24] vs 21 [16.5-24] days; median difference, 0 [95% CI, -1 to 2] days; P = .85). Patients assigned to PES-guided PEEP were significantly less likely to receive rescue therapy (4/102 [3.9%] vs 12/98 [12.2%]; risk difference, -8.3% [95% CI, -15.8% to -0.8%]; P = .04). None of the 7 other prespecified secondary clinical end points were significantly different. Adverse events included gross barotrauma, which occurred in 6 patients with PES-guided PEEP and 5 patients with empirical PEEP-Fio2.

CONCLUSIONS AND RELEVANCE

Among patients with moderate to severe ARDS, PES-guided PEEP, compared with empirical high PEEP-Fio2, resulted in no significant difference in death and days free from mechanical ventilation. These findings do not support PES-guided PEEP titration in ARDS.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier NCT01681225.

Shock subtypes by left ventricular ejection fraction following out-of-hospital cardiac arrest

Background

Post-resuscitation hemodynamic instability following out-of-hospital cardiac arrest (OHCA) may occur from myocardial dysfunction underlying cardiogenic shock and/or inflammation-mediated distributive shock. Distinguishing the predominant shock subtype with widely available clinical metrics may have prognostic and therapeutic value.

Methods

A two-hospital cohort was assembled of patients in shock following OHCA. Left ventricular ejection fraction (LVEF) was assessed via echocardiography or cardiac ventriculography within 1 day post arrest and used to delineate shock physiology. The study evaluated whether higher LVEF, indicating distributive-predominant shock physiology, was associated with neurocognitive outcome (primary endpoint), survival, and duration of multiple organ failures. The study also investigated whether volume resuscitation exhibited a subtype-specific association with outcome.

Results

Of 162 patients with post-resuscitation shock, 48% had normal LVEF (> 40%), consistent with distributive shock physiology. Higher LVEF was associated with less favorable neurocognitive outcome (OR 0.74, 95% CI 0.58–0.94 per 10% increase in LVEF; p = 0.01). Higher LVEF also was associated with worse survival (OR 0.81, 95% CI 0.67–0.97; p = 0.02) and fewer organ failure-free days (β = – 0.67, 95% CI – 1.28 to − 0.06; p = 0.03). Only 51% of patients received a volume challenge of at least 30 ml/kg body weight in the first 6 h post arrest, and the volume received did not differ by LVEF. Greater volume resuscitation in the first 6 h post arrest was associated with favorable neurocognitive outcome (OR 1.59, 95% CI 0.99–2.55 per liter; p = 0.03) and survival (OR 1.44, 95% CI 1.02–2.04; p = 0.02) among patients with normal LVEF but not low LVEF.

Conclusions

In post-resuscitation shock, higher LVEF—indicating distributive shock physiology—was associated with less favorable neurocognitive outcome, fewer days without organ failure, and higher mortality. Greater early volume resuscitation was associated with more favorable neurocognitive outcome and survival in patients with this shock subtype. Additional studies with repeated measures of complementary hemodynamic parameters are warranted to validate the clinical utility for subtyping post-resuscitation shock.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2078-x) contains supplementary material, which is available to authorized users.

Factors and outcomes associated with inpatient cardiac arrest following emergent endotracheal intubation

BACKGROUND

Inpatient peri-intubation cardiac arrest (PICA) following emergent endotracheal intubation (ETI) is an uncommon but potentially preventable type of cardiac arrest (CA). Limited published data exist describing factors associated with inpatient PICA and patient outcomes. This study identifies risk factors associated with PICA among hospitalized patients emergently intubated out of the operating room and compares PICA to other types of inpatient CA.

METHODS

Retrospective case-control study of patients at our institution over a five-year period. Cases were defined as inpatients emergently intubated outside of the operating room that experienced cardiac arrest within 20min after ETI. The control group consisted of inpatients emergently intubated out of the operating room without CA. Predictors of PICA were identified through univariate and multivariate analysis. Clinical outcomes were compared between PICA and other inpatient CAs, identified through a prospectively enrolled CA registry at our institution.

RESULTS

29 episodes of PICA occurred over 5 years, accounting for 5% of all inpatient arrests. Shock index ≥1.0, intubation within one hour of nursing shift change, and use of succinylcholine were independently associated with PICA. Sustained ROSC, survival to discharge, and neurocognitive outcome did not differ significantly between groups.

CONCLUSION

Patients outcomes following PICA were comparable to other causes of inpatient CA. Potentially modifiable factors were associated with PICA. Hemodynamic resuscitation, optimized staffing strategies, and possible avoidance of succinylcholine were associated with decreased risk of PICA. Clinical trials testing targeted strategies to optimize peri-intubation care are needed to identify effective interventions to prevent this potentially avoidable type of CA.

Favorable Neurocognitive Outcome with Low Tidal Volume Ventilation after Cardiac Arrest

RATIONALE

Neurocognitive outcome after out-of-hospital cardiac arrest (OHCA) is often poor, even when initial resuscitation succeeds. Lower tidal volumes (Vts) attenuate extrapulmonary organ injury in other disease states and are neuroprotective in preclinical models of critical illness.

OBJECTIVE

To evaluate the association between Vt and neurocognitive outcome after OHCA.

METHODS

We performed a propensity-adjusted analysis of a two-center retrospective cohort of patients experiencing OHCA who received mechanical ventilation for at least the first 48 hours of hospitalization. Vt was calculated as the time-weighted average over the first 48 hours, in milliliters per kilogram of predicted body weight (PBW). The primary endpoint was favorable neurocognitive outcome (cerebral performance category of 1 or 2) at discharge.

MEASUREMENTS AND MAIN RESULTS

Of 256 included patients, 38% received time-weighted average Vt greater than 8 ml/kg PBW during the first 48 hours. Lower Vt was independently associated with favorable neurocognitive outcome in propensity-adjusted analysis (odds ratio, 1.61; 95% confidence interval [CI], 1.13-2.28 per 1-ml/kg PBW decrease in Vt; P = 0.008). This finding was robust to several sensitivity analyses. Lower Vt also was associated with more ventilator-free days (β = 1.78; 95% CI, 0.39-3.16 per 1-ml/kg PBW decrease; P = 0.012) and shock-free days (β = 1.31; 95% CI, 0.10-2.51; P = 0.034). Vt was not associated with hypercapnia (P = 1.00). Although the propensity score incorporated several biologically relevant covariates, only height, weight, and admitting hospital were independent predictors of Vt less than or equal to 8 ml/kg PBW.

CONCLUSIONS

Lower Vt after OHCA is independently associated with favorable neurocognitive outcome, more ventilator-free days, and more shock-free days. These findings suggest a role for low-Vt ventilation after cardiac arrest.

Ventilator-induced lung injury increases expression of endothelial inflammatory mediators in the kidney

In critical illness, such as sepsis or the acute respiratory distress syndrome, acute kidney injury (AKI) is common and associated with increased morbidity and mortality. Mechanical ventilation in critical illnesses is also a risk factor for AKI, but it is potentially modifiable. Injurious ventilation strategies may lead to the systemic release of inflammatory mediators from the lung due to ventilator induced lung injury (VILI). The systemic consequences of VILI are difficult to differentiate clinically from other systemic inflammatory syndromes, such as sepsis. The purpose of this study was to identify unique changes in the expression of inflammatory mediators in kidney tissue in response to VILI compared with systemic sepsis to gain insight into direct effects of VILI on the kidney. Four groups of mice were compared-mice with sepsis from cecal ligation and puncture (CLP), mice subjected to injurious mechanical ventilation with high tidal volumes (VILI), mice exposed to CLP followed by VILI (CLP+VILI), and sham controls. Protein expression of common inflammatory mediators in kidneys was analyzed using a proteome array and confirmed by Western blot analysis or ELISA. VEGF and VCAM-1 were found to be significantly elevated in kidneys from VILI mice compared with sham and CLP. Angiopoietin-2 was significantly increased in CLP+VILI compared with CLP alone and was also correlated with higher levels of AKI biomarker, neutrophil gelatinase-associated lipocalin. These results suggest that VILI alters the renal expression of VEGF, VCAM-1, and angiopoietin-2, and these proteins warrant further investigation as potential biomarkers and therapeutic targets.

Treatment of ARDS With Prone Positioning

Prone positioning was first proposed in the 1970s as a method to improve gas exchange in ARDS. Subsequent observations of dramatic improvement in oxygenation with simple patient rotation motivated the next several decades of research. This work elucidated the physiological mechanisms underlying changes in gas exchange and respiratory mechanics with prone ventilation. However, translating physiological improvements into a clinical benefit has proved challenging; several contemporary trials showed no major clinical benefits with prone positioning. By optimizing patient selection and treatment protocols, the recent Proning Severe ARDS Patients (PROSEVA) trial demonstrated a significant mortality benefit with prone ventilation. This trial, and subsequent meta-analyses, support the role of prone positioning as an effective therapy to reduce mortality in severe ARDS, particularly when applied early with other lung-protective strategies. This review discusses the physiological principles, clinical evidence, and practical application of prone ventilation in ARDS.

Personalizing mechanical ventilation for acute respiratory distress syndrome

Lung-protective ventilation with low tidal volumes remains the cornerstone for treating patient with acute respiratory distress syndrome (ARDS). Personalizing such an approach to each patient's unique physiology may improve outcomes further. Many factors should be considered when mechanically ventilating a critically ill patient with ARDS. Estimations of transpulmonary pressures as well as individual's hemodynamics and respiratory mechanics should influence PEEP decisions as well as response to therapy (recruitability). This summary will emphasize the potential role of personalized therapy in mechanical ventilation.