Reversibility of lung collapse and hypoxemia in early acute respiratory distress syndrome

Assessment of recruitment from CT to the bedside: challenges and future directions

Assessing and quantifying recruitability are important for characterizing ARDS severity and for reducing or preventing the atelectrauma caused by the cyclic opening and closing of pulmonary units. Over the years, several methods for recruitment assessment have been developed, grouped into three main approaches: 1) Quantitative CT Scanning: This method accurately measures the amount of atelectatic lung tissue that regains aeration; 2) Regional Gas Volume Measurement: Based on anatomical markers, this approach assesses gas volume within a specified lung region; 3) Compliance-Based Gas Volume Measurement: This technique compares actual gas volume at a given pressure to expected values, assuming respiratory system compliance is constant within the explored pressure range. Additional methods, such as lung ultrasonography and electrical impedance variation, have also been explored. This paper details the distribution of opening and closing pressures throughout the lung parenchyma, which underpin the concept of recruitability. The distribution of recruitable regions corresponds to atelectasis distribution, with the pressure needed for recruitment varying according to whether the atelectasis is "loose" or "sticky." We also discuss the effects of different PEEP levels on preventing atelectrauma, the importance of keeping some lung areas closed throughout the respiratory cycle, and briefly cover the roles of sigh ventilation, prone positioning, and the closed lung approach.

Quantification of pulmonary edema using automated lung segmentation on computed tomography in mechanically ventilated patients with acute respiratory distress syndrome

BACKGROUND

Quantification of pulmonary edema in patients with acute respiratory distress syndrome (ARDS) by chest computed tomography (CT) scan has not been validated in routine diagnostics due to its complexity and time-consuming nature. Therefore, the single-indicator transpulmonary thermodilution (TPTD) technique to measure extravascular lung water (EVLW) has been used in the clinical setting. Advances in artificial intelligence (AI) have now enabled CT images of inhomogeneous lungs to be segmented automatically by an intensive care physician with no prior radiology training within a relatively short time. Nevertheless, there is a paucity of data validating the quantification of pulmonary edema using automated lung segmentation on CT compared with TPTD.

METHODS

A retrospective study (January 2016 to December 2021) analyzed patients with ARDS, admitted to the intensive care unit of the Department of Anesthesiology and Critical Care Medicine, University Hospital Mannheim, who underwent a chest CT scan and hemodynamic monitoring using TPTD at the same time. Pulmonary edema was estimated using manually and automated lung segmentation on CT and then compared to the pulmonary edema calculated from EVLW determined using TPTD.

RESULTS

145 comparative measurements of pulmonary edema with TPTD and CT were included in the study. Estimating pulmonary edema using either automated lung segmentation on CT or TPTD showed a low bias overall (- 104 ml) but wide levels of agreement (upper: 936 ml, lower: - 1144 ml). In 13% of the analyzed CT scans, the agreement between the segmentation of the AI algorithm and a dedicated investigator was poor. Manual segmentation and automated segmentation adjusted for contrast agent did not improve the agreement levels.

CONCLUSIONS

Automated lung segmentation on CT can be considered an unbiased but imprecise measurement of pulmonary edema in mechanically ventilated patients with ARDS.

Recruitment-Potential-Oriented Mechanical Ventilation Protocol and Narrative Review for Patients with Acute Respiratory Distress Syndrome

Even though much progress has been made to improve clinical outcomes, acute respiratory distress syndrome (ARDS) remains a significant cause of acute respiratory failure. Protective mechanical ventilation is the backbone of supportive care for these patients; however, there are still many unresolved issues in its setting. The primary goal of mechanical ventilation is to improve oxygenation and ventilation. The use of positive pressure, especially positive end-expiratory pressure (PEEP), is mandatory in this approach. However, PEEP is a double-edged sword. How to safely set positive end-inspiratory pressure has long been elusive to clinicians. We hereby propose a pressure-volume curve measurement-based method to assess whether injured lungs are recruitable in order to set an appropriate PEEP. For the most severe form of ARDS, extracorporeal membrane oxygenation (ECMO) is considered as the salvage therapy. However, the high level of medical resources required and associated complications make its use in patients with severe ARDS controversial. Our proposed protocol also attempts to propose how to improve patient outcomes by balancing the possible overuse of resources with minimizing patient harm due to dangerous ventilator settings. A recruitment-potential-oriented evaluation-based protocol can effectively stabilize hypoxemic conditions quickly and screen out truly serious patients.

Multicentre, parallel, open-label, two-arm, randomised controlled trial on the prognosis of electrical impedance tomography-guided versus low PEEP/FiO2 table-guided PEEP setting: a trial protocol

INTRODUCTION

Previous studies suggested that electrical impedance tomography (EIT) has the potential to guide positive end-expiratory pressure (PEEP) titration via quantifying the alveolar collapse and overdistension. The aim of this trial is to compare the effect of EIT-guided PEEP and acute respiratory distress syndrome (ARDS) network low PEEP/fraction of inspired oxygen (FiO2) table strategy on mortality and other clinical outcomes in patients with ARDS.

METHODS

This is a parallel, two-arm, multicentre, randomised, controlled trial, conducted in China. All patients with ARDS under mechanical ventilation admitted to the intensive care unit will be screened for eligibility. The enrolled patients are stratified by the aetiology (pulmonary/extrapulmonary) and partial pressure of arterial oxygen/FiO2 (≥150 mm Hg or <150 mm Hg) and randomised into the intervention group or the control group. The intervention group will receive recruitment manoeuvre and EIT-guided PEEP titration. The EIT-guided PEEP will be set for at least 12 hours after titration. The control group will not receive recruitment manoeuvre routinely and the PEEP will be set according to the lower PEEP/FiO2 table proposed by the ARDS Network. The primary outcome is 28-day survival.

ANALYSIS

Qualitative data will be analysed using the χ2 test or Fisher's exact test, quantitative data will be analysed using independent samples t-test or Mann-Whitney U test. Kaplan-Meier analysis with log-rank test will be used to evaluate the 28-day survival rate between two groups. All outcomes will be analysed based on the intention-to-treat principle.

ETHICS AND DISSEMINATION

The trial is approved by the Institutional Research and Ethics Committee of the Peking Union Medical College Hospital. Data will be published in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT05307913.

Time-Controlled Adaptive Ventilation (TCAV): a personalized strategy for lung protection

Acute respiratory distress syndrome (ARDS) alters the dynamics of lung inflation during mechanical ventilation. Repetitive alveolar collapse and expansion (RACE) predisposes the lung to ventilator-induced lung injury (VILI). Two broad approaches are currently used to minimize VILI: (1) low tidal volume (LVT) with low-moderate positive end-expiratory pressure (PEEP); and (2) open lung approach (OLA). The LVT approach attempts to protect already open lung tissue from overdistension, while simultaneously resting collapsed tissue by excluding it from the cycle of mechanical ventilation. By contrast, the OLA attempts to reinflate potentially recruitable lung, usually over a period of seconds to minutes using higher PEEP used to prevent progressive loss of end-expiratory lung volume (EELV) and RACE. However, even with these protective strategies, clinical studies have shown that ARDS-related mortality remains unacceptably high with a scarcity of effective interventions over the last two decades. One of the main limitations these varied interventions demonstrate to benefit is the observed clinical and pathologic heterogeneity in ARDS. We have developed an alternative ventilation strategy known as the Time Controlled Adaptive Ventilation (TCAV) method of applying the Airway Pressure Release Ventilation (APRV) mode, which takes advantage of the heterogeneous time- and pressure-dependent collapse and reopening of lung units. The TCAV method is a closed-loop system where the expiratory duration personalizes VT and EELV. Personalization of TCAV is informed and tuned with changes in respiratory system compliance (CRS) measured by the slope of the expiratory flow curve during passive exhalation. Two potentially beneficial features of TCAV are: (i) the expiratory duration is personalized to a given patient's lung physiology, which promotes alveolar stabilization by halting the progressive collapse of alveoli, thereby minimizing the time for the reopened lung to collapse again in the next expiration, and (ii) an extended inspiratory phase at a fixed inflation pressure after alveolar stabilization gradually reopens a small amount of tissue with each breath. Subsequently, densely collapsed regions are slowly ratcheted open over a period of hours, or even days. Thus, TCAV has the potential to minimize VILI, reducing ARDS-related morbidity and mortality.

Effects of THE PEEP-ZEEP Maneuver in Adults Receiving Mechanical Ventilation: A Systematic Review with Meta-Analysis

INTRODUCTION

It is important to clarify the secretion clearance and lung-related effects of the PEEP-ZEEP maneuver in adults undergoing mechanical ventilation (MV). There is no published comprehensive meta-analysis of the effects of PEEP-ZEEP in adults receiving MV.

OBJECTIVES

The aim of this study was to analyze published randomized controlled trials, investigating the effects of the PEEP-ZEEP maneuver in adults undergoing mechanical ventilation.

METHODS

We searched Embase, PubMed, Cochrane Central Register of Controlled Trials, Scopus, and Web of Science from the date of inception of the databases until 6 May 2023. Quality assessment was using the Cochrane Systematic Assessment Handbook. The GRADE system was used to grade the quality of the evidence.

RESULTS

A total of 12 trials were included, and the results of the meta-analysis showed that PEEP-ZEEP was not superior to bag squeezing for the removal of bronchial secretions. One study showed a significant increase in the amount of secretion retrieved with the PEEP-ZEEP when compared with tracheal suctioning. Additionally, PEEP-ZEEP was more effective than bag squeezing at improving oxygen saturation. However, one trial showed that bag squeezing was better at improving dynamic compliance. No other differences were found between PEEP-ZEEP and other techniques, except for one study showing more frequent changes in diastolic blood pressure with PEEP-ZEEP compared with ventilator hyperinflation.

CONCLUSION

PEEP-ZEEP was not superior to bag squeezing in removing bronchial secretions. However, it improves oxygen saturation when compared to bag squeezing, and no adverse effects on patients' respiratory systems have yet been observed.

American Association for the Surgery of Trauma/American College of Surgeons Committee on Trauma clinical protocol for management of acute respiratory distress syndrome and severe hypoxemia

LEVEL OF EVIDENCE

Therapeutic/Care Management: Level V.

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.

Lung Recruitment Assessed by Electrical Impedance Tomography (RECRUIT): A Multicenter Study of COVID-19 Acute Respiratory Distress Syndrome

Rationale: Defining lung recruitability is needed for safe positive end-expiratory pressure (PEEP) selection in mechanically ventilated patients. However, there is no simple bedside method including both assessment of recruitability and risks of overdistension as well as personalized PEEP titration. Objectives: To describe the range of recruitability using electrical impedance tomography (EIT), effects of PEEP on recruitability, respiratory mechanics and gas exchange, and a method to select optimal EIT-based PEEP. Methods: This is the analysis of patients with coronavirus disease (COVID-19) from an ongoing multicenter prospective physiological study including patients with moderate-severe acute respiratory distress syndrome of different causes. EIT, ventilator data, hemodynamics, and arterial blood gases were obtained during PEEP titration maneuvers. EIT-based optimal PEEP was defined as the crossing point of the overdistension and collapse curves during a decremental PEEP trial. Recruitability was defined as the amount of modifiable collapse when increasing PEEP from 6 to 24 cm H2O (ΔCollapse24-6). Patients were classified as low, medium, or high recruiters on the basis of tertiles of ΔCollapse24-6. Measurements and Main Results: In 108 patients with COVID-19, recruitability varied from 0.3% to 66.9% and was unrelated to acute respiratory distress syndrome severity. Median EIT-based PEEP differed between groups: 10 versus 13.5 versus 15.5 cm H2O for low versus medium versus high recruitability (P < 0.05). This approach assigned a different PEEP level from the highest compliance approach in 81% of patients. The protocol was well tolerated; in four patients, the PEEP level did not reach 24 cm H2O because of hemodynamic instability. Conclusions: Recruitability varies widely among patients with COVID-19. EIT allows personalizing PEEP setting as a compromise between recruitability and overdistension. Clinical trial registered with www.clinicaltrials.gov (NCT04460859).

Pulmonary Recruitment Prior to Intraoperative Multiple Pulmonary Ground-Glass Nodule Localization Increases the Localization Accuracy-A Retrospective Study

The standard treatment for early-stage lung cancer is complete tumor excision by limited resection of the lung. Preoperative localization is used before video-assisted thoracoscopic surgery (VATS) to improve the accuracy of pulmonary nodule excision. However, lung atelectasis and hypoxia resulting from controlling apnea during the localization procedure may affect the localization accuracy. Pre-procedural pulmonary recruitment may improve the respiratory mechanics and oxygenation during localization. In this study, we investigated the potential benefits of pre-localization pulmonary recruitment prior to pulmonary ground-glass nodule localization in a hybrid operating room. We hypothesized that pre-localization pulmonary recruitment would increase the localization accuracy, improve oxygenation, and prevent the need for re-inflation during the localization procedure. We retrospectively enrolled patients with multiple pulmonary nodule localizations before surgical intervention in our hybrid operating room. We compared the localization accuracy between patients who had undergone pre-procedure pulmonary recruitment and patients who had not. Saturation, re-inflation rate, apnea time, procedure-related pneumothorax, and procedure time were also recorded as secondary outcomes. The patients who had undergone pre-procedure recruitment had better saturation, shorter procedure time, and higher localization accuracy. The pre-procedure pulmonary recruitment maneuver was effective in increasing regional lung ventilation, leading to improved oxygenation and localization accuracy.

Acute Lung Injury in aortic dissection : new insights in anesthetic management strategies

Acute aortic dissection (AAD) is a severe cardiovascular disease characterized by rapid progress and a high mortality rate. The incidence of acute aortic dissection is approximately 5 to 30 per 1 million people worldwide. In clinical practice, about 35% of AAD patients are complicated with acute lung injury (ALI). AAD complicated with ALI can seriously affect patients' prognosis and even increase mortality. However, the pathogenesis of AAD combined with ALI remains largely unknown. Given the public health burden of AAD combined with ALI, we reviewed the anesthetic management advances and highlighted potential areas for clinical practice.

Real-time effects of lateral positioning on regional ventilation and perfusion in an experimental model of acute respiratory distress syndrome

Low-volume lung injury encompasses local concentration of stresses in the vicinity of collapsed regions in heterogeneously ventilated lungs. We aimed to study the effects on ventilation and perfusion distributions of a sequential lateral positioning (30°) strategy using electrical impedance tomography imaging in a porcine experimental model of early acute respiratory distress syndrome (ARDS). We hypothesized that such strategy, including a real-time individualization of positive end-expiratory pressure (PEEP) whenever in lateral positioning, would provide attenuation of collapse in the dependent lung regions. A two-hit injury acute respiratory distress syndrome experimental model was established by lung lavages followed by injurious mechanical ventilation. Then, all animals were studied in five body positions in a sequential order, 15 min each: Supine 1; Lateral Left; Supine 2; Lateral Right; Supine 3. The following functional images were analyzed by electrical impedance tomography: ventilation distributions and regional lung volumes, and perfusion distributions. The induction of the acute respiratory distress syndrome model resulted in a marked fall in oxygenation along with low regional ventilation and compliance of the dorsal half of the lung (gravitational-dependent in supine position). Both the regional ventilation and compliance of the dorsal half of the lung greatly increased along of the sequential lateral positioning strategy, and maximally at its end. In addition, a corresponding improvement of oxygenation occurred. In conclusion, our sequential lateral positioning strategy, with sufficient positive end-expiratory pressure to prevent collapse of the dependent lung units during lateral positioning, provided a relevant diminution of collapse in the dorsal lung in a porcine experimental model of early acute respiratory distress syndrome.

Management of refractory hypoxemia using recruitment maneuvers and rescue therapies: A comprehensive review

Refractory hypoxemia in patients with acute respiratory distress syndrome treated with mechanical ventilation is one of the most challenging conditions in human and veterinary intensive care units. When a conventional lung protective approach fails to restore adequate oxygenation to the patient, the use of recruitment maneuvers and positive end-expiratory pressure to maximize alveolar recruitment, improve gas exchange and respiratory mechanics, while reducing the risk of ventilator-induced lung injury has been suggested in people as the open lung approach. Although the proposed physiological rationale of opening and keeping open previously collapsed or obstructed airways is sound, the technique for doing so, as well as the potential benefits regarding patient outcome are highly controversial in light of recent randomized controlled trials. Moreover, a variety of alternative therapies that provide even less robust evidence have been investigated, including prone positioning, neuromuscular blockade, inhaled pulmonary vasodilators, extracorporeal membrane oxygenation, and unconventional ventilatory modes such as airway pressure release ventilation. With the exception of prone positioning, these modalities are limited by their own balance of risks and benefits, which can be significantly influenced by the practitioner's experience. This review explores the rationale, evidence, advantages and disadvantages of each of these therapies as well as available methods to identify suitable candidates for recruitment maneuvers, with a summary on their application in veterinary medicine. Undoubtedly, the heterogeneous and evolving nature of acute respiratory distress syndrome and individual lung phenotypes call for a personalized approach using new non-invasive bedside assessment tools, such as electrical impedance tomography, lung ultrasound, and the recruitment-to-inflation ratio to assess lung recruitability. Data available in human medicine provide valuable insights that could, and should, be used to improve the management of veterinary patients with severe respiratory failure with respect to their intrinsic anatomy and physiology.

Flow-controlled expiration reduces positive end-expiratory pressure requirement in dorsally recumbent, anesthetized horses

Introduction

Equine peri-anesthetic mortality is higher than that for other commonly anesthetized veterinary species. Unique equine pulmonary pathophysiologic aspects are believed to contribute to this mortality due to impairment of gas exchange and subsequent hypoxemia. No consistently reliable solution for the treatment of peri-anesthetic gas exchange impairment is available. Flow-controlled expiration (FLEX) is a ventilatory mode that linearizes gas flow throughout the expiratory phase, reducing the rate of lung emptying and alveolar collapse. FLEX has been shown to improve gas exchange and pulmonary mechanics in anesthetized horses. This study further evaluated FLEX ventilation in anesthetized horses positioned in dorsal recumbency, hypothesizing that after alveolar recruitment, horses ventilated using FLEX would require a lower positive end-expiratory pressure (PEEP) to prevent alveolar closure than horses conventionally ventilated.

Methods

Twelve adult horses were used in this prospective, randomized study. Horses were assigned either to conventional volume-controlled ventilation (VCV) or to FLEX. Following induction of general anesthesia, horses were placed in dorsal recumbency mechanically ventilated for a total of approximately 6.5 hours. Thirty-minutes after starting ventilation with VCV or FLEX, a PEEP-titration alveolar recruitment maneuver was performed at the end of which the PEEP was reduced in decrements of 3 cmH₂O until the alveolar closure pressure was determined. The PEEP was then increased to the previous level and maintained for additional three hours. During this time, the mean arterial blood pressure, pulmonary arterial pressure, central venous blood pressure, cardiac output (CO), dynamic respiratory system compliance and arterial blood gas values were measured.

Results

The alveolar closure pressure was significantly lower (6.5 ± 1.2 vs 11.0 ± 1.5 cmH₂O) and significantly less PEEP was required to prevent alveolar closure (9.5 ± 1.2 vs 14.0 ± 1.5 cmH₂O) for horses ventilated using FLEX compared with VCV. The CO was significantly higher in the horses ventilated with FLEX (37.5 ± 4 vs 30 ± 6 l/min).

Discussion

We concluded that FLEX ventilation was associated with a lower PEEP requirement due to a more homogenous distribution of ventilation in the lungs during expiration. This lower PEEP requirement led to more stable and improved cardiovascular conditions in horses ventilated with FLEX.

Gas distribution by EIT during PEEP inflation: PEEP response and optimal PEEP with lowest trans-pulmonary driving pressure can be determined without esophageal pressure during a rapid PEEP trial in patients with acute respiratory failure

Objective. Protective ventilation should be based onlungmechanics and transpulmonary driving pressure (ΔPTP), as this 'hits' the lung directly.Approach. The change in end-expiratory lung volume (ΔEELV) is determined by the size of the PEEP step and the elastic properties of the lung (EL), ΔEELV/ΔPEEP. Consequently, EL can be determined as ΔPEEP/ΔEELV. By calibration of tidal inspiratory impedance change with ventilator inspiratory tidal volume, end-expiratory lung impedance changes were converted to volume changes and lung P/V curves were obtained during a PEEP trial in ten patients with acute respiratory failure. The PEEP level where ΔPTP was lowest (optimal PEEP) was determined as the steepest point of the lung P/V curve.Main results. Over-all EL ranged between 7.0-23.2 cmH₂O/L. Optimal PEEP was 12.9 cmH₂O (10-16) with ΔPTP of 4.1 cmH₂O (2.8-7.6). Patients with highest EL were PEEP non-responders, where EL increased in non-dependent and dependent lung at high PEEP, indicating over-distension in all lung. Patients with lower EL were PEEP responders with decreasing EL in dependent lung when increasing PEEP.Significance. PEEP non-responders could be identified by regional lung P/V curves derived from ventilator calibrated EIT. Optimal PEEP could be determined from the equation for the lung P/V curve.

Advances in Ventilator Management for Patients with Acute Respiratory Distress Syndrome

The ventilatory care of patients with acute respiratory distress syndrome (ARDS) is evolving as our understanding of physiologic mechanisms of respiratory failure improves. Despite several decades of research, the mortality rate for ARDS remains high. Over the years, we continue to expand strategies to identify and mitigate ventilator-induced lung injury. This now includes a greater understanding of the benefits and harms associated with spontaneous breathing.

Imaging the acute respiratory distress syndrome: past, present and future

In patients with the acute respiratory distress syndrome (ARDS), lung imaging is a fundamental tool in the study of the morphological and mechanistic features of the lungs. Chest computed tomography studies led to major advances in the understanding of ARDS physiology. They allowed the in vivo study of the syndrome's lung features in relation with its impact on respiratory physiology and physiology, but also explored the lungs' response to mechanical ventilation, be it alveolar recruitment or ventilator-induced lung injuries. Coupled with positron emission tomography, morphological findings were put in relation with ventilation, perfusion or acute lung inflammation. Lung imaging has always been central in the care of patients with ARDS, with modern point-of-care tools such as electrical impedance tomography or lung ultrasounds guiding clinical reasoning beyond macro-respiratory mechanics. Finally, artificial intelligence and machine learning now assist imaging post-processing software, which allows real-time analysis of quantitative parameters that describe the syndrome's complexity. This narrative review aims to draw a didactic and comprehensive picture of how modern imaging techniques improved our understanding of the syndrome, and have the potential to help the clinician guide ventilatory treatment and refine patient prognostication.

Thoracic Computed Tomography to Assess ARDS and COVID-19 Lungs

This review was designed to discuss the role of thoracic-computed tomography (CT) in the evaluation and treatment of patients with ARDS and COVID-19 lung disease. Non-aerated lungs characterize the ARDS lungs, compared to normal lungs in the lowermost lung regions, compressive atelectasis. Heterogenous ARDS lungs have a tomographic vertical gradient characterized by progressively more aerated lung tissues from the gravity-dependent to gravity-independent lungs levels. The application of positive pressure ventilation to these heterogeneous ARDS lungs provides some areas of high shear stress, others of tidal hyperdistension or tidal recruitment that increases the chances of appearance and perpetuation of ventilator-induced lung injury. Other than helping to the correct diagnosis of ARDS, thoracic-computed tomography can help to the adjustments of PEEP, ideal tidal volume, and a better choice of patient position during invasive mechanical ventilation. Thoracic tomography can also help detect possible intra-thoracic complications and in the follow-up of the ARDS patients’ evolution during their hospital stay. In COVID-19 patients, thoracic-computed tomography was the most sensitive imaging technique for diagnosing pulmonary involvement. The most common finding is diffuse pulmonary infiltrates, ranging from ground-glass opacities to parenchymal consolidations, especially in the lower portions of the lungs’ periphery. Tomographic lung volume loss was associated with an increased risk for oxygenation support and patient intubation and the use of invasive mechanical ventilation. Pulmonary dual-energy angio-tomography in COVID-19 patients showed a significant number of pulmonary ischemic areas even in the absence of visible pulmonary arterial thrombosis, which may reflect micro-thrombosis associated with COVID-19 pneumonia. A greater thoracic tomography severity score in ARDS was independently related to poor outcomes.

Study protocol for a single-centre randomised controlled trial to investigate the effect of lung recruitment in paediatric patients after cardiac surgery

INTRODUCTION

A number of published studies have revealed that lung recruitment can improve oxygenation, shorten the duration of mechanical ventilation (MV) and decrease mortality in adults with acute hypoxaemic respiratory failure, especially patients with acute respiratory distress syndrome. However, few articles have assessed lung recruitment in paediatric patients, especially after cardiac surgery. This clinical trial aimed to determine whether lung recruitment can reduce the duration of MV in paediatric patients with hypoxaemic respiratory failure after cardiac surgery.

METHOD AND ANALYSIS

In this trial, we will randomly assign 234 paediatric patients (aged 28 days to 14 years) within 72 hours after cardiac surgery with an arterial oxygen tension (PaO₂) to fraction of inspired oxygen (FiO₂) ratio (PaO₂/FiO₂) of <300 to either a lung recruitment group or a conventional group. The primary endpoint will be the duration of MV. The secondary endpoints will be ventilator-free days, PaO₂/FiO₂, respiratory system compliance, duration of non-invasive ventilation, reintubation rate, length of intensive care unit stay, length of hospital stay, occurrence of serious adverse events (barotrauma, persistent hypotension and arrhythmia), postoperative pulmonary complications.

ETHICS AND DISSEMINATION

The ethics committee of West China Hospital of Sichuan University granted ethics approval for this study (20 August 2019). The results will be published in peer-reviewed journals and presented at conferences.

TRIAL REGISTRATION NUMBER

ChiCTR1900025990.

Does airway pressure release ventilation offer new hope for treating acute respiratory distress syndrome?

Mechanical ventilation (MV) is an essential life support method for patients with acute respiratory distress syndrome (ARDS), which is one of the most common critical illnesses with high mortality in the intensive care unit (ICU). A lung-protective ventilation strategy based on low tidal volume (LTV) has been recommended since a few years; however, as this did not result in a significant decrease of ARDS-related mortality, a more optimal ventilation mode was required. Airway pressure release ventilation (APRV) is an old method defined as a continuous positive airway pressure (CPAP) with a brief intermittent release phase based on the open lung concept; it also perfectly fits the ARDS treatment principle. Despite this, APRV has not been widely used in the past, rather only as a rescue measure for ARDS patients who are difficult to oxygenate. Over recent years, with an increased understanding of the pathophysiology of ARDS, APRV has been reproposed to improve patient prognosis. Nevertheless, this mode is still not routinely used in ARDS patients given its vague definition and complexity. Consequently, in this paper, we summarize the studies that used APRV in ARDS, including adults, children, and animals, to illustrate the settings of parameters, effectiveness in the population, safety (especially in children), incidence, and mechanism of ventilator-induced lung injury (VILI) and effects on extrapulmonary organs. Finally, we found that APRV is likely associated with improvement in ARDS outcomes, and does not increase injury to the lungs and other organs, thereby indicating that personalized APRV settings may be the new hope for ARDS treatment.

Optimizing Mechanical Ventilation in Refractory ARDS

Mechanical ventilation in patients with refractory acute respiratory distress syndrome (ARDS) must provide lung protection. This is achieved by limiting tidal volume (VT) and plateau pressure (Pplat). With the current evidence available VT should be initially set around 6 mL per kg predicted body weight and PPlat maintained below 30 cmH₂O and monitored. Positive end-expiratory pressure (PEEP), which also contributes to lung protection, should be set > 12 cmH₂O, provided oxygenation gets improved, with same Pplat target. Recruitment maneuvers should be used with caution avoiding higher PEEP. Neuromuscular blockade should be started and prone position performed for sessions longer than 16 h. High frequency oscillation ventilation should be used in expert centers only if previous management failed to improve oxygenation.

Intraoperative open lung condition and postoperative pulmonary complications. A secondary analysis of iPROVE and iPROVE-O2 trials

BACKGROUND

The preventive role of an intraoperative recruitment maneuver plus open lung approach (RM + OLA) ventilation on postoperative pulmonary complications (PPC) remains unclear. We aimed at investigating whether an intraoperative open lung condition reduces the risk of developing a composite of PPCs.

METHODS

Post hoc analysis of two randomized controlled trials including patients undergoing abdominal surgery. Patients were classified according to the intraoperative lung condition as "open" (OL) or "non-open" (NOL) if PaO₂ /FIO₂ ratio was ≥ or <400 mmHg, respectively. We used a multivariable logistic regression model that included potential confounders selected with directed acyclic graphs (DAG) using Dagitty software built with variables that were considered clinically relevant based on biological mechanism or evidence from previously published data. PPCs included severe acute respiratory failure, acute respiratory distress syndrome, and pneumonia.

RESULTS

A total of 1480 patients were included in the final analysis, with 718 (49%) classified as OL. The rate of severe PPCs during the first seven postoperative days was 6.0% (7.9% in the NOL and 4.4% in the OL group, p = .007). OL was independently associated with a lower risk for severe PPCs during the first 7 and 30 postoperative days [odds ratio of 0.58 (95% CI 0.34-0.99, p = .04) and 0.56 (95% CI 0.34-0.94, p = .03), respectively].

CONCLUSIONS

An intraoperative open lung condition was associated with a reduced risk of developing severe PPCs in intermediate-to-high risk patients undergoing abdominal surgery.

TRIAL REGISTRATION

Registered at clinicaltrials.gov NCT02158923 (iPROVE), NCT02776046 (iPROVE-O2).

Mechanisms of oxygenation responses to proning and recruitment in COVID-19 pneumonia

PURPOSE

This study aimed at investigating the mechanisms underlying the oxygenation response to proning and recruitment maneuvers in coronavirus disease 2019 (COVID-19) pneumonia.

METHODS

Twenty-five patients with COVID-19 pneumonia, at variable times since admission (from 1 to 3 weeks), underwent computed tomography (CT) lung scans, gas-exchange and lung-mechanics measurement in supine and prone positions at 5 cmH₂O and during recruiting maneuver (supine, 35 cmH₂O). Within the non-aerated tissue, we differentiated the atelectatic and consolidated tissue (recruitable and non-recruitable at 35 cmH₂O of airway pressure). Positive/negative response to proning/recruitment was defined as increase/decrease of PaO₂/FiO₂. Apparent perfusion ratio was computed as venous admixture/non aerated tissue fraction.

RESULTS

The average values of venous admixture and PaO₂/FiO₂ ratio were similar in supine-5 and prone-5. However, the PaO₂/FiO₂ changes (increasing in 65% of the patients and decreasing in 35%, from supine to prone) correlated with the balance between resolution of dorsal atelectasis and formation of ventral atelectasis (p = 0.002). Dorsal consolidated tissue determined this balance, being inversely related with dorsal recruitment (p = 0.012). From supine-5 to supine-35, the apparent perfusion ratio increased from 1.38 ± 0.71 to 2.15 ± 1.15 (p = 0.004) while PaO₂/FiO₂ ratio increased in 52% and decreased in 48% of patients. Non-responders had consolidated tissue fraction of 0.27 ± 0.1 vs. 0.18 ± 0.1 in the responding cohort (p = 0.04). Consolidated tissue, PaCO₂ and respiratory system elastance were higher in patients assessed late (all p < 0.05), suggesting, all together, "fibrotic-like" changes of the lung over time.

CONCLUSION

The amount of consolidated tissue was higher in patients assessed during the third week and determined the oxygenation responses following pronation and recruitment maneuvers.

Electrical Impedance Tomography Analysis Between Two Similar Respiratory System Compliance During Decremetal PEEP Titration in ARDS Patients

Purpose

The positive end-expiratory pressure (PEEP) level with best respiratory system compliance (Crs) is frequently used for PEEP selection in acute respiratory distress syndrome (ARDS) patients. On occasion, two similar best Crs (where the difference between the Crs of two PEEP levels is < 1 ml/cm H₂O) may be identified during decremental PEEP titration. Selecting PEEP under such conditions is challenging. The aim of this study was to provide supplementary rationale for PEEP selection by assessing the global and regional ventilation distributions between two PEEP levels in this situation.

Methods

Eight ARDS cases with similar best Crs at two different PEEP levels were analyzed using examination-specific electrical impedance tomography (EIT) measures and airway stress index (SIaw). Five Crs were measured at PEEP values of 25 cm H₂O (PEEP₂₅), 20 cm H₂O (PEEP₂₀), 15 cm H₂O (PEEP_H), 11 cm H₂O (PEEP_I), and 7 cm H₂O (PEEP_L). The higher PEEP value of the two PEEPs with similar best Crs was designated as PEEP_upper, while the lower designated as PEEP_lower.

Results

PEEP_H and PEEP_I shared the best Crs in two cases, while similar Crs was found at PEEP_I and PEEP_L in the remaining six cases. SIaw was higher with PEEP_upper as compared to PEEP_lower (1.06 ± 0.10 versus 0.99 ± 0.09, p = 0.05). Proportion of lung hyperdistension was significantly higher with PEEP_upper than PEEP_lower (7.0 ± 5.1% versus 0.3 ± 0.5%, p = 0.0002). In contrast, proportion of recruitable lung collapse was higher with PEEP_lower than PEEP_upper (18.6 ± 4.4% versus 5.9 ± 3.7%, p < 0.0001). Cyclic alveolar collapse and reopening during tidal breathing was higher at PEEP_lower than PEEP_upper (34.4 ± 19.3% versus 16.0 ± 9.1%, p = 0.046). The intratidal gas distribution (ITV) index was also significantly higher at PEEP_lower than PEEP_upper (2.6 ± 1.3 versus 1.8 ± 0.7, p = 0.042).

Conclusions

PEEP_upper is a rational selection in ARDS cases with two similar best Crs. EIT provides additional information for the selection of PEEP in such circumstances.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40846-021-00668-2.

Higher PEEP versus lower PEEP strategies for patients in ICU without acute respiratory distress syndrome: A systematic review and meta-analysis

PURPOSE

To evaluate the effects of high and low levels of PEEP on ICU patients without ARDS.

METHODS

We searched public databases (including PubMed, EMBASE, Cochrane Library and Clinicaltrial.gov). The Cochrane Risk of Bias Assessment tool was used to evaluate the quality of the included studies.

RESULTS

We included 2307 patients from 24 trials. Although no significant difference was found between high and low PEEP applications in in-hospital mortality (risk ratio[RR] 0.98, 95% confidence interval[CI] [0.81, 1.19], P = 0.87), high PEEP indeed decreased the incidence of ARDS, hypoxemia, and increased the level of PaO₂/FIO₂. In addition, although the overall results did not reveal any advantages of high PEEP in terms of secondary outcomes regarding 28-day mortality, the duration of ventilation, atelectasis, pulmonary barotrauma, hypotension, and so forth, the subgroup analysis concerning the level of low PEEP (ZEEP or not) and patient type (postoperative or medical ones) yielded different results. The TSA results suggested that more RCTs are needed.

CONCLUSIONS

Although ventilation with high PEEP in ICU patients without ARDS may not reduce in-hospital mortality, the decreased incidences of ARDS and hypoxemia and the improvement in PaO₂/FIO₂ were found in the high PEEP arm.

Individualized positive end-expiratory pressure following alveolar recruitment manoeuvres in lung-healthy anaesthetized dogs: a randomized clinical trial on early postoperative arterial oxygenation

OBJECTIVE

To assess and compare the effect of intraoperative stepwise alveolar recruitment manoeuvres (ARMs), followed by individualized positive end-expiratory pressure (PEEP), defined as PEEP at maximal respiratory system compliance + 2 cmH₂O (PEEP_maxCrs+2), with that of spontaneous ventilation (SV) and controlled mechanical ventilation (CMV) without ARM or PEEP on early postoperative arterial oxygenation in anaesthetized healthy dogs.

STUDY DESIGN

Prospective, randomized, nonblinded clinical study.

ANIMALS

A total of 32 healthy client-owned dogs undergoing surgery in dorsal recumbency.

METHODS

Dogs were ventilated intraoperatively (inspired oxygen fraction: 0.5) with one of the following strategies: SV, CMV alone, and CMV with PEEP_maxCrs+2 following a single ARM (ARM1) or two ARMs (ARM2, the second ARM at the end of surgery). Arterial blood gas analyses were performed before starting the ventilatory strategy, at the end of surgery, and at 5, 10, 15, 30 and 60 minutes after extubation while breathing room air. Data were analysed using Kruskal-Wallis and Friedman tests (p < 0.050).

RESULTS

At any time point after extubation, PaO₂ was not significantly different between groups. At 5 minutes after extubation, PaO₂ was 95.1 (78.1-104.0), 93.8 (88.3-104.0), 96.9 (86.6-115.0) and 89.1 (87.6-102.0) mmHg in the SV, CMV, ARM1 and ARM2 groups, respectively. PaO₂ decreased at 30 minutes after extubation in the CMV, ARM1 and ARM2 groups (p < 0.050), but it did not decrease after 30 minutes in the SV group. Moderate hypoxaemia (PaO₂, 60-80 mmHg) was observed in one dog in the ARM1 group and two dogs each in the SV and ARM2 groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Intraoperative ARMs, followed by PEEP_maxCrs+2, did not improve early postoperative arterial oxygenation compared with SV or CMV alone in healthy anaesthetized dogs. Therefore, this ventilatory strategy might not be clinically advantageous for improving postoperative arterial oxygenation in healthy dogs undergoing surgery when positioned in dorsal recumbency.

Association between increased nonaerated lung weight and treatment failure in patients with de novo acute respiratory failure: Difference between high-flow nasal oxygen therapy and noninvasive ventilation in a multicentre retrospective study

PURPOSE

To determine the association between lung collapse and treatment failure in high-flow nasal cannula oxygen therapy (HFNC) or noninvasive ventilation (NIV).

METHODS

We performed a quantitative analysis of chest computed tomography in patients with de novo acute respiratory failure who received HFNC (HFNC group) or NIV (NIV group) between January 2012 and December 2017. In the HFNC and NIV group, the nonaerated lung weight were compared between patients in whom respiratory treatment succeeded or failed, respectively. We used logistic regression to examine the association between the nonaerated lung weight and treatment failure.

RESULTS

Treatment failed in 70/118 (59%) patients in the HFNC group and 66/101 (65%) patients in the NIV group. The nonaerated lung weight was significantly greater in unsuccessfully treated patients than in successfully treated patients in the HFNC group (p = 0.005), but not in the NIV group (p = 0.535). Logistic regression revealed that greater nonaerated lung weight was associated with increased risk of HFNC failure (adjusted odds ratio 1.30 per 5% increase, 95% confidence interval 1.09-1.55, p = 0.003) but not of NIV failure.

CONCLUSIONS

Patients with a greater nonaerated lung weight had a higher risk of HFNC failure, but not of NIV failure.

Measurement of Electrical Impedance Tomography-Based Regional Ventilation Delay for Individualized Titration of End-Expiratory Pressure

RATIONALE

Individualized positive end-expiratory pressure (PEEP) titration might be beneficial in preventing tidal recruitment. To detect tidal recruitment by electrical impedance tomography (EIT), the time disparity between the regional ventilation curves (regional ventilation delay inhomogeneity [RVDI]) can be measured during controlled mechanical ventilation when applying a slow inflation of 12 mL/kg of body weight (BW). However, repeated large slow inflations may result in high end-inspiratory pressure (P_EI), which might limit the clinical applicability of this method. We hypothesized that PEEP levels that minimize tidal recruitment can also be derived from EIT-based RVDI through the use of reduced slow inflation volumes.

METHODS

Decremental PEEP trials were performed in 15 lung-injured pigs. The PEEP level that minimized tidal recruitment was estimated from EIT-based RVDI measurement during slow inflations of 12, 9, 7.5, or 6 mL/kg BW. We compared RVDI and P_EI values resulting from different slow inflation volumes and estimated individualized PEEP levels.

RESULTS

RVDI values from slow inflations of 12 and 9 mL/kg BW showed excellent linear correlation (R² = 0.87, p < 0.001). Correlations decreased for RVDI values from inflations of 7.5 (R² = 0.68, p < 0.001) and 6 (R² = 0.42, p < 0.001) mL/kg BW. Individualized PEEP levels estimated from 12 and 9 mL/kg BW were comparable (bias -0.3 cm H₂O ± 1.2 cm H₂O). Bias and scatter increased with further reduction in slow inflation volumes (for 7.5 mL/kg BW, bias 0 ± 3.2 cm H₂O; for 6 mL/kg BW, bias 1.2 ± 4.0 cm H₂O). P_EI resulting from 9 mL/kg BW inflations were comparable with P_EI during regular tidal volumes.

CONCLUSIONS

PEEP titration to minimize tidal recruitment can be individualized according to EIT-based measurement of the time disparity of regional ventilation courses during slow inflations with low inflation volumes_. This sufficiently decreases P_EI and may reduce potential clinical risks.

Assessment of the Effect of Recruitment Maneuver on Lung Aeration Through Imaging Analysis in Invasively Ventilated Patients: A Systematic Review

Background: Recruitment maneuvers (RMs) have heterogeneous effects on lung aeration and have adverse side effects. We aimed to identify morphological, anatomical, and functional imaging characteristics that might be used to predict the RMs on lung aeration in invasively ventilated patients.

Methods: We performed a systemic review. Studies included invasively ventilated patients who received an RM and in whom re-aeration was examined with chest computed tomography (CT), electrical impedance tomography (EIT), and lung ultrasound (LUS) were included.

Results: Twenty studies were identified. Different types of RMs were applied. The amount of re-aerated lung tissue after an RM was highly variable between patients in all studies, irrespective of the used imaging technique and the type of patients (ARDS or non-ARDS). Imaging findings suggesting a non-focal morphology (i.e., radiologic findings consistent with attenuations with diffuse or patchy loss of aeration) were associated with higher likelihood of recruitment and lower chance of overdistention than a focal morphology (i.e., radiological findings suggestive of lobar or segmental loss of aeration). This was independent of the used imaging technique but only observed in patients with ARDS. In patients without ARDS, the results were inconclusive.

Conclusions: ARDS patients with imaging findings suggestive of non-focal morphology show most re-aeration of previously consolidated lung tissue after RMs. The role of imaging techniques in predicting the effect of RMs on re-aeration in patients without ARDS remains uncertain.

High versus low positive end-expiratory pressure (PEEP) levels for mechanically ventilated adult patients with acute lung injury and acute respiratory distress syndrome

BACKGROUND

In patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), mortality remains high. These patients require mechanical ventilation, which has been associated with ventilator-induced lung injury. High levels of positive end-expiratory pressure (PEEP) could reduce this condition and improve patient survival. This is an updated version of the review first published in 2013.

OBJECTIVES

To assess the benefits and harms of high versus low levels of PEEP in adults with ALI and ARDS.

SEARCH METHODS

For our previous review, we searched databases from inception until 2013. For this updated review, we searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, LILACS, and the Web of Science from inception until May 2020. We also searched for ongoing trials (www.trialscentral.org; www.clinicaltrial.gov; www.controlled-trials.com), and we screened the reference lists of included studies.

SELECTION CRITERIA

We included randomised controlled trials that compared high versus low levels of PEEP in ALI and ARDS participants who were intubated and mechanically ventilated in intensive care for at least 24 hours.

DATA COLLECTION AND ANALYSIS

Two review authors assessed risk of bias and extracted data independently. We contacted investigators to identify additional published and unpublished studies. We used standard methodological procedures expected by Cochrane.

MAIN RESULTS

We included four new studies (1343 participants) in this review update. In total, we included 10 studies (3851 participants). We found evidence of risk of bias in six studies, and the remaining studies fulfilled all criteria for low risk of bias. In eight studies (3703 participants), a comparison was made between high and low levels of PEEP, with the same tidal volume in both groups. In the remaining two studies (148 participants), the tidal volume was different between high- and low-level groups. In the main analysis, we assessed mortality occurring before hospital discharge only in studies that compared high versus low PEEP, with the same tidal volume in both groups. Evidence suggests that high PEEP may result in little to no difference in mortality compared to low PEEP (risk ratio (RR) 0.97, 95% confidence interval (CI) 0.90 to 1.04; I² = 15%; 7 studies, 3640 participants; moderate-certainty evidence). In addition, high PEEP may result in little to no difference in barotrauma (RR 1.00, 95% CI 0.64 to 1.57; I² = 63%; 9 studies, 3791 participants; low-certainty evidence). High PEEP may improve oxygenation in patients up to the first and third days of mechanical ventilation (first day: mean difference (MD) 51.03, 95% CI 35.86 to 66.20; I² = 85%; 6 studies, 2594 participants; low-certainty evidence; third day: MD 50.32, 95% CI 34.92 to 65.72; I² = 83%; 6 studies, 2309 participants; low-certainty evidence) and probably improves oxygenation up to the seventh day (MD 28.52, 95% CI 20.82 to 36.21; I² = 0%; 5 studies, 1611 participants; moderate-certainty evidence). Evidence suggests that high PEEP results in little to no difference in the number of ventilator-free days (MD 0.45, 95% CI -2.02 to 2.92; I² = 81%; 3 studies, 1654 participants; low-certainty evidence). Available data were insufficient to pool the evidence for length of stay in the intensive care unit.

AUTHORS' CONCLUSIONS

Moderate-certainty evidence shows that high levels compared to low levels of PEEP do not reduce mortality before hospital discharge. Low-certainty evidence suggests that high levels of PEEP result in little to no difference in the risk of barotrauma. Low-certainty evidence also suggests that high levels of PEEP improve oxygenation up to the first and third days of mechanical ventilation, and moderate-certainty evidence indicates that high levels of PEEP improve oxygenation up to the seventh day of mechanical ventilation. As in our previous review, we found clinical heterogeneity - mainly within participant characteristics and methods of titrating PEEP - that does not allow us to draw definitive conclusions regarding the use of high levels of PEEP in patients with ALI and ARDS. Further studies should aim to determine the appropriate method of using high levels of PEEP and the advantages and disadvantages associated with high levels of PEEP in different ARDS and ALI patient populations.

BD, Salazar Gutierrez G, Gómez González JF, Echeverry Piedrahita DR, Galvis JC, Aguirre-Flórez M. Mechanical ventilation in SARS-CoV-2 patients: state of art

COVID-19-associated infection leads to a pathology of yet unknown clinical behavior, confronting the clinician with various challenges. An extensive search was conducted based on review articles on SARS-CoV-2 infection and studies including mechanical ventilation management strategies in order to complete this narrative review. Evidenced-based treatment for SARS-CoV2 infection is still in the works. We have some tools from our knowledge from past experiences indicating that a step-wise management approach should be used, without neglecting other joint therapeutic measures for improved clinical outcomes of a condition with a high mortality. The current recommendations indicate that patients with severe acute respiratory failure due to SARS-CoV-2 should be managed with protective mechanical ventilation measures. No strong evidence is yet available on the individualization of mechanical ventilation therapy according to phenotypes.

Emergency Department Management of Severe Hypoxemic Respiratory Failure in Adults With COVID-19

Background

While emergency physicians are familiar with the management of hypoxemic respiratory failure, management of mechanical ventilation and advanced therapies for oxygenation in the emergency department have become essential during the coronavirus disease 2019 (COVID-19) pandemic.

Objective

We review the current evidence on hypoxemia in COVID-19 and place it in the context of known evidence-based management of hypoxemic respiratory failure in the emergency department.

Discussion

COVID-19 causes mortality primarily through the development of acute respiratory distress syndrome (ARDS), with hypoxemia arising from shunt, a mismatch of ventilation and perfusion. Management of patients developing ARDS should focus on mitigating derecruitment and avoiding volutrauma or barotrauma.

Conclusions

High flow nasal cannula and noninvasive positive pressure ventilation have a more limited role in COVID-19 because of the risk of aerosolization and minimal benefit in severe cases, but can be considered. Stable patients who can tolerate repositioning should be placed in a prone position while awake. Once intubated, patients should be managed with ventilation strategies appropriate for ARDS, including targeting lung-protective volumes and low pressures. Increasing positive end-expiratory pressure can be beneficial. Inhaled pulmonary vasodilators do not decrease mortality but may be given to improve refractory hypoxemia. Prone positioning of intubated patients is associated with a mortality reduction in ARDS and can be considered for patients with persistent hypoxemia. Neuromuscular blockade should also be administered in patients who remain dyssynchronous with the ventilator despite adequate sedation. Finally, patients with refractory severe hypoxemic respiratory failure in COVID-19 should be considered for venovenous extracorporeal membrane oxygenation.

Physiological effects of different recruitment maneuvers in a pig model of ARDS

Background

In acute respiratory distress syndrome (ARDS), lung recruitment maneuvers can recruit collapsed alveoli in gravity-dependent lung regions, improving the homogeneity of ventilation distribution. This study used electrical impedance tomography to investigate the physiological effects of different recruitment maneuvers for alveolar recruitment in a pig model of ARDS.

Methods

ARDS was induced in ten healthy male pigs with repeated bronchoalveolar lavage until the ratio of arterial partial pressure of oxygen (PaO₂) of fraction of inspired oxygen (P/F) was < 100 mmHg and remained stable for 30 min (T_ARDS). ARDS pigs underwent three sequential recruitment maneuvers, including sustained inflation, increments of positive end-expiratory pressure (PEEP), and pressure-controlled ventilation (PCV) applied in random order, with 30 mins at a PEEP of 5 cmH₂O between maneuvers. Respiratory mechanics, hemodynamics, arterial blood gas, and electrical impedance tomography were recorded at baseline, T_ARDS, and before and after each recruitment maneuver.

Results

In all ten pigs, ARDS was successfully induced with a mean 2.8 ± 1.03 L bronchoalveolar lavages. PaO₂, P/F, and compliance were significantly improved after recruitment with sustained inflation, increments of PEEP or PCV (all p < 0.05), and there were no significant differences between maneuvers. Global inhomogeneity index significantly decreased after recruitment with sustained inflation, increments of PEEP, or PCV. There were no significant differences in global inhomogeneity before or after recruitment with the different maneuvers. The decrease in global inhomogeneity index (ΔGI) was significantly greater after recruitment with increments of PEEP compared to sustained inflation (p = 0.023), but there was no significant difference in ΔGI between increments of PEEP and PCV or between sustained inflation and PCV.

Conclusion

Sustained inflation, increments of PEEP, and PCV increased oxygenation, and regional and global compliance of the respiratory system, and decreased inhomogeneous gas distribution in ARDS pigs. Increments of PEEP significantly improved inhomogeneity of the lung compared to sustained inflation, while there was no difference between increments of PEEP and PCV or between sustained inflation and PCV.

Individualized positive end-expiratory pressure setting in patients with severe acute respiratory distress syndrome supported with veno-venous extracorporeal membrane oxygenation

BACKGROUND

Patients with acute respiratory distress syndrome supported with veno-venous extracorporeal membrane oxygenation benefit from higher positive end-expiratory pressure combined with conventional ventilation during the early extracorporeal membrane oxygenation period. The role of incremental positive end-expiratory pressure titration in patients with severe acute respiratory distress syndrome supported with veno-venous extracorporeal membrane oxygenation remains unclear. This study aimed to determine the preferred method for setting positive end-expiratory pressure in patients with severe acute respiratory distress syndrome on veno-venous extracorporeal membrane oxygenation support.

METHODS

We retrospectively reviewed all subjects supported with veno-venous extracorporeal membrane oxygenation for severe acute respiratory distress syndrome from 2009 to 2019 in the intensive care units in Tianjin Third Central Hospital. Subjects were divided into two groups according to the positive end-expiratory pressure titration method used: P-V curve (quasi-static pressure-volume curve-guided positive end-expiratory pressure setting) group or Crs (respiratory system compliance-guided positive end-expiratory pressure setting) group.

RESULTS

Forty-three subjects were included in the clinical outcome analysis: 20 in the P-V curve group and 23 in the Crs group. Initial positive end-expiratory pressure levels during veno-venous extracorporeal membrane oxygenation were similar in both groups. Incidence rates of barotrauma and hemodynamic events were significantly lower in the Crs group (all p < 0.05). Mechanical ventilation duration, intensive care unit length of stay, and hospital length of stay were significantly shorter in the Crs group than the P-V curve group (all p < 0.05). Subjects in the Crs group showed non-significant improvements in the duration of extracorporeal membrane oxygenation support and 28-day mortality (p > 0.05).

CONCLUSION

Respiratory system compliance-guided positive end-expiratory pressure setting may lead to more optimal clinical outcomes for patients with severe acute respiratory distress syndrome supported by veno-venous extracorporeal membrane oxygenation. Moreover, the operation is simple, safe, and convenient in clinical practice.

Emerging approaches in pediatric mechanical ventilation

INTRODUCTION

The use of mechanical ventilation is an invaluable tool in caring for critically ill patients. Enhancing our capabilities in mechanical ventilation has been instrumental in the ability to support clinical conditions and diseases which were once associated with high mortality. Areas covered: Within this manuscript, we will look to discuss emerging approaches to improving the care of pediatric patients who require mechanical ventilation. After an extensive literature search, we will provide a brief review of the history and pathophysiology of acute respiratory distress syndrome, an assessment of several ventilator settings, a discussion on assisted ventilation, review of therapy used to rescue in severe respiratory failure, methods of monitoring the effects of mechanical ventilation, and nutrition. Expert opinion: As we have advanced in our care, we are seeing children survive illnesses that would have once claimed their lives. Given this knowledge, we must continue to advance the research in pediatric critical care to understand the means in which we can tailor the therapy to the patient in efforts to efficiently liberate them from mechanical ventilation once their illness has resolved.

Lung ultrasound evaluation of incremental PEEP recruitment maneuver in children undergoing cardiac surgery

AIM

To explore the effect of incremental positive end-expiratory pressure recruitment maneuver (iPEEPRM) in children with congenital heart diseases (CHDs) using lung ultrasound.

METHODS

Thirty-six children aged 3 months to 5 years scheduled for cardiac surgery participated. iPEEPRM was performed with PEEP stepwise increase (0-5-10-15 cmH₂ O) and decrease at the same rate before and after surgery. Atelectatic areas, ultrasound scores, arterial oxygen pressure (PaO₂ ), and respiratory system dynamic compliance per kilogram body weight (CDyn/kg) were analyzed before and after iPEEPRM. The primary outcome is the incidence of atelectasis. Secondary outcomes are oxygenation, ventilation, CDyn/kg, and atelectasis area.

RESULTS

iPEEPRM was successfully applied in 92% (33/36) children before surgery and 71% (24/34) children after surgery. The incidence of atelectasis was significantly reduced by iPEEPRM from 76% to 15% before surgery and from 92% to 38% after surgery, respectively (P < .001). Before surgery, iPEEPRM significantly reduced atelectatic areas and ultrasound scores: 32.5 (0-128.1) mm² vs 0 (0-0) mm² and 8 (3-12) vs 2 (0-4). PaO₂ and CDyn/kg were significantly increased after iPEEPRM: 243 (129-275) mm Hg vs 278 (207-323) mm Hg and 0.6 (0.4-0.7) mL/cmH₂ O/kg vs 0.8 (0.6-1.0) mL/cmH₂ O/kg. After surgery, iPEEPRM significantly reduced atelectatic areas and ultrasound scores: 45.7 (13.1-115.8) mm² vs 0 (0-34.7) mm² , and 9 (6-12) vs 3 (0-5). PaO₂ and CDyn/kg were also significantly increased after iPEEPRM.

CONCLUSIONS

iPEEPRM effectively reduced atelectasis, improved lung aeration, oxygenation, and CDyn/kg in children undergoing cardiac surgery.

Maximal Recruitment Open Lung Ventilation in Acute Respiratory Distress Syndrome (PHARLAP). A Phase II, Multicenter Randomized Controlled Clinical Trial

Rationale: Open lung ventilation strategies have been recommended in patients with acute respiratory distress syndrome (ARDS).Objectives: To determine whether a maximal lung recruitment strategy reduces ventilator-free days in patients with ARDS.Methods: A phase II, multicenter randomized controlled trial in adults with moderate to severe ARDS. Patients received maximal lung recruitment, titrated positive end expiratory pressure and further Vt limitation, or control "protective" ventilation.Measurements and Main Results: The primary outcome was ventilator-free days at Day 28. Secondary outcomes included mortality, barotrauma, new use of hypoxemic adjuvant therapies, and ICU and hospital stay. Enrollment halted October 2, 2017, after publication of ART (Alveolar Recruitment for Acute Respiratory Distress Syndrome Trial), when 115 of a planned 340 patients had been randomized (57% male; mean age, 53.6 yr). At 28 days after randomization, there was no difference between the maximal lung recruitment and control ventilation strategies in ventilator-free days (median, 16 d [interquartile range (IQR), 0-21 d], n = 57, vs. 14.5 d [IQR, 0-21.5 d], n = 56; P = 0.95), mortality (24.6% [n = 14/56] vs. 26.8% [n = 15/56]; P = 0.79), or the rate of barotrauma (5.2% [n = 3/57] vs. 10.7% [n = 6/56]; P = 0.32). However, the intervention group showed reduced use of new hypoxemic adjuvant therapies (i.e., inhaled nitric oxide, extracorporeal membrane oxygenation, prone; median change from baseline 0 [IQR, 0-1] vs. 1 [IQR, 0-1]; P = 0.004) and increased rates of new cardiac arrhythmia (n = 17 [29%] vs. n = 7 [13%]; P = 0.03).Conclusions: Compared with control ventilation, maximal lung recruitment did not reduce the duration of ventilation-free days or mortality and was associated with increased cardiovascular adverse events but lower use of hypoxemic adjuvant therapies.Clinical trial registered with www.clinicaltrials.gov (NCT01667146).

Lung Recruitment in Obese Patients with Acute Respiratory Distress Syndrome

BACKGROUND

Obese patients are characterized by normal chest-wall elastance and high pleural pressure and have been excluded from trials assessing best strategies to set positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS). The authors hypothesized that severely obese patients with ARDS present with a high degree of lung collapse, reversible by titrated PEEP preceded by a lung recruitment maneuver.

METHODS

Severely obese ARDS patients were enrolled in a physiologic crossover study evaluating the effects of three PEEP titration strategies applied in the following order: (1) PEEPARDSNET: the low PEEP/FIO2 ARDSnet table; (2) PEEPINCREMENTAL: PEEP levels set to determine a positive end-expiratory transpulmonary pressure; and (3) PEEPDECREMENTAL: PEEP levels set to determine the lowest respiratory system elastance during a decremental PEEP trial following a recruitment maneuver on respiratory mechanics, regional lung collapse, and overdistension according to electrical impedance tomography and gas exchange.

RESULTS

Fourteen patients underwent the study procedures. At PEEPARDSNET (13 ± 1 cm H2O) end-expiratory transpulmonary pressure was negative (-5 ± 5 cm H2O), lung elastance was 27 ± 12 cm H2O/L, and PaO2/FIO2 was 194 ± 111 mmHg. Compared to PEEPARDSNET, at PEEPINCREMENTAL level (22 ± 3 cm H2O) lung volume increased (977 ± 708 ml), lung elastance decreased (23 ± 7 cm H2O/l), lung collapse decreased (18 ± 10%), and ventilation homogeneity increased thus rising oxygenation (251 ± 105 mmHg), despite higher overdistension levels (16 ± 12%), all values P < 0.05 versus PEEPARDSnet. Setting PEEP according to a PEEPDECREMENTAL trial after a recruitment maneuver (21 ± 4 cm H2O, P = 0.99 vs. PEEPINCREMENTAL) further lowered lung elastance (19 ± 6 cm H2O/l) and increased oxygenation (329 ± 82 mmHg) while reducing lung collapse (9 ± 2%) and overdistension (11 ± 2%), all values P < 0.05 versus PEEPARDSnet and PEEPINCREMENTAL. All patients were maintained on titrated PEEP levels up to 24 h without hemodynamic or ventilation related complications.

CONCLUSIONS

Among the PEEP titration strategies tested, setting PEEP according to a PEEPDECREMENTAL trial preceded by a recruitment maneuver obtained the best lung function by decreasing lung overdistension and collapse, restoring lung elastance, and oxygenation suggesting lung tissue recruitment.

Flow-controlled ventilation improves gas exchange in lung-healthy patients- a randomized interventional cross-over study

BACKGROUND

Flow-controlled ventilation (FCV) is a new ventilation mode that provides constant inspiratory and expiratory flow. FCV was shown to improve gas exchange and lung recruitment in porcine models of healthy and injured ventilated lungs. The primary aim of our study was to verify the influences of FCV on gas exchange, respiratory mechanics and haemodynamic variables in mechanically ventilated lung-healthy patients.

METHODS

After obtaining ethical approval and informed consent, we measured arterial blood gases, respiratory and haemodynamic variables during volume-controlled ventilation (VCV) and FCV in 20 consecutive patients before they underwent abdominal surgery. After baseline (BL) ventilation, patients were randomly assigned to either BL-VCV-FCV or BL-FCV-VCV. Thereby, BL ventilation settings were kept, except for the ventilation mode-related differences (FCV is supposed to be used with an I:E ratio of 1:1).

RESULTS

Compared to BL and VCV, PaO₂ was higher [PaO₂ : FCV: 38.2 (7.1), BL ventilation: 35.0 (5.8), VCV: 35.2 (7.0) kPa, P < .001] and PaCO₂ lower [PaCO₂ : FCV: 4.8 (0.5), BL ventilation: 5.1 (0.5), VCV: 5.1 (0.5) kPa, P < .001] during FCV. With comparable plateau pressure [BL: 14.9 (1.9), VCV: 15.3 (1.6), FCV: 15.2 (1.5) cm H₂ O), P = .185], tracheal mean pressure was higher during FCV [BL: 10.2 (1.1), VCV: 10.4 (0.7), FCV: 11.5 (1.0) cm H₂ O, P < .001]. Haemodynamic variables did not differ between ventilation phases.

CONCLUSION

Flow-controlled ventilation improves oxygenation and carbon dioxide elimination within a short time, compared to VCV with identical tidal volume, inspiratory plateau pressure and end-expiratory pressure.

Individualized Positive End-expiratory Pressure and Regional Gas Exchange in Porcine Lung Injury

Background

In acute respiratory failure elevated intraabdominal pressure aggravates lung collapse, tidal recruitment, and ventilation inhomogeneity. Low positive end-expiratory pressure (PEEP) may promote lung collapse and intrapulmonary shunting, whereas high PEEP may increase dead space by inspiratory overdistension. The authors hypothesized that an electrical impedance tomography–guided PEEP approach minimizing tidal recruitment improves regional ventilation and perfusion matching when compared to a table-based low PEEP/no recruitment and an oxygenation-guided high PEEP/full recruitment strategy in a hybrid model of lung injury and elevated intraabdominal pressure.

Methods

In 15 pigs with oleic acid–induced lung injury intraabdominal pressure was increased by intraabdominal saline infusion. PEEP was set in randomized order: (1) guided by a PEEP/inspired oxygen fraction table, without recruitment maneuver; (2) minimizing tidal recruitment guided by electrical impedance tomography after a recruitment maneuver; and (3) maximizing oxygenation after a recruitment maneuver. Single photon emission computed tomography was used to analyze regional ventilation, perfusion, and aeration. Primary outcome measures were differences in PEEP levels and regional ventilation/perfusion matching.

Results

Resulting PEEP levels were different (mean ± SD) with (1) table PEEP: 11 ± 3 cm H2O; (2) minimal tidal recruitment PEEP: 22 ± 3 cm H2O; and (3) maximal oxygenation PEEP: 25 ± 4 cm H2O; P &lt; 0.001. Table PEEP without recruitment maneuver caused highest lung collapse (28 ± 11% vs. 5 ± 5% vs. 4 ± 4%; P &lt; 0.001), shunt perfusion (3.2 ± 0.8 l/min vs. 1.0 ± 0.8 l/min vs. 0.7 ± 0.6 l/min; P &lt; 0.001) and dead space ventilation (2.9 ± 1.0 l/min vs. 1.5 ± 0.7 l/min vs. 1.7 ± 0.8 l/min; P &lt; 0.001). Although resulting in different PEEP levels, minimal tidal recruitment and maximal oxygenation PEEP, both following a recruitment maneuver, had similar effects on regional ventilation/perfusion matching.

Conclusions

When compared to table PEEP without a recruitment maneuver, both minimal tidal recruitment PEEP and maximal oxygenation PEEP following a recruitment maneuver decreased shunting and dead space ventilation, and the effects of minimal tidal recruitment PEEP and maximal oxygenation PEEP were comparable.

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Microcirculatory dysfunction and dead-space ventilation in early ARDS: a hypothesis-generating observational study

BACKGROUND

Ventilation/perfusion inequalities impair gas exchange in acute respiratory distress syndrome (ARDS). Although increased dead-space ventilation (V_D/V_T) has been described in ARDS, its mechanism is not clearly understood. We sought to evaluate the relationships between dynamic variations in V_D/V_T and extra-pulmonary microcirculatory blood flow detected at sublingual mucosa hypothesizing that an altered microcirculation, which is a generalized phenomenon during severe inflammatory conditions, could influence ventilation/perfusion mismatching manifested by increases in V_D/V_T fraction during early stages of ARDS.

METHODS

Forty-two consecutive patients with early moderate and severe ARDS were included. PEEP was set targeting the best respiratory-system compliance after a PEEP-decremental recruitment maneuver. After 60 min of stabilization, hemodynamics and respiratory mechanics were recorded and blood gases collected. V_D/V_T was calculated from the CO₂ production ([Formula: see text]) and CO₂ exhaled fraction ([Formula: see text]) measurements by volumetric capnography. Sublingual microcirculatory images were simultaneously acquired using a sidestream dark-field device for an ulterior blinded semi-quantitative analysis. All measurements were repeated 24 h after.

RESULTS

Percentage of small vessels perfused (PPV) and microcirculatory flow index (MFI) were inverse and significantly related to V_D/V_T at baseline (Spearman's rho = - 0.76 and - 0.63, p < 0.001; R² = 0.63, and 0.48, p < 0.001, respectively) and 24 h after (Spearman's rho = - 0.71, and - 0.65; p < 0.001; R² = 0.66 and 0.60, p < 0.001, respectively). Other respiratory, macro-hemodynamic and oxygenation parameters did not correlate with V_D/V_T. Variations in PPV between baseline and 24 h were inverse and significantly related to simultaneous changes in V_D/V_T (Spearman's rho = - 0.66, p < 0.001; R² = 0.67, p < 0.001).

CONCLUSION

Increased heterogeneity of microcirculatory blood flow evaluated at sublingual mucosa seems to be related to increases in V_D/V_T, while respiratory mechanics and oxygenation parameters do not. Whether there is a cause-effect relationship between microcirculatory dysfunction and dead-space ventilation in ARDS should be addressed in future research.

Changes in shunt, ventilation/perfusion mismatch, and lung aeration with PEEP in patients with ARDS: a prospective single-arm interventional study

Background

Several studies have found only a weak to moderate correlation between oxygenation and lung aeration in response to changes in PEEP. This study aimed to investigate the association between changes in shunt, low and high ventilation/perfusion (V/Q) mismatch, and computed tomography-measured lung aeration following an increase in PEEP in patients with ARDS.

Methods

In this preliminary study, 12 ARDS patients were subjected to recruitment maneuvers followed by setting PEEP at 5 and then either 15 or 20 cmH₂O. Lung aeration was measured by computed tomography. Values of pulmonary shunt and low and high V/Q mismatch were calculated by a model-based method from measurements of oxygenation, ventilation, and metabolism taken at different inspired oxygen levels and an arterial blood gas sample.

Results

Increasing PEEP resulted in reduced values of pulmonary shunt and the percentage of non-aerated tissue, and an increased percentage of normally aerated tissue (p < 0.05). Changes in shunt and normally aerated tissue were significantly correlated (r = − 0.665, p = 0.018). Three distinct responses to increase in PEEP were observed in values of shunt and V/Q mismatch: a beneficial response in seven patients, where shunt decreased without increasing high V/Q; a detrimental response in four patients where both shunt and high V/Q increased; and a detrimental response in a patient with reduced shunt but increased high V/Q mismatch. Non-aerated tissue decreased with increased PEEP in all patients, and hyperinflated tissue increased only in patients with a detrimental response in shunt and V/Q mismatch.

Conclusions

The results show that improved lung aeration following an increase in PEEP is not always consistent with reduced shunt and V/Q mismatch. Poorly matched redistribution of ventilation and perfusion, between dependent and non-dependent regions of the lung, may explain why patients showed detrimental changes in shunt and V/Q mismatch on increase in PEEP, despite improved aeration.

Trial registration

ClinicalTrails.gov, NCT04067154. Retrospectively registered on August 26, 2019.

A Physiologically Informed Strategy to Effectively Open, Stabilize, and Protect the Acutely Injured Lung

Acute respiratory distress syndrome (ARDS) causes a heterogeneous lung injury and remains a serious medical problem, with one of the only treatments being supportive care in the form of mechanical ventilation. It is very difficult, however, to mechanically ventilate the heterogeneously damaged lung without causing secondary ventilator-induced lung injury (VILI). The acutely injured lung becomes time and pressure dependent, meaning that it takes more time and pressure to open the lung, and it recollapses more quickly and at higher pressure. Current protective ventilation strategies, ARDSnet low tidal volume (LVt) and the open lung approach (OLA), have been unsuccessful at further reducing ARDS mortality. We postulate that this is because the LVt strategy is constrained to ventilating a lung with a heterogeneous mix of normal and focalized injured tissue, and the OLA, although designed to fully open and stabilize the lung, is often unsuccessful at doing so. In this review we analyzed the pathophysiology of ARDS that renders the lung susceptible to VILI. We also analyzed the alterations in alveolar and alveolar duct mechanics that occur in the acutely injured lung and discussed how these alterations are a key mechanism driving VILI. Our analysis suggests that the time component of each mechanical breath, at both inspiration and expiration, is critical to normalize alveolar mechanics and protect the lung from VILI. Animal studies and a meta-analysis have suggested that the time-controlled adaptive ventilation (TCAV) method, using the airway pressure release ventilation mode, eliminates the constraints of ventilating a lung with heterogeneous injury, since it is highly effective at opening and stabilizing the time- and pressure-dependent lung. In animal studies it has been shown that by “casting open” the acutely injured lung with TCAV we can (1) reestablish normal expiratory lung volume as assessed by direct observation of subpleural alveoli; (2) return normal parenchymal microanatomical structural support, known as alveolar interdependence and parenchymal tethering, as assessed by morphometric analysis of lung histology; (3) facilitate regeneration of normal surfactant function measured as increases in surfactant proteins A and B; and (4) significantly increase lung compliance, which reduces the pathologic impact of driving pressure and mechanical power at any given tidal volume.

Real-time effects of PEEP and tidal volume on regional ventilation and perfusion in experimental lung injury

BACKGROUND

Real-time bedside information on regional ventilation and perfusion during mechanical ventilation (MV) may help to elucidate the physiological and pathophysiological effects of MV settings in healthy and injured lungs. We aimed to study the effects of positive end-expiratory pressure (PEEP) and tidal volume (V_T) on the distributions of regional ventilation and perfusion by electrical impedance tomography (EIT) in healthy and injured lungs.

METHODS

One-hit acute lung injury model was established in 6 piglets by repeated lung lavages (injured group). Four ventilated piglets served as the control group. A randomized sequence of any possible combination of three V_T (7, 10, and 15 ml/kg) and four levels of PEEP (5, 8, 10, and 12 cmH₂O) was performed in all animals. Ventilation and perfusion distributions were computed by EIT within three regions-of-interest (ROIs): nondependent, middle, dependent. A mixed design with one between-subjects factor (group: intervention or control), and two within-subjects factors (PEEP and V_T) was used, with a three-way mixed analysis of variance (ANOVA).

RESULTS

Two-way interactions between PEEP and group, and V_T and group, were observed for the dependent ROI (p = 0.035 and 0.012, respectively), indicating that the increase in the dependent ROI ventilation was greater at higher PEEP and V_T in the injured group than in the control group. A two-way interaction between PEEP and V_T was observed for perfusion distribution in each ROI: nondependent (p = 0.030), middle (p = 0.006), and dependent (p = 0.001); no interaction was observed between injured and control groups.

CONCLUSIONS

Large PEEP and V_T levels were associated with greater pulmonary ventilation of the dependent lung region in experimental lung injury, whereas they affected pulmonary perfusion of all lung regions both in the control and in the experimental lung injury groups.