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Rationale: Lung-protective strategies using low Vt and moderate positive end-expiratory pressure (PEEP) are considered best practice in critical care, but interventional trials have never been conducted in patients with acute brain injuries because of concerns about carbon dioxide control and the effect of PEEP on cerebral hemodynamics. Objectives: To test the hypothesis that ventilation with lower VT and higher PEEP compared to conventional ventilation would improve clinical outcomes in patients with acute brain injury. Methods: In this multicenter, open-label, controlled clinical trial, 190 adult patients with acute brain injury were assigned to receive either a lung-protective or a conventional ventilatory strategy. The primary outcome was a composite endpoint of death, ventilator dependency, and acute respiratory distress syndrome (ARDS) at Day 28. Neurological outcome was assessed at ICU discharge by the Oxford Handicap Scale and at 6 months by the Glasgow Outcome Scale. Measurements and Main Results: The two study arms had similar characteristics at baseline. In the lung-protective and conventional strategy groups, using an intention-to-treat approach, the composite outcome at 28 days was 61.5% and 45.3% (relative risk [RR], 1.35; 95% confidence interval [CI], 1.03–1.79; P = 0.025). Mortality was 28.9% and 15.1% (RR, 1.91; 95% CI, 1.06–3.42; P = 0.02), ventilator dependency was 42.3% and 27.9% (RR, 1.52; 95% CI, 1.01–2.28; P = 0.039), and incidence of ARDS was 30.8% and 22.1% (RR, 1.39; 95% CI, 0.85–2.27; P = 0.179), respectively. The trial was stopped after enrolling 190 subjects because of termination of funding. Conclusions: In patients with acute brain injury without ARDS, a lung-protective ventilatory strategy, as compared with a conventional strategy, did not reduce mortality, percentage of patients weaned from mechanical ventilation, or incidence of ARDS and was not beneficial in terms of neurological outcomes. Because of the early termination, these preliminary results require confirmation in larger trials. Clinical trial registered with (NCT01690819). [ABSTRACT FROM AUTHOR]

Rationale: A U-shaped relationship should exist between lung volume and pulmonary vascular resistance (PVR), with minimal PVR at FRC. Thus, positive end-expiratory pressure (PEEP) in patients with acute respiratory distress syndrome (ARDS) should increase PVR if it induces significant lung distension compared with recruitment. However, this has never been proved in patients. Objectives: To study the effects of PEEP on PVR according to lung recruitability, evaluated by the recruitment-to-inflation (R/I) ratio. Methods: In patients with ARDS, we measured hemodynamic (pulmonary artery catheter), echocardiographic, and ventilatory variables (including esophageal pressure) at both low PEEP and higher PEEP by 10 cm H2O. Preload responsiveness was assessed by the passive leg-raising test at high PEEP. Measurements and Main Results: We enrolled 23 patients, including 10 low recruiters (R/I <0.5) and 13 high recruiters (R/I ⩾0.5). Raising PEEP from 4 (2–5) to 14 (12–15) cm H2O increased PVR in low recruiters (from 160 [120–297] to 243 [166–380] dyn·s/cm5; P < 0.01), whereas PVR was unchanged in high recruiters (from 224 [185–289] to 235 [168–300] dyn·s/cm5; P = 0.55). Right-to-left ventricular end-diastolic area ratio simultaneously increased in low recruiters (from 0.54 [0.50–0.59] to 0.64 [0.56–0.70]; P < 0.01) while remaining stable in high recruiters (from 0.70 [0.65–0.79] to 0.68 [0.58–0.80]; P = 0.48). Raising PEEP decreased cardiac index only in preload responsive patients. Conclusions: PEEP increases PVR only when it induces significant lung distension compared with recruitment according to the R/I ratio. Tailoring PEEP on this recruitability index should mitigate its hemodynamic effects. [ABSTRACT FROM AUTHOR]

The article discusses the challenges faced by clinicians when determining the optimal ventilator settings for patients with acute respiratory distress syndrome (ARDS). The article explains that ARDS causes both lung stiffness and increased dead space, leading to difficulties in maintaining lung volume and oxygenation. The authors propose the use of positive end-expiratory pressure (PEEP) to recruit collapsed alveoli and minimize overdistention, but note that the effectiveness of PEEP varies among patients. The study suggests that personalized PEEP settings based on an assessment of recruitability may be beneficial in managing ARDS. However, the article acknowledges that further research is needed to determine the optimal PEEP and its impact on lung-protective ventilation and outcomes. [Extracted from the article]

Rationale: It is unknown whether preventing overdistention or collapse is more important when titrating positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS). Objectives: To compare PEEP targeting minimal overdistention or minimal collapse or using a compromise between collapse and overdistention in a randomized trial and to assess the impact on respiratory mechanics, gas exchange, inflammation, and hemodynamics. Methods: In a porcine model of ARDS, lung collapse and overdistention were estimated using electrical impedance tomography during a decremental PEEP titration. Pigs were randomized to three groups and ventilated for 12 hours: PEEP set at ⩽3% of overdistention (low overdistention), ⩽3% of collapse (low collapse), and the crossing point of collapse and overdistention. Measurements and Main Results: Thirty-six pigs (12 per group) were included. Median (interquartile range) values of PEEP were 7 (6–8), 11 (10–11), and 15 (12–16) cm H2O in the three groups (P < 0.001). With low overdistension, 6 (50%) pigs died, whereas survival was 100% in both other groups. Cause of death was hemodynamic in nature, with high transpulmonary vascular gradient and high epinephrine requirements. Compared with the other groups, pigs surviving with low overdistension had worse respiratory mechanics and gas exchange during the entire protocol. Minimal differences existed between crossing-point and low-collapse animals in physiological parameters, but postmortem alveolar density was more homogeneous in the crossing-point group. Inflammatory markers were not significantly different. Conclusions: PEEP to minimize overdistention resulted in high mortality in an animal model of ARDS. Minimizing collapse or choosing a compromise between collapse and overdistention may result in less lung injury, with potential benefits of the compromise approach. [ABSTRACT FROM AUTHOR]

This letter to the editor discusses a study that evaluated the usefulness of noninvasive measures of respiratory effort in monitoring patients receiving mechanical ventilation for acute hypoxemic respiratory failure. The study found correlations between these noninvasive measures and more invasive measures of respiratory effort, but noted that one measure may not be reliable. The authors suggest that these noninvasive measurements may be valuable for monitoring and adjusting interventions in clinical trials. Overall, the study provides valuable information on the comparative value of these noninvasive measures for longitudinal monitoring of respiratory effort. [Extracted from the article]

Hypoxemic respiratory failure is one of the leading causes of mortality in intensive care. Frequent assessment of individual physiological characteristics and delivery of personalized mechanical ventilation (MV) settings is a constant challenge for clinicians caring for these patients. Electrical impedance tomography (EIT) is a radiation-free bedside monitoring device that is able to assess regional lung ventilation and changes in aeration. With real-time tomographic functional images of the lungs obtained through a thoracic belt, clinicians can visualize and estimate the distribution of ventilation at different ventilation settings or following procedures such as prone positioning. Several studies have evaluated the performance of EIT to monitor the effects of different MV settings in patients with acute respiratory distress syndrome, allowing more personalized MV. For instance, EIT could help clinicians find the positive end-expiratory pressure that represents a compromise between recruitment and overdistension and assess the effect of prone positioning on ventilation distribution. The clinical impact of the personalization of MV remains to be explored. Despite inherent limitations such as limited spatial resolution, EIT also offers a unique noninvasive bedside assessment of regional ventilation changes in the ICU. This technology offers the possibility of a continuous, operator-free diagnosis and real-time detection of common problems during MV. This review provides an overview of the functioning of EIT, its main indices, and its performance in monitoring patients with acute respiratory failure. Future perspectives for use in intensive care are also addressed. [ABSTRACT FROM AUTHOR]

Rationale: Hypoxemia during mechanical ventilation might be worsened by expiratory muscle activity, which reduces end-expiratory lung volume through lung collapse. A proposed mechanism of benefit of neuromuscular blockade in acute respiratory distress syndrome (ARDS) is the abolition of expiratory efforts. This may contribute to the restoration of lung volumes. The prevalence of this phenomenon, however, is unknown. Objectives: To investigate the incidence and amount of end-expiratory lung impedance (EELI) increase after the administration of neuromuscular blocking agents (NMBAs), clinical factors associated with this phenomenon, its impact on regional lung ventilation, and any association with changes in pleural pressure. Methods: We included mechanically ventilated patients with ARDS monitored with electrical impedance tomography (EIT) who received NMBAs in one of two centers. We measured changes in EELI, a surrogate for end-expiratory lung volume, before and after NMBA administration. In an additional 10 patients, we investigated the characteristic signatures of expiratory muscle activity depicted by EIT and esophageal catheters simultaneously. Clinical factors associated with EELI changes were assessed. Measurements and Main Results: We included 46 patients, half of whom showed an increase in EELI of >10% of the corresponding Vt (46.2%; IQR, 23.9–60.9%). The degree of EELI increase correlated positively with fentanyl dosage and negatively with changes in end-expiratory pleural pressures. This suggests that expiratory muscle activity might exert strong counter-effects against positive end-expiratory pressure that are possibly aggravated by fentanyl. Conclusions: Administration of NMBAs during EIT monitoring revealed activity of expiratory muscles in half of patients with ARDS. The resultant increase in EELI had a dose–response relationship with fentanyl dosage. This suggests a potential side effect of fentanyl during protective ventilation. [ABSTRACT FROM AUTHOR]

The article informs about the potential impact of positive end-expiratory pressure (PEEP) on coronary artery flow in patients with acute respiratory distress syndrome (ARDS), highlighting the scarcity of data on this topic. Topic include the biphasic nature of normal coronary blood flow and hypothesizes that high levels of PEEP during ARDS management may lead to decreased coronary artery perfusion, prompting a study to evaluate this effect using echocardiography.

The article informs about the evaluation of regional ventilation distributions in newborns with congenital diaphragmatic hernia (CDH), highlighting the importance of optimizing positive end-expiratory pressure (PEEP) settings for mechanical ventilation. Topic include It discusses the use of electrical impedance tomography (EIT) to assess regional ventilation distribution and lung mechanics, aiming to analyze the effects of various PEEP levels on newborns with CDH.

Background: This document updates previously published Clinical Practice Guidelines for the management of patients with acute respiratory distress syndrome (ARDS), incorporating new evidence addressing the use of corticosteroids, venovenous extracorporeal membrane oxygenation, neuromuscular blocking agents, and positive end-expiratory pressure (PEEP). Methods: We summarized evidence addressing four "PICO questions" (patient, intervention, comparison, and outcome). A multidisciplinary panel with expertise in ARDS used the Grading of Recommendations, Assessment, Development, and Evaluation framework to develop clinical recommendations. Results: We suggest the use of: 1) corticosteroids for patients with ARDS (conditional recommendation, moderate certainty of evidence), 2) venovenous extracorporeal membrane oxygenation in selected patients with severe ARDS (conditional recommendation, low certainty of evidence), 3) neuromuscular blockers in patients with early severe ARDS (conditional recommendation, low certainty of evidence), and 4) higher PEEP without lung recruitment maneuvers as opposed to lower PEEP in patients with moderate to severe ARDS (conditional recommendation, low to moderate certainty), and 5) we recommend against using prolonged lung recruitment maneuvers in patients with moderate to severe ARDS (strong recommendation, moderate certainty). Conclusions: We provide updated evidence-based recommendations for the management of ARDS. Individual patient and illness characteristics should be factored into clinical decision making and implementation of these recommendations while additional evidence is generated from much-needed clinical trials. [ABSTRACT FROM AUTHOR]

Background: Since publication of the 2012 Berlin definition of acute respiratory distress syndrome (ARDS), several developments have supported the need for an expansion of the definition, including the use of high-flow nasal oxygen, the expansion of the use of pulse oximetry in place of arterial blood gases, the use of ultrasound for chest imaging, and the need for applicability in resource-limited settings. Methods: A consensus conference of 32 critical care ARDS experts was convened, had six virtual meetings (June 2021 to March 2022), and subsequently obtained input from members of several critical care societies. The goal was to develop a definition that would 1) identify patients with the currently accepted conceptual framework for ARDS, 2) facilitate rapid ARDS diagnosis for clinical care and research, 3) be applicable in resource-limited settings, 4) be useful for testing specific therapies, and 5) be practical for communication to patients and caregivers. Results: The committee made four main recommendations: 1) include high-flow nasal oxygen with a minimum flow rate of ⩾30 L/min; 2) use PaO2:FiO2 ⩽ 300 mm Hg or oxygen saturation as measured by pulse oximetry SpO2:FiO2 ⩽ 315 (if oxygen saturation as measured by pulse oximetry is ⩽97%) to identify hypoxemia; 3) retain bilateral opacities for imaging criteria but add ultrasound as an imaging modality, especially in resource-limited areas; and 4) in resource-limited settings, do not require positive end-expiratory pressure, oxygen flow rate, or specific respiratory support devices. Conclusions: We propose a new global definition of ARDS that builds on the Berlin definition. The recommendations also identify areas for future research, including the need for prospective assessments of the feasibility, reliability, and prognostic validity of the proposed global definition. [ABSTRACT FROM AUTHOR]

The article discusses the application of electrical impedance tomography (EIT) in evaluating proper ventilator settings and classifying lung morphofunction. It highlights the study by Iwata et al. on categorizing EIT ventilation patterns based on the dorsal fraction of ventilation and its association with postoperative complications. It highlights the potential of EIT as a tool for understanding lung pathophysiology.

The article presents the discussion on highlighting the need for simpler methods to detect and estimate expiratory muscle activity detecting expiratory effort.

This article discusses a case study of an 18-year-old woman who was intubated due to severe lung injury caused by vaping. The patient was receiving pressure-controlled ventilation and venovenous extracorporeal membrane oxygenation (VV-ECMO) to provide lung rest for tissue regeneration. On the fifth day of VV-ECMO, the patient exhibited reverse triggering (RT), where the patient's efforts triggered the ventilator. The study found that increasing ventilator inspiratory pressure reduced the magnitude of RT efforts but increased the transpulmonary driving pressure. The authors suggest that lung/chest wall receptors, rather than CO2 levels, mediate the magnitude of RT efforts. [Extracted from the article]

This document is a reply to Bihari et al.'s interest in a recent publication on the impact of limiting lung overdistention or collapse when mechanically ventilating injured lungs. The authors agree that it is important to assess both alveolar collapse and airway closure in this scenario. Airway closure is a phenomenon where the airways, but not the alveoli, are collapsed until a minimum pressure is reached, known as the airway opening pressure (AOP). The authors measured the AOP in their experiments and found that it was low, ruling out the hypothesis that AOP would have affected their results. They acknowledge that there are differences between pigs and humans, but the physiological responses observed in the study provide valuable insights for clinical practice. [Extracted from the article]

The article informs about the concept of mechanical power as a metric to evaluate the risk of lung injury from mechanical ventilation, highlighting its association with clinical outcomes. Topic include Von Wedel and colleagues' study on surgical patients transitioning to the ICU suggests that changes in respiratory rate, rather than tidal volume or driving pressure, may be a critical factor in ventilator-induced lung injury, challenging the current paradigm of lung-protective ventilation.

Rationale: Inflation is essential for aeration at birth, but current inflating pressure settings are without an evidence base. Objectives: To determine the role of inflating pressure (ΔP), and its relationship with positive end-expiratory pressure (PEEP), in initiating early lung injury pathways in the preterm lamb lung. Methods: Preterm (124 to 127 d) steroid-exposed lambs (n = 45) were randomly allocated (8-10 per group) to 15minutes of respiratory support with placental circulation and 20 or 30 cm H2O ΔP, with an initial high PEEP (maximum, 20 cm H2O) recruitment maneuver known to facilitate aeration (dynamic PEEP), and compared with dynamic PEEP with no ΔP or 30cmH2O ΔP and low (4 cm H2O) PEEP. Lung mechanics and aeration were measured throughout. After an additional 30minutes of apneic placental support, lung tissue and bronchoalveolar fluid were analyzed for regional lung injury, including proteomics. Measurements and Main Results: The 30 cm H2O ΔP and dynamic PEEP strategies resulted in quicker aeration and better compliance but higher tidal volumes (often .8 ml/kg, all P,0.0001; mixed effects) and injury. ΔP 20cm H2O with dynamic PEEP resulted in the same lung mechanics and aeration, but less energy transmission (tidal mechanical power), as ΔP 30cm H2O with low PEEP. Dynamic PEEP without any tidal inflations resulted in the least lung injury. Use of any tidal inflating pressures altered metabolic, coagulation and complement protein pathways within the lung. Conclusions: Inflating pressure is essential for the preterm lung at birth, but it is also the primary mediator of lung injury. Greater focus is needed on strategies that identify the safest application of pressure in the delivery room. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A letter published in the American Journal of Respiratory & Critical Care Medicine discusses a recent study on lung injury in pigs. The study found that using positive end-expiratory pressure (PEEP) to minimize overdistension resulted in a high amount of lung collapse and increased mortality. The authors suggest that airway closure, rather than alveolar collapse, may be a more important factor in these findings. They propose that reporting airway opening pressure in future studies would help clarify these concerns. [Extracted from the article]

The article focuses on examining the effects of lung inflation on right ventricular afterload during passive and assisted mechanical ventilation. Topics include the differential impact of tidal volume and static driving transpulmonary pressure on right ventricular afterload during passive versus spontaneous breathing, highlighting the potential hemodynamic benefits of preserving inspiratory effort and improving ventilatory homogeneity during spontaneous breathing.

The article presents the discussion on reply Akoumianaki and colleagues for their interest in our study and for starting a constructive debate with additional insights into the interpretation of our data.

Rationale: The "Berlin definition" of acute respiratory distress syndrome (ARDS) does not allow inclusion of patients receiving high-flow nasal oxygen (HFNO). However, several articles have proposed that criteria for defining ARDS should be broadened to allow inclusion of patients receiving HFNO. Objectives: To compare the proportion of patients fulfilling ARDS criteria during HFNO and soon after intubation, and 28-day mortality between patients treated exclusively with HFNO and patients transitioned from HFNO to invasive mechanical ventilation (IMV). Methods: From previously published studies, we analyzed patients with coronavirus disease (COVID-19) who had PaO2/FiO2 of ⩽300 while treated with ⩾40 L/min HFNO, or noninvasive ventilation (NIV) with positive end-expiratory pressure of ⩾5 cm H2O (comparator). In patients transitioned from HFNO/NIV to invasive mechanical ventilation (IMV), we compared ARDS severity during HFNO/NIV and soon after IMV. We compared 28-day mortality in patients treated exclusively with HFNO/NIV versus patients transitioned to IMV. Measurements and Main Results: We analyzed 184 and 131 patients receiving HFNO or NIV, respectively. A total of 112 HFNO and 69 NIV patients transitioned to IMV. Of those, 104 (92.9%) patients on HFNO and 66 (95.7%) on NIV continued to have PaO2/FiO2 ⩽300 under IMV. Twenty-eight-day mortality in patients who remained on HFNO was 4.2% (3/72), whereas in patients transitioned from HFNO to IMV, it was 28.6% (32/112) (P < 0.001). Twenty-eight-day mortality in patients who remained on NIV was 1.6% (1/62), whereas in patients who transitioned from NIV to IMV, it was 44.9% (31/69) (P < 0.001). Overall mortality was 19.0% (35/184) and 24.4% (32/131) for HFNO and NIV, respectively (P = 0.2479). Conclusions: Broadening the ARDS definition to include patients on HFNO with PaO2/FiO2 ⩽300 may identify patients at earlier stages of disease but with lower mortality. [ABSTRACT FROM AUTHOR]

Ventilator-induced lung injury (VILI) is currently ascribed to volutrauma and/or atelectrauma, but the effect of constant Vt ventilation (CVtV) has received little attention. This Perspective summarizes the literature documenting that CVtV causes VILI and reviews the mechanisms by which it occurs. Surfactant is continuously inactivated, depleted, displaced, or desorbed as a function of the duration of ventilation, the Vt, the level of positive end-expiratory pressure (PEEP), and possibly the respiratory rate. Accordingly, surfactant must be continuously replenished, and secretion primarily depends on intermittent delivery of large ventilatory excursions. The surfactant abnormalities resulting from CVtV result in atelectasis and VILI. Although surfactant secretion is reduced by the absence of intermittent deep breaths, continuous administration of large Vts depletes surfactant and impairs subsequent secretion. Low or normal lung volumes result in desorption of surfactant. PEEP can be protective by reducing surface film collapse and subsequent film rupture on reexpansion, and/or by reducing surfactant displacement into the airways, but PEEP can also downregulate surfactant release. The effect of CVtV on surfactant is complex. If attention is not paid to facilitating surfactant secretion and limiting its inactivation, depletion, desorption, or displacement, surface tension will increase and atelectasis and VILI will occur. [ABSTRACT FROM AUTHOR]

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 (PES)-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). PES-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 PES-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. [ABSTRACT FROM AUTHOR]

Rationale: The transition to air breathing at birth is a seminal respiratory event common to all humans, but the intrathoracic processes remain poorly understood. Objectives: The objectives of this prospective, observational study were to describe the spatiotemporal gas flow, aeration, and ventilation patterns within the lung in term neonates undergoing successful respiratory transition. Methods: Electrical impedance tomography was used to image intrathoracic volume patterns for every breath until 6 minutes from birth in neonates born by elective cesearean section and not needing resuscitation. Breaths were classified by video data, and measures of lung aeration, tidal flow conditions, and intrathoracic volume distribution calculated for each inflation. Measurements and Main Results: A total of 1,401 breaths from 17 neonates met all eligibility and data analysis criteria. Stable FRC was obtained by median (interquartile range) 43 (21-77) breaths. Breathing patterns changed from predominantly crying (80.9% first min) to tidal breathing (65.3% sixth min). From birth, tidal ventilation was not uniform within the lung, favoring the right and nondependent regions; P < 0.001 versus left and dependent regions (mixed-effects model). Initial crying created a unique volumetric pattern with delayed midexpiratory gas flow associated with intrathoracic volume redistribution (pendelluft flow) within the lung. This preserved FRC, especially within the dorsal and right regions. Conclusions: The commencement of air breathing at birth generates unique flow and volume states associated with marked spatiotemporal ventilation inhomogeneity not seen elsewhere in respiratory physiology. At birth, neonates innately brake expiratory flow to defend FRC gains and redistribute gas to less aerated regions. [ABSTRACT FROM AUTHOR]

Rationale: Clinicians commonly use short-term physiologic markers to assess the benefit of ventilator adjustments. Improved arterial oxygen tension/pressure (PaO2)/fraction of inspired oxygen (FiO2) after ventilator adjustment in acute respiratory distress syndrome is associated with lower mortality. However, as driving pressure (ΔP) reflects lung stress and strain, changes in ΔP may more accurately reflect benefits or harms of ventilator adjustments compared with changes in oxygenation.Objectives: We aimed to compare the association between mortality and the changes in PaO2/FiO2 and ΔP following protocolized ventilator changes.Methods: We assessed associations between mortality and changes in PaO2/FiO2 (ΔPaO2/FiO2) and ΔP (ΔΔP) after postrandomization positive end-expiratory pressure (PEEP) and tidal volume adjustment in reanalyses of the ALVEOLI (Assessment of Low Tidal Volume and Elevated End-Expiratory Volume to Obviate Lung Injury) and ExPress (Expiratory Pressure) trials. We included subjects with available pre- and postintervention PaO2/FiO2 and ΔP (372 in ALVEOLI and 596 in ExPress). In each separate trial cohort, we performed multivariable Cox regression testing the association between ΔPaO2/FiO2 and ΔΔP with mortality.Results: In ALVEOLI, when analyzed as separate variables, ΔPaO2/FiO2 was associated with mortality only in subjects in whom PEEP increased, whereas ΔΔP was associated with mortality irrespective of direction of PEEP change. When modeled together, improved ΔPaO2/FiO2 was not associated with mortality, whereas ΔΔP remained associated with mortality (adjusted hazard ratio [aHR], 1.50 per 5 cm H2O increase; 95% confidence interval [95% CI], 1.21-1.85). When modeled together in ExPress, ΔΔP (aHR, 1.42; 95% CI, 1.14-1.78) was more strongly associated with mortality than ΔPaO2/FiO2 (aHR, 0.95 per 25 mm Hg increase; 95% CI, 0.90-1.00).Conclusions: Reduced ΔP following protocolized ventilator changes was more strongly and consistently associated with lower mortality than was increased PaO2/FiO2, making ΔΔP more informative about benefit from ventilator adjustments. Our results reinforce the primacy of ΔP, rather than oxygenation, as the key variable associated with outcome. [ABSTRACT FROM AUTHOR]

An editorial is presented on highlighting the potential for esophageal manometry in estimating . transpulmonary pressure (PL) in asymmetric lung injury. Topics include surfactant lavage and high tidal stretch instituted with temporary endobronchial blockade occluding the contralateral lung; electrical impedance tomography being used for evaluating heterogeneous insufflation; and mediastinal fibrosis resulting from thoracic surgery or chest radiation therapy.

Rationale: Asymmetrical lung injury is a frequent clinical presentation. Regional distribution of Vt and positive end-expiratory pressure (PEEP) could result in hyperinflation of the less-injured lung. The validity of esophageal pressure (Pes) is unknown.Objectives: To compare, in asymmetrical lung injury, Pes with directly measured pleural pressures (Ppl) of both sides and investigate how PEEP impacts ventilation distribution and the regional driving transpulmonary pressure (inspiratory - expiratory).Methods: Fourteen mechanically ventilated pigs with lung injury were studied. One lung was blocked while the contralateral one underwent surfactant lavage and injurious ventilation. Airway pressure and Pes were measured, as was Ppl in the dorsal and ventral pleural space adjacent to each lung. Distribution of ventilation was assessed by electrical impedance tomography. PEEP was studied through decremental steps.Measurements and Results: Ventral and dorsal Ppl were similar between the injured and the noninjured lung across all PEEP levels. Dorsal Ppl and Pes were similar. The driving transpulmonary pressure was similar in the two lungs. Vt distribution between lungs was different at zero end-expiratory pressure (≈70% of Vt going in noninjured lung) owing to different respiratory system compliance (8.3 ml/cm H2O noninjured lung vs. 3.7 ml/cm H2O injured lung). PEEP at 10 cm H2O with transpulmonary pressure around zero homogenized Vt distribution opening the lungs. PEEP ≥16 cm H2O equalized distribution of Vt but with overdistension for both lungs.Conclusions: Despite asymmetrical lung injury, Ppl between injured and noninjured lungs is equalized and esophageal pressure is a reliable estimate of dorsal Ppl. Driving transpulmonary pressure is similar for both lungs. Vt distribution results from regional respiratory system compliance. Moderate PEEP homogenizes Vt distribution between lungs without generating hyperinflation. [ABSTRACT FROM AUTHOR]

Rationale: Reverse triggering is an underexplored form of dyssynchrony with important clinical implications in patients with acute respiratory distress syndrome. Objectives: This retrospective study identified reverse trigger phenotypes and characterized their impacts on VT and transpulmonary pressure. Methods: Fifty-five patients with acute respiratory distress syndrome on pressure-regulated ventilator modes were included. Four phenotypes of reverse triggering with and without breath stacking and their impact on lung inflation and deflation were investigated. Measurements and Main Results: Inflation volumes, respiratory muscle pressure generation, and transpulmonary pressures were determined and phenotypes differentiated using Campbell diagrams of respiratory activity. Reverse triggering was detected in 25 patients, 15 with associated breath stacking, and 13 with stable reverse triggering consistent with respiratory entrainment. Phenotypes were associated with variable levels of inspiratory effort (mean 4-10 cm H2O per phenotype). Early reverse triggering with early expiratory relaxation increased VTs (88 [64-113] ml) and inspiratory transpulmonary pressures (3 [2-3] cm H2O) compared with passive breaths. Early reverse triggering with delayed expiratory relaxation increased VTs (128 [86-170]ml) and increased inspiratory andmeanexpiratory transpulmonary pressure (7 [5-9] cm H2O and 5 [4-6] cm H2O). Mid-cycle reverse triggering (initiation during inflation and maximal effort during deflation) increased VT (51 [38-64] ml), increased inspiratory and mean-expiratory transpulmonary pressure (3 [2-4] cm H2O and 3 [2-3] cm H2O), and caused incomplete exhalation. Late reverse triggering (occurring exclusively during exhalation) increased mean expiratory transpulmonary pressure (2 [1-2] cm H2O) and caused incomplete exhalation. Breath stacking resulted in large delivered volumes (176 [155-197] ml). Conclusions: Reverse triggering causes variable physiological effects, depending on the phenotype. Differentiation of phenotype effects may be important to understand the clinical impacts of these events. [ABSTRACT FROM AUTHOR]

The author comments on a research paper on a porcine model of reverse triggering and its impact on the diaphragm, which references a study by L. F. Damiani et al., published within the issue. Topics discussed include the characterization of reverse triggering, alterations in diaphragm muscle function, and transdiaphragmatic pressure in the groups on short-term and long-term ventilation.

The article presents a study on respiratory pathophysiology of mechanically ventilated patients with COVID-19. It reports descriptions of the pathophysiological characteristics of coronavirus disease (COVID-19) respiratory failure. It mentions that severe hypoxemia in early small series have led some investigators to hypothesize that a significant proportion of COVID-19 respiratory failure is not the typical acute respiratory distress syndrome (ARDS) and warrants alternative management.

The article looks at a study single-center observational study regarding lung recruitability in COVID-19–associated Acute Respiratory Distress Syndrome (ARDS). It mentions clinical question with regard to personalizing the management of these patients is whether the lungs are recruitable with high positive end-expiratory pressure (PEEP) for each individual patient. It also mentions increase in end expiratory lung volume induced by PEEP is distributed between the recruited lung.

Rationale: Evidence from observational studies suggests that driving pressure is strongly associated with pulmonary injury and mortality, regardless of positive end-expiratory pressure (PEEP) levels, tidal volume, or plateau pressure. Therefore, it is possible that targeting driving pressure may improve the safety of ventilation strategies for patients with acute respiratory distress syndrome (ARDS). However, the clinical effects of a driving pressure-limited strategy for ARDS has not been assessed in randomized controlled trials.Objectives: To evaluate the feasibility of testing a driving pressure-limited strategy in comparison with a conventional lung-protective ventilation strategy in patients with ARDS and a baseline driving pressure of ≥13 cm H2O.Methods: This was a randomized, controlled, nonblinded trial that included 31 patients with ARDS who were on invasive mechanical ventilation and had a driving pressure of ≥13 cm H2O. Patients allocated to the driving pressure-limited strategy were ventilated with volume-controlled or pressure-support ventilation modes, with tidal volume titrated to 4-8 ml/kg of predicted body weight (PBW), aiming at a driving pressure of 10 cm H2O, or the lowest possible. Patients in the control group were ventilated according to the ARDSNet (Acute Respiratory Distress Syndrome Network) protocol, using a tidal volume of 6 ml/kg PBW, which was allowed to be set down to 4 ml/kg PBW if the plateau pressure was >30 cm H2O. The primary endpoint was the driving pressure on Days 1-3.Results: Sixteen patients were randomized to the driving pressure-limited group and 15 were randomized to the conventional strategy group. All patients were considered in analyses. Most of the patients had mild ARDS with a mean arterial oxygen tension/fraction of inspired oxygen ratio of 215 (standard deviation [SD] = 95). The baseline driving pressure was 15.0 cm H2O (SD = 2.6) in both groups. In comparison with the conventional strategy, driving pressure from the first hour to the third day was 4.6 cm H2O lower in the driving pressure-limited group (95% confidence interval [CI], 6.5 to 2.8; P < 0.001). From the first hour up to the third day, tidal volume in the driving pressure-limited strategy group was kept lower than in the control group (mean difference [ml/kg of PBW], 1.3; 95% CI, 1.7 to 0.9; P < 0.001). We did not find statistically significant differences in the incidence of severe acidosis (pH < 7.10) within 7 days (absolute difference -12.1; 95% CI, -41.5 to -17.3) or any clinical secondary endpoint.Conclusions: In patients with ARDS, a trial assessing the effects of a driving pressure-limited strategy using very low tidal volumes versus a conventional ventilation strategy on clinical outcomes is feasible.Clinical trial registered with ClinicalTrials.gov (NCT02365038). [ABSTRACT FROM AUTHOR]

Rationale: Response to positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome depends on recruitability. We propose a bedside approach to estimate recruitability accounting for the presence of complete airway closure.Objectives: To validate a single-breath method for measuring recruited volume and test whether it differentiates patients with different responses to PEEP.Methods: Patients with acute respiratory distress syndrome were ventilated at 15 and 5 cm H2O of PEEP. Multiple pressure-volume curves were compared with a single-breath technique. Abruptly releasing PEEP (from 15 to 5 cm H2O) increases expired volume: the difference between this volume and the volume predicted by compliance at low PEEP (or above airway opening pressure) estimated the recruited volume by PEEP. This recruited volume divided by the effective pressure change gave the compliance of the recruited lung; the ratio of this compliance to the compliance at low PEEP gave the recruitment-to-inflation ratio. Response to PEEP was compared between high and low recruiters based on this ratio.Measurements and Main Results: Forty-five patients were enrolled. Four patients had airway closure higher than high PEEP, and thus recruitment could not be assessed. In others, recruited volume measured by the experimental and the reference methods were strongly correlated (R2 = 0.798; P < 0.0001) with small bias (-21 ml). The recruitment-to-inflation ratio (median, 0.5; range, 0-2.0) correlated with both oxygenation at low PEEP and the oxygenation response; at PEEP 15, high recruiters had better oxygenation (P = 0.004), whereas low recruiters experienced lower systolic arterial pressure (P = 0.008).Conclusions: A single-breath method quantifies recruited volume. The recruitment-to-inflation ratio might help to characterize lung recruitability at the bedside.Clinical trial registered with www.clinicaltrials.gov (NCT02457741). [ABSTRACT FROM AUTHOR]

The article presents the discussion on electrical impedance tomography (EIT)–based optimal positive end-expiratory pressure (PEEP) level where overdistention and collapse are jointly minimized.

The article presents the discussion on ventilatory strategies minimizing the pressure applied to the lung decreasing mortality. Topics include comprising the pressure in overcoming resistance and elastance of the respiratory system; and optimizing alveolar recruitment, minimizing the risk of hyperinflation, and hemodynamic impairment.

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). [ABSTRACT FROM AUTHOR]

Rationale: Limited data on the epidemiology of acute respiratory distress syndrome (ARDS) using a standardized screening program exist.Objectives: To describe the population-based incidence of hypoxemic respiratory failure and ARDS using a prospective standardized screening protocol; and to describe the mechanical ventilation practice and the mechanical power and examine their association with 28-day and 3-year survival outcomes.Methods: A prospective standardized screening program for ARDS, as a quality improvement initiative, was initiated at four adult intensive care units over a 27-month period. An ancillary analysis of this observational cohort was performed. Patients requiring mechanical ventilation for ≥24 hours underwent prospective and consecutive screening using standardized ventilator settings. Patient physiological data and outcomes were collected prospectively through an electronic clinical-information system and retrospectively analyzed to apply Berlin criteria.Results: Screened were 7,944 patients, among which 986 (12.4%) had hypoxemic respiratory failure (arterial oxygen tension to inspired fraction of oxygen ratio ≤300), and 731 (9.2%) met criteria for ARDS. Age-adjusted incidence of hypoxemic respiratory failure and ARDS were 37.7 and 27.6 cases per 100,000 person-years, respectively. Patients sustaining the diagnosis of ARDS had a hospital mortality of 26.5% for mild, 31.8% for moderate, and 60.0% for severe ARDS and a 3-year mortality of 43.5% for mild, 46.9% for moderate, and 71.1% for severe ARDS. Mechanical power >22 J/min was associated with increased 28-day hospital and 3-year mortality. Determinants of mechanical power associated with lower 28-day hospital and 3-year survival included plateau pressure >30 cm H2O and driving pressure >15 cm H2O, but not tidal volumes >8 ml/kg of predicted body weight.Conclusions: Using standardized screening, a large proportion of patients with hypoxemic respiratory failure met criteria for ARDS. Increasing ARDS severity was associated with increased 28-day hospital and 3-year mortality. Increased mechanical power was associated with increased mortality. Potentially modifiable determinants of mechanical power associated with lower survival included plateau pressure and driving pressure. [ABSTRACT FROM AUTHOR]

The article offers information on the study related to the assessment of airway driving pressure and respiratory system mechanics during neurally adjusted ventilatory assist. It discusses the electrical activity of the diaphragm and the driving pressure developed by the ventilator and the respiratory muscles.

The article offers information about the tools for improving the gas exchange and mechanics of patients with the acute respiratory distress syndrome (ARDS) positive end-expiratory pressure (PEEP) and prone positioning. It mentions that demonstrate experimentally in a porcine lung injury model that diverse local actions of PEEP regarding lung unit distention.

The author reflects on an article published within the issue which suggest that a simplified variant of such gas-based tidal mechanics methods may help clinicians to extract and separate. It mentions beneficial effects of positive end-expiratory pressure (PEEP) on oxygenation in acute respiratory distress syndrome (ARDS) on attributed to recruitment of gas exchange airspaces and prevention of terminal airway closure. It also mentions risks and benefits of preventing atelectrauma.