Personalizing mechanical ventilation according to physiologic parameters to stabilize alveoli and minimize ventilator induced lung injury (VILI)

Intraoperative Ventilation/Perfusion Mismatch and Postoperative Pulmonary Complications after Major Noncardiac Surgery: A Prospective Cohort Study

BACKGROUND

Postoperative pulmonary complications can increase hospital length of stay, postoperative morbidity, and mortality. Although many factors can increase the risk of postoperative pulmonary complications, it is not known whether intraoperative ventilation/perfusion (V/Q) mismatch can be associated with an increased risk of postoperative pulmonary complications after major noncardiac surgery.

METHODS

This study enrolled patients undergoing general anesthesia for noncardiac surgery and evaluated intraoperative V/Q distribution using the automatic lung parameter estimator technique. The assessment was done after anesthesia induction, after 1 h from surgery start, and at the end of surgery. Demographic and procedural information were collected, and intraoperative ventilatory and hemodynamic parameters were measured at each timepoint. Patients were followed up for 7 days after surgery and assessed daily for postoperative pulmonary complication occurrence.

RESULTS

The study enrolled 101 patients with a median age of 71 [62 to 77] years, a body mass index of 25 [22.4 to 27.9] kg/m2, and a preoperative Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) score of 41 [34 to 47]. Of these patients, 29 (29%) developed postoperative pulmonary complications, mainly acute respiratory failure (23%) and pleural effusion (11%). Patients with and without postoperative pulmonary complications did not differ in levels of shunt at T1 (postoperative pulmonary complications: 22.4% [10.4 to 35.9%] vs. no postoperative pulmonary complications:19.3% [9.4 to 24.1%]; P = 0.18) or during the protocol, whereas significantly different levels of high V/Q ratio were found during surgery (postoperative pulmonary complications: 13 [11 to 15] mmHg vs. no postoperative pulmonary complications: 10 [8 to 13.5] mmHg; P = 0.007) and before extubation (postoperative pulmonary complications: 13 [11 to 14] mmHg vs. no postoperative pulmonary complications: 10 [8 to 12] mmHg; P = 0.006). After adjusting for age, ARISCAT, body mass index, smoking, fluid balance, anesthesia type, laparoscopic procedure and surgery duration, high V/Q ratio before extubation was independently associated with the development of postoperative pulmonary complications (odds ratio, 1.147; 95% CI, 1.021 to 1.289; P = 0.02). The sensitivity analysis showed an E-value of 1.35 (CI, 1.11).

CONCLUSIONS

In patients with intermediate or high risk of postoperative pulmonary complications undergoing major noncardiac surgery, intraoperative V/Q mismatch is associated with the development of postoperative pulmonary complications. Increased high V/Q ratio before extubation is independently associated with the occurrence of postoperative pulmonary complications in the first 7 days after surgery.

EDITOR’S PERSPECTIVE

A Comparison of the Effects of Different Positive End-Expiratory Pressure Levels on Respiratory Parameters During Prone Positioning Under General Anaesthesia: A Randomized Controlled Trial

Background and objective In general anesthesia, for certain surgical procedures in the prone position, patients often face increased airway pressures, reduced pulmonary and thoracic compliance, and restricted chest expansion, all of which can affect venous return and cardiac output, impacting overall hemodynamic stability. Positive end-expiratory pressure (PEEP) is used to address these issues by improving lung recruitment and ventilation while reducing stress on lung units. However, different PEEP levels also present risks such as increased parenchymal strain, higher pulmonary vascular resistance, and impaired venous return.  Proper positioning and frequent monitoring are key to ensuring adequate oxygenation and minimizing complications arising from prolonged periods in the prone position. This study aimed to evaluate the effects of different PEEP levels (0 cmH2O, 5 cmH2O, and 10 cmH2O) in the prone position to determine the optimal setting for balancing improved oxygenation and lung recruitment against potential adverse effects. The goal is to refine individualized PEEP strategies beyond what is typically outlined in standard PEEP tables. We endeavored to examine the impact of different PEEP levels during pressure-controlled ventilation (PCV) on arterial oxygenation, respiratory parameters, and intraoperative blood loss in patients undergoing spine surgery in a prone position under general anesthesia. Methodology This randomized, single-blinded, controlled study enrolled 90 patients scheduled for elective spine fixation surgeries. Patients were randomized into three groups: Group A (PEEP 0), Group B (PEEP 5), and Group C (PEEP 10). Standardized anesthesia protocols were administered to all groups, with ventilation set to pressure-controlled mode at desired levels. PEEP levels were adjusted according to group allocation. Arterial blood gases were measured before induction, 30 minutes after prone positioning, and 30 minutes post-extubation. Arterial line insertion was performed, and dynamic compliance, mean arterial pressure (MAP), heart rate (HR), and intraoperative blood loss were recorded at regular intervals. Data were analyzed using SPSS Statistics version 21 (IBM Corp., Armonk, NY). Results Arterial oxygenation was significantly higher in Groups B (PEEP 5) and C (PEEP 10) compared to Group A (PEEP 0) at both 30 minutes post-intubation and post-extubation. Specifically, at 30 minutes post-intubation, arterial oxygenation was 142.26 ±24.7 in Group B and 154.9 ±29.88 in Group C, compared to 128.18 ±13.3 in Group A (p=0.002). Similarly, post-extubation arterial oxygenation levels were 105.1 ±8.28 for Group B and 115.46 ±15.2 for Group C, while Group A had levels of 97.07 ±9.90 (p<0.001). MAP decreased significantly in Groups B and C compared to Group A. Dynamic compliance was also improved in Groups B and C. Furthermore, intraoperative blood loss was notably lower in Group C (329.66 ±93.93) and Group B (421.16 ±104.52) compared to Group A (466.66 ±153.76), and these differences were statistically significant. Conclusions Higher levels of PEEP (10 and 5 cmH2O) during prone positioning in spine surgery improve arterial oxygenation, dynamic compliance, and hemodynamic stability while reducing intraoperative blood loss. These findings emphasize the importance of optimizing ventilatory support to enhance patient outcomes during prone-position surgeries.

Lung-protective ventilation in the management of congenital diaphragmatic hernia

Prioritizing lung-protective ventilation has produced a clear mortality benefit in neonates with congenital diaphragmatic hernia (CDH). While there is a paucity of CDH-specific evidence to support any particular approach to lung-protective ventilation, a growing body of data in adults is beginning to clarify the mechanisms behind ventilator-induced lung injury and inform safer management of mechanical ventilation in general. This review summarizes the adult data and attempts to relate the findings, conceptually, to the CDH population. Critical lessons from the adult studies are that much of the damage done during conventional mechanical ventilation affects normal lung tissue and that most of this damage occurs at the low-volume and high-volume extremes of the respiratory cycle. Consequently, it is important to prevent atelectasis by using sufficient positive end-expiratory pressure while also avoiding overdistention by scaling tidal volume to the amount of functional lung tissue rather than body weight. Paralysis early in acute respiratory distress syndrome improves outcomes, possibly because consistent respiratory mechanics facilitate avoidance of both atelectasis and overdistention-a mechanism that may also apply to the CDH population. Volume-targeted conventional modes may be advantageous in CDH, but determining optimal tidal volume is challenging. Both high-frequency oscillatory ventilation and high-frequency jet ventilation have been used successfully as 'rescue modes' to avoid extracorporeal membrane oxygenation, and a prospective trial comparing the two high-frequency modalities as the primary ventilation strategy for CDH is underway.

Effect of flow-optimized pressure control ventilation-volume guaranteed (PCV-VG) on postoperative pulmonary complications: a consort study

BACKGROUND

Postoperative pulmonary complications (PPCs) after one-lung ventilation (OLV) significantly impact patient prognosis and quality of life.

OBJECTIVE

To study the impact of an optimal inspiratory flow rate on PPCs in thoracic surgery patients.

METHODS

One hundred eight elective thoracic surgery patients were randomly assigned to 2 groups in this consort study (control group: n = 53 with a fixed inspiratory expiratory ratio of 1:2; and experimental group [flow rate optimization group]: n = 55). Measurements of Ppeak, Pplat, PETCO2, lung dynamic compliance (Cdyn), respiratory rate, and oxygen concentration were obtained at the following specific time points: immediately after intubation (T0); immediately after starting OLV (T1); 30 min after OLV (T2); and 10 min after 2-lung ventilation (T4). The PaO2:FiO2 ratio was measured using blood gas analysis 30 min after initiating one-lung breathing (T2) and immediately when OLV ended (T3). The lung ultrasound score (LUS) was assessed following anesthesia and resuscitation (T5). The occurrence of atelectasis was documented immediately after the surgery. PPCs occurrences were noted 3 days after surgery.

RESULTS

The treatment group had a significantly lower total prevalence of PPCs compared to the control group (3.64% vs. 16.98%; P = 0.022). There were no notable variations in peak airway pressure, airway plateau pressure, dynamic lung compliance, PETCO2, respiratory rate, and oxygen concentration between the two groups during intubation (T0). Dynamic lung compliance and the oxygenation index were significantly increased at T1, T2, and T4 (P < 0.05), whereas the CRP level and number of inflammatory cells decreased dramatically (P < 0.05).

CONCLUSION

Optimizing inspiratory flow rate and utilizing pressure control ventilation -volume guaranteed (PCV-VG) mode can decrease PPCs and enhance lung dynamic compliance in OLV patients.

Recruitment-to-inflation ratio reflects the impact of peep on dynamic lung strain in a highly recruitable model of ARDS

BACKGROUND

The recruitment-to-inflation ratio (R/I) has been recently proposed to bedside assess response to PEEP. The impact of PEEP on ventilator-induced lung injury depends on the extent of dynamic strain reduction. We hypothesized that R/I may reflect the potential for lung recruitment (i.e. recruitability) and, consequently, estimate the impact of PEEP on dynamic lung strain, both assessed through computed tomography scan.

METHODS

Fourteen lung-damaged pigs (lipopolysaccharide infusion) underwent ventilation at low (5 cmH2O) and high PEEP (i.e., PEEP generating a plateau pressure of 28-30 cmH2O). R/I was measured through a one-breath derecruitment maneuver from high to low PEEP. PEEP-induced changes in dynamic lung strain, difference in nonaerated lung tissue weight (tissue recruitment) and amount of gas entering previously nonaerated lung units (gas recruitment) were assessed through computed tomography scan. Tissue and gas recruitment were normalized to the weight and gas volume of previously ventilated lung areas at low PEEP (normalized-tissue recruitment and normalized-gas recruitment, respectively).

RESULTS

Between high (median [interquartile range] 20 cmH2O [18-21]) and low PEEP, median R/I was 1.08 [0.88-1.82], indicating high lung recruitability. Compared to low PEEP, tissue and gas recruitment at high PEEP were 246 g [182-288] and 385 ml [318-668], respectively. R/I was linearly related to normalized-gas recruitment (r = 0.90; [95% CI 0.71 to 0.97) and normalized-tissue recruitment (r = 0.69; [95% CI 0.25 to 0.89]). Dynamic lung strain was 0.37 [0.29-0.44] at high PEEP and 0.59 [0.46-0.80] at low PEEP (p < 0.001). R/I was significantly related to PEEP-induced reduction in dynamic (r = - 0.93; [95% CI - 0.78 to - 0.98]) and global lung strain (r = - 0.57; [95% CI - 0.05 to - 0.84]). No correlation was found between R/I and and PEEP-induced changes in static lung strain (r = 0.34; [95% CI - 0.23 to 0.74]).

CONCLUSIONS

In a highly recruitable ARDS model, R/I reflects the potential for lung recruitment and well estimates the extent of PEEP-induced reduction in dynamic lung strain.

Collagen Tubular Airway-on-Chip for Extended Epithelial Culture and Investigation of Ventilation Dynamics

The lower respiratory tract is a hierarchical network of compliant tubular structures that are made from extracellular matrix proteins with a wall lined by an epithelium. While microfluidic airway-on-a-chip models incorporate the effects of shear and stretch on the epithelium, week-long air-liquid-interface culture at physiological shear stresses, the circular cross-section, and compliance of native airway walls have yet to be recapitulated. To overcome these limitations, a collagen tube-based airway model is presented. The lumen is lined with a confluent epithelium during two-week continuous perfusion with warm, humid air while presenting culture medium from the outside and compensating for evaporation. The model recapitulates human small airways in extracellular matrix composition and mechanical microenvironment, allowing for the first time dynamic studies of elastocapillary phenomena associated with regular breathing and mechanical ventilation, as well as their impacts on the epithelium. A case study reveales increasing damage to the epithelium during repetitive collapse and reopening cycles as opposed to overdistension, suggesting expiratory flow resistance to reduce atelectasis. The model is expected to promote systematic comparisons between different clinically used ventilation strategies and, more broadly, to enhance human organ-on-a-chip platforms for a variety of tubular tissues.

Electrical impedance tomography-guided positive end-expiratory pressure titration in ARDS: a systematic review and meta-analysis

PURPOSE

Assessing efficacy of electrical impedance tomography (EIT) in optimizing positive end-expiratory pressure (PEEP) for acute respiratory distress syndrome (ARDS) patients to enhance respiratory system mechanics and prevent ventilator-induced lung injury (VILI), compared to traditional methods.

METHODS

We carried out a systematic review and meta-analysis, spanning literature from January 2012 to May 2023, sourced from Scopus, PubMed, MEDLINE (Ovid), Cochrane, and LILACS, evaluated EIT-guided PEEP strategies in ARDS versus conventional methods. Thirteen studies (3 randomized, 10 non-randomized) involving 623 ARDS patients were analyzed using random-effects models for primary outcomes (respiratory mechanics and mechanical power) and secondary outcomes (PaO2/FiO2 ratio, mortality, stays in intensive care unit (ICU), ventilator-free days).

RESULTS

EIT-guided PEEP significantly improved lung compliance (n = 941 cases, mean difference (MD) = 4.33, 95% confidence interval (CI) [2.94, 5.71]), reduced mechanical power (n = 148, MD = - 1.99, 95% CI [- 3.51, - 0.47]), and lowered driving pressure (n = 903, MD = - 1.20, 95% CI [- 2.33, - 0.07]) compared to traditional methods. Sensitivity analysis showed consistent positive effect of EIT-guided PEEP on lung compliance in randomized clinical trials vs. non-randomized studies pooled (MD) = 2.43 (95% CI - 0.39 to 5.26), indicating a trend towards improvement. A reduction in mortality rate (259 patients, relative risk (RR) = 0.64, 95% CI [0.45, 0.91]) was associated with modest improvements in compliance and driving pressure in three studies.

CONCLUSIONS

EIT facilitates real-time, individualized PEEP adjustments, improving respiratory system mechanics. Integration of EIT as a guiding tool in mechanical ventilation holds potential benefits in preventing ventilator-induced lung injury. Larger-scale studies are essential to validate and optimize EIT's clinical utility in ARDS management.

Exploring alveolar recruitability using positive end-expiratory pressure in mice overexpressing TGF-β1: a structure-function analysis

Pre-injured lungs are prone to injury progression in response to mechanical ventilation. Heterogeneous ventilation due to (micro)atelectases imparts injurious strains on open alveoli (known as volutrauma). Hence, recruitment of (micro)atelectases by positive end-expiratory pressure (PEEP) is necessary to interrupt this vicious circle of injury but needs to be balanced against acinar overdistension. In this study, the lung-protective potential of alveolar recruitment was investigated and balanced against overdistension in pre-injured lungs. Mice, treated with empty vector (AdCl) or adenoviral active TGF-β1 (AdTGF-β1) were subjected to lung mechanical measurements during descending PEEP ventilation from 12 to 0 cmH2O. At each PEEP level, recruitability tests consisting of two recruitment maneuvers followed by repetitive forced oscillation perturbations to determine tissue elastance (H) and damping (G) were performed. Finally, lungs were fixed by vascular perfusion at end-expiratory airway opening pressures (Pao) of 20, 10, 5 and 2 cmH2O after a recruitment maneuver, and processed for design-based stereology to quantify derecruitment and distension. H and G were significantly elevated in AdTGF-β1 compared to AdCl across PEEP levels. H was minimized at PEEP = 5-8 cmH2O and increased at lower and higher PEEP in both groups. These findings correlated with increasing septal wall folding (= derecruitment) and reduced density of alveolar number and surface area (= distension), respectively. In AdTGF-β1 exposed mice, 27% of alveoli remained derecruited at Pao = 20 cmH2O. A further decrease in Pao down to 2 cmH2O showed derecruitment of an additional 1.1 million alveoli (48%), which was linked with an increase in alveolar size heterogeneity at Pao = 2-5 cmH2O. In AdCl, decreased Pao resulted in septal folding with virtually no alveolar collapse. In essence, in healthy mice alveoli do not derecruit at low PEEP ventilation. The potential of alveolar recruitability in AdTGF-β1 exposed mice is high. H is optimized at PEEP 5-8 cmH2O. Lower PEEP folds and larger PEEP stretches septa which results in higher H and is more pronounced in AdTGF-β1 than in AdCl. The increased alveolar size heterogeneity at Pao = 5 cmH2O argues for the use of PEEP = 8 cmH2O for lung protective mechanical ventilation in this animal model.

High vs. low tidal volume and pulmonary complications in patients with cervical spinal cord injury on mechanical ventilation: systematic review

Introduction

Cervical spinal cord injury (CSCI) patients on mechanical ventilation often lack standardized guidelines for optimal ventilatory support. This study reviews existing literature to compare outcomes between high tidal volume (HTV) and low tidal volume (LTV) strategies in this unique patient population.

Methods

We searched for studies published up to August 30, 2023, in five databases, following a PECO/PICO strategy. We found six studies for quantitative analysis and meta-analyzed five studies.

Results

This meta-analysis included 396 patients with CSCI and mechanical ventilation (MV), 119 patients treated with high tidal volume (HTV), and 277 with low tidal volume (LTV). This first meta-analysis incorporates the few studies that show contradictory findings. Our meta-analysis shows that there is no significant statistical difference in developing VAP between both comparison groups (HTV vs. LTV) (OR 0.46; 95% CI 0.13 to 1.66; p > 0.05; I2: 0%), nor are there differences between the presence of other pulmonary complications when treating with HTV such as acute respiratory distress syndrome (ARDS), atelectasis, onset of weaning.

Conclusion

In patients with CSCI in MV, the use of HTV does not carry a greater risk of pneumonia compared to LTV; in turn, it is shown as a safe ventilatory strategy as it does not establish an increase in other pulmonary complications such as ARDS, atelectasis, the onset of weaning nor others associated with volutrauma. It is necessary to evaluate the role of HTV ventilation in this group of patients in primary RCT-type studies.

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.

Machine learning prediction of the total duration of invasive and non-invasive ventilation During ICU Stay

Predicting the duration of ventilation in the ICU helps in assessing the risk of ventilator-induced lung injury, ensuring sufficient oxygenation, and optimizing resource allocation. Prior models provided a prediction of total duration without distinguishing between invasive and non-invasive ventilation. This work proposes two independent gradient boosting regression models for predicting the duration of invasive and non-invasive ventilation based on commonly available ICU features. These models are trained on 2.6 million patient stays across 350 US hospitals between 2010 to 2019. The mean absolute error (MAE) for the prediction of duration was 2.08 days for invasive ventilation and 0.36 days for non-invasive ventilation. The total ventilation duration predicted by our model had MAE of 2.38 days, which outperformed the gold standard (APACHE) with MAE of 3.02 days. The feature importance analysis of the trained models showed that, for invasive ventilation, high average heart rate, diagnosis of respiratory infection and admissions from locations other than the operating room were associated with longer ventilation durations. For non-invasive ventilation, higher respiratory rates and having any GCS measurement were associated with longer durations.

Differential effects of two-hit models of acute and ventilator-induced lung injury on lung structure, function, and inflammation

Acute respiratory distress syndrome (ARDS) and acute lung injury have a diverse spectrum of causative factors including sepsis, aspiration of gastric contents, and near drowning. Clinical management of severe lung injury typically includes mechanical ventilation to maintain gas exchange which can lead to ventilator-induced lung injury (VILI). The cause of respiratory failure is acknowledged to affect the degree of lung inflammation, changes in lung structure, and the mechanical function of the injured lung. However, these differential effects of injury and the role of etiology in the structure-function relationship are not fully understood. To address this knowledge gap we caused lung injury with intratracheal hydrochloric acid (HCL) or endotoxin (LPS) 2 days prior to ventilation or with an injurious lavage (LAV) immediately prior to ventilation. These injury groups were then ventilated with high inspiratory pressures and positive end expiratory pressure (PEEP) = 0 cmH2O to cause VILI and model the clinical course of ARDS followed by supportive ventilation. The effects of injury were quantified using invasive lung function measurements recorded during PEEP ladders where the end-expiratory pressure was increased from 0 to 15 cm H2O and decreased back to 0 cmH2O in steps of 3 cmH2O. Design-based stereology was used to quantify the parenchymal structure of lungs air-inflated to 2, 5, and 10 cmH2O. Pro-inflammatory gene expression was measured with real-time quantitative polymerase chain reaction and alveolocapillary leak was estimated by measuring bronchoalveolar lavage protein content. The LAV group had small, stiff lungs that were recruitable at higher pressures, but did not demonstrate substantial inflammation. The LPS group showed septal swelling and high pro-inflammatory gene expression that was exacerbated by VILI. Despite widespread alveolar collapse, elastance in LPS was only modestly elevated above healthy mice (CTL) and there was no evidence of recruitability. The HCL group showed increased elastance and some recruitability, although to a lesser degree than LAV. Pro-inflammatory gene expression was elevated, but less than LPS, and the airspace dimensions were reduced. Taken together, those data highlight how different modes of injury, in combination with a 2nd hit of VILI, yield markedly different effects.

A Focused Review of the Initial Management of Patients with Acute Respiratory Distress Syndrome

At present, the management of patients with acute respiratory distress syndrome (ARDS) largely focuses on ventilator settings to limit intrathoracic pressures by using low tidal volumes and on FiO₂/PEEP relationships to maintain optimal gas exchange. Acute respiratory distress syndrome is a complex medical disorder that can develop in several primary acute disorders, has a rapid time course, and has several classifications that can reflect either the degree of hypoxemia, the extent of radiographic involvement, or the underlying pathogenesis. The identification of subtypes of patients with ARDS would potentially make precision medicine possible in these patients. This is a very difficult challenge given the heterogeneity in the clinical presentation, pathogenesis, and treatment responses in these patients. The analysis of large databases of patients with acute respiratory failure using statistical methods such as cluster analysis could identify phenotypes that have different outcomes or treatment strategies. However, clinical information available on presentation is unlikely to separate patients into groups that allow for secure treatment decisions or outcome predictions. In some patients, non-invasive positive pressure ventilation provides adequate support through episodes of acute respiratory failure, and the development of specialized units to manage patients with this support might lead to the better use of hospital resources. Patients with ARDS have capillary leak, which results in interstitial and alveolar edema. Early attention to fluid balance in these patients might improve gas exchange and alter the pathophysiology underlying the development of severe ARDS. Finally, more attention to the interaction of patients with ventilators through complex monitoring systems has the potential to identify ventilator dyssynchrony, leading to ventilator adjustments and potentially better outcomes. Recent studies with COVID-19 patients provide tentative answers to some of these questions. In addition, expert clinical investigators have analyzed the promise and difficulties associated with the development of precision medicine in patients with ARDS.

First Stabilize and then Gradually Recruit: A Paradigm Shift in Protective Mechanical Ventilation for Acute Lung Injury

Acute respiratory distress syndrome (ARDS) is associated with a heterogeneous pattern of injury throughout the lung parenchyma that alters regional alveolar opening and collapse time constants. Such heterogeneity leads to atelectasis and repetitive alveolar collapse and expansion (RACE). The net effect is a progressive loss of lung volume with secondary ventilator-induced lung injury (VILI). Previous concepts of ARDS pathophysiology envisioned a two-compartment system: a small amount of normally aerated lung tissue in the non-dependent regions (termed "baby lung"); and a collapsed and edematous tissue in dependent regions. Based on such compartmentalization, two protective ventilation strategies have been developed: (1) a "protective lung approach" (PLA), designed to reduce overdistension in the remaining aerated compartment using a low tidal volume; and (2) an "open lung approach" (OLA), which first attempts to open the collapsed lung tissue over a short time frame (seconds or minutes) with an initial recruitment maneuver, and then stabilize newly recruited tissue using titrated positive end-expiratory pressure (PEEP). A more recent understanding of ARDS pathophysiology identifies regional alveolar instability and collapse (i.e., hidden micro-atelectasis) in both lung compartments as a primary VILI mechanism. Based on this understanding, we propose an alternative strategy to ventilating the injured lung, which we term a "stabilize lung approach" (SLA). The SLA is designed to immediately stabilize the lung and reduce RACE while gradually reopening collapsed tissue over hours or days. At the core of SLA is time-controlled adaptive ventilation (TCAV), a method to adjust the parameters of the airway pressure release ventilation (APRV) modality. Since the acutely injured lung at any given airway pressure requires more time for alveolar recruitment and less time for alveolar collapse, SLA adjusts inspiratory and expiratory durations and inflation pressure levels. The TCAV method SLA reverses the open first and stabilize second OLA method by: (i) immediately stabilizing lung tissue using a very brief exhalation time (≤0.5 s), so that alveoli simply do not have sufficient time to collapse. The exhalation duration is personalized and adaptive to individual respiratory mechanical properties (i.e., elastic recoil); and (ii) gradually recruiting collapsed lung tissue using an inflate and brake ratchet combined with an extended inspiratory duration (4-6 s) method. Translational animal studies, clinical statistical analysis, and case reports support the use of TCAV as an efficacious lung protective strategy.

Optimal positive end-expiratory pressure reduces right ventricular dysfunction in COVID-19 patients on venovenous extracorporeal membrane oxygenation: A retrospective single-center study

While mechanical ventilation practices on venovenous extracorporeal membrane oxygenation (VV ECMO) are variable, most institutions utilize a lung rest strategy utilizing relatively low positive end-expiratory pressure (PEEP). The effect of PEEP titration using esophageal manometry during VV ECMO on pulmonary and cardiac function is unknown. This was a retrospective study of 69 patients initiated on VV ECMO between March 2020 through November 2021. Patients underwent standard PEEP (typically 10 cm H₂O) or optimal PEEP (PEEP titrated to an end-expiratory transpulmonary pressure 0-3 cm H₂O) throughout the ECMO run. The optimal PEEP strategy had higher levels of applied PEEP (17.9 vs. 10.8 cm H₂O on day 2 of ECMO), decreased incidence of hemodynamically significant RV dysfunction (4.55% vs. 44.0%, p = 0.0001), and higher survival to decannulation (72.7% vs. 44.0%, p = 0.022). Survival to discharge did not reach statistical significance (27% vs. 11%, p = 0.211). In univariate logistic regression analysis, optimal PEEP was associated with less hemodynamically significant RV dysfunction with an odds ratio (OR) of 0.06 (95% confidence interval [CI] = 0.01-0.27, p = 0.0008) and increased survival to decannulation with an OR of 3.39 (95% CI 1.23-9.79), p = 0.02), though other confounding factors may have contributed.

Intraoperative Ventilator Management of the Critically Ill Patient

Strategies for the intraoperative ventilator management of the critically ill patient focus on parameters used for lung protective ventilation with acute respiratory distress syndrome, preventing or limiting the deleterious effects of mechanical ventilation, and optimizing anesthetic and surgical conditions to limit postoperative pulmonary complications for patients at risk. Patient conditions such as obesity, sepsis, the need for laparoscopic surgery, or one-lung ventilation may benefit from intraoperative lung protective ventilation strategies. Anesthesiologists can use risk evaluation and prediction tools, monitor advanced physiologic targets, and incorporate new innovative monitoring techniques to develop an individualized approach for patients.

A structured narrative review of clinical and experimental studies of the use of different positive end-expiratory pressure levels during thoracic surgery

OBJECTIVES

This study aimed to present a review on the general effects of different positive end-expiratory pressure (PEEP) levels during thoracic surgery by qualitatively categorizing the effects into detrimental, beneficial, and inconclusive.

DATA SOURCE

Literature search of Pubmed, CNKI, and Wanfang was made to find relative articles about PEEP levels during thoracic surgery. We used the following keywords as one-lung ventilation, PEEP, and thoracic surgery.

RESULTS

We divide the non-individualized PEEP value into five grades, that is, less than 5, 5, 5-10, 10, and more than 10 cmH₂ O, among which 5 cmH₂ O is the most commonly used in clinic at present to maintain alveolar dilatation and reduce the shunt fraction and the occurrence of atelectasis, whereas individualized PEEP, adjusted by test titration or imaging method to adapt to patients' personal characteristics, can effectively ameliorate intraoperative oxygenation and obtain optimal pulmonary compliance and better indexes relating to respiratory mechanics.

CONCLUSIONS

Available data suggest that PEEP might play an important role in one-lung ventilation, the understanding of which will help in exploring a simple and economical method to set the appropriate PEEP level.

Unshrinking the baby lung to calm the VILI vortex

A hallmark of ARDS is progressive shrinking of the ‘baby lung,’ now referred to as the ventilator-induced lung injury (VILI) ‘vortex.’ Reducing the risk of the VILI vortex is the goal of current ventilation strategies; unfortunately, this goal has not been achieved nor has mortality been reduced. However, the temporal aspects of a mechanical breath have not been considered. A brief expiration prevents alveolar collapse, and an extended inspiration can recruit the atelectatic lung over hours. Time-controlled adaptive ventilation (TCAV) is a novel ventilator approach to achieve these goals, since it considers many of the temporal aspects of dynamic lung mechanics.

Induction of severe hypoxemia and low lung recruitability for the evaluation of therapeutic ventilation strategies: a translational model of combined surfactant-depletion and ventilator-induced lung injury

BACKGROUND

Models of hypoxemic lung injury caused by lavage-induced pulmonary surfactant depletion are prone to prompt recovery of blood oxygenation following recruitment maneuvers and have limited translational validity. We hypothesized that addition of injurious ventilation following surfactant-depletion creates a model of the acute respiratory distress syndrome (ARDS) with persistently low recruitability and higher levels of titrated "best" positive end-expiratory pressure (PEEP) during protective ventilation.

METHODS

Two types of porcine lung injury were induced by lung lavage and 3 h of either protective or injurious ventilation, followed by 3 h of protective ventilation (N = 6 per group). Recruitment maneuvers (RM) and decremental PEEP trials comparing oxygenation versus dynamic compliance were performed after lavage and at 3 h intervals of ventilation. Pulmonary gas exchange function, respiratory mechanics, and ventilator-derived parameters were assessed after each RM to map the course of injury severity and recruitability.

RESULTS

Lung lavage impaired respiratory system compliance (C_rs) and produced arterial oxygen tensions (P_aO₂) of 84±13 and 80±15 (F_IO₂ = 1.0) with prompt increase after RM to 270-395 mmHg in both groups. After subsequent 3 h of either protective or injurious ventilation, P_aO₂/F_IO₂ was 104±26 vs. 154±123 and increased to 369±132 vs. 167±87 mmHg in response to RM, respectively. After additional 3 h of protective ventilation, P_aO₂/F_IO₂ was 120±15 vs. 128±37 and increased to 470±68 vs. 185±129 mmHg in response to RM, respectively. Subsequently, decremental PEEP titration revealed that C_rs peaked at 36 ± 10 vs. 25 ± 5 ml/cm H₂O with PEEP of 12 vs. 16 cmH₂O, and P_aO₂/F_IO₂ peaked at 563 ± 83 vs. 334 ± 148 mm Hg with PEEP of 16 vs. 22 cmH₂O in the protective vs. injurious ventilation groups, respectively. The large disparity of recruitability between groups was not reflected in the C_rs nor the magnitude of mechanical power present after injurious ventilation, once protective ventilation was resumed.

CONCLUSION

Addition of transitory injurious ventilation after lung lavage causes prolonged acute lung injury with diffuse alveolar damage and low recruitability yielding high titrated PEEP levels. Mimicking lung mechanical and functional characteristics of ARDS, this porcine model rectifies the constraints of single-hit lavage models and may enhance the translation of experimental research on mechanical ventilation strategies.

Myths and Misconceptions of Airway Pressure Release Ventilation: Getting Past the Noise and on to the Signal

In the pursuit of science, competitive ideas and debate are necessary means to attain knowledge and expose our ignorance. To quote Murray Gell-Mann (1969 Nobel Prize laureate in Physics): "Scientific orthodoxy kills truth". In mechanical ventilation, the goal is to provide the best approach to support patients with respiratory failure until the underlying disease resolves, while minimizing iatrogenic damage. This compromise characterizes the philosophy behind the concept of "lung protective" ventilation. Unfortunately, inadequacies of the current conceptual model-that focuses exclusively on a nominal value of low tidal volume and promotes shrinking of the "baby lung" - is reflected in the high mortality rate of patients with moderate and severe acute respiratory distress syndrome. These data call for exploration and investigation of competitive models evaluated thoroughly through a scientific process. Airway Pressure Release Ventilation (APRV) is one of the most studied yet controversial modes of mechanical ventilation that shows promise in experimental and clinical data. Over the last 3 decades APRV has evolved from a rescue strategy to a preemptive lung injury prevention approach with potential to stabilize the lung and restore alveolar homogeneity. However, several obstacles have so far impeded the evaluation of APRV's clinical efficacy in large, randomized trials. For instance, there is no universally accepted standardized method of setting APRV and thus, it is not established whether its effects on clinical outcomes are due to the ventilator mode per se or the method applied. In addition, one distinctive issue that hinders proper scientific evaluation of APRV is the ubiquitous presence of myths and misconceptions repeatedly presented in the literature. In this review we discuss some of these misleading notions and present data to advance scientific discourse around the uses and misuses of APRV in the current literature.

ARDS Clinical Practice Guideline 2021

BACKGROUND

The joint committee of the Japanese Society of Intensive Care Medicine/Japanese Respiratory Society/Japanese Society of Respiratory Care Medicine on ARDS Clinical Practice Guideline has created and released the ARDS Clinical Practice Guideline 2021.

METHODS

The 2016 edition of the Clinical Practice Guideline covered clinical questions (CQs) that targeted only adults, but the present guideline includes 15 CQs for children in addition to 46 CQs for adults. As with the previous edition, we used a systematic review method with the Grading of Recommendations Assessment Development and Evaluation (GRADE) system as well as a degree of recommendation determination method. We also conducted systematic reviews that used meta-analyses of diagnostic accuracy and network meta-analyses as a new method.

RESULTS

Recommendations for adult patients with ARDS are described: we suggest against using serum C-reactive protein and procalcitonin levels to identify bacterial pneumonia as the underlying disease (GRADE 2D); we recommend limiting tidal volume to 4-8 mL/kg for mechanical ventilation (GRADE 1D); we recommend against managements targeting an excessively low SpO2 (PaO2) (GRADE 2D); we suggest against using transpulmonary pressure as a routine basis in positive end-expiratory pressure settings (GRADE 2B); we suggest implementing extracorporeal membrane oxygenation for those with severe ARDS (GRADE 2B); we suggest against using high-dose steroids (GRADE 2C); and we recommend using low-dose steroids (GRADE 1B). The recommendations for pediatric patients with ARDS are as follows: we suggest against using non-invasive respiratory support (non-invasive positive pressure ventilation/high-flow nasal cannula oxygen therapy) (GRADE 2D), we suggest placing pediatric patients with moderate ARDS in the prone position (GRADE 2D), we suggest against routinely implementing NO inhalation therapy (GRADE 2C), and we suggest against implementing daily sedation interruption for pediatric patients with respiratory failure (GRADE 2D).

CONCLUSIONS

This article is a translated summary of the full version of the ARDS Clinical Practice Guideline 2021 published in Japanese (URL: https://www.jsicm.org/publication/guideline.html ). The original text, which was written for Japanese healthcare professionals, may include different perspectives from healthcare professionals of other countries.

ARDS clinical practice guideline 2021

BACKGROUND

The joint committee of the Japanese Society of Intensive Care Medicine/Japanese Respiratory Society/Japanese Society of Respiratory Care Medicine on ARDS Clinical Practice Guideline has created and released the ARDS Clinical Practice Guideline 2021.

METHODS

The 2016 edition of the Clinical Practice Guideline covered clinical questions (CQs) that targeted only adults, but the present guideline includes 15 CQs for children in addition to 46 CQs for adults. As with the previous edition, we used a systematic review method with the Grading of Recommendations Assessment Development and Evaluation (GRADE) system as well as a degree of recommendation determination method. We also conducted systematic reviews that used meta-analyses of diagnostic accuracy and network meta-analyses as a new method.

RESULTS

Recommendations for adult patients with ARDS are described: we suggest against using serum C-reactive protein and procalcitonin levels to identify bacterial pneumonia as the underlying disease (GRADE 2D); we recommend limiting tidal volume to 4-8 mL/kg for mechanical ventilation (GRADE 1D); we recommend against managements targeting an excessively low SpO₂ (PaO₂) (GRADE 2D); we suggest against using transpulmonary pressure as a routine basis in positive end-expiratory pressure settings (GRADE 2B); we suggest implementing extracorporeal membrane oxygenation for those with severe ARDS (GRADE 2B); we suggest against using high-dose steroids (GRADE 2C); and we recommend using low-dose steroids (GRADE 1B). The recommendations for pediatric patients with ARDS are as follows: we suggest against using non-invasive respiratory support (non-invasive positive pressure ventilation/high-flow nasal cannula oxygen therapy) (GRADE 2D); we suggest placing pediatric patients with moderate ARDS in the prone position (GRADE 2D); we suggest against routinely implementing NO inhalation therapy (GRADE 2C); and we suggest against implementing daily sedation interruption for pediatric patients with respiratory failure (GRADE 2D).

CONCLUSIONS

This article is a translated summary of the full version of the ARDS Clinical Practice Guideline 2021 published in Japanese (URL: https://www.jrs.or.jp/publication/jrs_guidelines/). The original text, which was written for Japanese healthcare professionals, may include different perspectives from healthcare professionals of other countries.

Electric Cell-Substrate Impedance Sensing (ECIS) as a Platform for Evaluating Barrier-Function Susceptibility and Damage from Pulmonary Atelectrauma

Biophysical insults that either reduce barrier function (COVID-19, smoke inhalation, aspiration, and inflammation) or increase mechanical stress (surfactant dysfunction) make the lung more susceptible to atelectrauma. We investigate the susceptibility and time-dependent disruption of barrier function associated with pulmonary atelectrauma of epithelial cells that occurs in acute respiratory distress syndrome (ARDS) and ventilator-induced lung injury (VILI). This in vitro study was performed using Electric Cell-substrate Impedance Sensing (ECIS) as a noninvasive evaluating technique for repetitive stress stimulus/response on monolayers of the human lung epithelial cell line NCI-H441. Atelectrauma was mimicked through recruitment/derecruitment (RD) of a semi-infinite air bubble to the fluid-occluded micro-channel. We show that a confluent monolayer with a high level of barrier function is nearly impervious to atelectrauma for hundreds of RD events. Nevertheless, barrier function is eventually diminished, and after a critical number of RD insults, the monolayer disintegrates exponentially. Confluent layers with lower initial barrier function are less resilient. These results indicate that the first line of defense from atelectrauma resides with intercellular binding. After disruption, the epithelial layer community protection is diminished and atelectrauma ensues. ECIS may provide a platform for identifying damaging stimuli, ventilation scenarios, or pharmaceuticals that can reduce susceptibility or enhance barrier-function recovery.

Examining lung mechanical strains as influenced by breathing volumes and rates using experimental digital image correlation

BACKGROUND

Mechanical ventilation is often employed to facilitate breathing in patients suffering from respiratory illnesses and disabilities. Despite the benefits, there are risks associated with ventilator-induced lung injuries and death, driving investigations for alternative ventilation techniques to improve mechanical ventilation, such as multi-oscillatory and high-frequency ventilation; however, few studies have evaluated fundamental lung mechanical local deformations under variable loading.

METHODS

Porcine whole lung samples were analyzed using a novel application of digital image correlation interfaced with an electromechanical ventilation system to associate the local behavior to the global volume and pressure loading in response to various inflation volumes and breathing rates. Strains, anisotropy, tissue compliance, and the evolutionary response of the inflating lung were analyzed.

RESULTS

Experiments demonstrated a direct and near one-to-one linear relationship between applied lung volumes and resulting local mean strain, and a nonlinear relationship between lung pressures and strains. As the applied air delivery volume was doubled, the tissue surface mean strains approximately increased from 20 to 40%, and average maximum strains measured 70-110%. The tissue strain anisotropic ratio ranged from 0.81 to 0.86 and decreased with greater inflation volumes. Local tissue compliance during the inflation cycle, associating evolutionary strains in response to inflation pressures, was also quantified.

CONCLUSION

Ventilation frequencies were not found to influence the local stretch response. Strain measures significantly increased and the anisotropic ratio decreased between the smallest and greatest tidal volumes. Tissue compliance did not exhibit a unifying trend. The insights provided by the real-time continuous measures, and the kinetics to kinematics pulmonary linkage established by this study offers valuable characterizations for computational models and establishes a framework for future studies to compare healthy and diseased lung mechanics to further consider alternatives for effective ventilation strategies.

Neutrophil-Derived IL-17 Promotes Ventilator-Induced Lung Injury via p38 MAPK/MCP-1 Pathway Activation

Ventilator-induced lung injury (VILI) is one of the most common complications of mechanical ventilation and can severely affect health. VILI appears to involve excessive inflammatory responses, but its pathogenesis has not yet been clarified. Since interleukin-17 (IL-17) plays a critical role in the immune system and the development of infectious and inflammatory diseases, we investigated here whether it plays a role in VILI. In a mouse model of VILI, mechanical ventilation with high tidal volume promoted the accumulation of lung neutrophils, leading to increased IL-17 levels in the lung, which in turn upregulated macrophage chemoattractant protein-1 via p38 mitogen-activated protein kinase. Depletion of neutrophils decreases the production IL-17 in mice and inhibition of IL-17 significantly reduced HTV-induced lung injury and inflammatory response. These results were confirmed in vitro using RAW264.7 macrophage cultures. Our results suggest that IL-17 plays a pro-inflammatory role in VILI and could serve as a new target for its treatment.

Ventilator-Associated Lung Injury

Ventilatory support, while life saving, can also cause or aggravate lung injury through several mechanisms which are encompassed within ventilator-associated lung injury (VALI). The important realizationin the acute respiratory distress syndrome that the “baby” lung resided in non-dependent areas led to the conceptualization of “lung rest” to reduce stress and strain to exposed alveolar units. We discuss concepts and mechanisms within VALI that ultimately induce maladaptive lung responses, as well as, current and future management strategies to detect and mitigate VALI at the bedside.

Individualized positive end-expiratory pressure titration on respiration and circulation in elderly patients undergoing spinal surgery in prone position under general anesthesia

OBJECTIVE

To investigate the effect of individualized positive end-expiratory pressure (PEEP) titration on intraoperative respiration and circulation in elderly patients undergoing spinal surgery in prone position under general anesthesia.

METHODS

We prospectively selected 80 elderly patients (39 males and 41 females) aged over 65 years old, at American Society of Anesthesiologists (ASA) grade II or III, who underwent elective prone spinal surgery under general anesthesia, for this study. These patients were randomly divided into titration group and control group, with 40 cases in each group. PEEP of the titration group was increased from 0 to 20 cmH₂O by steps of 2 cmH₂O. For the control group, PEEP was constantly at 5 cmH₂O and ventilation was maintained throughout the surgery. Dynamic pulmonary compliance (Cdyn) measurements were recorded when each PEEP level was kept for 1 min during titration, and individualized PEEP was determined by maximal Cdyn. MAP (mean arterial pressure), heart rate (HR), and CVP (Central venous pressure) were recorded at the set of prone position (T₀), PEEP ventilation for 10 min (T₁), 30 min (T₂), 60 min (T₃), end of surgery (T₄), and 20 min after extubation (T₅). Mean airway pressure (Pmean) and Cdyn were recorded from T₀ to T₄. Blood gas analysis was performed from T₀ to T₅ to calculate intrapulmonary shunt fraction (Qs/Qt) and OI (PaO₂/FiO₂). The rate of phenylephrine use during mechanical ventilation and the incidence of postoperative pulmonary complications were also recorded.

RESULTS

The individualized PEEP obtained by titration for 1 min in the titration group was (12.38±2.67) cmH₂O, which was significantly higher than the 5 cmH₂O in constant PEEP of the control group (P<0.05). There was no significant difference in MAP, HR, and CVP between the two groups at different time points, and no significant difference was noted in Pmean between the two groups from T₀ to T₄ (all P>0.05). From T₂ to T₄, Cdyn was significantly higher, and Qs/Qt was lower in the titration group than those in the control group (all P<0.05). From T₂ to T₅, the OI in the titration group was significantly higher than that in the control group (P<0.05). The rate of phenylephrine use was significantly higher in the titration group than that in the control group (10 patients (25%) vs. 3 patients (8%), P<0.05). The incidence of postoperative pulmonary complications in the titration group was significantly lower than that in the control group (2 cases (5%) vs. 8 cases (20%), P<0.05).

CONCLUSION

Compared with a constant PEEP of 5 cmH₂O, intraoperative individualized PEEP titration in elderly patients undergoing spinal surgery in prone position can improve oxygenation, reduce intrapulmonary shunt and postoperative pulmonary complications. (Chinese Clinical Trial Registry, registration number ChiCTR2000040722, https://www.chictr.org.cn).

Mechanobiology of Pulmonary Diseases: A Review of Engineering Tools to Understand Lung Mechanotransduction

Cells within the lung micro-environment are continuously subjected to dynamic mechanical stimuli which are converted into biochemical signaling events in a process known as mechanotransduction. In pulmonary diseases, the abrogated mechanical conditions modify the homeostatic signaling which influences cellular phenotype and disease progression. The use of in vitro models has significantly expanded our understanding of lung mechanotransduction mechanisms. However, our ability to match complex facets of the lung including three-dimensionality, multicellular interactions, and multiple simultaneous forces is limited and it has proven difficult to replicate and control these factors in vitro. The goal of this review is to (a) outline the anatomy of the pulmonary system and the mechanical stimuli that reside therein, (b) describe how disease impacts the mechanical micro-environment of the lung, and (c) summarize how existing in vitro models have contributed to our current understanding of pulmonary mechanotransduction. We also highlight critical needs in the pulmonary mechanotransduction field with an emphasis on next-generation devices that can simulate the complex mechanical and cellular environment of the lung. This review provides a comprehensive basis for understanding the current state of knowledge in pulmonary mechanotransduction and identifying the areas for future research.

The Elk1/MMP-9 axis regulates E-cadherin and occludin in ventilator-induced lung injury

Background

Ventilator-induced lung injury (VILI) is a common complication in the treatment of respiratory diseases with high morbidity and mortality. ETS-domain containing protein (Elk1) and Matrix metalloproteinase (MMP) 9 are involved in VILI, but the roles have not been fully elucidated. This study examined the mechanisms of the activation of MMP-9 and Elk1 regulating barrier function in VILI in vitro and in vivo.

Methods

For the in vitro study, Mouse lung epithelial cells (MLE-12) were pre-treated with Elk1 siRNA or MMP-9 siRNA for 48 h prior to cyclic stretch at 20% for 4 h. For the in vivo study, C57BL/6 mice were pre-treated with Elk1 siRNA or MMP-9 siRNA for 72 h prior to 4 h of mechanical ventilation. The expressions of Elk1, MMP-9, Tissue inhibitor of metalloproteinase 1 (TIMP-1), E-cadherin, and occludin were measured by Western blotting. The intracellular distribution of E-cadherin and occludin was shown by immunofluorescence. The degree of pulmonary edema and lung injury were evaluated by Hematoxylin–eosin (HE) staining, lung injury scores, Wet/Dry (W/D) weight ratio, total cell counts, and Evans blue dye.

Results

20% cyclic stretch and high tidal volume increases the expressions of Elk1, MMP-9, and TIMP-1, increases the ratio of MMP-9/TIMP-1, decreases the E-cadherin and occludin level. Elk1 siRNA or MMP-9 siRNA reverses the degradations of E-cadherin, occludin, and the ratio of MMP-9/TIMP-1 caused by cyclic stretch. Elk1 siRNA decreases the MMP-9 level with or not 20% cyclic stretch and high tidal volume.

Conclusions

The results demonstrate mechanical stretch damages the tight junctions and aggravates the permeability in VILI, Elk1 plays an important role in affecting the tight junctions and permeability by regulating the balance of MMP-9 and TIMP-1, thus indicating the therapeutic potential of Elk1 to treat VILI.

Calculation of Transpulmonary Pressure From Regional Ventilation Displayed by Electrical Impedance Tomography in Acute Respiratory Distress Syndrome

Transpulmonary driving pressure (DP_L) corresponds to the cyclical stress imposed on the lung parenchyma during tidal breathing and, therefore, can be used to assess the risk of ventilator-induced lung injury (VILI). Its measurement at the bedside requires the use of esophageal pressure (Peso), which is sometimes technically challenging. Recently, it has been demonstrated how in an animal model of ARDS, the transpulmonary pressure (P_L) measured with Peso calculated with the absolute values method (P_L = Paw—Peso) is equivalent to the transpulmonary pressure directly measured using pleural sensors in the central-dependent part of the lung. We hypothesized that, since the P_L derived from Peso reflects the regional behavior of the lung, it could exist a relationship between regional parameters measured by electrical impedance tomography (EIT) and driving P_L (DP_L). Moreover, we explored if, by integrating airways pressure data and EIT data, it could be possible to estimate non-invasively DP_L and consequently lung elastance (EL) and elastance-derived inspiratory P_L (PI). We analyzed 59 measurements from 20 patients with ARDS. There was a significant intra-patient correlation between EIT derived regional compliance in regions of interest (ROI1) (r = 0.5, p = 0.001), ROI2 (r = −0.68, p < 0.001), and ROI3 (r = −0.4, p = 0.002), and DP_L. A multiple linear regression successfully predicted DP_L based on respiratory system elastance (Ers), ideal body weight (IBW), roi1%, roi2%, and roi3% (R² = 0.84, p < 0.001). The corresponding Bland-Altmann analysis showed a bias of −1.4e-007 cmH₂O and limits of agreement (LoA) of −2.4–2.4 cmH₂O. EL and PI calculated using EIT showed good agreement (R² = 0.89, p < 0.001 and R² = 0.75, p < 0.001) with the esophageal derived correspondent variables. In conclusion, DP_L has a good correlation with EIT-derived parameters in the central lung. DP_L, PI, and EL can be estimated with good accuracy non-invasively combining information coming from EIT and airway pressure.

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.

A Peptide Inhibitor of Peroxiredoxin 6 Phospholipase A2 Activity Significantly Protects against Lung Injury in a Mouse Model of Ventilator Induced Lung Injury (VILI)

Ventilator induced lung injury (VILI) is a lung injury syndrome associated with mechanical ventilation, most frequently for treatment of Acute Lung Injury (ALI), and generally secondary to the use of greater than physiologic tidal volumes. To reproduce this syndrome experimentally, C57Bl/6 mice were intubated and ventilated with low (4 mL/Kg body weight) or high (12 mL/Kg) tidal volume for 6 h. Lung parameters with low volume ventilation were unchanged from non-ventilated (control) mice. High tidal volume ventilation resulted in marked lung injury with increased neutrophils in the bronchoalveolar lavage fluid (BALf) indicating lung inflammation, increase in both protein in BALf and lung dry/wet weight indicating lung edema, increased lung thiobarbituric acid reactive substances (TBARS) and 8-isoprostanes indicating lung lipid peroxidation, and increased lung protein carbonyls indicating protein oxidation. Either intratracheal or intravenous pretreatment of mice with a 9 amino acid peptide called peroxiredoxin 6 inhibitor peptide-2 (PIP-2) significantly reduced all parameters of lung injury by ~50–80%. PIP-2 inhibits NADPH oxidase type 2 (NOX2) activation. We propose that PIP-2 does not affect the mechanically induced lung damage component of VILI but does significantly reduce the secondary inflammatory component.

Airway Pressure Release Ventilation Mode Improves Circulatory and Respiratory Function in Patients After Cardiopulmonary Bypass, a Randomized Trial

Importance

Postoperative pulmonary complications and cardiovascular complications are major causes of morbidity, mortality, and resource utilization in cardiac surgery patients.

Objectives

To investigate the effects of airway pressure release ventilation (APRV) on respiration and hemodynamics in post cardiac surgery patients.

Main Outcomes and Measures

A single-center randomized control trial was performed. In total, 138 patients undergoing cardiopulmonary bypass were prospectively screened. Ultimately 39 patients met the inclusion criteria and were randomized into two groups: 19 patients were managed with pressure control ventilation (PCV) and 20 patients were managed with APRV. Respiratory mechanics after 4 h, hemodynamics within the first day, and Chest radiograph score (CRS) and blood gasses within the first three days were recorded and compared.

Results

A higher cardiac index (3.1 ± 0.7 vs. 2.8 ± 0.8 L⋅min^–1⋅m²; p < 0.05), and shock volume index (35.4 ± 9.2 vs. 33.1 ± 9.7 ml m^–2; p < 0.05) were also observed in the APRV group after 4 h as well as within the first day (p < 0.05). Compared to the PCV group, the PaO2/FiO₂ was significantly higher after 4 h in patients of APRV group (340 ± 97 vs. 301 ± 82, p < 0.05) and within the first three days (p < 0.05) in the APRV group. CRS revealed less overall lung injury in the APRV group (p < 0.001). The duration of mechanical ventilation and ICU length of stay were not significantly (p = 0.248 and 0.424, respectively).

Conclusions and Relevance

Compared to PCV, APRV may be associated with increased cardiac output improved oxygenation, and decreased lung injury in postoperative cardiac surgery patients.

Mining the key genes for ventilator-induced lung injury using co-expression network analysis

Mechanical ventilation is extensively adopted in general anesthesia and respiratory failure management, but it can also induce ventilator-induced lung injury (VILI). Therefore, it is of great urgency to explore the mechanisms involved in the VILI pathogenesis, which might contribute to its future prevention and treatment. Four microarray datasets from the GEO database were selected in our investigation, and were subjected to the Weighted Gene Co-Expression Network Analysis (WGCNA) to identify the VILI-correlated gene modules. The limma package in R software was used to identify the differentially expressed genes (DEGs) between the VILI and control groups. WGCNA was constructed by merging the GSE9314, GSE9368, GSE11434 and GSE11662 datasets. A total of 49 co-expression network modules were determined as associated with VILI. The intersected genes between hub genes screened from DEGs for VILI and those identified using WGCNA were as follows: Tlr2, Hmox1, Serpine1, Mmp9, Il6, Il1b, Ptgs2, Fos and Atf3, which were determined to be key genes for VILI. Those key genes were validated by GSE86229 and quantitative PCR (qPCR) experiment to have significantly statistical difference in their expression between the VILI and control groups. In a nutshell, nine key genes with expression differences in VILI were screened by WGCNA by integrating multiple datasets.

Assessment of Electrical Impedance Tomography to Set Optimal Positive End-Expiratory Pressure for Venoarterial Extracorporeal Membrane Oxygenation-Treated Patients

OBJECTIVES

Patients on venoarterial extracorporeal membrane oxygenation have many risk factors for pulmonary complications in addition to their heart failure. Optimal positive end-expiratory pressure is unknown in these patients. The aim was to evaluate the ability of electrical impedance tomography to help the physician to select the optimal positive end-expiratory pressure in venoarterial extracorporeal membrane oxygenation treated and mechanically ventilated patients during a positive end-expiratory pressure trial.

DESIGN

Observational prospective monocentric.

SETTING

University hospital.

PATIENTS

Patients (n = 23) older than 18 years old, on mechanical ventilation and venoarterial extracorporeal membrane oxygenation.

INTERVENTIONS

A decreasing positive end-expiratory pressure trial (20-5 cm H2O) in increments of 5 cm H2O was performed and monitored by a collection of clinical parameters, ventilatory and ultrasonographic (cardiac and pulmonary) to define an optimal positive end-expiratory pressure according to respiratory criteria (optimal positive end-expiratory pressure selected by physician with respiratory parameters), and then adjusted according to hemodynamic and cardiac tolerances (optimal positive end-expiratory pressure selected by physician with respiratory, hemodynamic, and echocardiographic parameters). At the same time, electrical impedance tomography data (regional distribution of ventilation, compliance, and overdistension collapse) were recorded and analyzed retrospectively to define the optimal positive end-expiratory pressure.

MEASUREMENTS AND MAIN RESULTS

The median of this optimal positive end-expiratory pressure was 10 cm H2O in our population. Electrical impedance tomography showed that increasing positive end-expiratory pressure promoted overdistention of ventral lung, maximum at positive end-expiratory pressure 20 cm H20 (34% [interquartile range, 24.5-40]). Decreasing positive end-expiratory pressure resulted in collapse of dorsal lung (29% [interquartile range, 21-45.8]). The optimal positive end-expiratory pressure selected by physician with respiratory parameters was not different from the positive end-expiratory pressure chosen by the electrical impedance tomography. However, there is a negative impact of a high level of intrathoracic pressure on hemodynamic and cardiac tolerances.

CONCLUSIONS

Our results support that electrical impedance tomography appears predictive to define optimal positive end-expiratory pressure on venoarterial extracorporeal membrane oxygenation, aided by echocardiography to optimize hemodynamic assessment and management.

Comparing the Effects of Tidal Volume, Driving Pressure, and Mechanical Power on Mortality in Trials of Lung-Protective Mechanical Ventilation

BACKGROUND

The unifying goal of lung-protective ventilation strategies in ARDS is to minimize the strain and stress applied by mechanical ventilation to the lung to reduce ventilator-induced lung injury (VILI). The relative contributions of the magnitude and frequency of mechanical stress and the end-expiratory pressure to the development of VILI is unknown. Consequently, it is uncertain whether the risk of VILI is best quantified in terms of tidal volume (V_T), driving pressure (ΔP), or mechanical power.

METHODS

The correlation between differences in V_T, ΔP, and mechanical power and the magnitude of mortality benefit in trials of lung-protective ventilation strategies in adult subjects with ARDS was assessed by meta-regression. Modified mechanical power was computed including PEEP (Power_elastic), excluding PEEP (Power_dynamic), and using ΔP (Power_driving). The primary analysis incorporated all included trials. A secondary subgroup analysis was restricted to trials of lower versus higher PEEP strategies.

RESULTS

We included 9 trials involving 4,731 subjects in the analysis. Odds ratios for moderation derived from meta-regression showed that variations in V_T, ΔP, and Power_dynamic were associated with increased mortality with odds ratios of 1.24 (95% CI 1.03-1.49), 1.31 (95% CI 1.03-1.66), and 1.37 (95% CI 1.05-1.78), respectively. In trials comparing higher versus lower PEEP strategies, Power_elastic was increased in the higher PEEP arm (24 ± 1.7 vs 20 ± 1.5 J/min, respectively), whereas the other parameters were not affected on average by a higher PEEP ventilation strategy.

CONCLUSIONS

In trials of lung-protective ventilation strategies, V_T, ΔP, Power_elastic, Power_dynamic, and Power_driving exhibited similar moderation of treatment effect on mortality. In this study, modified mechanical power did not add important information on the risk of death from VILI in comparison to V_T or ΔP.

PEEP in thoracic anesthesia: pros and cons

Protective ventilation includes a strategy with low tidal volume, Plateau pressure, driving pressure, positive end-expiratory pressure (PEEP), and recruitment maneuvers on the ventilated lung. The rationale for the application of PEEP during one-lung ventilation (OLV) is that PEEP may contribute to minimize atelectrauma, preventing airway closure and alveolar collapse and improving the ventilation/perfusion to the ventilated lung. However, in case of high partial pressure of oxygen the application of PEEP may cause increased pulmonary vascular resistance, thus diverting blood flow to the non-ventilated lung, and worsening ventilation/perfusion. Further, PEEP may be associated with higher risk of hemodynamic impairment, increased need for fluids and vasoactive drugs. Positive effects on outcome have been reported by titrating PEEP according to driving pressure, targeted to obtain the optimum respiratory as well as pulmonary system compliance. This may vary according to the method employed for titration and should be performed individually for each patient. In summary, the potential for harm combined with the lack of evidence for improved outcome suggest that PEEP must be judiciously used during OLV even when titrated to a safe target, and only as much as necessary to maintain an appropriate gas exchange under low protective tidal volumes and driving pressures.

Individualized flow-controlled ventilation compared to best clinical practice pressure-controlled ventilation: a prospective randomized porcine study

BACKGROUND

Flow-controlled ventilation is a novel ventilation method which allows to individualize ventilation according to dynamic lung mechanic limits based on direct tracheal pressure measurement at a stable constant gas flow during inspiration and expiration. The aim of this porcine study was to compare individualized flow-controlled ventilation (FCV) and current guideline-conform pressure-controlled ventilation (PCV) in long-term ventilation.

METHODS

Anesthetized pigs were ventilated with either FCV or PCV over a period of 10 h with a fixed FiO₂ of 0.3. FCV settings were individualized by compliance-guided positive end-expiratory pressure (PEEP) and peak pressure (P_peak) titration. Flow was adjusted to maintain normocapnia and the inspiration to expiration ratio (I:E ratio) was set at 1:1. PCV was performed with a PEEP of 5 cm H₂O and P_peak was set to achieve a tidal volume (V_T) of 7 ml/kg. The respiratory rate was adjusted to maintain normocapnia and the I:E ratio was set at 1:1.5. Repeated measurements during observation period were assessed by linear mixed-effects model.

RESULTS

In FCV (n = 6), respiratory minute volume was significantly reduced (6.0 vs 12.7, MD - 6.8 (- 8.2 to - 5.4) l/min; p < 0.001) as compared to PCV (n = 6). Oxygenation was improved in the FCV group (paO₂ 119.8 vs 96.6, MD 23.2 (9.0 to 37.5) Torr; 15.97 vs 12.87, MD 3.10 (1.19 to 5.00) kPa; p = 0.010) and CO₂ removal was more efficient (paCO₂ 40.1 vs 44.9, MD - 4.7 (- 7.4 to - 2.0) Torr; 5.35 vs 5.98, MD - 0.63 (- 0.99 to - 0.27) kPa; p = 0.006). P_peak and driving pressure were comparable in both groups, whereas PEEP was significantly lower in FCV (p = 0.002). Computed tomography revealed a significant reduction in non-aerated lung tissue in individualized FCV (p = 0.026) and no significant difference in overdistended lung tissue, although a significantly higher V_T was applied (8.2 vs 7.6, MD 0.7 (0.2 to 1.2) ml/kg; p = 0.025).

CONCLUSION

Our long-term ventilation study demonstrates the applicability of a compliance-guided individualization of FCV settings, which resulted in significantly improved gas exchange and lung tissue aeration without signs of overinflation as compared to best clinical practice PCV.

The POOR Get POORer: A Hypothesis for the Pathogenesis of Ventilator-induced Lung Injury

Protective ventilation strategies for the injured lung currently revolve around the use of low Vt, ostensibly to avoid volutrauma, together with positive end-expiratory pressure to increase the fraction of open lung and reduce atelectrauma. Protective ventilation is currently applied in a one-size-fits-all manner, and although this practical approach has reduced acute respiratory distress syndrome deaths, mortality is still high and improvements are at a standstill. Furthermore, how to minimize ventilator-induced lung injury (VILI) for any given lung remains controversial and poorly understood. Here we present a hypothesis of VILI pathogenesis that potentially serves as a basis upon which minimally injurious ventilation strategies might be developed. This hypothesis is based on evidence demonstrating that VILI begins in isolated lung regions manifesting a Permeability-Originated Obstruction Response (POOR) in which alveolar leak leads to surfactant dysfunction and increases local tissue stresses. VILI progresses topographically outward from these regions in a POOR-get-POORer fashion unless steps are taken to interrupt it. We propose that interrupting the POOR-get-POORer progression of lung injury relies on two principles: 1) open the lung to minimize the presence of heterogeneity-induced stress concentrators that are focused around the regions of atelectasis, and 2) ventilate in a patient-dependent manner that minimizes the number of lung units that close during each expiration so that they are not forced to rerecruit during the subsequent inspiration. These principles appear to be borne out in both patient and animal studies in which expiration is terminated before derecruitment of lung units has enough time to occur.

Lung heterogeneity and deadspace volume in acute respiratory distress syndrome animals using the inspired sinewave test

The acute respiratory distress syndrome is associated with a high rate of morbidity and mortality, as patients undergoing mechanical ventilation are at risk of ventilator-induced lung injuries.

OBJECTIVE

To measure the lung heterogeneity and deadspace volume to find safer ventilator strategies. Then, the ventilator settings could offer homogeneous ventilation and theoretically equalise and reduce tidal strain/stress in the lung parenchyma.

APPROACH

The Inspired Sinewave Test (IST) is a non-invasive lung measurement tool, which does not require patients' cooperation. The IST can measure the effective lung volume, pulmonary blood flow and deadspace volume. We developed a computational simulation of the cardiopulmonary system to allow lung heterogeneity to be quantified using data solely derived from the IST. Then, the method to quantify lung heterogeneity using two IST tracer gas frequencies (180s and 60s) was introduced and experimented in the simulation lungs and in animal models. Thirteen anaesthetised pigs were studied with the IST, both before and after experimental lung injury (saline-lavage ARDS model). The deadspace volume is compared between IST and the SF_{6} Washout method.

RESULTS

The IST could measure the lung heterogeneity using two frequencies tracer gases. Furthermore, the value of IST ventilation heterogeneity in ARDS lungs were higher than in control lungs at PEEP 10cmH_{2}O (AuC=0.85, p<0.001). Deadspace volume values measured by the IST has a strong relationship with the measured values of the SF_{6} (9mL bias and limits of agreement from -79mL to 57mL in control animals).

SIGNIFICANCE

the potential impact of the IST technique in the identification of ventilation and perfusion heterogeneity during ventilator support.

Mechanical stretch and LPS affect the proliferation, extracellular matrix remodeling and viscoelasticity of lung fibroblasts

The present study aimed to investigate the effects of mechanical stretch and lipopolysaccharides (LPS) on the expression of transforming growth factor-β1 (TGF-β1) and collagen and viscoelasticity in human embryonic MRC-5 lung fibroblasts cultured in vitro and to assess the mechanisms of ARDS-associated ventilator-induced lung injury using an in vitro model. Human embryonic MRC-5 lung fibroblasts were treated with different concentrations of LPS to establish an acute respiratory distress syndrome (ARDS) cell injury model, followed by further culture under different mechanical stretch amplitudes using the Flexcell system to establish a cellular mechanical damage model. The proliferation of MRC-5 cells and the protein and gene expression levels of TGF-β1 and collagen were detected by flow cytometry, ELISA and reverse transcription-quantitative PCR, respectively. As the concentration of LPS increased, the proliferation activity of MRC-5 cells gradually decreased. Low concentrations of LPS led to upregulation of the secretion levels of TGF-β1 and collagen I and the expression of their mRNA, TGF-β1 mRNA and collagen type 1, α1. Conversely, high concentrations of LPS reduced TGF-β1 and collagen I levels and their gene expression. Mechanical stimulation with a stretch of 5% increased the cell proliferation activity; however, it had no significant effect on the expression levels of TGF-β1 and collagen. Mechanical stimulation with a stretching force of 10% inhibited the cell proliferation but increased the expression levels of TGF-β1 and collagen I. A higher mechanical stimulation (15 and 20%) had a significantly greater effect. Mechanical stretch and LPS stimulation led to changes in the structure and viscoelastic behavior of human embryonic MRC-5 lung fibroblasts. In terms of cell function, mechanical stretch may cause an increase in the expression of TGF-β1 in MRC-5 cells, in turn affecting the transcription and translation of collagen genes. This present study provides provides cell-level evidence for understand the mechanisms of action behind the ARDS ventilator-induced lung injury and lung structural remodeling.

Personalized Positive End-Expiratory Pressure in Acute Respiratory Distress Syndrome: Comparison Between Optimal Distribution of Regional Ventilation and Positive Transpulmonary Pressure

OBJECTIVES

Different techniques exist to select personalized positive end-expiratory pressure in patients affected by the acute respiratory distress syndrome. The positive end-expiratory transpulmonary pressure strategy aims to counteract dorsal lung collapse, whereas electrical impedance tomography could guide positive end-expiratory pressure selection based on optimal homogeneity of ventilation distribution. We compared the physiologic effects of positive end-expiratory pressure guided by electrical impedance tomography versus transpulmonary pressure in patients affected by acute respiratory distress syndrome.

DESIGN

Cross-over prospective physiologic study.

SETTING

Two academic ICUs.

PATIENTS

Twenty ICU patients affected by acute respiratory distress syndrome undergoing mechanical ventilation.

INTERVENTION

Patients monitored by an esophageal catheter and a 32-electrode electrical impedance tomography monitor underwent two positive end-expiratory pressure titration trials by randomized cross-over design to find the level of positive end-expiratory pressure associated with: 1) positive end-expiratory transpulmonary pressure (PEEPPL) and 2) proportion of poorly or nonventilated lung units (Silent Spaces) less than or equal to 15% (PEEPEIT). Each positive end-expiratory pressure level was maintained for 20 minutes, and afterward, lung mechanics, gas exchange, and electrical impedance tomography data were collected.

MEASUREMENTS AND MAIN RESULTS

PEEPEIT and PEEPPL differed in all patients, and there was no correlation between the levels identified by the two methods (Rs = 0.25; p = 0.29). PEEPEIT determined a more homogeneous distribution of ventilation with a lower percentage of dependent Silent Spaces (p = 0.02), whereas PEEPPL was characterized by lower airway-but not transpulmonary-driving pressure (p = 0.04). PEEPEIT was significantly higher than PEEPPL in subjects with extrapulmonary acute respiratory distress syndrome (p = 0.006), whereas the opposite was true for pulmonary acute respiratory distress syndrome (p = 0.03).

CONCLUSIONS

Personalized positive end-expiratory pressure levels selected by electrical impedance tomography- and transpulmonary pressure-based methods are not correlated at the individual patient level. PEEPPL is associated with lower dynamic stress, whereas PEEPEIT may help to optimize lung recruitment and homogeneity of ventilation. The underlying etiology of acute respiratory distress syndrome could deeply influence results from each method.

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).

Individualized lung protective ventilation vs. conventional ventilation during general anesthesia in laparoscopic total hysterectomy

Laparoscopic total hysterectomy is performed by carbon dioxide insufflation, Trendelenburg position and mechanical ventilation of patients under general anesthesia. However, this may induce pulmonary atelectasis and/or hyperdistention of the lungs. Multiple studies have indicated that mechanical ventilation with the use of low tidal volumes, moderate positive end-expiratory pressure (PEEP) and regular alveolar recruitment maneuvers may improve post-operative outcomes. However, the benefits of an individualized level of PEEP have not been clearly established. In the present study, it was hypothesized that a moderate fixed PEEP may not suit all patients and an individually-titrated PEEP during anesthesia may improve the peri-operative pulmonary oxygenation function. The aim of the present study was to compare the pulmonary oxygenation function and post-operative pulmonary complications (PPCs) in patients receiving individualized lung-protective mechanical ventilation (LPV) vs. conventional ventilation (CV) during laparoscopic total hysterectomy. The present study was a randomized double-blinded clinical trial on 87 patients who were randomly divided to receive CV or protective ventilation (PV). An optimal individualized PEEP value was determined using a static pulmonary compliance-directed PEEP titration procedure. Pulmonary oxygenation function, serum inflammatory factors, including interleukin-8 and Clara cell protein 16, the incidence of PPCs and the post-operative length of stay were also determined. Patients in the PV group exhibited improved pulmonary oxygenation function during and after the operation. The total percentage of PPCs during the first 7 days after surgery was significantly lower in the PV group compared with those in the CV group. In conclusion, as compared to CV, intra-operative individualized LPV significantly improved pulmonary oxygenation function and reduced the incidence of PPCs during the first 7 days after laparoscopic total hysterectomy (Clinical trial registration no. ChiCTR1900027738).

Bioinformatic identification of hub genes and key pathways in neutrophils of patients with acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized as a neutrophil-dominant disorder without effective pharmacological interventions. Knowledge of neutrophils in ARDS patients at the transcriptome level is still limited. We aimed to identify the hub genes and key pathways in neutrophils of patients with ARDS. The transcriptional profiles of neutrophils from ARDS patients and healthy volunteers were obtained from the GSE76293 dataset. The differentially expressed genes (DEGs) between ARDS and healthy samples were screened using the limma R package. Subsequently, functional and pathway enrichment analyses were performed based on the database for annotation, visualization, and integrated discovery (DAVID). The construction of a protein-protein interaction network was carried out using the search tool for the retrieval of interacting genes (STRING) database and the network was visualized by Cytoscape software. The Cytoscape plugins cytoHubba and MCODE were used to identify hub genes and significant modules. Finally, 136 upregulated genes and 95 downregulated genes were identified. Gene ontology analyses revealed MHC class II plays a major role in functional annotations. SLC11A1, ARG1, CHI3L1, HP, LCN2, and MMP8 were identified as hub genes, and they were all involved in the neutrophil degranulation pathway. The MAPK and neutrophil degranulation pathways in neutrophils were considered as key pathways in the pathogenesis of ARDS. This study improves our understanding of the biological characteristics of neutrophils and the mechanisms underlying ARDS, and key pathways and hub genes identified in this work can serve as targets for novel ARDS treatment strategies.

Driving Pressure during Thoracic Surgery: A Randomized Clinical Trial

WHAT WE ALREADY KNOW ABOUT THIS TOPIC

Driving pressure (plateau minus end-expiratory airway pressure) is a target in patients with acute respiratory distress syndrome, and is proposed as a target during general anesthesia for patients with normal lungs. It has not been reported for thoracic anesthesia where isolated, inflated lungs may be especially at risk.

WHAT THIS ARTICLE TELLS US THAT IS NEW

In a double-blinded, randomized trial (292 patients), minimized driving pressure compared with standard protective ventilation was associated with less postoperative pneumonia or acute respiratory distress syndrome.

BACKGROUND

Recently, several retrospective studies have suggested that pulmonary complication is related with driving pressure more than any other ventilatory parameter. Thus, the authors compared driving pressure-guided ventilation with conventional protective ventilation in thoracic surgery, where lung protection is of the utmost importance. The authors hypothesized that driving pressure-guided ventilation decreases postoperative pulmonary complications more than conventional protective ventilation.

METHODS

In this double-blind, randomized, controlled study, 292 patients scheduled for elective thoracic surgery were included in the analysis. The protective ventilation group (n = 147) received conventional protective ventilation during one-lung ventilation: tidal volume 6 ml/kg of ideal body weight, positive end-expiratory pressure (PEEP) 5 cm H2O, and recruitment maneuver. The driving pressure group (n = 145) received the same tidal volume and recruitment, but with individualized PEEP which produces the lowest driving pressure (plateau pressure-PEEP) during one-lung ventilation. The primary outcome was postoperative pulmonary complications based on the Melbourne Group Scale (at least 4) until postoperative day 3.

RESULTS

Melbourne Group Scale of at least 4 occurred in 8 of 145 patients (5.5%) in the driving pressure group, as compared with 18 of 147 (12.2%) in the protective ventilation group (P = 0.047, odds ratio 0.42; 95% CI, 0.18 to 0.99). The number of patients who developed pneumonia or acute respiratory distress syndrome was less in the driving pressure group than in the protective ventilation group (10/145 [6.9%] vs. 22/147 [15.0%], P = 0.028, odds ratio 0.42; 95% CI, 0.19 to 0.92).

CONCLUSIONS

Application of driving pressure-guided ventilation during one-lung ventilation was associated with a lower incidence of postoperative pulmonary complications compared with conventional protective ventilation in thoracic surgery.

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.

Airway Pressure Release Ventilation: A Review of the Evidence, Theoretical Benefits, and Alternative Titration Strategies

Objective:

To review the theoretical benefits of airway pressure release ventilation (APRV), summarize the evidence for its use in clinical practice, and discuss different titration strategies.

Data Source:

Published randomized controlled trials in humans, observational human studies, animal studies, review articles, ventilator textbooks, and editorials.

Data Summary:

Airway pressure release ventilation optimizes alveolar recruitment, reduces airway pressures, allows for spontaneous breathing, and offers many hemodynamic benefits. Despite these physiologic advantages, there are inconsistent data to support the use of APRV over other modes of ventilation. There is considerable heterogeneity in the application of APRV among providers and a shortage of information describing initiation and titration strategies. To date, no direct comparison studies of APRV strategies have been performed. This review describes 2 common management approaches that bedside providers can use to optimally tailor APRV to their patients.

Conclusion:

Airway pressure release ventilation remains a form of mechanical ventilation primarily used for refractory hypoxemia. It offers unique physiological advantages over other ventilatory modes, and providers must be familiar with different titration methods. Given its inconsistent outcome data and heterogeneous use in practice, future trials should directly compare APRV strategies to determine the optimal management approach.