Injurious ventilatory strategies increase cytokines and c-fos m-RNA expression in an isolated rat lung model

Lung injury does not aggravate mechanical ventilation-induced early cerebral inflammation or apoptosis in an animal model

Introduction

The acute respiratory distress syndrome is not only associated with a high mortality, but also goes along with cognitive impairment in survivors. The cause for this cognitive impairment is still not clear. One possible mechanism could be cerebral inflammation as result of a “lung-brain-crosstalk”. Even mechanical ventilation itself can induce cerebral inflammation. We hypothesized, that an acute lung injury aggravates the cerebral inflammation induced by mechanical ventilation itself and leads to neuronal damage.

Methods

After approval of the institutional and state animal care committee 20 pigs were randomized to one of three groups: lung injury by central venous injection of oleic acid (n = 8), lung injury by bronchoalveolar lavage in combination with one hour of injurious ventilation (n = 8) or control (n = 6). Brain tissue of four native animals from a different study served as native group. For six hours all animals were ventilated with a tidal volume of 7 ml kg^-1 and a scheme for positive end-expiratory pressure and inspired oxygen fraction, which was adapted from the ARDS network tables. Afterwards the animals were killed and the brains were harvested for histological (number of neurons and microglia) and molecular biologic (TNFalpha, IL-1beta, and IL-6) examinations.

Results

There was no difference in the number of neurons or microglia cells between the groups. TNFalpha was significantly higher in all groups compared to native (p < 0.05), IL-6 was only increased in the lavage group compared to native (p < 0.05), IL-1beta showed no difference between the groups.

Discussion

With our data we can confirm earlier results, that mechanical ventilation itself seems to trigger cerebral inflammation. This is not aggravated by acute lung injury, at least not within the first 6 hours after onset. Nevertheless, it seems too early to dismiss the idea of lung-injury induced cerebral inflammation, as 6 hours might be just not enough time to see any profound effect.

First tidal volume greater than 8 mL/kg is associated with increased mortality in complicated influenza infection with acute respiratory distress syndrome

BACKGROUNDS

Severe influenza infection causes substantial morbidity and mortality worldwide and remains an important threat to global health. This study addressed factors related to treatment outcomes in subjects of complicated influenza infection with acute respiratory distress syndrome (ARDS) during the Taiwan epidemic in the Spring of 2016.

METHODS

This is a retrospective study conducted by Taiwan Severe Influenza Research Consortium (TSIRC), including eight tertiary referral medical centers. Patients with virology-proven influenza infection admitted to intensive care unit (ICU) between January and March 2016 were included for analysis.

RESULTS

We identified 263 patients with complicated influenza infection who fulfilled ARDS criteria; the mean age was 59.8 ± 14.6 (years), and 66.1% (166/263) were male. Type A influenza (77.9%, 205/263) virus was the main pathogen during this epidemic. The 30-day mortality rate was 23.2% (61/263). The mean tidal volume (V_T) in the first three days after intubation was greater than 8 mL/kg of predicted body weight (PBW). Patients whose first measured V_T was >8 mL/kg PBW had an increased 30-day mortality (p = 0.04, log-rank test). In a multivariate Cox proportional hazard regression model, an increase of 1 mL/kg PBW of first V_T was associated with 26.1% increase in 30-day mortality (adjusted hazard ratio 1.261, 95% confidence interval [CI] 1.072-1.484, p < 0.01).

CONCLUSION

First tidal volume, shortly after intubation, greater than 8 mL/kg PBW is an independent risk factor for mortality in complicated influenza infection with ARDS. Timely recognition of ARDS with strict adherence to protective ventilation strategy of lowering V_T may be important in reducing mortality.

High-Frequency Oscillation for Adult Patients with Acute Respiratory Distress Syndrome. A Systematic Review and Meta-Analysis

RATIONALE

By minimizing tidal lung strain and maintaining alveolar recruitment, high-frequency oscillatory ventilation (HFOV) may protect against ventilator-induced lung injury.

OBJECTIVES

To summarize the current evidence in support of the use of HFOV in adult patients with acute respiratory distress syndrome.

METHODS

We conducted a systematic review and meta-analysis of randomized trials comparing mortality rates with the use of HFOV versus conventional mechanical ventilation for adult patients with acute respiratory distress syndrome. Eligible trials were identified from previously published systematic reviews and an updated literature search. Data on 28-day mortality, oxygenation, adverse events, and use of rescue therapies were collected; effects were pooled using random effects models weighted by inverse variance. Strength of evidence was assessed using Grading of Recommendations Assessment, Development, and Evaluation methodology.

RESULTS

Six trials were eligible for inclusion (total n = 1,715 patients). Four trials mandated lung-protective ventilation in the control group and one trial applied a higher positive end-expiratory pressure (PEEP) ventilation strategy in the control group. None of the trials were judged to be at high risk of bias, though all were unblinded. In trials that did not systematically employ any cointerventions with HFOV and that targeted low tidal volumes in the patients randomized to conventional ventilation (primary analysis), HFOV had no significant effect on mortality (three trials; risk ratio [RR], 1.14; 95% confidence interval [CI], 0.88 to 1.48; evidence grade = high). Pooled analysis of all six trials also did not suggest a significant mortality reduction (RR, 0.94; 95% CI, 0.71 to 1.24; evidence grade = low). The single trial that employed a conventional ventilation strategy with both lower tidal volumes and higher PEEP as control reported higher mortality in patients receiving HFOV (RR, 1.41; 95% CI, 1.12 to 1.79). HFOV was not associated with improved oxygenation after 24 hours (five trials; mean increase of 10 mm Hg; 95% CI, -16 to 37 mm Hg). Rates of barotrauma were not different between HFOV and conventional ventilation, although significant benefit or harm could not be excluded (RR, 1.15; 95% CI, 0.61 to 2.17).

CONCLUSIONS

Published randomized trials suggest that HFOV is not associated with a mortality benefit, and may even be harmful in comparison to ventilation with low tidal volumes and higher levels of PEEP.

LL202 protects against dextran sulfate sodium-induced experimental colitis in mice by inhibiting MAPK/AP-1 signaling

LL202, a newly-synthesized flavonoid derivative, has been reported to inhibit inflammatory-induced angiogenesis. However, the exact role of LL202 in inflammation along with its mechanism has not been explored. In this study, we investigated the anti-inflammatory effect of LL202 on intestinal inflammation by establishing dextran sulfate sodium (DSS)-induced experimental colitis. LL202 attenuated DSS-induced body weight loss, colon length shortening and colonic pathological damage. The inflammatory cells infiltration, myeloperoxidase (MPO) and inducible nitric oxide synthase (iNOS) activities were decreased by LL202 in a dose-dependent manner. LL202 reduced the production of pro-inflammatory cytokines in serum and colon of DSS-induced mice as well. Mechanically, LL202 could decrease the expression and nuclear translation of AP-1 to protect against DSS-induced colitis. In lipopolysaccharide (LPS)-induced THP-1 cells, LL202 markedly decreased the secretion, mRNA level and protein expression of IL-1β, IL-6 and TNF-α via inhibiting ERK/JNK/p38 MAPK pathways and the nuclear translocation of AP-1. Furthermore, these findings were confirmed in LPS-induced bone marrow derived macrophages (BMDM). In conclusion, our study demonstrated that LL202 could exert its anti-inflammatory effect via inhibiting MAPK/AP-1 signaling, which suggested that LL202 might be a potential effective drug for the treatment of inflammatory bowel diseases.

Short-term one-lung ventilation does not influence local inflammatory cytokine response after lung resection

BACKGROUND

One-lung ventilation (OLV) is a ventilation procedure used for pulmonary resection which may results in lung injury. The aim of this study was to evaluate the local inflammatory cytokine response from the dependent lung after OLV and its correlation to VT. The secondary aim was to evaluate the clinical outcome of each patient.

METHODS

Twenty-eight consecutive patients were enrolled. Ventilation was delivered in volume-controlled mode with a VT based on predicted body weight (PBW). 5 cmH2O positive end-expiratory pressure (PEEP) and FiO2 0.5 were applied. Bronchoalveolar lavage (BAL) was performed in the dependent lung before and after OLV. The levels of pro-inflammatory interleukins (IL-1α, IL-1β, IL-6, IL-8), tumor necrosis factor alpha (TNFα), vascular endothelial growth factor (VEGF), endothelial growth factor (EGF), monocyte chemoattractant protein-1 (MCP-1) and anti-inflammatory cytokines, such as interleukins (IL-2, IL-4, IL-10) and interferon (IFN-γ), were evaluated. Subgroup analysis: to analyze the VT setting during OLV, all patients were ventilated within a range of 5-10 mL/kg. Thirteen patients, classified as a conventional ventilation (CV) subgroup, received 8-10 mL/kg, while 15 patients, classified as a protective ventilation (PV) subgroup, received 5-7 mL/kg.

RESULTS

Cytokine BAL levels after surgery showed no significant increase after OLV, and no significant differences were recorded between the two subgroups. The mean duration of OLV was 64.44±21.68 minutes. No postoperative respiratory complications were recorded. The mean length of stay was for 4.00±1.41 days in the PV subgroup and 4.45±2.07 days in the CV group; no statistically significant differences were recorded between the two subgroups (P=0.511).

CONCLUSIONS

Localized inflammatory cytokine response after OLV was not influenced by the use of different VT. Potentially, the application of PEEP in both ventilation strategies and the short duration of OLV could prevent postoperative complications.

Pediatric acute respiratory distress syndrome - current views

Acute respiratory distress syndrome (ARDS) mainly involves acute respiratory failure. In addition to this affected patients feel progressive arterial hypoxemia, dyspnea, and a marked increase in the work of breathing. The only clinical solution for the above pathological state is ventilation. Mechanical ventilation is necessary to support life in ARDs but it itself worsen lung injury and the term is known clinically as ‘ventilation induced lung injury’ (VILI). At the cellular level, respiratory epithelial cells are subjected to cyclic stretch, i.e. repeated cycles of positive and negative strain, during normal tidal ventilation. In aerated areas of diseased lungs, or even normal lungs subjected to injurious positive pressure mechanical ventilation, the cells are at risk of being over distended, and worsening injury by disrupting the alveolar epithelial barrier. Further, hypercapnic acidosis (HCA) in itself confers protection from stretch injury, potentially via a mechanisms involving inhibition of nuclear factor κB (NF-κB), a transcription factor central to inflammation, injury and repair. Mesenchymal stem cells are the latest in the field and are being investigated as a possible therapy for ARDS.

Inflammasome in the Pathogenesis of Pulmonary Diseases

Lung diseases are common and significant causes of illness and death around the world. Inflammasomes have emerged as an important regulator of lung diseases. The important role of IL-1 beta and IL-18 in the inflammatory response of many lung diseases has been elucidated. The cleavage to turn IL-1 beta and IL-18 from their precursors into the active forms is tightly regulated by inflammasomes. In this chapter, we structurally review current evidence of inflammasome-related components in the pathogenesis of acute and chronic lung diseases, focusing on the "inflammasome-caspase-1-IL-1 beta/IL-18" axis.

Fifty Years of Research in ARDS. Vt Selection in Acute Respiratory Distress Syndrome

Mechanical ventilation (MV) is critical in the management of many patients with acute respiratory distress syndrome (ARDS). However, MV can also cause ventilator-induced lung injury (VILI). The selection of an appropriate Vt is an essential part of a lung-protective MV strategy. Since the publication of a large randomized clinical trial demonstrating the benefit of lower Vts, the use of Vts of 6 ml/kg predicted body weight (based on sex and height) has been recommended in clinical practice guidelines. However, the predicted body weight approach is imperfect in patients with ARDS because the amount of aerated lung varies considerably due to differences in inflammation, consolidation, flooding, and atelectasis. Better approaches to setting Vt may include limits on end-inspiratory transpulmonary pressure, lung strain, and driving pressure. The limits of lowering Vt have not yet been established, and some patients may benefit from Vts that are lower than those in current use. However, lowering Vts may result in respiratory acidosis. Tactics to reduce respiratory acidosis include reductions in ventilation circuit dead space, increases in respiratory rate, higher positive end-expiratory pressures in patients who recruit lung in response to positive end-expiratory pressure, recruitment maneuvers, and prone positioning. Mechanical adjuncts such as extracorporeal carbon dioxide removal may be useful to normalize pH and carbon dioxide levels, but further studies will be necessary to demonstrate benefit with this technology.

Neutrophil Extracellular Traps Are Pathogenic in Ventilator-Induced Lung Injury and Partially Dependent on TLR4

The pathogenesis of ventilator-induced lung injury (VILI) is associated with neutrophils. Neutrophils release neutrophil extracellular traps (NETs), which are composed of DNA and granular proteins. However, the role of NETs in VILI remains incompletely understood. Normal saline and deoxyribonuclease (DNase) were used to study the role of NETs in VILI. To further determine the role of Toll-like receptor 4 (TLR4) in NETosis, we evaluated the lung injury and NET formation in TLR4 knockout mice and wild-type mice that were mechanically ventilated. Some measures of lung injury and the NETs markers were significantly increased in the VILI group. DNase treatment markedly reduced NETs markers and lung injury. After high-tidal mechanical ventilation, the NETs markers in the TLR4 KO mice were significantly lower than in the WT mice. These data suggest that NETs are generated in VILI and pathogenic in a mouse model of VILI, and their formation is partially dependent on TLR4.

Spinal cord injury modulates the lung inflammatory response in mechanically ventilated rats: a comparative animal study

Mechanical ventilation (MV) is widely used in spinal injury patients to compensate for respiratory muscle failure. MV is known to induce lung inflammation, while spinal cord injury (SCI) is known to contribute to local inflammatory response. Interaction between MV and SCI was evaluated in order to assess the impact it may have on the pulmonary inflammatory profile. Sprague Dawley rats were anesthetized for 24 h and randomized to receive either MV or not. The MV group included C4-C5 SCI, T10 SCI and uninjured animals. The nonventilated (NV) group included T10 SCI and uninjured animals. Inflammatory cytokine profile, inflammation related to the SCI level, and oxidative stress mediators were measured in the bronchoalveolar lavage (BAL). The cytokine profile in BAL of MV animals showed increased levels of TNF-α, IL-1β, IL-6 and a decrease in IL-10 (P = 0.007) compared to the NV group. SCI did not modify IL-6 and IL-10 levels either in the MV or the NV groups, but cervical injury induced a decrease in IL-1β levels in MV animals. Cervical injury also reduced MV-induced pulmonary oxidative stress responses by decreasing isoprostane levels while increasing heme oxygenase-1 level. The thoracic SCI in NV animals increased M-CSF expression and promoted antioxidant pulmonary responses with low isoprostane and high heme oxygenase-1 levels. SCI shows a positive impact on MV-induced pulmonary inflammation, modulating specific lung immune and oxidative stress responses. Inflammation induced by MV and SCI interact closely and may have strong clinical implications since effective treatment of ventilated SCI patients may amplify pulmonary biotrauma.

Effect of sivelestat sodium in patients with acute lung injury or acute respiratory distress syndrome: a meta-analysis of randomized controlled trials

Background

Sivelestat is widely used in treating acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), although the clinical efficacy of sivelestat remains controversial. This study aimed to evaluate the impact of sivelestat in patients with ALI/ARDS.

Methods

Electronic databases, PubMed, Embase, and the Cochrane Library, were searched to identify trials through April 2017. Randomized controlled trials (RCTs) were included irrespective of blinding or language that compared patients with and without sivelestat therapy in ALI/ARDS. A random-effects model was used to process the data, and the relative risk (RR) and standard mean difference (SMD) with corresponding 95% confidence intervals (CIs) were used to evaluate the effect of sivelestat.

Results

Six RCTs reporting data on 804 patients with ALI/ARDS were included. Overall, no significant difference was found between sivelestat and control for the risk of 28–30 days mortality (RR: 0.94; 95% CI: 0.71–1.23; P = 0.718). Sivelestat therapy had no significant effect on ventilation days (SMD: 0.05; 95% CI: −0.27 to 0.38; P = 0.748), arterial oxygen partial pressure (PaO2)/fractional inspired oxygen (FiO2) level (SMD: 0.48; 95% CI: −0.45 to 1.41; P = 0.315), and intensive care unit (ICU) stays (SMD: −9.87; 95% CI: −24.30 to 4.56; P = 0.180). The results of sensitivity analysis indicated that sivelestat therapy might affect the PaO₂/FiO₂ level in patients with ALI/ARDS (SMD: 0.87; 95% CI: 0.39 to 1.35; P < 0.001).

Conclusions

Sivelestat therapy might increase the PaO₂/FiO₂ level, while it had little or no effect on 28–30 days mortality, ventilation days, and ICU stays. These findings need to be verified in large-scale trials.

Electronic supplementary material

The online version of this article (10.1186/s12890-017-0498-z) contains supplementary material, which is available to authorized users.

A respiratory-gated micro-CT comparison of respiratory patterns in free-breathing and mechanically ventilated rats

In this study, we aim to quantify the differences in lung metrics measured in free-breathing and mechanically ventilated rodents using respiratory-gated micro-computed tomography. Healthy male Sprague-Dawley rats were anesthetized with ketamine/xylazine and scanned with a retrospective respiratory gating protocol on a GE Locus Ultra micro-CT scanner. Each animal was scanned while free-breathing, then intubated and mechanically ventilated (MV) and rescanned with a standard ventilation protocol (56 bpm, 8 mL/kg and PEEP of 5 cm H₂O) and again with a ventilation protocol that approximates the free-breathing parameters (88 bpm, 2.14 mL/kg and PEEP of 2.5 cm H₂O). Images were reconstructed representing inspiration and end expiration with 0.15 mm voxel spacing. Image-based measurements of the lung lengths, airway diameters, lung volume, and air content were compared and used to calculate the functional residual capacity (FRC) and tidal volume. Images acquired during MV appeared darker in the airspaces and the airways appeared larger. Image-based measurements showed an increase in lung volume and air content during standard MV, for both respiratory phases, compared with matched MV and free-breathing. Comparisons of the functional metrics showed an increase in FRC for mechanically ventilated rats, but only the standard MV exhibited a significantly higher tidal volume than free-breathing or matched MV Although standard mechanical ventilation protocols may be useful in promoting consistent respiratory patterns, the amount of air in the lungs is higher than in free-breathing animals. Matching the respiratory patterns with the free-breathing case allowed similar lung morphology and physiology measurements while reducing the variability in the measurements.

Mechanical Ventilation to Minimize Progression of Lung Injury in Acute Respiratory Failure

Mechanical ventilation is used to sustain life in patients with acute respiratory failure. A major concern in mechanically ventilated patients is the risk of ventilator-induced lung injury, which is partially prevented by lung-protective ventilation. Spontaneously breathing, nonintubated patients with acute respiratory failure may have a high respiratory drive and breathe with large tidal volumes and potentially injurious transpulmonary pressure swings. In patients with existing lung injury, regional forces generated by the respiratory muscles may lead to injurious effects on a regional level. In addition, the increase in transmural pulmonary vascular pressure swings caused by inspiratory effort may worsen vascular leakage. Recent data suggest that these patients may develop lung injury that is similar to the ventilator-induced lung injury observed in mechanically ventilated patients. As such, we argue that application of a lung-protective ventilation, today best applied with sedation and endotracheal intubation, might be considered a prophylactic therapy, rather than just a supportive therapy, to minimize the progression of lung injury from a form of patient self-inflicted lung injury. This has important implications for the management of these patients.

An Official American Thoracic Society Research Statement: Implementation Science in Pulmonary, Critical Care, and Sleep Medicine

BACKGROUND

Many advances in health care fail to reach patients. Implementation science is the study of novel approaches to mitigate this evidence-to-practice gap.

METHODS

The American Thoracic Society (ATS) created a multidisciplinary ad hoc committee to develop a research statement on implementation science in pulmonary, critical care, and sleep medicine. The committee used an iterative consensus process to define implementation science and review the use of conceptual frameworks to guide implementation science for the pulmonary, critical care, and sleep community and to explore how professional medical societies such as the ATS can promote implementation science.

RESULTS

The committee defined implementation science as the study of the mechanisms by which effective health care interventions are either adopted or not adopted in clinical and community settings. The committee also distinguished implementation science from the act of implementation. Ideally, implementation science should include early and continuous stakeholder involvement and the use of conceptual frameworks (i.e., models to systematize the conduct of studies and standardize the communication of findings). Multiple conceptual frameworks are available, and we suggest the selection of one or more frameworks on the basis of the specific research question and setting. Professional medical societies such as the ATS can have an important role in promoting implementation science. Recommendations for professional societies to consider include: unifying implementation science activities through a single organizational structure, linking front-line clinicians with implementation scientists, seeking collaborations to prioritize and conduct implementation science studies, supporting implementation science projects through funding opportunities, working with research funding bodies to set the research agenda in the field, collaborating with external bodies responsible for health care delivery, disseminating results of implementation science through scientific journals and conferences, and teaching the next generation about implementation science through courses and other media.

CONCLUSIONS

Implementation science plays an increasingly important role in health care. Through support of implementation science, the ATS and other professional medical societies can work with other stakeholders to lead this effort.

High-Frequency Oscillatory Ventilation in Adults With ARDS: Past, Present, and Future

High-frequency oscillatory ventilation (HFOV) is a unique mode of mechanical ventilation that uses nonconventional gas exchange mechanisms to deliver ventilation at very low tidal volumes and high frequencies. The properties of HFOV make it a potentially ideal mode to prevent ventilator-induced lung injury in patients with ARDS. Despite a compelling physiological basis and promising experimental data, large randomized controlled trials have not detected an improvement in survival with the use of HFOV, and its use as an early lung-protective strategy in patients with ARDS may be harmful. Nevertheless, HFOV still has an important potential role in the management of refractory hypoxemia. Careful attention should be paid to right ventricular function and lung stress when applying HFOV. This review discusses the physiological principles, clinical evidence, practical applications, and future prospects for the use of HFOV in patients with ARDS.

Driving pressure and mechanical power: new targets for VILI prevention

Several factors have been recognized as possible triggers of ventilator-induced lung injury (VILI). The first is pressure (thus the 'barotrauma'), then the volume (hence the 'volutrauma'), finally the cyclic opening-closing of the lung units ('atelectrauma'). Less attention has been paid to the respiratory rate and the flow, although both theoretical considerations and experimental evidence attribute them a significant role in the generation of VILI. The initial injury to the lung parenchyma is necessarily mechanical and it could manifest as an unphysiological distortion of the extracellular matrix and/or as micro-fractures in the hyaluronan, likely the most fragile polymer embedded in the matrix. The order of magnitude of the energy required to break a molecular bond between the hyaluronan and the associated protein is 1.12×10^-16 Joules (J), 70-90% higher than the average energy delivered by a single breath of 1L assuming a lung elastance of 10 cmH₂O/L (0.5 J). With a normal statistical distribution of the bond strength some polymers will be exposed each cycle to an energy large enough to rupture. Both the extracellular matrix distortion and the polymer fractures lead to inflammatory increase of capillary permeability with edema if a pulmonary blood flow is sufficient. The mediation analysis of higher vs. lower tidal volume and PEEP studies suggests that the driving pressure, more than tidal volume, is the best predictor of VILI, as inferred by increased mortality. This is not surprising, as both tidal volume and respiratory system elastance (resulting in driving pressure) may independently contribute to the mortality. For the same elastance driving pressure is a predictor similar to plateau pressure or tidal volume. Driving pressure is one of the components of the mechanical power, which also includes respiratory rate, flow and PEEP. Finding the threshold for mechanical power would greatly simplify assessment and prevention of VILI.

Positive end-expiratory pressure: how to set it at the individual level

The positive end-expiratory pressure (PEEP), since its introduction in the treatment of acute respiratory failure, up to the 1980s was uniquely aimed to provide a viable oxygenation. Since the first application, a large debate about the criteria for selecting the PEEP levels arose within the scientific community. Lung mechanics, oxygen transport, venous admixture thresholds were all proposed, leading to PEEP recommendations from 5 up to 25 cmH₂O. Throughout this period, the main concern was the hemodynamics. This paradigm changed during the 1980s after the wide acceptance of atelectrauma as one of the leading causes of ventilator induced lung injury. Accordingly, the PEEP aim shifted from oxygenation to lung protection. In this framework, the prevention of lung opening and closing became an almost unquestioned dogma. Consequently, as PEEP keeps open the pulmonary units opened during the previous inspiratory phase, new methods were designed to identify the 'optimal' PEEP during the expiratory phase. The open lung approach requires that every collapsed unit potentially openable is opened and maintained open. The methods to assess the recruitment are based on imaging (computed tomography, electric impedance tomography, ultrasound) or mechanically-driven gas exchange modifications. All the latest assume that whatever change in respiratory system compliance is due to changes in lung compliance, which in turn is uniquely function of the recruitment. Comparative studies, however, showed that the only possible approach to measure the amount of collapsed tissue regaining inflation is the CT scan. In fact, all the other methods estimate as recruitment the gas entry in pulmonary units already open at lower PEEP, but increasing their compliance at higher PEEP. Since higher PEEP is usually more indicated (also for oxygenation) when the recruitability is higher, as occurs with increasing severity, a meaningful PEEP selection requires the assessment of recruitment. The Berlin definition may help in this assessment.

Fifty Years of Research in ARDS. Setting Positive End-Expiratory Pressure in Acute Respiratory Distress Syndrome

Positive end-expiratory pressure (PEEP) has been used during mechanical ventilation since the first description of acute respiratory distress syndrome (ARDS). In the subsequent decades, many different strategies for optimally titrating PEEP have been proposed. Higher PEEP can improve arterial oxygenation, reduce tidal lung stress and strain, and promote more homogenous ventilation by preventing alveolar collapse at end expiration. However, PEEP may also cause circulatory depression and contribute to ventilator-induced lung injury through alveolar overdistention. The overall effect of PEEP is primarily related to the balance between the number of alveoli that are recruited to participate in ventilation and the amount of lung that is overdistended when PEEP is applied. Techniques to assess lung recruitment from PEEP may help to direct safer and more effective PEEP titration. Some PEEP titration strategies attempt to weigh beneficial effects on arterial oxygenation and on prevention of cyclic alveolar collapse with the harmful potential of overdistention. One method for PEEP titration is a PEEP/FiO2 table that prioritizes support for arterial oxygenation. Other methods set PEEP based on mechanical parameters, such as the plateau pressure, respiratory system compliance, or transpulmonary pressure. No single method of PEEP titration has been shown to improve clinical outcomes compared with other approaches of setting PEEP. Future trials should focus on identifying individuals who respond to higher PEEP with recruitment and on clinically important outcomes (e.g., mortality).

Mechanical ventilation in the acute respiratory distress syndrome

The management of the acute respiratory distress syndrome (ARDS) patient is fundamental to the field of intensive care medicine, and it presents unique challenges owing to the specialized mechanical ventilation techniques that such patients require. ARDS is a highly lethal disease, and there is compelling evidence that mechanical ventilation itself, if applied in an injurious fashion, can be a contributor to ARDS mortality. Therefore, it is imperative for any clinician central to the care of ARDS patients to understand the fundamental framework that underpins the approach to mechanical ventilation in this special scenario. The current review summarizes the major components of the mechanical ventilation strategy as it applies to ARDS.

Opening pressures and atelectrauma in acute respiratory distress syndrome

PURPOSE

Open lung strategy during ARDS aims to decrease the ventilator-induced lung injury by minimizing the atelectrauma and stress/strain maldistribution. We aim to assess how much of the lung is opened and kept open within the limits of mechanical ventilation considered safe (i.e., plateau pressure 30 cmH2O, PEEP 15 cmH2O).

METHODS

Prospective study from two university hospitals. Thirty-three ARDS patients (5 mild, 10 moderate, 9 severe without extracorporeal support, ECMO, and 9 severe with it) underwent two low-dose end-expiratory CT scans at PEEP 5 and 15 cmH2O and four end-inspiratory CT scans (from 19 to 40 cmH2O). Recruitment was defined as the fraction of lung tissue which regained inflation. The atelectrauma was estimated as the difference between the intratidal tissue collapse at 5 and 15 cmH2O PEEP. Lung ventilation inhomogeneities were estimated as the ratio of inflation between neighboring lung units.

RESULTS

The lung tissue which is opened between 30 and 45 cmH2O (i.e., always closed at plateau 30 cmH2O) was 10 ± 29, 54 ± 86, 162 ± 92, and 185 ± 134 g in mild, moderate, and severe ARDS without and with ECMO, respectively (p < 0.05 mild versus severe without or with ECMO). The intratidal collapses were similar at PEEP 5 and 15 cmH2O (63 ± 26 vs 39 ± 32 g in mild ARDS, p = 0.23; 92 ± 53 vs 78 ± 142 g in moderate ARDS, p = 0.76; 110 ± 91 vs 89 ± 93, p = 0.57 in severe ARDS without ECMO; 135 ± 100 vs 104 ± 80, p = 0.32 in severe ARDS with ECMO). Increasing the applied airway pressure up to 45 cmH2O decreased the lung inhomogeneity slightly (but significantly) in mild and moderate ARDS, but not in severe ARDS.

CONCLUSIONS

Data show that the prerequisites of the open lung strategy are not satisfied using PEEP up to 15 cmH2O and plateau pressure up to 30 cmH2O. For an effective open lung strategy, higher pressures are required. Therefore, risks of atelectrauma must be weighted versus risks of volutrauma.

TRIAL REGISTRATION

Clinicaltrials.gov identifier: NCT01670747 ( www.clinicaltrials.gov ).

Comprendre le poumon agressé. Actes du séminaire de recherche translationnelle de la Société de Réanimation de Langue Française (6 décembre 2016)

Le séminaire de recherche translationnelle 2016 organisé par la Société de Réanimation de Langue Française s’est focalisé sur les mécanismes de réponse à l’agression et de réparation pulmonaire. Le poumon représente une interface essentielle entre l’hôte et son environnement et est à ce titre soumis à des agressions constantes et multiples. La réanimation s’est en grande partie construite autour de la prise en charge de la défaillance respiratoire. Au-delà du traitement étiologique et du support ventilatoire, se pose la problématique récurrente du développement de thérapeutiques adjuvantes à visée immunomodulatrice. Le développement de telles thérapeutiques innovantes est conditionné par les avancées dans la compréhension de la physiopathologie de l’agression pulmonaire aiguë, ainsi que par la validation au lit du patient d’outils d’évaluation permettant de quantifier l’effet des interventions thérapeutiques.

Interleukin-6 displays lung anti-inflammatory properties and exerts protective hemodynamic effects in a double-hit murine acute lung injury

Background

Interleukin 6 (IL-6) is a predictive factor of poor prognosis in patients with acute respiratory distress syndrome (ARDS). However, its acute pulmonary hemodynamic effects and role in lung injury have not been investigated in a clinically relevant murine model of ARDS.

Methods

We used adult C57Bl6 wild-type (WT) and IL-6 knock-out (IL-6KO) mice. The animals received intravenous recombinant human IL-6 (rHuIL-6) or vehicle followed by intratracheal lipopolysaccharide (LPS) or saline before undergoing low tidal volume mechanical ventilation (MV) for 5 h. Before sacrifice, right ventricular systolic pressure and cardiac output were measured and total pulmonary resistance was calculated. After sacrifice, lung inflammation, edema and injury were assessed with bronchoalveolar lavage (BAL) and histology. In other experiments, right ventricular systolic pressure was recorded during hypoxic challenges in uninjured WT mice pretreated with rHuIL-6 or rHuIL-6 + non-selective nitric oxide synthase inhibitor L-NAME or vehicle.

Results

IL-6KO_(LPS+MV) mice showed a faster deterioration of lung elastic properties and more severe bronchoalveolar cellular inflammation as compared to WT_(LPS+MV). Treatment with rHuIL-6 partially prevented this lung deterioration. Total pulmonary resistance was higher in IL-6KO_(LPS+MV) mice and this increase was abolished in rHuIL-6-treated IL-6KO mice. Finally, rHuIL-6 reduced hypoxic pulmonary vasoconstriction in uninjured WT mice, an effect that was abolished by co-treatment with L-NAME.

Conclusions

In a double-hit murine model of ARDS, IL-6 deficient mice experienced more severe bronchoalveolar cellular inflammation as compared to wild-type littermates. Furthermore, IL-6 deficiency caused marked acute pulmonary hypertension, which may be, at least partially, due to vasoactive mechanisms. A dysregulation of nitric oxide synthase may account for this observation, a hypothesis that will need to be investigated in future studies.

[Does intraoperative lung-protective ventilation reduce postoperative pulmonary complications?]

BACKGROUND

Recent studies show that intraoperative protective ventilation is able to reduce postoperative pulmonary complications (PPC).

OBJECTIVES

This article provides an overview of the definition and ways to predict PPC. We present different factors that lead to ventilator-induced lung injury and explain the concepts of stress and strain as well as driving pressure. Different strategies of mechanical ventilation to avoid PPC are discussed in light of clinical evidence.

MATERIALS AND METHODS

The Medline database was used to selectively search for randomized controlled trials dealing with intraoperative mechanical ventilation and outcomes.

RESULTS

Low tidal volumes (VT) and high levels of positive end-expiratory pressure (PEEP), combined with recruitment maneuvers, are able to prevent PPC. Non-obese patients undergoing open abdominal surgery show better lung function with the use of higher PEEP levels and recruitment maneuvers, however such strategy can lead to hemodynamic impairment, while not reducing the incidence of PPC, hospital length of stay and mortality. An increase in the level of PEEP that results in an increase in driving pressure is associated with a greater risk of PPC.

CONCLUSIONS

The use of intraoperative VT ranging from 6 to 8 ml/kg based on ideal body weight is strongly recommended. Currently, a recommendation regarding the level of PEEP during surgery is not possible. However, a PEEP increase that leads to a rise in driving pressure should be avoided.

Animal models of hospital-acquired pneumonia: current practices and future perspectives

Lower respiratory tract infections are amongst the leading causes of mortality and morbidity worldwide. Especially in hospital settings and more particularly in critically ill ventilated patients, nosocomial pneumonia is one of the most serious infectious complications frequently caused by opportunistic pathogens. Pseudomonas aeruginosa is one of the most important causes of ventilator-associated pneumonia as well as the major cause of chronic pneumonia in cystic fibrosis patients. Animal models of pneumonia allow us to investigate distinct types of pneumonia at various disease stages, studies that are not possible in patients. Different animal models of pneumonia such as one-hit acute pneumonia models, ventilator-associated pneumonia models and biofilm pneumonia models associated with cystic fibrosis have been extensively studied and have considerably aided our understanding of disease pathogenesis and testing and developing new treatment strategies. The present review aims to guide investigators in choosing appropriate animal pneumonia models by describing and comparing the relevant characteristics of each model using P. aeruginosa as a model etiology for hospital-acquired pneumonia. Key to establishing and studying these animal models of infection are well-defined end-points that allow precise monitoring and characterization of disease development that could ultimately aid in translating these findings to patient populations in order to guide therapy. In this respect, and discussed here, is the development of humanized animal models of bacterial pneumonia that could offer unique advantages to study bacterial virulence factor expression and host cytokine production for translational purposes.

Plasma membrane wounding and repair in pulmonary diseases

Various pathophysiological conditions such as surfactant dysfunction, mechanical ventilation, inflammation, pathogen products, environmental exposures, and gastric acid aspiration stress lung cells, and the compromise of plasma membranes occurs as a result. The mechanisms necessary for cells to repair plasma membrane defects have been extensively investigated in the last two decades, and some of these key repair mechanisms are also shown to occur following lung cell injury. Because it was theorized that lung wounding and repair are involved in the pathogenesis of acute respiratory distress syndrome (ARDS) and idiopathic pulmonary fibrosis (IPF), in this review, we summarized the experimental evidence of lung cell injury in these two devastating syndromes and discuss relevant genetic, physical, and biological injury mechanisms, as well as mechanisms used by lung cells for cell survival and membrane repair. Finally, we discuss relevant signaling pathways that may be activated by chronic or repeated lung cell injury as an extension of our cell injury and repair focus in this review. We hope that a holistic view of injurious stimuli relevant for ARDS and IPF could lead to updated experimental models. In addition, parallel discussion of membrane repair mechanisms in lung cells and injury-activated signaling pathways would encourage research to bridge gaps in current knowledge. Indeed, deep understanding of lung cell wounding and repair, and discovery of relevant repair moieties for lung cells, should inspire the development of new therapies that are likely preventive and broadly effective for targeting injurious pulmonary diseases.

Neural control of ventilation prevents both over-distension and de-recruitment of experimentally injured lungs

BACKGROUND

Endogenous pulmonary reflexes may protect the lungs during mechanical ventilation. We aimed to assess integration of continuous neurally adjusted ventilatory assist (cNAVA), delivering assist in proportion to diaphragm's electrical activity during inspiration and expiration, and Hering-Breuer inflation and deflation reflexes on lung recruitment, distension, and aeration before and after acute lung injury (ALI).

METHODS

In 7 anesthetised rabbits with bilateral pneumothoraces, we identified adequate cNAVA level (cNAVA_AL) at the plateau in peak ventilator pressure during titration procedures before (healthy lungs with endotracheal tube, [HL_ETT]) and after ALI (endotracheal tube [ALI_ETT] and during non-invasive ventilation [ALI_NIV]). Following titration, cNAVA_AL was maintained for 5min. In 2 rabbits, procedures were repeated after vagotomy (ALI_ETT+VAG). In 3 rabbits delivery of assist was temporarily modulated to provide assist on inspiration only. Computed tomography was performed before intubation, before ALI, during cNAVA titration, and after maintenance at cNAVA_AL.

RESULTS

During ALI_ETT and ALI_NIV, normally aerated lung-regions doubled and poorly aerated lung-regions decreased to less than a third (p<0.05) compared to HL_ETT; no over-distension was observed. Tidal volumes were<5ml/kg throughout. Removing assist during expiration resulted in lung de-recruitment during ALI_ETT, but not during ALI_NIV. During ALI_ETT+VAG the expiratory portion of EAdi disappeared, resulting in cyclic lung collapse and recruitment.

CONCLUSIONS

When using cNAVA in ALI, vagally mediated reflexes regulated lung recruitment preventing both lung over-distension and atelectasis. During non-invasive cNAVA the upper airway muscles play a role in preventing atelectasis. Future studies should be performed to compare these findings with conventional lung-protective approaches.

Ex Vivo Lung Perfusion in the Rat: Detailed Procedure and Videos

Ex vivo lung perfusion (EVLP) is a promising procedure for evaluation, reconditioning, and treatment of marginal lungs before transplantation. Small animal models can contribute to improve clinical development of this technique and represent a substantial platform for bio-molecular investigations. However, to accomplish this purpose, EVLP models must sustain a prolonged reperfusion without pharmacological interventions. Currently available protocols only partly satisfy this need. The aim of the present research was accomplishment and optimization of a reproducible model for a protracted rat EVLP in the absence of anti-inflammatory treatment. A 180 min, uninjured and untreated perfusion was achieved through a stepwise implementation of the protocol. Flow rate, temperature, and tidal volume were gradually increased during the initial reperfusion phase to reduce hemodynamic and oxidative stress. Low flow rate combined with open atrium and protective ventilation strategy were applied to prevent lung damage. The videos enclosed show management of the most critical technical steps. The stability and reproducibility of the present procedure were confirmed by lung function evaluation and edema assessment. The meticulous description of the protocol provided in this paper can enable other laboratories to reproduce it effortlessly, supporting research in the EVLP field.

Ventilator-induced Lung Injury

Prevention of ventilator-induced lung injury (VILI) can attenuate multiorgan failure and improve survival in at-risk patients. Clinically significant VILI occurs from volutrauma, barotrauma, atelectrauma, biotrauma, and shear strain. Differences in regional mechanics are important in VILI pathogenesis. Several interventions are available to protect against VILI. However, most patients at risk of lung injury do not develop VILI. VILI occurs most readily in patients with concomitant physiologic insults. VILI prevention strategies must balance risk of lung injury with untoward side effects from the preventive effort, and may be most effective when targeted to subsets of patients at increased risk.

Ventilator-related causes of lung injury: the mechanical power

PURPOSE

We hypothesized that the ventilator-related causes of lung injury may be unified in a single variable: the mechanical power. We assessed whether the mechanical power measured by the pressure-volume loops can be computed from its components: tidal volume (TV)/driving pressure (∆P aw), flow, positive end-expiratory pressure (PEEP), and respiratory rate (RR). If so, the relative contributions of each variable to the mechanical power can be estimated.

METHODS

We computed the mechanical power by multiplying each component of the equation of motion by the variation of volume and RR: [Formula: see text]where ∆V is the tidal volume, ELrs is the elastance of the respiratory system, I:E is the inspiratory-to-expiratory time ratio, and R aw is the airway resistance. In 30 patients with normal lungs and in 50 ARDS patients, mechanical power was computed via the power equation and measured from the dynamic pressure-volume curve at 5 and 15 cmH2O PEEP and 6, 8, 10, and 12 ml/kg TV. We then computed the effects of the individual component variables on the mechanical power.

RESULTS

Computed and measured mechanical powers were similar at 5 and 15 cmH2O PEEP both in normal subjects and in ARDS patients (slopes = 0.96, 1.06, 1.01, 1.12 respectively, R (2) > 0.96 and p < 0.0001 for all). The mechanical power increases exponentially with TV, ∆P aw, and flow (exponent = 2) as well as with RR (exponent = 1.4) and linearly with PEEP.

CONCLUSIONS

The mechanical power equation may help estimate the contribution of the different ventilator-related causes of lung injury and of their variations. The equation can be easily implemented in every ventilator's software.

Open lung approach ventilation abolishes the negative effects of respiratory rate in experimental lung injury

BACKGROUND

We recently reported that a high respiratory rate was associated with less inflammation than a low respiratory rate, but caused more pulmonary edema in a model of ARDS when an ARDSNet ventilatory strategy was used. We hypothesized that an open lung approach (OLA) strategy would neutralize the independent effects of respiratory rate on lung inflammation and edema. This hypothesis was tested in an ARDS model using two clinically relevant respiratory rates during OLA strategy.

METHODS

Twelve piglets were subjected to an experimental model of ARDS and randomized into two groups: LRR (20 breaths/min) and HRR (40 breaths/min). They were mechanically ventilated for 6 h according to an OLA strategy. We assessed respiratory mechanics, hemodynamics, and extravascular lung water (EVLW). At the end of the experiment, wet/dry ratio, regional histology, and cytokines were evaluated.

RESULTS

After the ARDS model was established, Cdyn,rs decreased from 21 ± 3.3 to 9.0 ± 1.8 ml/cmH2 O (P < 0.0001). After the lung recruitment maneuver, Cdyn,rs increased to the pre-injury value. During OLA ventilation, no differences in respiratory mechanics, hemodynamics, or EVLW were observed between groups. Wet/dry ratio and histological scores were not different between groups. Cytokine quantification was similar and showed a homogeneous distribution throughout the lung in both groups.

CONCLUSION

Contrary to previous findings with the ARDSNet strategy, respiratory rate did not influence lung inflammatory response or pulmonary edema during OLA ventilation in experimental ARDS. This indicates that changing the respiratory rate when OLA ventilation is used will not exacerbate lung injury.

Biotrauma and Ventilator-Induced Lung Injury: Clinical Implications

The pathophysiological mechanisms by which mechanical ventilation can contribute to lung injury, termed "ventilator-induced lung injury" (VILI), is increasingly well understood. "Biotrauma" describes the release of mediators by injurious ventilatory strategies, which can lead to lung and distal organ injury. Insights from preclinical models demonstrating that traditional high tidal volumes drove the inflammatory response helped lead to clinical trials demonstrating lower mortality in patients who underwent ventilation with a lower-tidal-volume strategy. Other approaches that minimize VILI, such as higher positive end-expiratory pressure, prone positioning, and neuromuscular blockade have each been demonstrated to decrease indices of activation of the inflammatory response. This review examines the evolution of our understanding of the mechanisms underlying VILI, particularly regarding biotrauma. We will assess evidence that ventilatory and other "adjunctive" strategies that decrease biotrauma offer great potential to minimize the adverse consequences of VILI and to improve the outcomes of patients with respiratory failure.

Mechanical Ventilation Alters the Development of Staphylococcus aureus Pneumonia in Rabbit

Ventilator-associated pneumonia (VAP) is common during mechanical ventilation (MV). Beside obvious deleterious effects on muco-ciliary clearance, MV could adversely shift the host immune response towards a pro-inflammatory pattern through toll-like receptor (TLRs) up-regulation. We tested this hypothesis in a rabbit model of Staphylococcus aureus VAP. Pneumonia was caused by airway challenge with S. aureus, in either spontaneously breathing (SB) or MV rabbits (n = 13 and 17, respectively). Pneumonia assessment regarding pulmonary and systemic bacterial burden, as well as inflammatory response was done 8 and 24 hours after S. aureus challenge. In addition, ex vivo stimulations of whole blood taken from SB or MV rabbits (n = 7 and 5, respectively) with TLR2 agonist or heat-killed S. aureus were performed. Data were expressed as mean±standard deviation. After 8 hours of infection, lung injury was more severe in MV animals (1.40±0.33 versus [vs] 2.40±0.55, p = 0.007), along with greater bacterial concentrations (6.13±0.63 vs. 4.96±1.31 colony forming units/gram, p = 0.002). Interleukin (IL)-8 and tumor necrosis factor (TNF)-αserum concentrations reached higher levels in MV animals (p = 0.010). Whole blood obtained from MV animals released larger amounts of cytokines if stimulated with TLR2 agonist or heat-killed S. aureus (e.g., TNF-α: 1656±166 vs. 1005±89; p = 0.014). Moreover, MV induced TLR2 overexpression in both lung and spleen tissue. MV hastened tissue injury, impaired lung bacterial clearance, and promoted a systemic inflammatory response, maybe through TLR2 overexpression.

Pediatric Acute Hypoxemic Respiratory Failure: Management of Oxygenation

Acute hypoxemic respiratory failure (AHRF) is one of the hallmarks of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), which are caused by an inflammatory process initiated by any of a number of potential systemic and/or pulmonary insults that result in heterogeneous disruption of the capillary-pithelial interface. In these critically sick patients, optimizing the management of oxygenation is crucial. Physicians managing pediatric patients with ALI or ARDS are faced with a complex array of options influencing oxygenation. Certain treatment strategies can influence clinical outcomes, such as a lung protective ventilation strategy that specifies a low tidal volume (6 mL/kg) and a plateau pressure limit (30 cm H2O). Other strategies such as different levels of positive end expiratory pressure, altered inspiration to expiration time ratios, recruitment maneuvers, prone positioning, and extraneous gases or drugs may also affect clinical outcomes. This article reviews state-of-the-art strategies on the management of oxygenation in acute hypoxemic respiratory failure in children.

Magnetic resonance imaging provides sensitive in vivo assessment of experimental ventilator-induced lung injury

Animal models play a critical role in the study of acute respiratory distress syndrome (ARDS) and ventilator-induced lung injury (VILI). One limitation has been the lack of a suitable method for serial assessment of acute lung injury (ALI) in vivo. In this study, we demonstrate the sensitivity of magnetic resonance imaging (MRI) to assess ALI in real time in rat models of VILI. Sprague-Dawley rats were untreated or treated with intratracheal lipopolysaccharide or PBS. After 48 h, animals were mechanically ventilated for up to 15 h to induce VILI. Free induction decay (FID)-projection images were made hourly. Image data were collected continuously for 30 min and divided into 13 phases of the ventilatory cycle to make cinematic images. Interleaved measurements of respiratory mechanics were performed using a flexiVent ventilator. The degree of lung infiltration was quantified in serial images throughout the progression or resolution of VILI. MRI detected VILI significantly earlier (3.8 ± 1.6 h) than it was detected by altered lung mechanics (9.5 ± 3.9 h, P = 0.0156). Animals with VILI had a significant increase in the Index of Infiltration (P = 0.0027), and early regional lung infiltrates detected by MRI correlated with edema and inflammatory lung injury on histopathology. We were also able to visualize and quantify regression of VILI in real time upon institution of protective mechanical ventilation. Magnetic resonance lung imaging can be utilized to investigate mechanisms underlying the development and propagation of ALI, and to test the therapeutic effects of new treatments and ventilator strategies on the resolution of ALI.

Preventing Ventilator-Associated Lung Injury: A Perioperative Perspective

Introduction

Research into the prevention of ventilator-associated lung injury (VALI) in patients with acute respiratory distress syndrome (ARDS) in the intensive care unit (ICU) has resulted in the development of a number of lung protective strategies, which have become commonplace in the treatment of critically ill patients. An increasing number of studies have applied lung protective ventilation in the operating room to otherwise healthy individuals. We review the history of lung protective strategies in patients with acute respiratory failure and explore their use in patients undergoing mechanical ventilation during general anesthesia. We aim to provide context for a discussion of the benefits and drawbacks of lung protective ventilation, as well as to inform future areas of research.

Methods

We completed a database search and reviewed articles investigating lung protective ventilation in both the ICU and in patients receiving general anesthesia through May 2015.

Results

Lung protective ventilation was associated with improved outcomes in patients with acute respiratory failure in the ICU. Clinical evidence is less clear regarding lung protective ventilation for patients undergoing surgery.

Conclusion

Lung protective ventilation strategies, including low tidal volume ventilation and moderate positive end-expiratory pressure, are well established therapies to minimize lung injury in critically ill patients with and without lung disease, and may provide benefit to patients undergoing general anesthesia.

Clinical challenges in mechanical ventilation

Mechanical ventilation supports gas exchange and alleviates the work of breathing when the respiratory muscles are overwhelmed by an acute pulmonary or systemic insult. Although mechanical ventilation is not generally considered a treatment for acute respiratory failure per se, ventilator management warrants close attention because inappropriate ventilation can result in injury to the lungs or respiratory muscles and worsen morbidity and mortality. Key clinical challenges include averting intubation in patients with respiratory failure with non-invasive techniques for respiratory support; delivering lung-protective ventilation to prevent ventilator-induced lung injury; maintaining adequate gas exchange in severely hypoxaemic patients; avoiding the development of ventilator-induced diaphragm dysfunction; and diagnosing and treating the many pathophysiological mechanisms that impair liberation from mechanical ventilation. Personalisation of mechanical ventilation based on individual physiological characteristics and responses to therapy can further improve outcomes.

Open Lung Approach for the Acute Respiratory Distress Syndrome: A Pilot, Randomized Controlled Trial

OBJECTIVE

The open lung approach is a mechanical ventilation strategy involving lung recruitment and a decremental positive end-expiratory pressure trial. We compared the Acute Respiratory Distress Syndrome network protocol using low levels of positive end-expiratory pressure with open lung approach resulting in moderate to high levels of positive end-expiratory pressure for the management of established moderate/severe acute respiratory distress syndrome.

DESIGN

A prospective, multicenter, pilot, randomized controlled trial.

SETTING

A network of 20 multidisciplinary ICUs.

PATIENTS

Patients meeting the American-European Consensus Conference definition for acute respiratory distress syndrome were considered for the study.

INTERVENTIONS

At 12-36 hours after acute respiratory distress syndrome onset, patients were assessed under standardized ventilator settings (FIO2≥0.5, positive end-expiratory pressure ≥10 cm H2O). If Pao2/FIO2 ratio remained less than or equal to 200 mm Hg, patients were randomized to open lung approach or Acute Respiratory Distress Syndrome network protocol. All patients were ventilated with a tidal volume of 4 to 8 ml/kg predicted body weight.

MEASUREMENTS AND MAIN RESULTS

From 1,874 screened patients with acute respiratory distress syndrome, 200 were randomized: 99 to open lung approach and 101 to Acute Respiratory Distress Syndrome network protocol. Main outcome measures were 60-day and ICU mortalities, and ventilator-free days. Mortality at day-60 (29% open lung approach vs. 33% Acute Respiratory Distress Syndrome Network protocol, p = 0.18, log rank test), ICU mortality (25% open lung approach vs. 30% Acute Respiratory Distress Syndrome network protocol, p = 0.53 Fisher's exact test), and ventilator-free days (8 [0-20] open lung approach vs. 7 [0-20] d Acute Respiratory Distress Syndrome network protocol, p = 0.53 Wilcoxon rank test) were not significantly different. Airway driving pressure (plateau pressure - positive end-expiratory pressure) and PaO2/FIO2 improved significantly at 24, 48 and 72 hours in patients in open lung approach compared with patients in Acute Respiratory Distress Syndrome network protocol. Barotrauma rate was similar in both groups.

CONCLUSIONS

In patients with established acute respiratory distress syndrome, open lung approach improved oxygenation and driving pressure, without detrimental effects on mortality, ventilator-free days, or barotrauma. This pilot study supports the need for a large, multicenter trial using recruitment maneuvers and a decremental positive end-expiratory pressure trial in persistent acute respiratory distress syndrome.