Bedside respiratory physiology to detect risk of lung injury in acute respiratory distress syndrome

S14G-humanin alleviates acute lung injury by inhibiting the activation of NF-κB

Acute lung injury (ALI) is characterized by severely damaged alveoli and blood vessels, seriously affecting the health of patients and causing a high mortality rate. The pathogenesis of ALI is complex, with inflammatory reactions and oxidative stress (OS) mainly involved. S14G humanin (HNG) is derived from humanin (HN), which is claimed with promising anti-inflammatory functions. Herein, the protective influence of HNG on ALI will be explored in a mouse model. The ALI model was established in mice via intratracheal instillation of 3 mg/kg LPS, followed by an intraperitoneal injection of 3 and 6 mg/kg HNG, respectively. Thicker alveolar walls, aggravated neutrophil infiltration, and increased wet weight/dry weight (W/D) ratio were observed in ALI mice, accompanied by an aggravated apoptotic state, all of which were notably alleviated by HNG. Furthermore, increased number of total cells and neutrophils in bronchoalveolar lavage fluid (BALF), elevated secretion of inflammatory cytokines, enhanced reactive oxygen species (ROS) and Malondialdehyde (MDA) levels, and declined superoxide dismutase-2 (SOD2) levels were observed in ALI mice, which were markedly ameliorated by HNG. Moreover, the upregulated levels of NOD-like receptor family pyrin domain containing 3 (NLRP3), caspase-1, and caspases cleave gasdermin D N/caspases cleave gasdermin D FL (GSDMD N/GSDMD FL) in ALI mice were signally repressed by HNG. Lastly, the upregulation of Toll-like receptor 4 (TLR4) and p-p65/p65, and downregulation of IκB-α observed in ALI mice were sharply reversed by HNG. Collectively, HNG alleviated the ALI in mice by inhibiting the activation of nuclear factor kappa B (NF-κB) signaling.

Mechanical power of ventilation and driving pressure: two undervalued parameters for pre extracorporeal membrane oxygenation ventilation and during daily management?

The current ARDS guidelines highly recommend lung protective ventilation which include plateau pressure (P_plat < 30 cm H₂O), positive end expiratory pressure (PEEP > 5 cm H₂O) and tidal volume (V_t of 6 ml/kg) of predicted body weight. In contrast, the ELSO guidelines suggest the evaluation of an indication of veno-venous extracorporeal membrane oxygenation (ECMO) due to hypoxemic or hypercapnic respiratory failure or as bridge to lung transplantation. Finally, these recommendations remain a wide range of scope of interpretation. However, particularly patients with moderate-severe to severe ARDS might benefit from strict adherence to lung protective ventilation strategies. Subsequently, we discuss whether extended physiological ventilation parameter analysis might be relevant for indication of ECMO support and can be implemented during the daily routine evaluation of ARDS patients. Particularly, this viewpoint focus on driving pressure and mechanical power.

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

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

Advancing precision medicine for acute respiratory distress syndrome

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

Lung protection in acute respiratory distress syndrome: what should we target?

PURPOSE OF REVIEW

Most clinical trials of lung-protective ventilation have tested one-size-fits-all strategies with mixed results. Data are lacking on how best to tailor mechanical ventilation to patient-specific risk of lung injury.

RECENT FINDINGS

Risk of ventilation-induced lung injury is determined by biological predisposition to biophysical lung injury and physical mechanical perturbations that concentrate stress and strain regionally within the lung. Recent investigations have identified molecular subphenotypes classified as hyperinflammatory and hypoinflammatory acute respiratory distress syndrome (ARDS), which may have dissimilar risk for ventilation-induced lung injury. Mechanically, gravity-dependent atelectasis has long been recognized to decrease total aerated lung volume available for tidal ventilation, a concept termed the 'ARDS baby lung'. Recent studies have demonstrated that the aerated baby lung also has nonuniform stress/strain distribution, with potentially injurious forces concentrated in zones of heterogeneity where aerated alveoli are adjacent to flooded or atelectatic alveoli. The preponderance of evidence also indicates that current standard-of-care tidal volume management is not universally protective in ARDS. When considering escalation of lung-protective interventions, potential benefits of the intervention should be weighed against tradeoffs of accompanying cointerventions required, for example, deeper sedation or neuromuscular blockade. A precision medicine approach to lung-protection would weigh.

SUMMARY

A precision medicine approach to lung-protective ventilation requires weighing four key factors in each patient: biological predisposition to biophysical lung injury, mechanical predisposition to biophysical injury accounting for spatial mechanical heterogeneity within the lung, anticipated benefits of escalating lung-protective interventions, and potential unintended adverse effects of mandatory cointerventions.

Phenotypes and personalized medicine in the acute respiratory distress syndrome

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

Emerging concepts in ventilation-induced lung injury

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