The American-European Consensus Conference definition of the acute respiratory distress syndrome is dead, long live positive end-expiratory pressure!

Reactive Oxygen Species and Strategies for Antioxidant Intervention in Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a life-threatening pulmonary condition characterized by the sudden onset of respiratory failure, pulmonary edema, dysfunction of endothelial and epithelial barriers, and the activation of inflammatory cascades. Despite the increasing number of deaths attributed to ARDS, a comprehensive therapeutic approach for managing patients with ARDS remains elusive. To elucidate the pathological mechanisms underlying ARDS, numerous studies have employed various preclinical models, often utilizing lipopolysaccharide as the ARDS inducer. Accumulating evidence emphasizes the pivotal role of reactive oxygen species (ROS) in the pathophysiology of ARDS. Both preclinical and clinical investigations have asserted the potential of antioxidants in ameliorating ARDS. This review focuses on various sources of ROS, including NADPH oxidase, uncoupled endothelial nitric oxide synthase, cytochrome P450, and xanthine oxidase, and provides a comprehensive overview of their roles in ARDS. Additionally, we discuss the potential of using antioxidants as a strategy for treating ARDS.

Endothelial dysfunction in COVID-19: an overview of evidence, biomarkers, mechanisms and potential therapies

The fight against coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 infection is still raging. However, the pathophysiology of acute and post-acute manifestations of COVID-19 (long COVID-19) is understudied. Endothelial cells are sentinels lining the innermost layer of blood vessel that gatekeep micro- and macro-vascular health by sensing pathogen/danger signals and secreting vasoactive molecules. SARS-CoV-2 infection primarily affects the pulmonary system, but accumulating evidence suggests that it also affects the pan-vasculature in the extrapulmonary systems by directly (via virus infection) or indirectly (via cytokine storm), causing endothelial dysfunction (endotheliitis, endothelialitis and endotheliopathy) and multi-organ injury. Mounting evidence suggests that SARS-CoV-2 infection leads to multiple instances of endothelial dysfunction, including reduced nitric oxide (NO) bioavailability, oxidative stress, endothelial injury, glycocalyx/barrier disruption, hyperpermeability, inflammation/leukocyte adhesion, senescence, endothelial-to-mesenchymal transition (EndoMT), hypercoagulability, thrombosis and many others. Thus, COVID-19 is deemed as a (micro)vascular and endothelial disease. Of translational relevance, several candidate drugs which are endothelial protective have been shown to improve clinical manifestations of COVID-19 patients. The purpose of this review is to provide a latest summary of biomarkers associated with endothelial cell activation in COVID-19 and offer mechanistic insights into the molecular basis of endothelial activation/dysfunction in macro- and micro-vasculature of COVID-19 patients. We envisage further development of cellular models and suitable animal models mimicking endothelial dysfunction aspect of COVID-19 being able to accelerate the discovery of new drugs targeting endothelial dysfunction in pan-vasculature from COVID-19 patients.

Paediatrics: how to manage acute respiratory distress syndrome

Background

Acute respiratory distress syndrome (ARDS) is a significant cause of mortality and morbidity amongst critically ill children. The purpose of this narrative review is to provide an up-to-date review on the evaluation and management of paediatric ARDS (PARDS).

Methods

A PubMed search was performed with Clinical Queries using the key term "acute respiratory distress syndrome". The search strategy included clinical trials, meta-analyses, randomized controlled trials, observational studies and reviews. Google, Wikipedia and UpToDate were also searched to enrich the review. The search was restricted to the English literature and children.

Discussion

Non-invasive positive pressure ventilation, lung-protective ventilation strategies, conservative fluid management and adequate nutritional support all have proven efficacy in the management of PARDS. The Pediatric Acute Lung Injury Consensus Conference recommends the use of corticosteroids, high-frequency oscillation ventilation and inhaled nitric oxide in selected scenarios. Partial liquid ventilation and surfactant are not considered efficacious based on evidence from clinical trials.

Conclusion

PARDS is a serious but relatively rare cause of admission into the paediatric intensive care unit and is associated with high mortality. Non-invasive positive pressure ventilation, lung-protective ventilation strategies, conservative fluid management and adequate nutrition are advocated. As there has been a lack of progress in the management of PARDS in recent years, further well-designed, large-scale, randomized controlled trials in this field are urgently needed.

Biomedical engineer's guide to the clinical aspects of intensive care mechanical ventilation

Background

Mechanical ventilation is an essential therapy to support critically ill respiratory failure patients. Current standards of care consist of generalised approaches, such as the use of positive end expiratory pressure to inspired oxygen fraction (PEEP–FiO₂) tables, which fail to account for the inter- and intra-patient variability between and within patients. The benefits of higher or lower tidal volume, PEEP, and other settings are highly debated and no consensus has been reached. Moreover, clinicians implicitly account for patient-specific factors such as disease condition and progression as they manually titrate ventilator settings. Hence, care is highly variable and potentially often non-optimal. These conditions create a situation that could benefit greatly from an engineered approach. The overall goal is a review of ventilation that is accessible to both clinicians and engineers, to bridge the divide between the two fields and enable collaboration to improve patient care and outcomes. This review does not take the form of a typical systematic review. Instead, it defines the standard terminology and introduces key clinical and biomedical measurements before introducing the key clinical studies and their influence in clinical practice which in turn flows into the needs and requirements around how biomedical engineering research can play a role in improving care. Given the significant clinical research to date and its impact on this complex area of care, this review thus provides a tutorial introduction around the review of the state of the art relevant to a biomedical engineering perspective.

Discussion

This review presents the significant clinical aspects and variables of ventilation management, the potential risks associated with suboptimal ventilation management, and a review of the major recent attempts to improve ventilation in the context of these variables. The unique aspect of this review is a focus on these key elements relevant to engineering new approaches. In particular, the need for ventilation strategies which consider, and directly account for, the significant differences in patient condition, disease etiology, and progression within patients is demonstrated with the subsequent requirement for optimal ventilation strategies to titrate for patient- and time-specific conditions.

Conclusion

Engineered, protective lung strategies that can directly account for and manage inter- and intra-patient variability thus offer great potential to improve both individual care, as well as cohort clinical outcomes.

Pediatric Acute Respiratory Distress Syndrome: Fibrosis versus Repair

Clinical and basic experimental approaches to pediatric acute lung injury (ALI), including acute respiratory distress syndrome (ARDS), have historically focused on acute care and management of the patient. Additional efforts have focused on the etiology of pediatric ALI and ARDS, clinically defined as diffuse, bilateral diseases of the lung that compromise function leading to severe hypoxemia within 7 days of defined insult. Insults can include ancillary events related to prematurity, can follow trauma and/or transfusion, or can present as sequelae of pulmonary infections and cardiovascular disease and/or injury. Pediatric ALI/ARDS remains one of the leading causes of infant and childhood morbidity and mortality, particularly in the developing world. Though incidence is relatively low, ranging from 2.9 to 9.5 cases/100,000 patients/year, mortality remains high, approaching 35% in some studies. However, this is a significant decrease from the historical mortality rate of over 50%. Several decades of advances in acute management and treatment, as well as better understanding of approaches to ventilation, oxygenation, and surfactant regulation have contributed to improvements in patient recovery. As such, there is a burgeoning interest in the long-term impact of pediatric ALI/ARDS. Chronic pulmonary deficiencies in survivors appear to be caused by inappropriate injury repair, with fibrosis and predisposition to emphysema arising as irreversible secondary events that can severely compromise pulmonary development and function, as well as the overall health of the patient. In this chapter, the long-term effectiveness of current treatments will be examined, as will the potential efficacy of novel, acute, and long-term therapies that support repair and delay or even impede the onset of secondary events, including fibrosis.

Update in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by permeability pulmonary edema and refractory hypoxemia. Recently, the new definition of ARDS has been published, and this definition suggested severity-oriented respiratory treatment by introducing three levels of severity according to PaO₂/FiO₂ and positive end-expiratory pressure. Lung-protective ventilation is still the key of better outcome in ARDS. Through randomized trials, short-term use of neuromuscular blockade at initial stage of mechanical ventilation, prone ventilation in severe ARDS, and extracorporeal membrane oxygenation in ARDS with influenza pneumonia showed beneficial efficacy. However, ARDS mortality still remains high. Therefore, early recognition of ARDS modified risk factors and the avoidance of aggravating factors during the patient's hospital stay can help decrease its development. In addition, efficient antifibrotic strategies in late-stage ARDS should be developed to improve the outcome.

Acute respiratory distress syndrome after pulmonary resection

Postoperative acute respiratory distress syndrome (ARDS) is a recognized complication of pulmonary resection. It is characterized by the acute onset of hypoxemia with radiographic infiltrates consistent with pulmonary edema, without elevations in the pulmonary capillary wedge pressure. Many studies suggest that around 2-5 % of patients develop some degree of lung injury, and the mortality from ARDS following pulmonary resection remains high. ARDS following thoracotomy and lung resection has a miserable prognosis, with overall hospital mortality rates over 25 %. The present review evaluates the evidence available in the literature tracking perioperative mortality and morbidity as well as the pathogenesis and management of ARDS in patients undergoing pulmonary resection.