Acute lung injury: pathophysiology, assessment and current therapy

Diffuse Alveolar Damage Correlation with Clinical Diagnosis of Pediatric Acute Respiratory Distress Syndrome

Diffuse alveolar damage (DAD) is one of the pathological hallmarks of acute respiratory distress syndrome (ARDS). We aimed to compare pathological findings of DAD with clinical ARDS criteria. We re-evaluated 20 patients whose clinical autopsy revealed DAD. Total 11/20 patients with DAD (55%) met the 1994 American-European Consensus Conference and 7/17 (41%) met the 2012 Berlin clinical criteria. DAD showed only moderate correlation with current clinical ARDS definition. Oxygenation index (OI), seems to be the most valuable tool in predicting pulmonary damage severity, though OI is not listed in either of the previous definitions. We support the recommended use of OI by 2015 consensus conference.

Protective effect of TM6 on LPS-induced acute lung injury in mice

Acute lung injury (ALI) is an acute failure of the respiratory system for which effective treatment is urgently necessary. Previous studies found that several peptides potently inhibited the production of cytokines induced by lipopolysaccharide (LPS). In this study, we synthetized a cell-permeable TIR domain-derived decoy peptide (TM6) and examined its substance for the ability to inhibit TLR signaling in the model of ALI induced by LPS. We demonstrated that TM6 (2.5, 5 and 10 nmol/g) alleviated the histological changes in the lung tissues as well as myeloperoxtidase (MPO) activity, lung W/D ratio, the production of TNF-α, IL-1β and IL-6 induced by LPS. Furthermore, the numbers of total cells, neutrophils and macrophages in the BALF were suppressed by TM6. In vitro, TM6 (5, 10 and 20 µM) inhibited the production of TNF-α, IL-1β and IL-6 in LPS-stimulated alveolar macrophages. Moreover, the activation of Nuclear factor-kappaB (NF-κB) and Mitogen activated protein kinases (MAPK) signaling pathways induced by LPS were also inhibited by TM6. Collectively, our results suggested that TM6 was an effective inhibitor of ALI induced by LPS, and this peptide may very well serve as a future treatment for ALI.

Temporal evolution of acute respiratory distress syndrome definitions

OBJECTIVE

to review the evolution of acute respiratory distress syndrome (ARDS) definitions and present the current definition for the syndrome.

DATA SOURCE

a literature review and selection of the most relevant articles on ARDS definitions was performed using the MEDLINE®/PubMed® Resource Guide database (last ten years), in addition to including the most important articles (classic articles) that described the disease evolution.

DATA SYNTHESIS

the review included the following subjects: introduction; importance of definition; description of the first diagnostic criterion and subsequently used definitions, such as acute lung injury score; definition by the American-European Consensus Conference, and its limitations; description of the definition by Delphi, and its problems; accuracy of the aforementioned definitions; description of most recent definition (the Berlin definition), and its limitations; and practical importance of the new definition.

CONCLUSIONS

ARDS is a serious disease that remains an ongoing diagnostic and therapeutic challenge. The evolution of definitions used to describe the disease shows that studies are needed to validate the current definition, especially in pediatrics, where the data are very scarce.

Matrix metalloproteinase activity in pediatric acute lung injury

Pediatric Acute Lung Injury (ALI) is associated with a high mortality and morbidity, and dysregulation of matrix metalloproteinases (MMPs) may play an important role in the pathogenesis and evolution of ALI. Here we examined MMP expression and activity in pediatric ALI compared with controls. MMP-8, -9, and to a lesser extent, MMP-2, -3, -11 and -12 were identified at higher levels in lung secretions of pediatric ALI patients compared with controls. Tissue Inhibitor of Matrix metalloproteinase-1 (TIMP-1), a natural inhibitor of MMPs was detected in most ALI samples, but MMP-9:TIMP-1 ratios were high relative to controls. In subjects who remained intubated for >or=10 days, MMP-9 activity decreased, with > 80% found in the latent form. In contrast, almost all MMP-8 detected at later disease course was constitutively active. Discriminating MMP-9:TIMP-1 ratios were found in those who had a prolonged ALI course. These results identify a specific repertoire of MMP isoforms in the lung secretions of pediatric ALI patients, and demonstrate inverse changes in MMPs -8 and -9 with protracted disease.

Lung Volume Recruitment after Surfactant Administration Modifies Spatial Distribution of Ventilation

RATIONALE

Although surfactant replacement therapy is an established treatment in infant respiratory distress syndrome, the optimum strategy for ventilatory management before, during, and after surfactant instillation remains to be elucidated.

OBJECTIVES

To determine the effects of surfactant and lung volume recruitment on the distribution of regional lung ventilation.

METHODS

Acute lung injury was induced in 16 newborn piglets by endotracheal lavage. Optimum positive end-expiratory pressure was identified after lung recruitment and surfactant was administered either at this pressure in the "open" lung or after disconnection of the endotracheal tube in the "closed" lung. An additional recruitment maneuver with subsequent optimum end-expiratory pressure finding was executed in eight animals; in the remaining eight animals, end-expiratory pressure was set at the same level as before surfactant without further recruitment. ("Open" and "closed" lung surfactant administration was evenly distributed in the groups.) Regional ventilation was assessed by electrical impedance tomography.

MEASUREMENTS AND MAIN RESULTS

Impedance tomography data, airway pressure, flow, and arterial blood gases were acquired during baseline conditions, after induction of lung injury, after the first lung recruitment, and before as well as 10 and 60 min after surfactant administration. Significant shift in ventilation toward the dependent lung regions and less asymmetry in the right-to-left lung ventilation distribution occurred in the postsurfactant period when an additional recruitment maneuver was performed. Surfactant instillation in an "open" versus "closed" lung did not influence ventilation distribution in a major way.

CONCLUSIONS

The spatial distribution of ventilation in the lavaged lung is modified by a recruitment maneuver performed after surfactant administration.