Ventilator-induced lung injury: historical perspectives and clinical implications

Mechanical ventilation can produce lung physiological and morphological alterations termed ventilator-induced lung injury (VILI). Early experimental studies demonstrated that the main determinant of VILI is lung end-inspiratory volume. The clinical relevance of these experimental findings received resounding confirmation with the results of the acute respiratory distress syndrome (ARDS) Network study, which showed a 22% reduction in mortality in patients with the acute respiratory distress syndrome through a simple reduction in tidal volume. In contrast, the clinical relevance of low lung volume injury remains debated and the application of high positive end-expiratory pressure levels can contribute to lung overdistension and thus be deleterious. The significance of inflammatory alterations observed during VILI is debated and has not translated into clinical application. This review examines seminal experimental studies that led to our current understanding of VILI and contributed to the current recommendations in the respiratory support of ARDS patients

Modeling 18F−FDG^{18}F-FDG Kinetics during Acute Lung Injury: Experimental Data and Estimation Errors

Background: There is increasing interest in Positron Emission Tomography (PET) of 2-deoxy-2-[18F]flouro-D-glucose ($^{18}F-FDG$) to evaluate pulmonary inflammation during acute lung injury (ALI). We assessed the effect of extra-vascular lung water on estimates of $^{18}F-FDG$-kinetics parameters in experimental and simulated data using the Patlak and Sokoloff methods, and our recently proposed four-compartment model. Methodology/Principal Findings Eleven sheep underwent unilateral lung lavage and 4 h mechanical ventilation. Five sheep received intravenous endotoxin (10 ng/kg/min). Dynamic $^{18}F-FDG$ PET was performed at the end of the 4 h period. $^{18}F-FDG$ net uptake rate (Ki), phosphorylation rate (k3), and volume of distribution (Fe) were estimated in three isogravitational regions for each method. Simulations of normal and ALI $^{18}F-FDG$-kinetics were conducted to study the dependence of estimated parameters on the transport rate constants to (k5) and from (k6) the extra-vascular extra-cellular compartment. The four-compartment model described 85.7% of the studied $^{18}F-FDG$-kinetics better than the Sokoloff model. Relative to the four-compartment model the Sokoloff model exhibited a consistent positive bias in Ki (3.32 [1.30–5.65] 10−4/min, p<0.001) and showed inaccurate estimates of the parameters composing Ki (k3 and Fe), even when Ki was similar for those methods. In simulations, errors in estimates of Ki due to the extra-vascular extra-cellular compartment depended on both k5 and k5/k6, with errors for the Patlak and Sokoloff methods of 0.02 [−0.01–0.18] and 0.40 [0.18–0.60] 10−3/min for normal lungs and of −0.47 [−0.89–0.72] and 2.35 [0.85–3.68] 10−3/min in ALI. Conclusions/Significance: $^{18}F-FDG$ accumulation in lung extra-vascular fluid, which is commonly increased during lung injury, can result in substantial estimation errors using the traditional Patlak and Sokoloff methods. These errors depend on the extra-vascular extra-cellular compartment volume and its transport rates with other compartments. The four-compartment model provides more accurate quantification of $^{18}F-FDG$-kinetics than those methods in the presence of increased extra-vascular fluid

Effects of ventilation strategy on distribution of lung inflammatory cell activity

Introduction: Leukocyte infiltration is central to the development of acute lung injury, but it is not known how mechanical ventilation strategy alters the distribution or activation of inflammatory cells. We explored how protective (vs. injurious) ventilation alters the magnitude and distribution of lung leukocyte activation following systemic endotoxin administration. Methods: Anesthetized sheep received intravenous endotoxin (10 ng/kg/min) followed by 2 h of either injurious or protective mechanical ventilation (n = 6 per group). We used positron emission tomography to obtain images of regional perfusion and shunting with infused 13N[nitrogen]-saline and images of neutrophilic inflammation with 18F-fluorodeoxyglucose (18F-FDG). The Sokoloff model was used to quantify 18F-FDG uptake (Ki), as well as its components: the phosphorylation rate (k3, a surrogate of hexokinase activity) and the distribution volume of 18F-FDG (Fe) as a fraction of lung volume (Ki = Fe × k3). Regional gas fractions (fgas) were assessed by examining transmission scans. Results: Before endotoxin administration, protective (vs. injurious) ventilation was associated with a higher ratio of partial pressure of oxygen in arterial blood to fraction of inspired oxygen (PaO2/FiO2) (351 ± 117 vs. 255 ± 74 mmHg; P < 0.01) and higher whole-lung fgas (0.71 ± 0.12 vs. 0.48 ± 0.08; P = 0.004), as well as, in dependent regions, lower shunt fractions. Following 2 h of endotoxemia, PaO2/FiO2 ratios decreased in both groups, but more so with injurious ventilation, which also increased the shunt fraction in dependent lung. Protective ventilation resulted in less nonaerated lung (20-fold; P < 0.01) and more normally aerated lung (14-fold; P < 0.01). Ki was lower during protective (vs. injurious) ventilation, especially in dependent lung regions (0.0075 ± 0.0043/min vs. 0.0157 ± 0.0072/min; P < 0.01). 18F-FDG phosphorylation rate (k3) was twofold higher with injurious ventilation and accounted for most of the between-group difference in Ki. Dependent regions of the protective ventilation group exhibited lower k3 values per neutrophil than those in the injurious ventilation group (P = 0.01). In contrast, Fe was not affected by ventilation strategy (P = 0.52). Lung neutrophil counts were not different between groups, even when regional inflation was accounted for. Conclusions: During systemic endotoxemia, protective ventilation may reduce the magnitude and heterogeneity of pulmonary inflammatory cell metabolic activity in early lung injury and may improve gas exchange through its effects predominantly in dependent lung regions. Such effects are likely related to a reduction in the metabolic activity, but not in the number, of lung-infiltrating neutrophils

Relationship between calcinosis cutis in epidermal necrolysis and caspofungin, a physicochemical investigation

Epidermal necrolysis (EN) is a rare life-threatening condition, usually drug-induced and characterised by a diffuse epidermal and mucosal detachment. Calcinosis cutis is reported in various skin diseases, occurring preferentially with tissue damage, but has never been described in EN. Clinical, biological and histopathological characteristics of three patients were retrospectively obtained from medical charts. Immunohistochemistry of classical osteogenic markers was used to explore the pathogenesis of the calcifications; their chemical composition was determined by $\mu$Fourier transform infra-red ($\mu$FTIR) spectroscopy and their localization and morphology by field-emission scanning electron microscopy (FE-SEM). In a recent letter, part of the results of this investigation has been already presented. In this contribution, we have added original data to this previous letter. We have investigated a set of biopsies corresponding to patients who presented atypical healing retardation due to calcinosis cutis. Through FE-SEM observations at the nanometre scale, we describe different areas where are present voluminous calcifications at the surface, submicrometre spherical entities within the papillary dermis and then large “normal” fibres. FE-SEM observations show clearly that “large” calcifications are the result of an agglomeration of small spherical entities. Moreover, micrometre scale spherical entities are the results of an agglomeration of nanometer scale spherical entities. Finally, the last set of data seems to show that the starting point of the calcifications process is “distant” from the epidermis in part of the dermis which appears undamaged. Regarding the chemical composition of large calcifications, different $\mu$FTIR maps which underlined the presence of calcium-phosphate apatite have been gathered. Moreover, histopathology indicates that these pathological calcifications are not induced following a trans-differentiation of the skin cells into an osteochondrogenic phenotype. The association of caspofungin administration, known to induce in vitro intracellular calcium influx, and inflammation, induced by EN, known to favor dystrophic calcifications in various inflammatory skin diseases, could explain this never-before reported occurrence of calcinosis cutis

Relationship between calcinosis cutis in epidermal necrolysis and caspofungin, a physicochemical investigation

Epidermal necrolysis (EN) is a rare life-threatening condition, usually drug-induced and characterised by a diffuse epidermal and mucosal detachment. Calcinosis cutis is reported in various skin diseases, occurring preferentially with tissue damage, but has never been described in EN. Clinical, biological and histopathological characteristics of three patients were retrospectively obtained from medical charts. Immunohistochemistry of classical osteogenic markers was used to explore the pathogenesis of the calcifications; their chemical composition was determined by $\mu$Fourier transform infra-red ($\mu$FTIR) spectroscopy and their localization and morphology by field-emission scanning electron microscopy (FE-SEM). In a recent letter, part of the results of this investigation has been already presented. In this contribution, we have added original data to this previous letter. We have investigated a set of biopsies corresponding to patients who presented atypical healing retardation due to calcinosis cutis. Through FE-SEM observations at the nanometre scale, we describe different areas where are present voluminous calcifications at the surface, submicrometre spherical entities within the papillary dermis and then large “normal” fibres. FE-SEM observations show clearly that “large” calcifications are the result of an agglomeration of small spherical entities. Moreover, micrometre scale spherical entities are the results of an agglomeration of nanometer scale spherical entities. Finally, the last set of data seems to show that the starting point of the calcifications process is “distant” from the epidermis in part of the dermis which appears undamaged. Regarding the chemical composition of large calcifications, different $\mu$FTIR maps which underlined the presence of calcium-phosphate apatite have been gathered. Moreover, histopathology indicates that these pathological calcifications are not induced following a trans-differentiation of the skin cells into an osteochondrogenic phenotype. The association of caspofungin administration, known to induce in vitro intracellular calcium influx, and inflammation, induced by EN, known to favor dystrophic calcifications in various inflammatory skin diseases, could explain this never-before reported occurrence of calcinosis cutis

Social security and retirement around the world:Lessons from a long-term collaboration

Declining labor force participation of older men throughout the 20th century and recent increases in participation have generated substantial interest in understanding the effect of public pensions on retirement. The National Bureau of Economic Research's International Social Security (ISS) Project, a long-term collaboration among researchers in a dozen developed countries, has explored this and related questions. The project employs a harmonized approach to conduct within-country analyses that are combined for meaningful cross-country comparisons. The key lesson is that the choices of policy makers affect the incentive to work at older ages and these incentives have important effects on retirement behavior.</p

Autoantibodies neutralizing type I IFNs are present in ~4% of uninfected individuals over 70 years old and account for ~20% of COVID-19 deaths

Publisher Copyright: © 2021 The Authors, some rights reserved.Circulating autoantibodies (auto-Abs) neutralizing high concentrations (10 ng/ml; in plasma diluted 1:10) of IFN-alpha and/or IFN-omega are found in about 10% of patients with critical COVID-19 (coronavirus disease 2019) pneumonia but not in individuals with asymptomatic infections. We detect auto-Abs neutralizing 100-fold lower, more physiological, concentrations of IFN-alpha and/or IFN-omega (100 pg/ml; in 1:10 dilutions of plasma) in 13.6% of 3595 patients with critical COVID-19, including 21% of 374 patients >80 years, and 6.5% of 522 patients with severe COVID-19. These antibodies are also detected in 18% of the 1124 deceased patients (aged 20 days to 99 years; mean: 70 years). Moreover, another 1.3% of patients with critical COVID-19 and 0.9% of the deceased patients have auto-Abs neutralizing high concentrations of IFN-beta. We also show, in a sample of 34,159 uninfected individuals from the general population, that auto-Abs neutralizing high concentrations of IFN-alpha and/or IFN-omega are present in 0.18% of individuals between 18 and 69 years, 1.1% between 70 and 79 years, and 3.4% >80 years. Moreover, the proportion of individuals carrying auto-Abs neutralizing lower concentrations is greater in a subsample of 10,778 uninfected individuals: 1% of individuals 80 years. By contrast, auto-Abs neutralizing IFN-beta do not become more frequent with age. Auto-Abs neutralizing type I IFNs predate SARS-CoV-2 infection and sharply increase in prevalence after the age of 70 years. They account for about 20% of both critical COVID-19 cases in the over 80s and total fatal COVID-19 cases.Peer reviewe

Hyperoxemia and excess oxygen use in early acute respiratory distress syndrome : Insights from the LUNG SAFE study

Publisher Copyright: © 2020 The Author(s). Copyright: Copyright 2020 Elsevier B.V., All rights reserved.Background: Concerns exist regarding the prevalence and impact of unnecessary oxygen use in patients with acute respiratory distress syndrome (ARDS). We examined this issue in patients with ARDS enrolled in the Large observational study to UNderstand the Global impact of Severe Acute respiratory FailurE (LUNG SAFE) study. Methods: In this secondary analysis of the LUNG SAFE study, we wished to determine the prevalence and the outcomes associated with hyperoxemia on day 1, sustained hyperoxemia, and excessive oxygen use in patients with early ARDS. Patients who fulfilled criteria of ARDS on day 1 and day 2 of acute hypoxemic respiratory failure were categorized based on the presence of hyperoxemia (PaO2 > 100 mmHg) on day 1, sustained (i.e., present on day 1 and day 2) hyperoxemia, or excessive oxygen use (FIO2 ≥ 0.60 during hyperoxemia). Results: Of 2005 patients that met the inclusion criteria, 131 (6.5%) were hypoxemic (PaO2 < 55 mmHg), 607 (30%) had hyperoxemia on day 1, and 250 (12%) had sustained hyperoxemia. Excess FIO2 use occurred in 400 (66%) out of 607 patients with hyperoxemia. Excess FIO2 use decreased from day 1 to day 2 of ARDS, with most hyperoxemic patients on day 2 receiving relatively low FIO2. Multivariate analyses found no independent relationship between day 1 hyperoxemia, sustained hyperoxemia, or excess FIO2 use and adverse clinical outcomes. Mortality was 42% in patients with excess FIO2 use, compared to 39% in a propensity-matched sample of normoxemic (PaO2 55-100 mmHg) patients (P = 0.47). Conclusions: Hyperoxemia and excess oxygen use are both prevalent in early ARDS but are most often non-sustained. No relationship was found between hyperoxemia or excessive oxygen use and patient outcome in this cohort. Trial registration: LUNG-SAFE is registered with ClinicalTrials.gov, NCT02010073publishersversionPeer reviewe