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

Advanced Multiphase Steels

We are currently experiencing an increasingly fast development of new steel grades with complex multiphase microstructures attempting to give tailored answers to industrial demands [...

Aceros avanzados de alta resistencia de matriz bainítica: Estudio de la transformación de fase y de las relaciones entre procesamiento, microestructura y propiedades mecánicas.

Debido a la creciente exigencia de la industria automovilística por aligerar el peso del vehículo e incrementar la seguridad, han surgido nuevos grados de acero de alta resistencia. Los aceros bainíticos libres de carburos, por sus buenas propiedades mecánicas, son candidatos a formar parte de la tercera generación de aceros avanzados de alta resistencia. Este tipo de acero se produce principalmente en forma de chapa en líneas de recocido continuo o galvanizado, por lo que las diferentes variables del proceso influyen de manera notable, tanto sobre su microestructura final como en las propiedades mecánicas. Esta tesis se ha centrado en el estudio de dos aceros bajo carbono con matriz bainitica aleados respectivamente con silicio y cromo. En primer lugar, se han analizado las cinéticas de transformación de ambos aceros durante su permanencia en la región bainítica y se ha estudiado en detalle la evolución microestructural de ambos con las variables del ciclo térmico. Para llevar a cabo este estudio, se han realizado ensayos de dilatometría donde se ha variado la temperatura de austenización, la velocidad de enfriamiento y la temperatura y tiempo de mantenimiento en la región bainitica. Además, ha sido necesario desarrollar una metodología para la preparación metalográfica de las muestras y la cuantificación de las fases que componen la microestructura a través de diferentes técnicas (óptico, FEG-SEM, EBSD y rayos X). En segundo lugar, se han estudiado las propiedades mecánicas de estos aceros atendiendo a tres puntos. En el primero, se ha tenido en cuenta el comportamiento mecánico de cada uno de los microconstituyentes: bainita, martensita de bajo carbono, martensita de alto carbono y austenita retenida. En concreto, se ha medido la dureza a través del empleo de la técnica de nanoindentación y se ha relacionado esta propiedad con las variables del proceso.Con el objeto de profundizar en las relaciones microestructura-proceso-propiedades mecánicas, se han realizado una serie de ensayos de tracción sobre las muestras extraídas de chapas recocidas en el simulador de recocido vertical que posee el CEIT. Estos ensayos, junto a otros ensayos incluidos dentro del proyecto Baseform, proyecto en el que se enmarca esta tesis, han dado lugar a una gran variabilidad de limite elástico, resistencia a la tracción y elongaciones. Esto ha permitido realizar un análisis exhaustivo de las relaciones entre propiedades mecánicas, microestructura y procesamiento. Además de las propiedades a tracción, como tercer punto, se ha estudiado la conformabilidad. La baja conformabilidad en frio y los problemas de agrietamiento de borde de los aceros multifásicos son las principales desventajas que presentan los aceros multifásicos. Por ello, se busca de manera incesante el modo de evitar estos problemas e incrementar la conformabilidad. En este trabajo se han empleado los resultados de los ensayos de expansión de orificio (HET), obtenidos dentro del proyecto Baseform, con ellos se mide de forma indirecta la conformabilidad, con el objeto de relacionar esta propiedad con la microestructura y así mejorarla a través de la optimización de la microestructura. Con el objeto de profundizar en las relaciones microestructura-proceso-propiedades mecánicas, se han realizado una serie de ensayos de tracción sobre las muestras extraídas de chapas recocidas en el simulador de recocido vertical que posee el CEIT. Estos ensayos, junto a otros ensayos incluidos dentro del proyecto Baseform, proyecto en el que se enmarca esta tesis, han dado lugar a una gran variabilidad de limite elástico, resistencia a la tracción y elongaciones. Esto ha permitido realizar un análisis exhaustivo de las relaciones entre propiedades mecánicas, microestructura y procesamiento. Además de las propiedades a tracción, como tercer punto, se ha estudiado la conformabilidad. La baja conformabilidad en frio y los problemas de agrietamiento de borde de los aceros multifásicos son las principales desventajas que presentan los aceros multifásicos. Por ello, se busca de manera incesante el modo de evitar estos problemas e incrementar la conformabilidad. En este trabajo se han empleado los resultados de los ensayos de expansión de orificio (HET), obtenidos dentro del proyecto Baseform, con ellos se mide de forma indirecta la conformabilidad, con el objeto de relacionar esta propiedad con la microestructura y así mejorarla a través de la optimización de la microestructura.Por último, se han realizado ensayos de tracción sobre diferentes geometrías de probeta para estudiar cómo evoluciona la microestructura con la deformación y cómo y dónde se produce el daño en el acero con alto contenido en Si. Se ha analizado la evolución de la austenita retenida, afectada por el efecto TRIP (transformation induced plasticity) y de la matriz bainítica, tanto en la región de deformación uniforme como dentro de la zona de estricción. Además, se ha evaluado los lugares donde se originan las cavidades y como tiene lugar la fractura.New grades of high strength steels have emerged in response to the growing demand of the automobile industry to lighten the weight and increase the safety. Carbide free steels are candidates to be part of the third AHSS steels due to their good mechanical properties. They are produced in the form of sheet and in a continuous annealing or galvanized, therefore the process conditions have an important influence on the microstructure and mechanical properties. This dissertation is focused on the study of two low carbon steels with bainitic matrix, one alloyed with silicon and another with chromium. Firstly, phase transformation kinetics and microstructural evolution of both steels as function of the process conditions has been analysed. In order to perform this study, dilatometry tests have been performed varying the austenitization temperature, cooling rate and temperature and time in the bainitic region. It was necessary to develop a methodology for the sample preparation and phase quantification with several techniques (optical, FEG-SEM, EBSD, X-ray diffraction).Secondly, the mechanical properties of these steels have been studied according to three points. Firstly, mechanical properties, specifically, the hardness of the phases, which compound the microstructure: bainite, low carbon martensite, high carbon martensite and retained austenite has been measured and associated with the processing conditions. Nanoindentation technique has been used to carry out this study. In order to evaluate the relationship between the microstructure, process conditions and mechanical properties, several tensile tests were carried out on the samples extracted from annealed sheets in the vertical annealing simulator that CEIT has. These tests together with the tests included in the project Baseform, project in which this thesis is framed, have led to a great variability of yield strength, tensile strength and elongation. This has allowed an in-depth analysis of the relationships between mechanical properties, microstructure and processing. In addition, formability has been studied. The low cold-formability and the problem of edge cracking are the principal disadvantages of the multiphase steel. Thus, considerable attention has been paid to the improvement in these properties. In this work, hole expansion test (HET) have been performed, in which formability is measured in an indirect way. These results have been related with microstructure with the purpose of understand the relationship to improving the formability.Lastly, tensile tests on specimens with different geometries have been performed to study how the microstructure evolves with the strain and how and where the damage is produced in high silicon steel. The bainitic matrix and retained austenite evolution have been analysed in the uniform and necking region. Retained austenite is affected by the TRIP effect (Transformation Induced Plasticity). Furthermore, the preferred sites where voids are originated and how the fracture is has been evaluated

Substructure Development and Damage Initiation in a Carbide-Free Bainitic Steel upon Tensile Test

Carbide-free bainitic (CFB) steels belong to the family of advanced high strength steels (AHSS) that are struggling to become part of the third-generation steels to be marketed for the automotive industry. The combined effects of the bainitic matrix and the retained austenite confers a significant strength with a remarkable ductility to these steels. However, CFB steels usually show much more complex microstructures that also contain MA (Martensite&ndash;Austenite) phase and auto-tempered martensite (ATM). These phases may compromise the ductility of CFB steels. The present work analyzes the substructure evolution during tensile tests in the necking zone, and deepens into the void and crack formation mechanisms and their relationship with the local microstructure. The combination of FEG-SEM imaging, EBSD, and X-ray diffraction has been necessary to characterize the substructure development and damage initiation. The bainite matrix has shown great ductility through the generation of high angle grain boundaries and/or large orientation gradients around voids, which are usually found close to the bainite and MA/auto-tempered martensite interfaces or fragmenting the MA phase. Special attention has been paid to the stability of the retained austenite (RA) during the test, which may eventually be transformed into martensite (Transformation Induced Plasticity, or TRIP effect)

Substructure development and damage initiation in a carbide-free bainitic steel upon tensile test

Carbide-free bainitic (CFB) steels belong to the family of advanced high strength steels (AHSS) that are struggling to become part of the third-generation steels to be marketed for the automotive industry. The combined effects of the bainitic matrix and the retained austenite confers a significant strength with a remarkable ductility to these steels. However, CFB steels usually show much more complex microstructures that also contain MA (Martensite–Austenite) phase and auto-tempered martensite (ATM). These phases may compromise the ductility of CFB steels. The present work analyzes the substructure evolution during tensile tests in the necking zone, and deepens into the void and crack formation mechanisms and their relationship with the local microstructure. The combination of FEG-SEM imaging, EBSD, and X-ray diffraction has been necessary to characterize the substructure development and damage initiation. The bainite matrix has shown great ductility through the generation of high angle grain boundaries and/or large orientation gradients around voids, which are usually found close to the bainite and MA/auto-tempered martensite interfaces or fragmenting the MA phase. Special attention has been paid to the stability of the retained austenite (RA) during the test, which may eventually be transformed into martensite (Transformation Induced Plasticity, or TRIP effect)

Substructure development and damage initiation in a carbide-free bainitic steel upon tensile test

Carbide-free bainitic (CFB) steels belong to the family of advanced high strength steels (AHSS) that are struggling to become part of the third-generation steels to be marketed for the automotive industry. The combined effects of the bainitic matrix and the retained austenite confers a significant strength with a remarkable ductility to these steels. However, CFB steels usually show much more complex microstructures that also contain MA (Martensite–Austenite) phase and auto-tempered martensite (ATM). These phases may compromise the ductility of CFB steels. The present work analyzes the substructure evolution during tensile tests in the necking zone, and deepens into the void and crack formation mechanisms and their relationship with the local microstructure. The combination of FEG-SEM imaging, EBSD, and X-ray diffraction has been necessary to characterize the substructure development and damage initiation. The bainite matrix has shown great ductility through the generation of high angle grain boundaries and/or large orientation gradients around voids, which are usually found close to the bainite and MA/auto-tempered martensite interfaces or fragmenting the MA phase. Special attention has been paid to the stability of the retained austenite (RA) during the test, which may eventually be transformed into martensite (Transformation Induced Plasticity, or TRIP effect)

An EBSD-based methodology for the characterization of intercritically deformed low carbon steel

Heavy gauge structural plates has been widely rolled in the austenite/ferrite two phase region, in order to meet the demanding market requirements regarding tensile properties. Even though strength levels can be increased by intercritical rolling, toughness properties may be impaired. Therefore, a greater knowledge of how different austenite-ferrite balances affect the microstructural evolution during intercritical deformation is required. With the aim of gaining a deep comprehension of the evolution of the microstructure during intercritical deformation, dilatometry tests were performed simulating intercritical rolling conditions. Different ferrite populations are identified in the resulting microstructures, composed of intercritically deformed ferrite and non-deformed ferrite transformed during final air cooling. In the deformed ferrite grains well defined substructure is clearly noticed, whereas the non-deformed grains formed during air cooling step do not show any evidence of substructure. In the current work, EBSD advanced characterization technique was used to develop a methodology that is able to differentiate the intercritically deformed ferrite from non-deformed ferrite for low carbon steels. Based on the Grain Orientation Spread (GOS) parameter, a threshold value of 2 degrees was defined to distinguish deformed and non deformed ferrite grains. The proposed procedure allows distinguishing both ferrite populations and quantifying microstructural parameters of each family. The effect of the addition of C and austenite-ferrite balance on the microstructural evolution of each ferrite type was analyzed

Magnetic NDT for Steel Microstructure Characterisation – Modelling the Effect of Ferrite Grain Size on Magnetic Properties

International audienceThe mechanical properties of steels are controlled by their microstructural parameters, such as grain size, phase balance and precipitates, which are developed during thermo-mechanical processing. It is desirable to be able to monitor microstructural changes during processing, allowing in-situ feedback control, or to characterize microstructure in steel products in a non-contact and non-destructive manner. Electromagnetic (EM) measurements are sensitive to changes in magnetic properties, which, in steels, vary with composition, microstructure and temperature. In order to interpret the EM signal for microstructure analysis, it is important to be able to predict the magnetic properties from the microstructural parameters.In this paper, an extra low carbon steel has been used to generate a single phase microstructure (ferrite) with a range of grain sizes of 14-78 μm. The grain structures were characterised by optical microscopy and EBSD. A Voronoi based algorithm (Multi Level Voronoi), which provides a parametric description of the microstructure, i.e. the boundaries, in a grid format, is used to generate 2D and 3D microstructure models with different grain sizes. Based on these microstructure models, multi scale 2D and 3D magnetic modelling approaches were applied to predict the magnetic properties. At the micro scale, a 3D micro-magnetic simulation code (EMicroM), which considers a finite volume (1003 μm3 cube blocks) of material at a resolution down to the thickness of the domain wall (0.2 μm), has been used to derive the dynamic magnetic behaviour (i.e. hysteresis curve). The predicted coercive fieldvalues have been shown to decrease when the grain size increases, in line with experimentalobservations. The modelled hysteresis loop has a similar coercive fieldvalue with the experimental measured one, although the slopes of the curves are different. At the meso level, a 2D finite element modelling approach using COMSOL Multiphysics was used tosimulate the EM response of an area of around 1000×1000μm2. The model predicts effective relative permeability by considering the ferrite grains and grain boundary regions as constituents with different relative permeability values. The modelled results agree well with the experimentally determined permeability values from EM sensor measurements