Nitretação por plasma em baixa temperatura dos aços inoxidáveis martensíticos : estudo da influência da composição química do aço na cinética de tratamento

Orientador: Prof. Dr. Rodrigo Perito CardosoCo-orientador: Prof. Dr. Silvio Francisco BrunattoDissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia e Ciência dos Materiais - PIPE. Defesa: Curitiba, 13/04/2015Inclui referências : f. 86-90Área de concentração: Engenharia e ciência de materiaisResumo: A crescente aplicação dos tratamentos termoquímicos assistidos por plasma no âmbito industrial motivou o desenvolvimento deste trabalho. Agregando bons resultados no tratamento de superfícies e sendo uma técnica pouco agressiva ambientalmente, a nitretação por plasma possui aplicações na substituição dos banhos de sais, conhecidos por gerar resíduos e gases nocivos ao ambiente. A nitretação por plasma em baixas temperaturas, abaixo de 400 °C, pode gerar benefícios ao melhorar o comportamento tribológico dos aços inoxidáveis, pelo aumento da dureza da camada tratada, mantendo sua resistência a corrosão. Isto se deve à difusão do nitrogênio e formação de uma camada nitretada com espessura dependente do tempo, temperatura, pressão, composição e fluxo da mistura gasosa. Neste contexto, o presente trabalho trata da influência da composição química dos aços inoxidáveis martensíticos AISI 410, AISI 410NiMo, AISI 416 e AISI 420, na cinética de tratamento. Para tanto foram realizados tratamentos primeiramente fixando o tempo em 4 h e variando a temperatura de 300 à 500 °C (de 50 em 50 °C), seguido de tratamentos a temperatura fixa de 350 °C e variando o tempo de 4 à 16 h (de 4 em 4 h). Dentre os aços estudados, a composição química apresentou influência significativa na cinética de crescimento da camada, pois os elementos de liga substitucionais aqui estudados, Ni e Mo, facilitam a difusão do nitrogênio devido a distorção causada na rede cristalina, e a composição influencia na cinética de precipitação de nitretos de cromo CrN, assim como no grau de supersaturação da matensita expandida, ainda há diferenças relacionada com a presença dos caminhos de alta difusividade. A cinética da sensitização é dependente da composição do aço sendo o AISI 410NiMo o aço com baixa cinética de precipitação de nitretos de cromo e maior espessura de camada para as mesmas condições de tratamento (temperatura fixa em 350 °C), entretanto menor dureza na camada nitretada em relação aos aços AISI 410, AISI 416 e AISI 420. Palavras-chave: nitretação em baixa temperatura, aço inoxidável martensítico, crescimento da camada nitretada, dependência com a composição.Abstract: The increasing application of plasma assisted thermo-chemical treatments in industry has motivated the development of this work. The main reasons for its application are the quality and performance of the treated surfaces and the fact that this process is environmental friendly. For example, plasma nitriding has applications in replacement of salt baths, known to generate solid waste and toxic gases. The plasma nitriding process at low temperatures, typically below 400 °C, can improves the tribological behavior of stainless steels, increasing surface hardness, and maintaining the steel corrosion resistance. This is due to the diffusion of nitrogen and to the formation of a nitrided layer with a thickness dependent on time, temperature, pressure, and composition of the gas mixture. In this context, the present work has studied the influence of the chemical composition of martensitic stainless steel AISI 410, AISI 410NiMo, AISI 416 and AISI 420, in the kinetic of the nitriding treatment. For this purpose treatments were carried out for fixed time of 4 h for temperatures ranging from 300 to 500 °C (in steps of 50 °C). Additionally, treatments were carried ou t at fixed temperature of 350 °C and for treatment time ranging from 4 to 16 h (in steps of 4 h). Among the treated steels, the chemical composition presented a significant influence on the layer growth kinetics. For the case of substitutional alloying elements studied here, Ni and Mo, seems to facilitate the diffusion of nitrogen due to distortion in the crystal lattice, and also influences the kinetics chromium nitride CrN precipitation and very probably the degree of supersaturation of the expanded matensite. So, the kinetics of sensitization is dependent upon the composition of the steel, being the AISI 410NiMo steel that presenting the lowest kinetics of chromium nitrides precipitation and the thicker layer, among the studied steels, for the same treatment conditions (temperature fixed at 350 °C), however i t presents the lowest nitrided surface hardness when compared to steel AISI 410, AISI 416 and AISI 420, what was attributed to different hardening mechanism. Keywords: low-temperature plasma nitriding, martensitic stainless steel, nitrided layer growth, composition dependence

Geoeconomic variations in epidemiology, ventilation management, and outcomes in invasively ventilated intensive care unit patients without acute respiratory distress syndrome: a pooled analysis of four observational studies

Background: Geoeconomic variations in epidemiology, the practice of ventilation, and outcome in invasively ventilated intensive care unit (ICU) patients without acute respiratory distress syndrome (ARDS) remain unexplored. In this analysis we aim to address these gaps using individual patient data of four large observational studies. Methods: In this pooled analysis we harmonised individual patient data from the ERICC, LUNG SAFE, PRoVENT, and PRoVENT-iMiC prospective observational studies, which were conducted from June, 2011, to December, 2018, in 534 ICUs in 54 countries. We used the 2016 World Bank classification to define two geoeconomic regions: middle-income countries (MICs) and high-income countries (HICs). ARDS was defined according to the Berlin criteria. Descriptive statistics were used to compare patients in MICs versus HICs. The primary outcome was the use of low tidal volume ventilation (LTVV) for the first 3 days of mechanical ventilation. Secondary outcomes were key ventilation parameters (tidal volume size, positive end-expiratory pressure, fraction of inspired oxygen, peak pressure, plateau pressure, driving pressure, and respiratory rate), patient characteristics, the risk for and actual development of acute respiratory distress syndrome after the first day of ventilation, duration of ventilation, ICU length of stay, and ICU mortality. Findings: Of the 7608 patients included in the original studies, this analysis included 3852 patients without ARDS, of whom 2345 were from MICs and 1507 were from HICs. Patients in MICs were younger, shorter and with a slightly lower body-mass index, more often had diabetes and active cancer, but less often chronic obstructive pulmonary disease and heart failure than patients from HICs. Sequential organ failure assessment scores were similar in MICs and HICs. Use of LTVV in MICs and HICs was comparable (42·4% vs 44·2%; absolute difference -1·69 [-9·58 to 6·11] p=0·67; data available in 3174 [82%] of 3852 patients). The median applied positive end expiratory pressure was lower in MICs than in HICs (5 [IQR 5-8] vs 6 [5-8] cm H2O; p=0·0011). ICU mortality was higher in MICs than in HICs (30·5% vs 19·9%; p=0·0004; adjusted effect 16·41% [95% CI 9·52-23·52]; p<0·0001) and was inversely associated with gross domestic product (adjusted odds ratio for a US$10 000 increase per capita 0·80 [95% CI 0·75-0·86]; p<0·0001). Interpretation: Despite similar disease severity and ventilation management, ICU mortality in patients without ARDS is higher in MICs than in HICs, with a strong association with country-level economic status

Global variation in postoperative mortality and complications after cancer surgery: a multicentre, prospective cohort study in 82 countries

© 2021 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY-NC-ND 4.0 licenseBackground: 80% of individuals with cancer will require a surgical procedure, yet little comparative data exist on early outcomes in low-income and middle-income countries (LMICs). We compared postoperative outcomes in breast, colorectal, and gastric cancer surgery in hospitals worldwide, focusing on the effect of disease stage and complications on postoperative mortality. Methods: This was a multicentre, international prospective cohort study of consecutive adult patients undergoing surgery for primary breast, colorectal, or gastric cancer requiring a skin incision done under general or neuraxial anaesthesia. The primary outcome was death or major complication within 30 days of surgery. Multilevel logistic regression determined relationships within three-level nested models of patients within hospitals and countries. Hospital-level infrastructure effects were explored with three-way mediation analyses. This study was registered with ClinicalTrials.gov, NCT03471494. Findings: Between April 1, 2018, and Jan 31, 2019, we enrolled 15 958 patients from 428 hospitals in 82 countries (high income 9106 patients, 31 countries; upper-middle income 2721 patients, 23 countries; or lower-middle income 4131 patients, 28 countries). Patients in LMICs presented with more advanced disease compared with patients in high-income countries. 30-day mortality was higher for gastric cancer in low-income or lower-middle-income countries (adjusted odds ratio 3·72, 95% CI 1·70–8·16) and for colorectal cancer in low-income or lower-middle-income countries (4·59, 2·39–8·80) and upper-middle-income countries (2·06, 1·11–3·83). No difference in 30-day mortality was seen in breast cancer. The proportion of patients who died after a major complication was greatest in low-income or lower-middle-income countries (6·15, 3·26–11·59) and upper-middle-income countries (3·89, 2·08–7·29). Postoperative death after complications was partly explained by patient factors (60%) and partly by hospital or country (40%). The absence of consistently available postoperative care facilities was associated with seven to 10 more deaths per 100 major complications in LMICs. Cancer stage alone explained little of the early variation in mortality or postoperative complications. Interpretation: Higher levels of mortality after cancer surgery in LMICs was not fully explained by later presentation of disease. The capacity to rescue patients from surgical complications is a tangible opportunity for meaningful intervention. Early death after cancer surgery might be reduced by policies focusing on strengthening perioperative care systems to detect and intervene in common complications. Funding: National Institute for Health Research Global Health Research Unit

Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study

© 2022 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 licenseBackground: Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide. Methods: A multimethods analysis was performed as part of the GlobalSurg 3 study—a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital. Findings: Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3·85 [95% CI 2·58–5·75]; p<0·0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63·0% vs 82·7%; OR 0·35 [0·23–0·53]; p<0·0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer. Interpretation: Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised. Funding: National Institute for Health and Care Research

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

Background Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks. Methods The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned. Results A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P &lt; 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31). Conclusion Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)