Brain protective effect of dexmedetomidine vs propofol for sedation during prolonged mechanical ventilation in non-brain injured patients

BACKGROUND Dexmedetomidine and propofol are two sedatives used for long-term sedation.It remains unclear whether dexmedetomidine provides superior cerebral protection for patients undergoing long-term mechanical ventilation.AIM To compare the neuroprotective effects of dexmedetomidine and propofol for sedation during prolonged mechanical ventilation in patients without brain injury.METHODS Patients who underwent mechanical ventilation for>72 h were randomly assigned to receive sedation with dexmedetomidine or propofol.The Richmond Agitation and Sedation Scale(RASS)was used to evaluate sedation effects,with a target range of-3 to 0.The primary outcomes were serum levels of S100-βand neuron-specific enolase(NSE)every 24 h.The secondary outcomes were remifentanil dosage,the proportion of patients requiring rescue sedation,and the time and frequency of RASS scores within the target range.RESULTS A total of 52 and 63 patients were allocated to the dexmedetomidine group and propofol group,respectively.Baseline data were comparable between groups.No significant differences were identified between groups within the median duration of study drug infusion[52.0(IQR:36.0-73.5)h vs 53.0(IQR:37.0-72.0)h,P=0.958],the median dose of remifentanil[4.5(IQR:4.0-5.0)μg/kg/h vs 4.6(IQR:4.0-5.0)μg/kg/h,P=0.395],the median percentage of time in the target RASS range without rescue sedation[85.6%(IQR:65.8%-96.6%)vs 86.7%(IQR:72.3%-95.3),P=0.592],and the median frequency within the target RASS range without rescue sedation[72.2%(60.8%-91.7%)vs 73.3%(60.0%-100.0%),P=0.880].The proportion of patients in the dexmedetomidine group who required rescue sedation was higher than in the propofol group with statistical significance(69.2%vs 50.8%,P=0.045).Serum S100-βand NSE levels in the propofol group were higher than in the dexmedetomidine group with statistical significance during the first six and five days of mechanical ventilation,respectively(all P<0.05).CONCLUSION Dexmedetomidine demonstrated stronger protective effects on the brain compared to propofol for long-term mechanical ventilation in patients without brain injury.

A preliminary study on selected methods of modeling the effect of shearer operation on methane propagation and ventilation at longwalls

Underground coal mining frequently uses longwalls.The occurrence of a potentially explosive mixture of methane and air is one of the most serious hazards.A large number of papers have applied numerical modeling of methane propagation in research aimed at this problem.To date,none of the CFD simulations has considered the movement of the shearer in the analyses.This paper proposes an adaptation of a method used for the description of the movement of trains in tunnels to a specific geometry of a longwall district.The flow of the air-methane mixture was calculated using the finite volume method,in particular the k-w SST and SAS turbulence models.Due to the movement of the shearer,moving and deforming meshes were used for simulation of unsteady flows.Examples of solutions for two hypothetical cases are presented.Finally,the drawbacks and advantages of presented methods are discussed.Further development with the application of either local mesh variability or overset meshes is outlined.

The Effectiveness of the Methane Drainage of the Rock-Mass with a Parallel Ventilation Heading during Longwall Mining

Methane drainage is used in Polish coal mines in order to reduce mine methane emission as well as to keep methane concentration in mine workings at safe levels. This article describes the method of methane drainage used in longwall 2 in seam 506. In Poland, coal seams are frequently mined in difficult conditions of very high methane hazard. Under such situations, methane is drained by means of parallel ventilation headings. This paper shows the influence of a specific ventilation system on the drainage efficiency at longwall 2 in seam 506. At this longwall, measurements of methane emission and the efficiency of drained methane were conducted. They consisted in gauging methane concentration, air velocity, absolute air pressure and the amount of methane removed via a drainage system. Experimental data were used to estimate the variations in absolute methane-bearing capacity, ventilation air methane and most importantly, to gauge the efficiency of methane drainage.

Experimental research on methane control of mining upper protective layers

In order to solve coal and gas outbursts during mining coal seam,studying on related problems were carried out. According to the theories of mining upper protective layer,proper mining plan were designed and performed through field experiment. By means of examining several parameters obtained from the field experiment,the protective effects were evaluated and the protective scope and related parameters were determined. The results of field experiment show that the danger of outbursts was evidently eliminated and the method of mining protective layers is effective and the safety and economic benefits are remarkable. The research has really applied worth and will give beneficial references to mining area with analogous conditions.

Study on the countermeasures against methane outburst of mining multiple upper protective layers in coal seams cluster

In order to prevent coal and methane outbursts, mining protective layers is an effective means, yet no precedents of mining multiple protective layers is discoveried in seams which includes several seams are prone to outburst like Xinzhuangzi Mine. This paper perfected the related theories through analyzing mining multiple upper protective layers. By means of examining several parameters, it synthetically analyzed and ascer- tains the protected effectiveness and scope and reasonable parameters, finally obtained the specific indexes and effectiveness of mining multiple protective layers in coal seams cluster.

Prediction of air flow, methane, and coal dust dispersion in a room and pillar mining face

In underground coal mines, uncontrolled accumulation of methane and fine coal dust often leads to serious incidents such as explosion. Therefore, methane and dust dispersion in underground mines is closely monitored and strictly regulated. Accordingly, significant efforts have been devoted to study methane and dust dispersion in underground mines. In this study, methane emission and dust concentration are numerically investigated using a computational fluid dynamics(CFD) approach. Various possible scenarios of underground mine configurations are evaluated. The results indicate that the presence of continuous miner adversely affects the air flow and leads to increased methane and dust concentrations.Nevertheless, it is found that such negative effect can be minimized or even neutralized by operating the scrubber fan in suction mode. In addition, it was found that the combination of scrubber fan in suction mode and brattice results in the best performance in terms of methane and dust removal from the mining face.

CFD modeling of methane distribution at a continuous miner face with various curtain setback distances

Knowledge of the airflow patterns and methane distributions at a continuous miner face under different ventilation conditions can minimize the risks of explosion and injury to miners by accurately forecasting potentially hazardous face methane levels. This study focused on validating a series of computational fluid dynamics(CFD) models using full-scale ventilation gallery data that assessed how curtain setback distance impacted airflow patterns and methane distributions at an empty mining face(no continuous miner present). Three CFD models of face ventilation with 4.6, 7.6 and 10.7 m(15, 25, and 35 ft) blowing curtain setback distances were constructed and validated with experimental data collected in a full-scale ventilation test facility. Good agreement was obtained between the CFD simulation results and this data.Detailed airflow and methane distribution information are provided. Elevated methane zones at the working faces were identified with the three curtain setback distances. Visualization of the setback distance impact on the face methane distribution was performed by utilizing the post-processing capability of the CFD software.

Designing coal panels in the conditions of associated methane and spontaneous fire hazards

An increase in methane,spontaneous fire and bumping hazards in Polish hard coal mines,observed in the last two decades,led to the need to elaborate the tools allowing proper selection of a range of preventive measures to fight them at the stage of designing coal extraction.Designing the production of a coal seams in the conditions of associated methane and spontaneous fires hazards in Polish hard coal mines requires elaboration of the design standards for coal panels in gassy coal seams.This paper presents the guidelines on how to design production in the conditions of associated methane and spontaneous fire hazards.Presented tools and methodology since the very first research were many times verified by daily mining operations in the conditions of associated methane and spontaneous fire hazards,which confirms their significant contribution to the development of safe and economical mining operations.

COMPUTER SIMULATION OF METHANE MIGRATION IN LONGWALL PANELS WITH DESCENSIONAL VENTLIATION

It is important to study the methane transport phenomenon in a longwall panel under descensional ventilation conditions. In this paper the gob area is divided into a number of nodes to represent the rectangular percolating elements. The connections between nodes (elements) become branches,so that a network can be formed. Using the mechanics of porous media fluid flow, the mathematical model of air and gas flows has been established. Based on the existing ground pressure theories,the porosity of the inhomogeneous porous media in the gob can be given. In computer simulation it is considered that air pressure and temperature are functions of position ; air density, viscosity, and natural ventilation pressure are functions of temperature,pressure and methane concentration,and the resistance varies with air density and viscosity. Finally,the calculation results are given to show the differences between ascensional and descensional ventilation methods.

Stochastic prediction and control to methane in coalmine

The ventilation system plays an essential role in underground workings, and improvements in dilution effect to stochastic methane build-up at cul-de-sac of a coalmine require the installation of mixed ventilation system. For 4-12-1 I N02.8A centrifugal ventilation fan, the characteristic operating function of its mixed ventilation system is calculated from ventilation quantity and total pressure in the actual working status. At cul-de-sac of the reference coalmine, the evolution of methane concentration is a compound Poisson process and equivalent to a Brownian motion for Gaussian distributed increments. Solution of stochastic differential equation driven by mixed ventilation system, with dilution equation for its closure, provides parameters of mine ventilation system for keeping methane concentration within the permissible limit at cul-de-sac of the reference coalmine. These results intend to shed some light on application of blowing-sucking mixed ventilation systems in underground workings, and establish stochastic trends to consider methane control in coalmines.

LaMnO_(3)(La_(0.8)Sr_(0.2)MnO_(3))Perovskites for Lean Methane Combustion:Effect of Synthesis Method

The effect of the preparation method on the properties of LaMnO3 and La0.8Sr0.2MnO3 perovskite was studied. Materials were prepared by four methods: sol-gel, chemical combustion, solvothermal and spray pyrolysis and characterized. The effect of the synthesis method on the texture, acid-base character of the surface, reducibility with hydrogen, oxygen desorption, surface composition and catalytic activity for combustion of lean methane was studied. It was found that synthesis method affects physicochemical properties of obtained materials-solvothermally produced materials exhibit well-developed surface area, presence of reactive oxygen species on surface and high catalytic activity for CH4 combustion. Generally, LaMnO3 and La0.8Sr0.2MnO3 perovskites show catalytic activity for lean CH4 combustion comparable or higher than the activity of 0.5 wt.% Pt/Al2O3 but lower than 1 wt.% Pd/Al2O3.

A logic-based controller for the mitigation of ventilation air methane in a catalytic flow reversal reactor

The control system of a catalytic flow reversal reactor （CFRR） for the mitigation of ventilation air methane was investigated. A one-dimensional heteroge- neous model with a logic-based controller was applied to simulate the CFRR. The simulation results indicated that the controller developed in this work performs well under normal conditions. Air dilution and auxiliary methane injection are effective to avoid the catalyst overheating and reaction extinction caused by prolonged rich and lean feed conditions, respectively. In contrast, the reactor is prone to lose control by adjusting the switching time solely. Air dilution exhibits the effects of two contradictory aspects on the operation of CFRR, i.e., cooling the bed and accumulating heat, though the former is in general more prominent. Lowering the reference temperature for flow reversal can decrease the bed temperature and benefit stable operation under rich methane feed condition.

Double perovskite anti-supported rare earth oxide catalyst CeO_(2)/La_(2)CoFeO_(6)for efficient ventilation air methane combustion

Ventilation air methane is one of available resources with a massive reserve.However,most of ventilation air methane is discharged into the air and pollutes the environment.Catalysts with high temperature resistance(>800℃)for ventilation air methane are very essential for utilization of the ventilation air methane.We mainly prepared catalysts CeO_(2)/La_(2)CoFeO_(6)and La_(2)CoFeO_(6)/CeO_(2)and comparative samples CeO_(2)and La_(2)CoFeO_(6)by the simple sol-gel method and calcined them under 9000C,and tested the catalytic performance of ventilation air methane combustion under the condition of 5 vol%H_(2)O.The experimental results show that the light-off temperature(T_(1O))and complete combustion temperature(T_(90))of the ventilation air methane combustion reaction of CeO_(2)/La_(2)CoFeO_(6)catalyst are 417.4 and 587.7℃,respectively.T_(1O)and Tgo of La_(2)CoFeO_(6)/CeO_(2)only reach 425.5 and 615.8℃.The T_(10)and T_(9O)of CeO_(2)/La_(2)CoFeO_(6)are 417.4 and 587.7℃,which are lower than those of La_(2)CoFeO_(6)[T_(10)=452.4℃and T_(90)=673.0℃)and La_(2)CoFeO_(6)/CeO_(2)(T_(10)=425.5℃and T_(90)=615.8℃).Therefore,the catalytic performance of the anti-supported rare earth oxide catalyst CeO_(2)/La_(2)CoFeO_(6)is better than that of La_(2)CoFeO_(6)and supported catalyst La_(2)CoFeO_(6)/CeO_(2).

Facile Synthesis of Mesoporous Co3O4 Nanoflowers for Catalytic Combustion of Ventilation Air Methane

Flower-like Co3O4 hierarchical microspheres composed of self-assembled porous nanoplates were pre- pared by employing Pluronic F127 block-copolymer as template. The samples were characterized by powder X-ray diffraction（PXRD）, scanning/transmission electron microscopy（SEM/TEM）, and nitrogen adsorption-desorption at 77 K. The results show that the catalytic activity of Co3O4 nanoflowers for the combustion of ventilation air methane is higher than that of commercial Co3O4. The superior catalytic performance of this material can be related to its dominantly exposed {112} crystal planes and higher content of surface Co3＋.

肺保护性通气加重呼吸机诱导的膈肌萎缩和无力

目的 肺保护性通气(LPV)可将呼吸机引起的肺损伤(VILI)的风险降至最低。然而,LPV是否能够减轻呼吸机引起的膈肌功能障碍(VIDD)目前尚不清楚。本研究旨在探索LPV能否保护膈肌避免发生VIDD。方法 成年雄性Wistar大鼠进行常规机械通气[潮气量(V_(T)):10 mL/kg,呼气末正压(PEEP):2 cmH_(2)O;CV组]或肺保护性通气(V_(T):5 mL/kg,PEEP:10 cmH_(2)O;LPV组)12 h。然后,收集膈肌和肺组织进行生化和组织学分析。结果 笔者的研究结果表明,与常规机械通气组相比,肺保护通气减轻了大鼠的肺损伤,并降低了肺组织氧化应激水平。然而,与常规机械通气组相比,肺保护通气组的大鼠的膈肌蛋白水解水平增加,肌纤维横萎缩,膈肌肌力降低。此外,肺保护通气组在膈肌中的氧化应激水平高于常规机械通气组(P<0.05)。结论 与常规机械通气相比,肺保护通气不能缓解大鼠膈肌发生VIDD。相比之下,肺保护通气可能通过诱导氧化应激使VIDD恶化。因此,找到一个合适的通气方式来同时保护肺和膈肌仍是具有挑战性和紧迫性的临床问题。

驱动压导向呼气末正压通气对原位肝移植患者术中氧合和术后并发症的影响

目的评价驱动压导向呼气末正压(PEEP)通气对原位肝移植术(OLT)患者术中氧合和术后并发症的影响。方法选择2020年1月至2023年9月行OLT患者118例,男89例,女29例,年龄18~70岁,BMI<28 kg/m^(2),ASAⅢ或Ⅳ级。采用随机数字表法将患者分为两组:驱动压组(D组)和固定PEEP组(P组),每组59例。两组全麻期间均采用容量控制通气,I∶E 1∶2,V_(T)6 ml/kg(理想体重),RR 10~15次/分。D组在机械通气5 min后开始PEEP滴定试验,将PEEP从2 cmH_(2)O逐渐递增到10 cmH_(2)O,选择能产生最低驱动压的PEEP,维持该PEEP直至手术结束。P组术中维持PEEP 5 cmH_(2)O。记录术中出入量、血管活性药物使用情况。记录插管后5 min(T_(1))、无肝期(T_(2))、新肝期(T_(3))、手术结束即刻(T_(4))的HR、SBP、DBP、气道峰压(Ppeak)、气道平台压(Pplat)、PEEP、血气分析结果,并计算驱动压、动态肺顺应性(Cdyn)、氧合指数(OI)、死腔率(V_(D)/V_(T))。记录术后7 d内术后肺部并发症(PPCs)的发生情况。结果与P组比较,D组晶体液输注量明显增加,去甲肾上腺素、去氧肾上腺素及肾上腺素使用率明显升高(P<0.05)。与T_(2)时比较,两组T_(1)、T_(3)、T_(4)时HR明显减慢,SBP、DBP明显升高(P<0.05)。与T_(1)时比较,两组T_(2)—T_(4)时Ppeak、Pplat、驱动压、OI明显升高,T_(3)、T_(4)时Cdyn明显降低(P<0.05)。与P组比较,D组术后7 d内PPCs发生率明显降低(P<0.05)。两组其余指标差异无统计学意义。结论驱动压导向PEEP通气可改善原位肝移植患者术中氧合,降低PPCs发生率,但术中血管活性药物的使用率升高。

如何准确实施俯卧位与俯卧位通气

俯卧位和俯卧位通气是拯救某些难治性低氧血症患者的有效方法,目前俯卧位已成为急性呼吸窘迫综合征(ARDS)的标准治疗手段.临床在实施俯卧位和俯卧位通气时首先应明确改善氧合的机制及对血流动力学的影响;使用俯卧位在保护性通气的同时应关注影响通气、氧合的常见因素,如呼吸力学的变化、腹内压(IAP)、血流动力学的变化.必须认识到俯卧位的临床应用在诸多方面尚未达成共识,导致急性低氧呼吸衰竭的病因、病情复杂,应准确评估.在规范应用俯卧位与俯卧位通气改善氧合的同时及时采用多种手段才能提高危重症患者的抢救成功率.

人工气胸在全腔镜食管癌根治术肺保护性通气策略中的应用研究

目的分析人工气胸在全腔镜食管癌根治术肺保护性通气策略中的应用效果。方法选取2021年1月-2023年3月在该院行人工气胸全腔镜食管癌根治术治疗的88例患者作为研究对象,按随机数表法分为两组,每组各44例,对照组采用常规通气模式,实验组采用肺保护性通气策略模式,比较不同通气模式的临床效果。结果实验组与对照组在气管插管后10 min(T_(1))、单肺通气1 h(T_(2))、手术完毕时(T_(3))和术后24 h(T_(4))的pH和二氧化碳分压(PCO_(2))比较,差异均无统计学意义(P>0.05),两组患者T_(1)、T_(2)、T_(3)和T_(4)时点的氧合指数比较,差异均有统计学意义(P<0.05);实验组与对照组T_(1)、T_(2)和T_(3)时点的静态肺顺应性(Cs)、平台压(Pplat)和气道峰压(Ppeak)比较,差异均有统计学意义(P<0.05);实验组与对照组T1时点的C反应蛋白(CRP)、肿瘤坏死因子-α(TNF-α)、白细胞介素-8(IL-8)和白细胞介素-6(IL-6)水平比较,差异均无统计意义(P>0.05),两组患者T_(2)、T_(3)和T_(4)时点上述指标比较,差异均有统计学意义(P<0.05);对照组肺部并发症发生率为25.00%,高于实验组的9.09%,差异有统计学意义(P<0.05)。结论潮气量(VT)6 mL/kg+100.00%吸入氧浓度+呼气末正压5 cmH_(2)O+肺复张的肺保护性通气策略,用于人工气胸全腔镜食管癌根治术中,能够明显降低术中气道压力,减轻炎症反应,提高通气安全性。

深煤层气井低伤害完井液分析

深煤层气井的开采通常是采用水敏损害的完井液,但这类完井液存在着严重的伤害问题,对煤层气井的开采效率有着不利影响。在煤层气开采过程中,需要不断向井底注入液体,在注入过程中不可避免地会对煤层造成一定的伤害。从深煤层气井开采过程中出现的问题出发,对煤层气井中常见的完井液进行了分析和讨论,并在此基础上提出了相应的低伤害完井液方案。分析结果表明:低伤害完井液能有效降低深井煤层气开采过程中出现的问题。

深井矿山热害防治及制冷降温技术应用

随着金属矿山开采深度的增加,高地温越加显现,而矿山在热害控制方面经验不足、个体防护及培训缺失、有效的机械制冷技术应用较少等,亟待加强深井金属矿山热害防治安全技术相关研究。本文分析了深井矿山热环境对作业人员、生产效率的影响,总结了热害防治的综合措施,包括通风系统优化、热源控制、个体防护、压缩空气制冷、机械制冷等方面,列举了南非、澳大利亚两座典型深井矿山机械制冷降温技术的典型应用,供其他深井矿山借鉴。