Adsorption of Diffusing Tracers, Apparent Tortuosity, and Application to Mesoporous Silica.

The apparent tortuosity due to adsorption of diffusing tracers in a porous material is determined by a scaling approach and is used to analyze recent data on LiCl and alkane diffusion in mesoporous silica. The slope of the adsorption isotherm at small loadings is written as ß = qA/qG, where qA is the adsorption-desorption ratio and qG = ϵ/(as) - 1 is a geometrical factor depending on the range a of the tracer-wall interaction, the porosity ϵ, and the specific surface area s. The adsorption leads to a decrease of effective diffusion coefficient, which is quantified by multiplying the geometrical tortuosity factor τgeom by an apparent tortuosity factor τapp. In wide pores or when the adsorption barrier is high, τapp = ß + 1, as obtained in previous works, but in narrow pores there is an additional contribution from frequent adsorption-desorption transitions. These results are obtained in media with parallel pores of constant cross sections, where the ratio between the effective pore width ϵ/s and the actual width is ≈0.25. Applications to mesoporous silica samples are justified by the small deviations from this ideal ratio. In the analysis of alkane self-diffusion data, the fractions of adsorbed molecules predicted in a recent theoretical work are used to estimate τgeom of the silica samples, which is ≫1 only in the sample with the narrowest pores (nominal 3 nm). The application of the model to Li+ ion diffusion leads to similar values of τgeom and to a difference of energy barriers of desorption and adsorption for those ions of ∼0.06 eV. Comparatively, alkane self-diffusion provides the correct order of magnitude of τgeom, with adsorption playing a less important role, whereas adsorption effects on Li+ diffusion are much more important.

Challenges and perspectives in applying the environmental sensitivity index to pipelines: a review on the prevention and management of oil spills disasters.

The oil spill environmental sensitivity index is a key tool for preventing and dealing with environmental disasters caused by oil spills. This study aims to review the available literature on the subject and highlight the importance of methodological advances to improve how the index is applied in continental areas, especially in regions crossed by pipelines. Most current mapping techniques focus on coastal areas and fail to consider the stretches of land that are vulnerable to geodynamic natural disasters. In this context, the need to implement environmental sensitivity indices specific for pipelines has become urgent. This study also presents an overview of the main accidents around the world and a detailed analysis of the history of Brazilian disasters related to oil spills along continental stretches, with a focus on pipelines and natural disasters. In addition, this work highlights the importance of carrying out new research in mountainous areas of Brazil and is aimed at preventing Natechs (natural hazard triggering technological disasters) and improving contingency plans. As a result, several pathways have been identified, which involves the necessity of resolving gaps in terrestrial environmental sensitivity mapping methodologies, particularly as applied to pipelines. Furthermore, solutions must be capable of integrating terrestrial, fluvial, coastal, and maritime environmental sensitivity mapping techniques. Moreover, the need to implement dynamic risk monitoring systems in real time is critical to help manage such a complex problem.

An electrodeposition model with surface relaxation predicts temperature and current effects in compact and dendritic film morphologies.

We study a thin-film electrodeposition model that represents the relaxation of the deposited material by adatom diffusion on quenched crystal topographies and considers simple mechanisms of cation flux in the electrolyte. The results of numerical simulations with collimated flux and a rapid cation reduction in contact with the deposit relate the surface roughness and the adatom hop numbers with two model parameters. A comparison with the results of a collective diffusion model for vapor deposition shows differences in the surface morphologies but similarities in scaling relations, which suggest thermally activated (Arrhenius) forms for the parameters of the electrodeposition model and relate one of them to the applied current. Simulations with purely diffusive cation flux and possible pore formation in simple cubic lattices show the growth of self-organized structures with leaf shapes (dendrites) above a compact layer that covers the flat electrode. The thickness of this layer and the average dendrite size also obey scaling relations in terms of the model parameters, which predict that both sizes decrease with the applied current, in agreement with recent experimental studies. Under all flux conditions, an increase in adatom diffusivity with temperature implies an increase in the average sizes of low-energy surface configurations, independently of their particular shapes. Finally, we note that a previously proposed model for electrodeposition produced similar morphologies, but the quantitative relations for the characteristic sizes differ from those of the present model, which also advances with a consistent interpretation of temperature effects.

Evolution of public policies on natural disasters in brazil and worldwide.

This work aims to carry out an analysis of the evolution of the civil defense protection policy in Brazil, as well as to present an overview of research related to public policies on natural disasters in the world. The research was developed by documentary analysis of Brazilian policies on the protection of civil defense and bibliometric analysis of the global data. The evolution of public policy on natural disasters in Brazil was divided into four different moments: a) military civil defense (1942-1946), b) disaster assistance policy (1967-1988), c) Civil Defense system in construction (1988-2005), and d) consolidation of the civil defense system (2005- to the present). The structuring of public policy reflected in 4 different stages in relation to the recording of information about disasters. Bibliometric analysis showed that the first works related to public civil defense policies in the world appeared only in 1980, and are mainly concentrated in the United States, which accounts for 42.56% of the works, while Brazil is the 6th country with 3.76% of global searches. Thus, it is possible to conclude that public policies and databases have a recent evolution both in Brazil and in the world, especially in developing countries.

Assessing Remotely Piloted Aerial Systems in the characterization of rocky shores for oil spills environmental sensitivity mapping, northern São Paulo littoral, Brazil.

The Environmental Sensitivity Index (ESI) for oil spills was developed to assist coordinators to evaluate oil spill impact along shorelines and also to coordinate the allocation of resources during and after the incident, aiming to reduce environmental damage and consequences. Recently, Remotely Piloted Aerial Systems (RPAS) are being used in a wide range of areas, since they complement traditional remote sensing data (e.g., satellite images) and offer a rapidly, precise, detail and high-resolution images that fit well for environmental studies. Herein, the use of high-resolution RPAS images for ESI analysis of rocky shores in the Brazilian territory was performed. Using RPAS images, with their higher-resolution compared with ArcGIS Pro Basemap satellite images, increased the detailed of ESI analysis for oil spills, increasing the number of regions in the rocky shore that are more sensitive to oil spills. The RPAS images were able to decrease the number of areas that were less sensitive to oil spills, and increase areas that are more sensitive to oil spills. This increase is important, since they were not detected in the ESI analysis using conventional ArcGIS Pro Basemap satellite images. The RPAS images permit to delineate precisely rocky shores, improving ESI interpretation in rocky shores.

Twenty years of paradigm-breaking studies of taxonomy and symbiotic nitrogen fixation by beta-rhizobia, and indication of Brazil as a hotspot of Paraburkholderia diversity.

Twenty years ago, the first members of the genus Burkholderia capable of nodulating and fixing N2 during symbiosis with leguminous plants were reported. The discovery that ß-proteobacteria could nodulate legumes represented a breakthrough event because, for over 100 years, it was thought that all rhizobia belonged exclusively to the α-Proteobacteria class. Over the past 20 years, efforts toward robust characterization of these bacteria with large-scale phylogenomic and taxonomic studies have led to the separation of clinically important and phytopathogenic members of Burkholderia from environmental ones, and the symbiotic nodulating species are now included in the genera Paraburkholderia and Trinickia. Paraburkholderia encompasses the vast majority of ß-rhizobia and has been mostly found in South America and South Africa, presenting greater symbiotic affinity with native members of the families Mimosoideae and Papilionoideae, respectively. Being the main center of Mimosa spp. diversity, Brazil is also known as the center of symbiotic Paraburkholderia diversity. Of the 21 symbiotic Paraburkholderia species described to date, 11 have been isolated in Brazil, and others first isolated in different countries have also been found in this country. Additionally, besides the symbiotic N2-fixation capacity of some of its members, Paraburkholderia is considered rich in other beneficial interactions with plants and can promote growth through several direct and indirect mechanisms. Therefore, these bacteria can be considered biological resources employed as environmentally friendly alternatives that could reduce the agricultural dependence on agrochemical inputs.

Landslides Zonation Hazard: relation between geological structures and landslides occurrence in hilly tropical regions of Brazil.

This paper presents a new approach of landslides zonation hazard studies, based on an integrated study of structural data along with geomorphological and external factors, in a hilly regions of Brazil, covered by a tropical humid rain-forest, called Serra do Mar. The Serra do Mar consists of a hilly region along the east coast of Brazil, with high slopes and many geological structures in a gneiss - migmatitic terrain. In contrast to traditional approaches, this method proposes that structural data (foliation, fractures and bedding planes) and its relation with the slope geometry, is important to be consider in the landslide zonation hazard, along with declivity, relative relief, soil and rock properties, land use and vegetation cover and hydrogeological and climate factors. Results show that slopes with high hazard have the same dip direction of geological structures. Landslide zonation hazard using structural data contributes to a better understanding of how these structures, preserved in tropical residual soils, influence on slope stability and generates landslides.

Geo-environmental zoning using physiographic compartmentalization: a proposal for supporting sustainable decision-making.

The geo-environmental zoning represents an important strategy in the territorial management. However, it requires a logical and structured procedure. Therefore, an approach using physiographic compartmentalization is proposed and applied as case study in a region covered by the topographic maps of São José dos Campos and Jacareí, Brazil. This region has great geological and geomorphological peculiarities, beyond being a place with large human interventions because of its quickly economic growth. The methodology is based on photointerpretation techniques and remote sensing in GIS environment. As a result, seven geo-environmental zones were obtained from a weighted integration by multicriteria analysis of physiographic units with land-use classes. In conclusion, taking into account potentialities and limitations, the proposed approach can be considered able to support sustainable decision-making, being applicable in other regions.

Universal superdiffusion of random walks in media with embedded fractal networks of low diffusivity.

Diffusion in composite media with high contrasts between diffusion coefficients in fractal sets of inclusions and in their embedding matrices is modeled by lattice random walks (RWs) with probabilities p<1 of hops from fractal sites and 1 from matrix sites. Superdiffusion is predicted in time intervals that depend on p and with diffusion exponents that depend on the dimensions of matrix (E) and fractal (D_{F}) as ν=1/(2+D_{F}-E). This contrasts with the nonuniversal subdiffusion of RWs confined to fractal media. Simulations with four fractals show the anomaly at several time decades for p≲10^{-3} and the crossover to the asymptotic normal diffusion. These results show that superdiffusion can be observed in isotropic RWs with finite moments of hop length distributions and allow the estimation of the dimension of the inclusion set from the diffusion exponent. However, displacements within single trajectories have normal scaling, which shows transient ergodicity breaking.

Adaptation of the TIMBRE methodology for brownfields gully erosion analysis in urban areas.

Soil erosion is a concern in many parts of the world, causing environmental and social impacts. Aiming at obtaining indicators of the recovery of brownfields created by gullies in urban areas, this study adapts the Tailored Improvement of Brownfield Regeneration in Europe (TIMBRE) for the analysis and classification of areas affected by gullies in the city of Bauru, Brazil. The TIMBRE methodology assists in the decision-making of priority areas for remediation and their reinsertion in urban spaces. The inventory of areas affected by gullies was compiled based on the analysis of two image sets (2004 and 2020) available on Google Earth. For the classification of brownfields, three classes were considered: Class 1 - local potential for business development, Class 2 - attractiveness and marketing, and Class 3 - environmental risks. These results demonstrate a correlation between gullies and urban expansion. The inventory identified 175 gullies in the municipality's urban perimeter in 2004, which affected an area of over 64 ha. In 2020, the number of gullies increased to 189, but the affected area decreased to 62 ha due to the recovery of some large gullies. The proposed methodology identified the area of Quinta da Bela Olinda as the one with the highest scores in all three classifications. Quinta da Bela Olinda is the location that has a local potential for business development, as it is the most attractive brownfield, as well as the area with the highest environmental risk. This area should, thus, be prioritized by public management for remediation. In conclusion, the proposed method of analysis can be transferred to other areas with adaptations in the criteria used and, therefore, may facilitate the management of urban areas affected by gullies in other places around the world.

The consequences of debris flows in Brazil: a historical analysis based on recorded events in the last 100 years.

This study aims at providing an overview of the socioeconomic consequences that debris-flow events have caused in Brazil, positioning the country in the international scenario and identifying areas where targeted actions are necessary. The analysis is conducted by calculating the debris-flow mortality rate (MR) and by using the so-called F-N plots (frequency of events that have caused N or more fatalities vs. the number of fatalities), based on a compilation of debris-flow-related disasters from 1920 to 2021. In total, 45 debris-flow events were documented in the considered period, responsible for 5771 fatalities and more than 5.5 billion USD in economic losses. The Serra do Mar Mountain Range is the main site of reported debris-flow occurrences (64.5%), followed by Serra da Mantiqueira (13.3%), and Serra Geral (13.3%). Southeast Brazil (SEB) is the region most affected by debris-flow events, due to the highest population density and the development of several cities in hilly areas, such as Petrópolis (Rio de Janeiro state) and Cubatão (São Paulo state). The debris-flow MR of SEB is higher than any other region in Brazil, pushing the national debris-flow MR upwards, and the F-N curve of SEB consolidates the region as the one with the highest risk to the phenomenon, indicating a higher probability of fatal events. The F-N plots further show that debris-flow events in Brazil represent a higher societal risk than in countries such as China, Japan and Italy. While there are differences in country size and the scale effect should be considered, these results highlight the urgent need for investments in disaster prevention and preparedness programs. Supplementary Information: The online version contains supplementary material available at 10.1007/s10346-022-01984-7.

Rationale for Adsorption in Extracorporeal Blood Purification.

A strong rationale supports the development of adsorption-based extracorporeal blood purification in conditions such as sepsis, acute kidney disease, uremia, and acute liver failure. The retention of compounds as a consequence of acute or chronic organ dysfunction might have detrimental effects. When a causative effect of an accumulated compound in a pathogenic condition is demonstrated, a rationale for the removal of this solute is also established. Adsorption is a mass transfer mechanism in which a solute chemically interacts with the surface of a solid structure (sorbent) and is removed from its solvent (i.e., blood or plasma). Traditional extracorporeal blood purification techniques utilize semipermeable membranes and depend mainly on diffusion and convection as mechanisms of mass transfer. Protein-bound solutes and water-soluble compounds with molecular weight above 25 kDa are scantly removed by either diffusive or convective clearances. In contrast, recently developed resins have demonstrated safety aligned with notable adsorptive capability, which enables the extraction of endotoxins, inflammatory mediators, and uremic toxins. The understanding of the kinetics of these elements and the improvement in patient selection are key factors to propel exploratory and confirmatory trials that ultimately will lead to the expected changes in clinical practice.

Scaling of surface roughness in film deposition with height-dependent step edge barriers.

We perform kinetic Monte Carlo simulations of film growth in simple cubic lattices with solid-on-solid conditions, Ehrlich-Schwoebel (ES) barriers at step edges, and a kinetic barrier related to the hidden off-plane diffusion at multilayer steps. Broad ranges of the diffusion-to-deposition ratio R, detachment probability per lateral neighbor, ε, and monolayer step crossing probability P=exp[-E_{ES}/(k_{B}T)] are studied. Without the ES barrier, four possible scaling regimes are shown as the coverage θ increases: nearly layer-by-layer growth with damped roughness oscillations; kinetic roughening in the Villain-Lai-Das Sarma (VLDS) universality class when the roughness is W∼1 (in lattice units); unstable roughening with mound nucleation and growth, where slopes of logW×logθ plots reach values larger than 0.5; and asymptotic statistical growth with W=θ^{1/2} solely due to the kinetic barrier at multilayer steps. If the ES barrier is present, the layer-by-layer growth crosses over directly to the unstable regime, with no transient VLDS scaling. However, in simulations up to θ=10^{4} (typical of films with a few micrometers), low temperatures (small R, Îµ, or P) may suppress the two or three initial regimes, while high temperatures and P∼1 produce smooth surfaces at all thicknesses. These crossovers help to explain proposals of nonuniversal exponents in previous works. We define a smooth film thickness θ_{c} where W=1 and show that VLDS scaling at that point indicates negligible ES barriers, while rapidly increasing roughness indicates a small ES barrier (E_{ES}∼k_{B}T). θ_{c} scales as ∼exp(const×P^{2/3}) if the other parameters are kept fixed, which represents a high sensitivity on the ES barrier. The analysis of recent experimental data in the light of our results distinguishes cases where E_{ES}/(k_{B}T) is negligible, ∼1, or ≪1.

Oil spill environmental sensitivity mapping of Rio de Janeiro, Brazil.

The current case study focuses on the Environmental Sensitivity Index (ESI) mapping of Guanabara Bay, Rio de Janeiro, Brazil - a region at risk from petroleum sector pollution. By mapping 981.5 km of coastline and classifying it in 10 oil sensitivity indices, we integrated biotic resources, socioeconomic attributes, and geoenvironmental diversity into a georeferenced database. Results reveal a high oil sensitivity of the bay, with approximately 89 % of the mapped coast scoring ESI 8 and ESI 10. These scores comprise, respectively, estuarine and solid substrate habitats that are sheltered from wave action. Notably, numerous manufacturing and oil handling plants, along with intensive urbanization, also contribute to the bay's oil sensitivity. Additionally, the rich biotic diversity in the study area, particularly in protected areas housing 79 conservation units, further amplifies its environmental vulnerability. This study aims to serve as a reference for detailed ESI mapping of coastal areas in tropical rainy zones with significant environmental diversity, industrial development, and a dense population.

Modeling growth of organized nanoporous structures by anodic oxidation.

Nanostructured porous oxides are produced by anodic dissolution of several metals. A scaling approach is introduced to explain pattern nucleation in an oxide layer, and a related microscopic model shows oxide growth with long nanopores. The scaling approach matches the time of ion transport across the thin oxide layer, which is related to metal corrosion, and the time of diffusion along the oxide/solution (OS) interface, which represents the extension of oxide dissolution. The selected pattern size is of order (dD(S)/v(O))(1/2), where d is the oxide thickness, v(O) is the migration velocity of oxygen ions across the oxide, and D(s) is the diffusion coefficient of H(+) ions along the oxide/solution interface. This result is consistent with available experimental data for those quantities, predicts the increase of pore size with the external voltage, and suggests the independence of pore size with the solution pH. Subsequently, we propose a microscopic model that expresses the main physicochemical processes as a set of characteristic lengths for diffusion and surface relaxation. It shows a randomly perturbed OS interface at short times, its evolution to pore nucleation and to stable growth of very long pores, in agreement with the mechanistic scenario suggested by two experimental groups. The decrease of the size of the walls between the pores with the interface tension is consistent with arguments for formation of titania nanotube arrays instead of nanopores. These models show that pattern nucleation and growth depend on matching a small number of physicochemical parameters, which is probably the reason for the production of nanostructured porous oxides from various materials under suitable electrochemical conditions.

Effects of Adsorbate Diffusion and Edges in a Transition from Particle to Dendritic Morphology during Silver Electrodeposition.

During silver electrodeposition on Au nanoparticle (NP)-covered highly oriented pyrolitic graphite, a transition from an initial growth of microsized particles to the growth of dendrites with pine tree shape (nanotrees) is observed, which is an advancement for material growth with hierarchical surface roughness. Using kinetic Monte Carlo simulations of an electrodeposition model, those results are explained by the interplay of diffusive cation flux in the electrolyte and relaxation of adsorbed atoms by diffusion on quenched crystal surfaces. First, simulations on NP-patterned substrates show the initial growth of faceted silver particles, followed by the growth of nanotrees with shapes similar to the experiments. Next, simulations on electrodes with large prebuilt particles explain the preferential nanotree growth at corners and edges as a tip effect. Simulations on wide flat electrodes relate the nanotree width with two model parameters describing surface diffusion of silver atoms: maximal number of random hops (G) and probability of hop per neighbor (P). Finally, simulations with small electrode seeds confirm the transition from initially compact particles to the nucleation of nanotrees and provide estimates of the transition sizes as a function of those parameters. The simulated compact and dendritic deposits show dominant (111) surface orientation, as observed in experiments. Extrapolations of simulation results to match microparticle and nanotree sizes lead to G = 4 × 1011 and P = 0.03, suggesting to interpret those sizes as diffusion lengths on the growing surfaces and giving diffusion coefficients 2 to 3 × 10-13 m2/s for deposited silver atoms. These results may motivate studies to relate diffusion coefficients with atomic-scale interactions.

Legume-nodulating betaproteobacteria: diversity, host range, and future prospects.

Rhizobia form specialized nodules on the roots of legumes (family Fabaceae) and fix nitrogen in exchange for carbon from the host plant. Although the majority of legumes form symbioses with members of genus Rhizobium and its relatives in class Alphaproteobacteria, some legumes, such as those in the large genus Mimosa, are nodulated predominantly by betaproteobacteria in the genera Burkholderia and Cupriavidus. The principal centers of diversity of these bacteria are in central Brazil and South Africa. Molecular phylogenetic studies have shown that betaproteobacteria have existed as legume symbionts for approximately 50 million years, and that, although they have a common origin, the symbiosis genes in both subclasses have evolved separately since then. Additionally, some species of genus Burkholderia, such as B. phymatum, are highly promiscuous, effectively nodulating several important legumes, including common bean (Phaseolus vulgaris). In contrast to genus Burkholderia, only one species of genus Cupriavidus (C. taiwanensis) has so far been shown to nodulate legumes. The recent availability of the genome sequences of C. taiwanensis, B. phymatum, and B. tuberum has paved the way for a more detailed analysis of the evolutionary and mechanistic differences between nodulating strains of alpha- and betaproteobacteria. Initial analyses of genome sequences have suggested that plant-associated Burkholderia spp. have lower G+C contents than Burkholderia spp. that are opportunistic human pathogens, thus supporting previous suggestions that the plant- and human-associated groups of Burkholderia actually belong in separate genera.

Time increasing rates of infiltration and reaction in porous media at the percolation thresholds.

The infiltration of a solute in a fractal porous medium is usually anomalous, but chemical reactions of the solute and that material may increase the porosity and affect the evolution of the infiltration. We study this problem in two- and three-dimensional lattices with randomly distributed porous sites at the critical percolation thresholds and with a border in contact with a reservoir of an aggressive solute. The solute infiltrates that medium by diffusion and the reactions with the impermeable sites produce new porous sites with a probability r, which is proportional to the ratio of reaction and diffusion rates at the scale of a lattice site. Numerical simulations for r≪1 show initial subdiffusive scaling and long time Fickean scaling of the infiltrated volumes or areas, but with an intermediate regime with time increasing rates of infiltration and reaction. The anomalous exponent of the initial regime agrees with a relation previously applied to infinitely ramified fractals. We develop a scaling approach that explains the subsequent time increase of the infiltration rate, the dependence of this rate on r, and the crossover to the Fickean regime. The exponents of the scaling relations depend on the fractal dimensions of the critical percolation clusters and on the dimensions of random walks in those clusters. The time increase of the reaction rate is also justified by that reasoning. As r decreases, there is an increase in the number of time decades of the intermediate regime, which suggests that the time increasing rates are more likely to be observed is slowly reacting systems.

Regional Hypertonic Citrate Anticoagulation in Membrane Therapeutic Plasma Exchange: A Case Series.

RATIONALE: Protocols for regional citrate anticoagulation with the hypertonic 4% trisodium citrate solution have been recently described as an anticoagulation strategy during membrane therapeutic plasma exchange (mTPE). The effect of citrate in the patient's systemic hemostasis is negligible, thus regional citrate anticoagulation application is advantageous in circumstances in which heparin-based protocols are deemed unsafe for patients with a high risk of bleeding. The downsides of using hypertonic citrate solutions are mainly hypocalcemia and hypernatremia that ultimately can cause adverse clinical events. PRESENTING CONCERNS OF THE PATIENT: (1) A 57-year-old Caucasian female with a history of active vaginal bleeding secondary to endometrial hyperplasia. She had a history of antiphospholipid syndrome, and systemic lupus erythematosus with marked refractory autoimmune thrombocytopenia. Her platelet count was persistently below 4,000/mm3 even after different immunosuppressive regimens and daily platelet transfusions. (1) A 70-year-old Caucasian female was hospitalized presenting acute kidney injury stage 3 due to rapidly progressive antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, however without the need for renal replacement therapy. At admission, serum creatinine (sCr) was 3.56 mg/dL (normal range: 0.53-1.00 mg/dL). Her baseline sCr was 0.8 mg/dL obtained 6 months earlier. Chest tomography revealed bilateral masses compatible with granulomatous lesions and no signs of alveolar bleeding. Since severe cases of ANCA vasculitis involving the lungs may evolve with alveolar hemorrhage, heparin was avoided. DIAGNOSES: (1) Systemic lupus erythematosus-associated autoimmune thrombocytopenia and (2) ANCA-associated vasculitis with kidney and lung involvement. INTERVENTIONS: Herein, we describe a case series of 12 consecutive mTPE treatments in 2 different patients using regional 4% trisodium citrate anticoagulation. OUTCOMES: All the sessions were uneventful, presented only minor electrolyte imbalances, and were effectively completed without early interruptions due to clotting of the plasmafilter. TEACHING POINTS: In our 2 cases, extracorporeal regional citrate anticoagulation was successful in optimizing plasmafilter patency without bleeding events in 2 high-risk patients using established protocols for the citrate and calcium infusions.

FONDEMENT: Les protocoles d'anticoagulation régionale avec une solution hypertonique à 4 % de citrate trisodique ont récemment été décrits comme stratégie d'anticoagulation pendant les séances d'échange plasmatique par filtration (mTPE ­ membrane therapeutic plasma exchange). L'effet du citrate étant négligeable sur l'hémostase systémique du patient, l'anticoagulation régionale au citrate s'avère avantageuse dans les cas où les protocoles avec l'héparine sont jugés dangereux pour les patients dont le risque d'hémorragie est élevé. Les inconvénients liés aux solutions hypertoniques de citrate sont principalement l'hypocalcémie et l'hypernatrémie, lesquelles peuvent éventuellement entraîner des effets indésirables sur le plan clinique. PRÉSENTATION DES CAS: a) Une femme de race blanche âgée de 57 ans qui présentait des saignements vaginaux actifs en raison d'une hyperplasie de l'endomètre. La patiente avait des antécédents de syndrome antiphospholipide et de lupus érythémateux disséminé avec thrombopénie autoimmune réfractaire marquée. Sa numération plaquettaire demeurait invariablement inférieure à 4 000/mm3 malgré différents traitements immunosuppresseurs et la transfusion quotidienne de plaquettes. b) Une femme de race blanche âgée de 70 ans hospitalisée pour une insuffisance rénale aiguë de stade 3 due à une vascularite à évolution rapide associée aux anticorps cytoplasmiques antineutrophiles (ANCA). La patiente ne nécessitait aucun traitement de remplacement rénal. Son taux de créatinine sérique (SCr) à l'admission était de 3,56 mg/dL (plage normale : 0,53 à 1,00 mg/dL) alors que son taux initial, mesuré 6 mois plus tôt, était de 0,8 mg/dL. Une tomographie thoracique a révélé des masses bilatérales compatibles avec les lésions granulomateuses et l'absence de saignement alvéolaire. L'héparine a été écartée puisque les cas graves de vascularite associée aux ANCA avec atteinte des poumons peuvent évoluer vers une hémorragie alvéolaire. DIAGNOSTICS: a) Thrombocytopénie autoimmune associée à un lupus érythémateux disséminé; b) vascularite associée aux ANCA avec atteinte des reins et des poumons. INTERVENTIONS: Nous décrivons une série de cas impliquant deux patientes ayant subi 12 séances de mTPE consécutives avec un anticoagulant régional à 4 % de citrate trisodique. RÉSULTATS: Toutes les séances se sont déroulées sans incident, seuls des déséquilibres électrolytiques mineurs ont été observés. Toutes les séances ont été réalisées efficacement, sans interruption précoce due au blocage du filtre à plasma. ENSEIGNEMENTS TIRÉS: Dans deux cas qui présentaient un risque élevé d'hémorragie, l'anticoagulation régionale extracorporelle avec citrate, réalisée conformément aux protocoles établis pour les perfusions de citrate et de calcium, a permis d'optimiser la perméabilité du filtre à plasma sans causer d'événement hémorragique.

Removal of middle molecules with medium cutoff dialyzer in patients on short frequent hemodialysis.

INTRODUCTION: Medium cutoff (MCO) membranes for hemodialysis (HD) remove more effectively large middle molecules than high-flux (HF) membranes. In patients on in-center short frequent HD regimen (5 sessions per week, 2 hours and 30 minutes per session) the effect of MCO on middle weight uremic toxins has not been elucidated. METHODS: This retrospective study included 15 patients previously performing short frequent HD with HF dialyzer (HF-HD), that were switched to short frequent HD with MCO dialyzer (MCO-HD) for 2 months, and returned to HF-HD. The primary endpoint was the predialysis concentration of α1-acid glycoprotein during the different study phases. Secondary endpoints were predialysis concentration of other middle molecules, albumin, and assessment of the quality of life using the 36-item short-form health survey (SF-36). FINDINGS: During MCO-HD phase there was a reduction in mean ± SD α1-acid glycoprotein concentration (98.71 ± 25.2 vs. 88.6 ± 24.6 mg/dL, P = 0.107), followed by an increment 2 months after returning to HF-HD (89.18 ± 26.12 vs. 97.33 ± 31.29 mg/dL, P = 0.002); however, only the second variation was statistically significant. MCO-HD provided lower median predialysis concentration of prolactin (16 [10.2-25.6] vs. 14.1 [11.7-34.8] ng/mL, P = 0.036). Single-pool Kt/V, standard Kt/V, predialysis ß2-microglobulin, myoglobin, and SF-36 questionnaire remained stable during the first two phases (pre-MCO and MCO). ß2-Microglobulin increased in the post-MCO phase (20.02 ± 8.14 vs. 21.27 ± 7.64 µg/mL, P = 0.000). Mean predialysis concentration of albumin reduced significantly from pre-MCO vs. MCO phases (39.9 ± 3.7 vs. 38.3 ± 3.3 g/L, P = 0.020) and rebounded significantly from MCO vs. post-MCO phases (38.7 ± 3.1 vs. 41.3 ± 3.0 g/L, P = 0.007). DISCUSSION: In this retrospective analysis, short frequent MCO-HD promotes a reduction in prolactin, a middle weight uremic toxin, and trends toward a reduction in α1-acid glycoprotein. No patients developed hypoalbuminemia. These findings are encouraging and deserve investigation in prospective studies.