Prospective observational cohort study of the association between antiplatelet therapy, bleeding and thrombosis in patients with coronary stents undergoing noncardiac surgery

Background: The perioperative management of antiplatelet therapy in noncardiac surgery patients who have undergone previous percutaneous coronary intervention (PCI) remains a dilemma. Continuing dual antiplatelet therapy (DAPT) may carry a risk of bleeding, while stopping antiplatelet therapy may increase the risk of perioperative major adverse cardiovascular events (MACE). Methods: Occurrence of Bleeding and Thrombosis during Antiplatelet Therapy In Non-Cardiac Surgery (OBTAIN) was an international prospective multicentre cohort study of perioperative antiplatelet treatment, MACE, and serious bleeding in noncardiac surgery. The incidences of MACE and bleeding were compared in patients receiving DAPT, monotherapy, and no antiplatelet therapy before surgery. Unadjusted risk ratios were calculated taking monotherapy as the baseline. The adjusted risks of bleeding and MACE were compared in patients receiving monotherapy and DAPT using propensity score matching. Results: A total of 917 patients were recruited and 847 were eligible for inclusion. Ninety-six patients received no antiplatelet therapy, 526 received monotherapy with aspirin, and 225 received DAPT. Thirty-two patients suffered MACE and 22 had bleeding. The unadjusted risk ratio for MACE in patients receiving DAPT compared with monotherapy was 1.9 (0.93–3.88), P=0.08. There was no difference in MACE between no antiplatelet treatment and monotherapy 1.03 (0.31–3.46), P=0.96. Bleeding was more frequent with DAPT 6.55 (2.3–17.96) P=0.0002. In a propensity matched analysis of 177 patients who received DAPT and 177 monotherapy patients, the risk ratio for MACE with DAPT was 1.83 (0.69–4.85), P=0.32. The risk of bleeding was significantly greater in the DAPT group 4.00 (1.15–13.93), P=0.031. Conclusions: OBTAIN showed an increased risk of bleeding with DAPT and found no evidence for protective effects of DAPT from perioperative MACE in patients who have undergone previous PCI

A composite medium approach for probabilistic modelling of contaminant travel time distribution to a pumping well in a heterogeneous aquifer

We analyse the probabilistic nature of the time of travel of conservative solutes to a pumping well operating within a heterogeneous aquifer. The latter is modelled as a three-dimensional, doubly stochastic composite medium, where distributions of geological materials and hydraulic properties are uncertain. The problem is tackled within a numerical Monte Carlo framework. We study the importance of uncertain facies geometry and uncertain hydraulic conductivity and porosity on predictions of solute time of travel to the pumping well by focusing on two special cases in which: (1) the facies distribution is random, but the hydraulic properties of each material are fixed, and (2) both facies geometry and material properties vary

Stochastic modeling of well head protection zones in highly heterogeneous aquifers

The assessment of well head protection zones is strongly related to spatial variability of hydrogeological properties. To set up a numerical model for probabilistic wellhead protection zone delineation, field and laboratory scale experiments for subsurface investigation were performed at the “Lauswiesen” site in southern Germany. At this site, spatial variations of hydraulic conductivity mainly dominate flow and transport processes. By means of a multivariate cluster analysis, three different types of aquifer materials (facies) were identified to characterize the heterogeneity of the aquifer lithology. Spatial variability of each material type was separately analysed by a geostatistical procedure based on indicator variography. Three-dimensional recombined distributions of the identified clusters were used to reconstruct the internal aquifer architecture. Then, three-dimensional time related mean well head protection zones and their associated uncertainty were obtained by a Monte Carlo stochastic simulation procedure

Multivariate geostatistical parameterization approach for 3D transient stochastic modeling of wellhead protection zones in a highly heterogeneous aquifer

Hydrogeological parameterization is a key step in modeling well head protection zones in alluvial heterogeneous deposits, often exploited for drinking water needs. We performed field and laboratory scale experiments for subsurface investigation at the “Lauswiesen” site in southern Germany, targeted to set up a numerical model for probabilistic wellhead protection zones assessment. The neighbouring Neckar river is the main boundary condition and strongly impacts the groundwater flow regime. Spatial variations of hydraulic conductivity, K, over several orders of magnitude, mainly dominate flow and transport processes. Sieve analyses performed on undisturbed core samples emphasized a very heterogeneous , highly conductive aquifer. By means of a multivariate cluster analysis, three different types of aquifer materials (clusters / facies) were identified to characterize the heterogeneity of the aquifer lithology. Spatial variability of each material type was separately analysed by a geostatistical procedure based on indicator variography. As a result, 3D recombined spatial distributions of the identified clusters were used to reconstruct the internal aquifer architecture. Since each cluster is completely characterized in terms of its hydraulic and transport parameters, internal variability as well as structural properties, the methodology yields three-dimensional pictures of aquifer parameter distributions, avoiding the usual difficulties of upscaling. The assessment of well head protection zones and their associated uncertainty are then obtained by a Monte Carlo procedure, based on equiprobable realizations of hydraulic conductivity fields. These are embedded within the numerical aquifer model to render the probabilistic well-capture zones distribution, subject to the initial and transient boundary conditions observed at the field site

Probabilistic study of well capture zones distribution at the Lauswiesen field site

The delineation of well capture zones is of utmost environmental and engineering relevance as pumping wells are commonly used both for drinking water supply needs, where protection zones have to be defined, and for investigation and remediation of contaminated aquifers. We analyze the probabilistic nature of well capture zones within the well field located at the “Lauswiesen” experimental site. The test site is part of an alluvial heterogeneous aquifer located in the Neckar river valley, close to the city of Tübingen in South- West Germany. We explore the effect of different conceptual models of the structure of aquifer heterogeneities on the delineation of three-dimensional probabilistic well catchment and time-related capture zones, in the presence of migration of conservative solutes. The aquifer is modeled as a threedimensional, doubly stochastic composite medium, where distributions of geo-materials and hydraulic properties are uncertain. We study the relative importance of uncertain facies geometry and uncertain hydraulic conductivity and porosity on predictions of catchment and solute time of travel to the pumping well by focusing on cases in which (1) the facies distribution is random, but the hydraulic properties of each material are fixed, and (2) both facies geometry and material properties vary stochastically. The problem is tackled within a conditional numerical Monte Carlo framework. Results are provided in terms of probabilistic demarcations of the three-dimensional well catchment and time-related capture zones. Our findings suggest that the uncertainty associated with the prediction of the location of the outer boundary of well catchment at the “Lauswiesen” site is significantly affected by the conceptual model adopted to incorporate the heterogeneous nature of the aquifer domain in a predictive framework. Taking into account randomness of both lithofacies distribution and materials hydraulic conductivity allows recognizing the existence of preferential flow paths that influence the extent of the well catchment and the solute travel time distribution at the site

SAFIRA. Teilprojekt C2.1: Erkundung der Schadstofffracht in kontaminierten Aquiferen zur Dimensionierung von in-situ-Sanierungsreaktoren Abschlussbericht

SIGLEAvailable from TIB Hannover: F04B1114 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung (BMBF), Bonn (Germany)DEGerman