Acute respiratory failure in kidney transplant recipients: a multicenter study

International audienceINTRODUCTION: Data on pulmonary complications in renal transplant recipients are scarce. The aim of this study was to evaluate acute respiratory failure (ARF) in renal transplant recipients. METHODS: We conducted a retrospective observational study in nine transplant centers of consecutive kidney transplant recipients admitted to the intensive care unit (ICU) for ARF from 2000 to 2008. RESULTS: Of 6,819 kidney transplant recipients, 452 (6.6%) required ICU admission, including 200 admitted for ARF. Fifteen (7.5%) of these patients had combined kidney-pancreas transplantations. The most common causes of ARF were bacterial pneumonia (35.5%), cardiogenic pulmonary edema (24.5%) and extrapulmonary acute respiratory distress syndrome (ARDS) (15.5%). Pneumocystis pneumonia occurred in 11.5% of patients. Mechanical ventilation was used in 93 patients (46.5%), vasopressors were used in 82 patients (41%) and dialysis was administered in 104 patients (52%). Both the in-hospital and 90-day mortality rates were 22.5%. Among the 155 day 90 survivors, 115 patients (74.2%) were dialysis-free, including 75 patients (65.2%) who recovered prior renal function. Factors independently associated with in-hospital mortality were shock at admission (odds ratio (OR) 8.70, 95% confidence interval (95% CI) 3.25 to 23.29), opportunistic fungal infection (OR 7.08, 95% CI 2.32 to 21.60) and bacterial infection (OR 2.53, 95% CI 1.07 to 5.96). Five factors were independently associated with day 90 dialysis-free survival: renal Sequential Organ Failure Assessment (SOFA) score on day 1 (OR 0.68/SOFA point, 95% CI 0.52 to 0.88), bacterial infection (OR 0.43, 95% CI 0.21 to 0.90), three or four quadrants involved on chest X-ray (OR 0.44, 95% CI 0.21 to 0.91), time from hospital to ICU admission (OR 0.98/day, 95% CI 0.95 to 0.99) and oxygen flow at admission (OR 0.93/liter, 95% CI 0.86 to 0.99). CONCLUSIONS: In kidney transplant recipients, ARF is associated with high mortality and graft loss rates. Increased Pneumocystis and bacterial prophylaxis might improve these outcomes. Early ICU admission might prevent graft loss

Investigation of the flow redistribution upstream of grid-like obstacles separated by a variable gap

International audienceIn nuclear Pressurized Water Reactors, fuel assemblies are slender structures composed of many rods held together by regularly spaced grids. Intense in-core conditions may sometimes result in permanent deformations impairing the reactor normal operation or even challenging its safety. Fluid-structure interactions are the central plot of this multiphysical storyline, and the water gaps between adjacent fuel assemblies act as the main character. More specifically, the flow redistribution upstream of grids, from the water gap to the rod bundle or the other way around, affects the force which is exerted by the coolant on the grids. Analytical models accounting for this effect can be found in the literature. The present article describes a simple experiment dedicated to providing validation data to such models. Mock-up grids were 3D printed and disposed in a hydraulic loop with a variable distance between them. For each configuration, the mean axial velocity was probed at hundreds of locations inside the water gap using an LDA acquisition system. The flow rate was then computed with several methods compensating the lack of velocity measures in unreachable areas. This experimental campaign helped to gain insight into the flow behavior across the grids of a fuel assembly. Notably, near proportionality was demonstrated between the water gap width and the flow rate through it. It was also observed that the redistribution cross-flows take place in a very limited region upstream of the grids

Modeling the Flow Redistribution Upstream From the Spacer Grid of a PWR

International audienceAbstract Fuel assemblies’ deformation is an industrial issue that has been first reported in the 90’s. This phenomenon has originally been pointed out for being the explanation of IRI (incomplete rod cluster insertion). Recently, fuel assembly bowing has regained attention for its impact over several core’s management issues, including core neutronics. When deformation occurs, it tends to alter bypasses geometry around the affected fuel assembly. The water gaps’ thicknesses along the assembly’s height does not match the nominal value anymore. As a result, spacer grids can get closer of farther to the surrounding ones. The redistribution between the bypasses and the grid is then involved, depending on the bypasses’ thicknesses and the grid geometry. This unfolding effect entails differences in pressure laterally along a grid, which thus brings about a lateral hydraulic force exerting on the grid. The following paper presents a method to esteem this redistribution thanks to an hydraulic network. Hydraulic resistances can be set up according to the bypass thickness. As a result, both pressure and volumetric flow rates can be calculated to further estimate lateral forces. The approach has been validated with both CFD simulations and an experimental mock-up

Semi-analytical fluid-structure model for the analysis of fuel assembly bow in full PWR cores

Fuel assembly bow is an intricate industrial issue occurring in PWR nuclear cores, which relies on multiphysics coupled phenomena based on mechanics, thermal hydraulics and neutronics.Amongst many causes, the hydraulic forces induced by in-core flow redistributions play an important role on the fuel assembly mechanical deflection.Because deformation spread out over days, weeks or months, fuel assembly bow is often studied as a quasistatic fluid-structure interaction with neutronics parameters as inputs only. In order to set up an efficient partitioned two-way coupling between mechanics and hydraulics representing a full PWR core, simplified models must be used.Regarding hydraulics, common strategies imply porous media, or even more time-saving 1D networks. In a previous study, we followed such a 1D approach to simulate the flow redistributions occurring near spacer grids, from fuel assemblies to the bypasses surrounding them or the other way around. In the current paper, we extend the latter local hydraulic networks to build up a full fuel assembly, which is then two-way coupled with an in-house CEA mechanical code. The simulations are compared with a CEA experiment. The lateral force exerting on spacer grids induced by the bypass-fuel assembly redistribution appears to play an important role on the shape of the fuel assembly.Finally, we propose further extensions to a row of fuel assemblies, and then to a whole core. Qualitative comparisons with the literature highlight proper bow patterns for the single row test case, with high sensitivity to the flow inlet and outlet conditions. At last, we demonstrate that hydraulic forces in a full core can indeed be estimated accurately through separated calculations on single rows in orthogonal directions, as suggested in the literature

Modeling the consequences of fuel assembly bowing on PWR core neutronics using a Monte-Carlo code

International audienceThe effect of assemblies bowing in PWR nuclear reactors onto core neutronics is an observed phenomenon still poorly understood which can lead to Power Ratio Tilt. Studies of the consequences of rod/assembly bowing involve many different fields addressed by nuclear power plant, such as neutronics, thermohydraulics, mechanics.. . in a complex combination of multi-physical interactions. For the neu-tronic part, the modeling of bowed assemblies in Monte Carlo codes must allow to correctly describe the shape of fuel rods. In this article, two discrete ways to model bowed geometries are tested: the first one consists in a stacking of vertical small cylinders following the shape of the fuel rod by small shifts between neighboring cylinders; the second one, newly introduced in the present research, consists in a sequence of rotated cylindrical segments arranged to as to follow the shape of the fuel rod more closely. Both models are used to reproduce two specific bowing patterns, namely C-shape and S-shape, for which a reference modeling involving an analytical toroidal volume cut by planes is available for use with CEA's Monte Carlo code Tripoli-4 Ò. Results of comparisons between both models and analytical reference show that, even if the segment modeling requires a specific effort to handle implementation constraints, it appears preferable compared to stacking modeling. It provides accuracy with fewer discrete entities and is therefore computationally affordable and it is far more robust when increasing bowing deflection. This approach is thus only considered ready for its application to any kind of bowing patterns

Semi-analytical modeling of the flow redistribution upstream from the mixing grids in a context of nuclear fuel assembly bow

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Severe Altered Immune Status After Burn Injury Is Associated With Bacterial Infection and Septic Shock.

Introduction: Burn injury is associated with a high risk of death. Whether a pattern of immune and inflammatory responses after burn is associated with outcome is unknown. The aim of this study was to explore the association between systemic immune and inflammatory responses and outcome in severely-ill burn patients. Materials and Methods: Innate immunity, adaptive immunity, activation and stress and inflammation biomarkers were collected at admission and days 2, 7, 14, and 28 in severely-ill adult burn patients. Primary endpoint was mortality at day 90, secondary endpoint was secondary infections. Healthy donors (HD) served as controls. Multiple Factorial Analysis (MFA) was used to identify patterns of immune response. Results: 50 patients were included. Age was 49.2 (44.2-54.2) years, total burn body surface area was 38.0% (32.7-43.3). Burn injury showed an upregulation of adaptive immunity and activation biomarkers and a down regulation of innate immunity and stress/inflammation biomarkers. High interleukin-10 (IL-10) at admission was associated with risk of death. However, no cluster of immune/inflammatory biomarkers at early timepoints was associated with mortality. HLA-DR molecules on monocytes at admission were associated with bacterial infections and septic shock. Later altered immune/inflammatory responses in patients who died may had been driven by the development of septic shock. Conclusion: Burn injury induced an early and profound upregulation of adaptive immunity and activation biomarkers and a down regulation of innate immunity and stress/inflammation biomarkers. Immune and inflammatory responses were associated with bacterial infection and septic shock. Absence of immune recovery patterns was associated with poor prognosis