Serum cystatin C is a sensitive early marker for changes in the glomerular filtration rate in patients undergoing laparoscopic surgery

OBJECTIVE: Pneumoperitoneum during laparoscopy results in transient oliguria and decreased glomerular filtration and renal blood flow. The presence of oliguria and elevated serum creatinine is suggestive of acute renal injury. Serum cystatin C has been described as a new marker for the detection of this type of injury. In this study, our aim was to compare the glomerular filtration rate estimated using cystatin C levels with the rate estimated using serum creatinine in patients with normal renal function who were undergoing laparoscopic surgery. METHODS: In total, 41 patients undergoing laparoscopic cholecystectomy or hiatoplasty were recruited for the study. Blood samples were collected at three time intervals: first, before intubation (T1); second, 30 minutes after the establishment of pneumoperitoneum (T2); and third, 30 minutes after deflation of the pneumoperitoneum (T3). These blood samples were then analyzed for serum cystatin C, creatinine, and vasopressin. The Larsson formula was used to calculate the glomerular filtration rate based on the serum cystatin C levels, and the Cockcroft-Gault formula was used to calculate the glomerular filtration rate according to the serum creatinine levels. RESULTS: Serum cystatin C levels increased during the study (T1 = T2T3; p<0.05). The calculated eGlomerular filtration rate-Larsson decreased, whereas the eGlomerular filtration rate-Cockcroft-Gault increased. There was no correlation between cystatin C and serum creatinine. Additionally, Pearson's analysis showed a better correlation between serum cystatin C and the eGlomerular filtration rate than between serum creatinine and the eGlomerular filtration rate. CONCLUSION: This study demonstrates that serum cystatin C is a more sensitive indicator of changes in the glomerular filtration rate than serum creatinine is in patients with normal renal function who are undergoing laparoscopic procedures.

Performance evaluation of multi-stage filtration with use of granular activated carbon and synthetic non-woven fabrics

The multi stage filtration (MSF) is an alternative that permits to enlarge the spectrum of application of the slow sand filtration as for the effluent quality and run duration. In this research the use of MSF technology associated to a granular activated carbon (GAC) column as polishing mechanism of the final effluent was evaluated; in the slow sand filters GAC was used as an intermediate layer and non-woven synthetic fabrics were utilized as a first layer of the filter media. Five different tests were conducted, where the systems subjected to the treatment were: water from the Ipe Lake (Ilha Solteira, Sao Paulo, Brazil); water from the lake with water from a recreational fish pond; water from the lake with a phytoplankton and cyanobacteria overload simulation, with and without the use of the pre-filters as a stage of the treatment. The synthetic fabrics and GAC use resulted in the best turbidity removal and an efficient apparent and true color removal; in spite that the polishing columns reported similar results for those parameters. The utilization of GAC as an intermediate layer contributed to a better organic matter removal and the fabrics improved chlorophyll-a removal. The pre-filtration columns made an efficient algae and cyanobacteria removal, a function that was completed by the filters and reached >98% efficiency. The synthetic non-woven fabrics and GAC inclusion in MSF operation improved performance of this technology with ease of application and operation.

Mathematical modeling and analysis of the particle interactions in the direct filtration using the colloidal theory

This work used the colloidal theory to describe forces and energy interactions of colloidal complexes in the water and those formed during filtration run in direct filtration. Many interactions of particle energy profiles between colloidal surfaces for three geometries are presented here in: spherical, plate and cylindrical; and four surface interactions arrangements: two cylinders, two spheres, two plates and a sphere and a plate. Two different situations were analyzed, before and after electrostatic destabilization by action of the alum sulfate as coagulant in water studies samples prepared with kaolin. In the case were used mathematical modeling by extended DLVO theory (from the names: Derjarguin-Landau-Verwey-Overbeek) or XDLVO, which include traditional approach of the electric double layer (EDL), surfaces attraction forces or London-van der Waals (LvdW), esteric forces and hydrophobic forces, additionally considering another forces in colloidal system, like molecular repulsion or Born Repulsion and Acid-Base (AB) chemical function forces from Lewis.

Hydrodynamic analysis of particle collection efficiency: comparing downflow and upflow filtration

Models of the filtration phenomenon describe the mass balance in bed filtration in terms of particle removal mechanisms, and allow for the determination of global particle removal efficiencies. These models are defined in terms of the geometry and characteristic elements of granule collectors, particles and fluid, and also the composition of the balance of forces that act in the particle collector system. This work analyzes particles collection efficiency comparing downflow and upflow direct filtration, taking into account the contribution of the gravitational factor of the settling removal efficiency in future proposal of initial collection efficiency models for upflow filtration. A qualitative analysis is also made of the proposal for the collection efficiency models for particle removal in direct downflow and upflow filtration using a Computational Fluid Dynamics (CFD) tool. This analysis showed a strong influence of gravitational factor in initial collection efficiency (t = 0) of particles, as well as the reasons of their values to be smaller for upflow filtration in comparison with the downflow filtration.

Copper filtration in pediatric digital X-ray imaging: its impact on image quality and dose

The effect of copper (Cu) filtration on image quality and dose in different digital X-ray systems was investigated. Two computed radiography systems and one digital radiography detector were used. Three different polymethylmethacrylate blocks simulated the pediatric body. The effect of Cu filters of 0.1, 0.2, and 0.3 mm thickness on the entrance surface dose (ESD) and the corresponding effective doses (EDs) were measured at tube voltages of 60, 66, and 73 kV. Image quality was evaluated in a contrast-detail phantom with an automated analyzer software. Cu filters of 0.1, 0.2, and 0.3 mm thickness decreased the ESD by 25-32%, 32-39%, and 40-44%, respectively, the ranges depending on the respective tube voltages. There was no consistent decline in image quality due to increasing Cu filtration. The estimated ED of anterior-posterior (AP) chest projections was reduced by up to 23%. No relevant reduction in the ED was noted in AP radiographs of the abdomen and pelvis or in posterior-anterior radiographs of the chest. Cu filtration reduces the ESD, but generally does not reduce the effective dose. Cu filters can help protect radiosensitive superficial organs, such as the mammary glands in AP chest projections.

Persistent decline in estimated but not measured glomerular filtration rate on tenofovir may reflect tubular rather than glomerular toxicity

Tenofovir disoproxil fumarate (TDF) has been associated with proximal renal tubulopathy and reduction in estimated glomerular filtration rate (eGFR), without accounting for the tubular secretion of creatinine.

Fluid balance, glomerular filtration rate, and urine output in dogs anesthetized for an orthopedic surgical procedure

OBJECTIVE: To determine fluid retention, glomerular filtration rate, and urine output in dogs anesthetized for a surgical orthopedic procedure. ANIMALS: 23 dogs treated with a tibial plateau leveling osteotomy. PROCEDURES: 12 dogs were used as a control group. Cardiac output was measured in 5 dogs, and 6 dogs received carprofen for at least 14 days. Dogs received oxymorphone, atropine, propofol, and isoflurane for anesthesia (duration, 4 hours). Urine and blood samples were obtained for analysis every 30 minutes. Lactated Ringer's solution was administered at 10 mL/kg/h. Urine output was measured and glomerular filtration rate was estimated. Fluid retention was measured by use of body weight, fluid balance, and bioimpedance spectroscopy. RESULTS: No difference was found among control, cardiac output, or carprofen groups, so data were combined. Median urine output and glomerular filtration rate were 0.46 mL/kg/h and 1.84 mL/kg/min. Dogs retained a large amount of fluids during anesthesia, as indicated by increased body weight, positive fluid balance, increased total body water volume, and increased extracellular fluid volume. The PCV, total protein concentration, and esophageal temperature decreased in a linear manner. CONCLUSIONS AND CLINICAL RELEVANCE: Dogs anesthetized for a tibial plateau leveling osteotomy retained a large amount of fluids, had low urinary output, and had decreased PCV, total protein concentration, and esophageal temperature. Evaluation of urine output alone in anesthetized dogs may not be an adequate indicator of fluid balance.

A comparison of measured and estimated glomerular filtration rate in successfully treated HIV-patients with preserved renal function

Monitoring of renal function becomes increasingly important in the aging population of HIV-1 infected patients. We compared Cockroft & Gault (C&G), Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), Modification of Diet in Renal Disease (MDRD), Cystatin C- and 24 h urine-based estimated GFR (eGFR) with the gold standard, measured GFR (mGFR) using [125I]-iothalamate.

Improvement in renal function after everolimus introduction and calcineurin inhibitor reduction in maintenance thoracic transplant recipients: the significance of baseline glomerular filtration rate

The NOCTET (NOrdic Certican Trial in HEart and lung Transplantation) trial demonstrated that everolimus improves renal function in maintenance thoracic transplant (TTx) recipients. Nevertheless, introduction of everolimus is not recommended for patients with advanced renal failure. We evaluated NOCTET data to assess everolimus introduction amongst TTx recipients with advanced renal failure.

Relationship between glomerular filtration rate and the adipokines adiponectin, resistin and leptin in coronary patients with predominantly normal or mildly impaired renal function

BACKGROUND: Due to their molecular weight, it is possible that the adipokines adiponectin, resistin and leptin accumulate when glomerular filtration rate (GFR) is decreased. In reduced renal clearance, altered serum concentrations of these proteins might affect cardiovascular risk. The objective of the study was to investigate the relationship between adipokine concentrations and GFR. METHODS: The association between GFR, as determined by the abbreviated MDRD equation, and the concentrations of the adipokines adiponectin, resistin and leptin was assessed in a cohort of coronary patients (n=538; 363 male, 165 female). After calculation of correlations between GFR and adipokine concentrations, the association was further assessed by analysis of covariance following adjustment for age, gender, BMI, presence of type 2 diabetes, presence of hypertension, history of smoking as well as for serum lipid concentrations. RESULTS: Mean GFR in our study population was 68.74+/-15.27 ml/min/1.73 m(2). 74.3% of the patients had a GFR >60 ml/min/1.73 m(2), 24% of the patients had a GFR between 30 and 60 ml/min/1.73 m(2), and 1.7% of the patients had a GFR <30 ml/min/1.73 m(2). There were significant inverse correlations between adiponectin (r=-0.372; p<0.001), resistin (r=-0.227; p<0.001) and leptin (r=-0.151; p=0.009) concentrations and GFR. After multivariate adjustment, the associations remained significant for adiponectin and resistin. Subgroup analysis in patients with GFR >60 ml/min/1.73 m(2) showed a significant correlation between GFR and adiponectin as well as leptin concentrations. However, after adjustment, these associations no longer were significant. CONCLUSIONS: There is an independent association between GFR and the serum concentrations of adiponectin and resistin. However, this association is not present at GFR >60 ml/min/1.73 m(2). This finding suggests that adipokine concentrations in mildly impaired and normal renal function are influenced by factors other than GFR.

Tenofovir use is associated with a reduction in calculated glomerular filtration rates in the Swiss HIV Cohort Study

BACKGROUND: A growing number of case reports have described tenofovir (TDF)-related proximal renal tubulopathy and impaired calculated glomerular filtration rates (cGFR). We assessed TDF-associated changes in cGFR in a large observational HIV cohort. METHODS: We compared treatment-naive patients or patients with treatment interruptions > or = 12 months starting either a TDF-based combination antiretroviral therapy (cART) (n = 363) or a TDF-sparing regime (n = 715). The predefined primary endpoint was the time to a 10 ml/min reduction in cGFR, based on the Cockcroft-Gault equation, confirmed by a follow-up measurement at least 1 month later. In sensitivity analyses, secondary endpoints including calculations based on the modified diet in renal disease (MDRD) formula were considered. Endpoints were modelled using pre-specified covariates in a multiple Cox proportional hazards model. RESULTS: Two-year event-free probabilities were 0.65 (95% confidence interval [CI] 0.58-0.72) and 0.80 (95% CI 0.76-0.83) for patients starting TDF-containing or TDF-sparing cART, respectively. In the multiple Cox model, diabetes mellitus (hazard ratio [HR] = 2.34 [95% CI 1.24-4.42]), higher baseline cGFR (HR = 1.03 [95% CI 1.02-1.04] by 10 ml/min), TDF use (HR = 1.84 [95% CI 1.35-2.51]) and boosted protease inhibitor use (HR = 1.71 [95% CI 1.30-2.24]) significantly increased the risk for reaching the primary endpoint. Sensitivity analyses showed high consistency. CONCLUSION: There is consistent evidence for a significant reduction in cGFR associated with TDF use in HIV-infected patients. Our findings call for a strict monitoring of renal function in long-term TDF users with tests that distinguish between glomerular dysfunction and proximal renal tubulopathy, a known adverse effect of TDF.

Modeling of diesel particulate filter filtration and regeneration for transient driving schedules

Due to their high thermal efficiency, diesel engines have excellent fuel economy and have been widely used as a power source for many vehicles. Diesel engines emit less greenhouse gases (carbon dioxide) compared with gasoline engines. However, diesel engines emit large amounts of particulate matter (PM) which can imperil human health. The best way to reduce the particulate matter is by using the Diesel Particulate Filter (DPF) system which consists of a wall-flow monolith which can trap particulates, and the DPF can be periodically regenerated to remove the collected particulates. The estimation of the PM mass accumulated in the DPF and total pressure drop across the filter are very important in order to determine when to carry out the active regeneration for the DPF. In this project, by developing a filtration model and a pressure drop model, we can estimate the PM mass and the total pressure drop, then, these two models can be linked with a regeneration model which has been developed previously to predict when to regenerate the filter. There results of this project were: 1 Reproduce a filtration model and simulate the processes of filtration. By studying the deep bed filtration and cake filtration, stages and quantity of mass accumulated in the DPF can be estimated. It was found that the filtration efficiency increases faster during the deep-bed filtration than that during the cake filtration. A “unit collector” theory was used in our filtration model which can explain the mechanism of the filtration very well. 2 Perform a parametric study on the pressure drop model for changes in engine exhaust flow rate, deposit layer thickness, and inlet temperature. It was found that there are five primary variables impacting the pressure drop in the DPF which are temperature gradient along the channel, deposit layer thickness, deposit layer permeability, wall thickness, and wall permeability. 3 Link the filtration model and the pressure drop model with the regeneration model to determine the time to carry out the regeneration of the DPF. It was found that the regeneration should be initiated when the cake layer is at a certain thickness, since a cake layer with either too big or too small an amount of particulates will need more thermal energy to reach a higher regeneration efficiency. 4 Formulate diesel particulate trap regeneration strategies for real world driving conditions to find out the best desirable conditions for DPF regeneration. It was found that the regeneration should be initiated when the vehicle’s speed is high and during which there should not be any stops from the vehicle. Moreover, the regeneration duration is about 120 seconds and the inlet temperature for the regeneration is 710K.

Design of a lab scale direct-filtration system and its application in process lab

The Environmental Process and Simulation Center (EPSC) at Michigan Technological University started accommodating laboratories for an Environmental Engineering senior level class CEE 4509 Environmental Process and Simulation Laboratory since 2004. Even though the five units that exist in EPSC provide the students opportunities to have hands-on experiences with a wide range of water/wastewater treatment technologies, a key module was still missing for the student to experience a full cycle of treatment. This project fabricated a direct-filtration pilot system in EPSC and generated a laboratory manual for education purpose. Engineering applications such as clean bed head loss calculation, backwash flowrate determination, multimedia density calculation and run length prediction are included in the laboratory manual. The system was tested for one semester and modifications have been made both to the direct filtration unit and the laboratory manual. Future work is also proposed to further refine the module.

Experimental and modeling study of the filtration and oxidation characteristics of a diesel oxidation catalyst and a catalyzed particulate filter

A diesel oxidation catalyst (DOC) with a catalyzed diesel particulate filter (CPF) is an effective exhaust aftertreatment device that reduces particulate emissions from diesel engines, and properly designed DOC-CPF systems provide passive regeneration of the filter by the oxidation of PM via thermal and NO2/temperature-assisted means under various vehicle duty cycles. However, controlling the backpressure on engines caused by the addition of the CPF to the exhaust system requires a good understanding of the filtration and oxidation processes taking place inside the filter as the deposition and oxidation of solid particulate matter (PM) change as functions of loading time. In order to understand the solid PM loading characteristics in the CPF, an experimental and modeling study was conducted using emissions data measured from the exhaust of a John Deere 6.8 liter, turbocharged and after-cooled engine with a low-pressure loop EGR system and a DOC-CPF system (or a CCRT® - Catalyzed Continuously Regenerating Trap®, as named by Johnson Matthey) in the exhaust system. A series of experiments were conducted to evaluate the performance of the DOC-only, CPF-only and DOC-CPF configurations at two engine speeds (2200 and 1650 rpm) and various loads on the engine ranging from 5 to 100% of maximum torque at both speeds. Pressure drop across the DOC and CPF, mass deposited in the CPF at the end of loading, upstream and downstream gaseous and particulate emissions, and particle size distributions were measured at different times during the experiments to characterize the pressure drop and filtration efficiency of the DOCCPF system as functions of loading time. Pressure drop characteristics measured experimentally across the DOC-CPF system showed a distinct deep-bed filtration region characterized by a non-linear pressure drop rise, followed by a transition region, and then by a cake-filtration region with steadily increasing pressure drop with loading time at engine load cases with CPF inlet temperatures less than 325 °C. At the engine load cases with CPF inlet temperatures greater than 360 °C, the deep-bed filtration region had a steep rise in pressure drop followed by a decrease in pressure drop (due to wall PM oxidation) in the cake filtration region. Filtration efficiencies observed during PM cake filtration were greater than 90% in all engine load cases. Two computer models, i.e., the MTU 1-D DOC model and the MTU 1-D 2-layer CPF model were developed and/or improved from existing models as part of this research and calibrated using the data obtained from these experiments. The 1-D DOC model employs a three-way catalytic reaction scheme for CO, HC and NO oxidation, and is used to predict CO, HC, NO and NO2 concentrations downstream of the DOC. Calibration results from the 1-D DOC model to experimental data at 2200 and 1650 rpm are presented. The 1-D 2-layer CPF model uses a ‘2-filters in series approach’ for filtration, PM deposition and oxidation in the PM cake and substrate wall via thermal (O2) and NO2/temperature-assisted mechanisms, and production of NO2 as the exhaust gas mixture passes through the CPF catalyst washcoat. Calibration results from the 1-D 2-layer CPF model to experimental data at 2200 rpm are presented. Comparisons of filtration and oxidation behavior of the CPF at sample load-cases in both configurations are also presented. The input parameters and selected results are also compared with a similar research work with an earlier version of the CCRT®, to compare and explain differences in the fundamental behavior of the CCRT® used in these two research studies. An analysis of the results from the calibrated CPF model suggests that pressure drop across the CPF depends mainly on PM loading and oxidation in the substrate wall, and also that the substrate wall initiates PM filtration and helps in forming a PM cake layer on the wall. After formation of the PM cake layer of about 1-2 µm on the wall, the PM cake becomes the primary filter and performs 98-99% of PM filtration. In all load cases, most of PM mass deposited was in the PM cake layer, and PM oxidation in the PM cake layer accounted for 95-99% of total PM mass oxidized during loading. Overall PM oxidation efficiency of the DOC-CPF device increased with increasing CPF inlet temperatures and NO2 flow rates, and was higher in the CCRT® configuration compared to the CPF-only configuration due to higher CPF inlet NO2 concentrations. Filtration efficiencies greater than 90% were observed within 90-100 minutes of loading time (starting with a clean filter) in all load cases, due to the fact that the PM cake on the substrate wall forms a very efficient filter. A good strategy for maintaining high filtration efficiency and low pressure drop of the device while performing active regeneration would be to clean the PM cake filter partially (i.e., by retaining a cake layer of 1-2 µm thickness on the substrate wall) and to completely oxidize the PM deposited in the substrate wall. The data presented support this strategy.