Chemical Kinetics of Metal Single Atom and Nanocluster Formation on Surfaces: An Example of Pt on Hexagonal Boron Nitride.

The production of atomically dispersed metal catalysts remains a significant challenge in the field of heterogeneous catalysis due to coexistence with continuously packed sites such as nanoclusters and nanoparticles. This work presents a comprehensive guidance on how to increase the degree of atomization through a selection of appropriate experimental conditions and supports. It is based on a rigorous macro-kinetic theory that captures relevant competing processes of nucleation and formation of single atoms stabilized by point defects. The effects of metal-support interactions and deposition parameters on the resulting single atom to nanocluster ratio as well as the role of metal centers formed on point defects in the kinetics of nucleation have been established, thus paving the way to guided synthesis of single atom catalysts. The predictions are supported by experimental results on sputter deposition of Pt on exfoliated hexagonal boron nitride, as imaged by aberration-corrected scanning transmission electron microscopy.

Membrane-based therapeutic plasma exchange: Proposed techniques for preventing filter failure.

BACKGROUND AND OBJECTIVES: Therapeutic plasma exchange (TPE) is commonly performed using membrane-based TPE (mTPE) and is prone to filter failure. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We report on 46 patients, with a total of 321 mTPE treatments using the NxStage machine. This was a retrospective study with an aim to evaluate the effect of heparin, pre-filter saline dilution and the impact of total plasma volume exchanged (< 3 L vs. ≥3 L) on the rate of filter failure. Primary outcome was the overall rate of filter failure. Secondary outcomes included factors that may have indirectly influenced the rate of filter failure, including hematocrit, platelet count, replacement fluid (Fresh Frozen Plasma vs. albumin), and access type. RESULTS: We found that treatments that received both pre-filter heparin and saline had a statistically significant decrease in filter failure rate as compared to those that received neither (28.6% vs. 5.3%, P = .001), and compared to the treatments that received pre-filter heparin alone (14.2% vs. 5.3%, P = .015). In treatments that received both pre-filter heparin and saline predilution, we noted a significantly higher filter failure rate when the plasma volume exchanged was ≥3 L as compared to those that had <3 L exchanged (12.2% vs. 0.9%, P = .001). CONCLUSIONS: Rate of filter failure in mTPE can be reduced by implementing several therapeutic interventions including pre-filter heparin and pre-filter saline solution. These interventions were not associated with any clinically significant adverse events. Despite the above-mentioned interventions, large plasma volume exchanges of ≥3 L can negatively impact filter life.

Therapeutic plasma exchange as adjunct therapy for bullous pemphigoid.

Bullous pemphigoid (BP) is a rare autoimmune blistering disease caused by pathogenic antibodies which deposit into the dermo-epidermal junction. We present a case of bullous pemphigoid in a young female refractory to initial therapy with immunosuppressives and steroids who experienced significant improvement in blister burden after a course of adjunct therapeutic plasma exchange (TPE). This case report provides valuable insight into the benefit of utilizing TPE for BP and provides treatment specifics regarding use of TPE in a patient with BP.

Impact of prefilter dilution on IgG removal in membrane-based therapeutic plasma exchange.

INTRODUCTION: Previous studies have demonstrated that a "one plasma volume exchange" would result in an estimated 63% decline in pretreatment IgG levels. We evaluated the use of prefilter dilution with normal saline as a method to prevent filter failure without decreasing the efficiency of IgG removal. METHODS: Twenty-one treatment sessions were analyzed and all received prefilter dilution with normal saline. Primary outcome was to determine whether prefilter dilution resulted in decreased treatment efficiency in removing the targeted IgG. Secondary outcome was filter failure in conjunction with the combined use of prefilter heparin and saline infusions. RESULTS: All 21 treatments (100%) received prefilter dilution with saline solution and 19/21 (90.47%) also received prefilter heparin (bolus and/or hourly infusion). We demonstrated a 60%-70% decline in pretreatment IgG levels. CONCLUSION: Prefilter dilution during membrane-based therapeutic plasma exchange based treatment did not result in a demonstrable decrease in efficiency of IgG removal while maintaining filter patency.

Membrane-based therapeutic plasma exchange: Hemodynamics and operational characteristics leading to procedure failure.

BACKGROUND AND OBJECTIVES: Therapeutic plasma exchange (TPE) is a blood purification treatment capable of removing large molecular weight substances from plasma. It is commonly used for the removal of circulating pathogenic immunoglobulins presumed to be the cause of many autoimmune diseases. TPE can be performed with a membrane-based system (mTPE) or a centrifugal-based system (cTPE). When plasma separation is performed with a membrane, filter clotting can lead to longer treatment time, higher cost and can negatively impact patient satisfaction. In this study, we examine the operational characteristics that might influence filter life. DESIGN, SETTING, PARTICIPANTS, & MEASURES: We report on 24 patients, with a total of 135 mTPE treatments in a single tertiary care academic center using the NxStage machine. The study focuses on treatment specific parameters that may lead to procedure failure. The main parameters of interest were transmembrane pressure (TMP) and the filtration fraction as displayed on the machine (FFd) compared to the calculated filtration fraction (FFc). Primary outcome was to measure whether TMP, FFc, and FFd influenced filter survival. Secondary outcomes included factors that might have indirectly resulted in filter failure, including hematocrit (Hct), platelet count, heparin use, and intra-treatment calcium administration. RESULTS: In this study, we demonstrated that machine displayed filtration fractions (FFd) were lower than FFc and this difference was significantly larger in TPE sessions that experienced a clotting event (7.58 vs 6.22, P = .031). TPE sessions that clotted had a higher mean TMP (57.48 mmHg vs 44.43 mmHg, P = .001) and clotting events tended to have a lower mean blood flow rate (175.83 mL/min vs 189.55 mL/min, P = .002). In TPE sessions that received prefilter calcium administration, a higher mean dose of calcium gluconate was found in the sessions that experienced clotting (3.27 g vs 2.70 g, P = .013). Patients who experienced at least one clotting event were noted to be heavier than those patients without any clotting events (91.52 kg vs 72.15 kg, P = .040). Prefilter heparin administration was not associated with a lower incidence of filter clotting. We did not find a statistically significant difference in clotting events based upon type of intravenous access, pretreatment hematocrit, or pretreatment platelet counts. CONCLUSION: Among patients undergoing mTPE, machine FFd on the NxStage system are consistently lower than FFc. Treatments where there was a greater difference between displayed and FFc had a greater likelihood of filter clotting. Treatments with higher TMP were associated with failed treatments. Prefilter calcium administration during treatment was associated with increased filter clotting. Lower blood flow rates and higher patient weight were also associated with increased filter clotting. Prefilter heparin administration did not reduce the incidence of filter clotting.

Therapeutic Plasma Exchange Using Membrane Plasma Separation.

Therapeutic plasma exchange is a blood purification technique designed for the removal of large molecular weight toxins such as pathogenic antibodies and lipoproteins. Plasma exchange can be performed either by membrane separation or centrifugation. Centrifugal plasma exchange is more common in the United States, while membrane separation is more popular in Germany and Japan. The membrane separation technique is similar to the ultrafiltration procedures performed with a standard dialysis machine but in which the membrane's pores are large enough to allow removal of all circulating molecules while retaining the cellular components. The current availability of plasma separation membranes compatible with CRRT systems has dramatically increased the potential for almost all nephrologists to perform these treatments. This review describes the membrane separation techniques available in the United States, the practical aspects of ordering and operating a membrane separation plasma exchange procedure, and its possible complications.

Moderator's view: High-volume plasma exchange: pro, con and consensus.

I have been asked to comment on the pro and con opinions regarding high-volume plasma exchange. The authors of both positions have provided cogent arguments and a reasonable approach to choosing the exchange volume for any given therapeutic plasma exchange. The major issue of relevance in this discussion is the nature of the toxins targeted for removal. These parameters include molecular weight, the apparent volume of distribution, the degree of protein binding, the biologic and chemical half-life, and the severity and rapidity of its toxicity.

Peritoneal Dialysis or Hemodialysis: Present and Future Trends in the United States.

In 2013, 88.4% of all incident end-stage renal disease (ESRD) patients began renal replacement therapy with hemodialysis (HD) while 9.0% began with peritoneal dialysis (PD). The remaining 2.6% received a preemptive kidney transplant. In the US, outpatient HD units are widely distributed and economy of scale has resulted in HD being the most common ESRD modality. Use of PD and preemptive kidney transplant were relatively more common in younger groups and relatively less common among Black and Hispanic patients. Of note is that the new Medicare reimbursement system, known as the 'bundle', provides substantial financial incentives to do PD as opposed to in-center HD. By the end of 2013, 63.9% of all prevalent ESRD cases were receiving HD, 6.9% were being treated with PD, and 29.3% had a functioning kidney transplant. Distributions of modality use by patient characteristics generally mirror those for incident patients. PD and kidney transplant were more commonly used among patients who were younger and were more likely to be non-Hispanic Whites. Differences in the use of home dialysis (PD and HD) are largely driven by differences among individual dialysis centers or groups of centers, rather than by large-scale regional effects. Thus, the future use of PD or home HD will be driven by the proclivities of the largest dialysis providers, which, in turn, are driven by financial reimbursement.

All-optical modulation in Mid-Wavelength Infrared using porous Si membranes.

We demonstrate for the first time the possibility of all-optical modulation of self-standing porous Silicon (pSi) membrane in the Mid-Wavelength Infrared (MWIR) range using femtosecond pump-probe techniques. To study optical modulation, we used pulses of an 800 nm, 60 femtosecond for pump and a MWIR tunable probe in the spectral range between 3.5 and 4.4 µm. We show that pSi possesses a natural transparency window centred around 4 µm. Yet, about 55% of modulation contrast can be achieved by means of optical excitation at the pump power of 60 mW (4.8 mJ/cm(2)). Our analysis shows that the main mechanism of the modulation is interaction of the MWIR signal with the free charge carrier excited by the pump. The time-resolved measurements showed a sub-picosecond rise time and a recovery time of about 66 ps, which suggests a modulation speed performance of ~15 GHz. This optical modulation of pSi membrane in MWIR can be applied to a variety of applications such as thermal imaging and free space communications.

Determination of recombination coefficients for nanocrystalline silicon embedded in hydrogenated amorphous silicon.

The spectroscopic pump-probe reflectance method was used to investigate recombination dynamics in samples of nanocrystalline silicon embedded in a matrix of hydrogenated amorphous silicon. We found that the dynamics can be described by a rate equation including linear and quadratic terms corresponding to recombination processes associated with impurities and impurity-assisted Auger ionization, respectively. We determined the values of the recombination coefficients using the initial concentrations method. We report the coefficients of 1.5×10(11) s(-1) and 1.1×10(-10) cm(3) s(-1) for the impurity-assisted recombination and Auger ionization, respectively.

Therapeutic plasma exchange: a technical and operational review.

Therapeutic plasma exchange (TPE) is an extracorporeal blood purification technique designed for the removal of large molecular weight substances. Examples of these substances include pathogenic autoantibodies, immune complexes, cryoglobulins, myeloma light chains, endotoxin and cholesterol containing lipoproteins. The basic premise of the treatment is that removal of these substances will allow for the reversal of the pathologic processes related to their presence. This review will cover the techniques for performing TPE, the kinetics of the removal of large molecules from the plasma and the benefits and risks of the different types of replacement fluids.

Retrospective study of microorganisms associated with vascular access infections in hemodialysis patients.

OBJECTIVE: The aim of this study was to assess microorganisms associated with vascular access-associated infections (VAIs) in hemodialysis patients, with respect to possible origin from the mouth. STUDY DESIGN: A retrospective and comparative analysis of the microbes associated with VAI in hemodialysis patients treated during a 10-year period was performed with the Human Oral Microbiome Database (HOMD). RESULTS: Of 218 patient records identified, 65 patients collectively experienced 115 VAI episodes. The most common microorganisms involved were Staphylococcus aureus (49.6% of infections), Staphylococcus epidermidis (10.4%), Serratia marcescens (10.4%), Pseudomonas aeruginosa (9.6%), and Enterococcus faecalis/fecum (8.7%). None of these was found in ≥1% of HOMD clone libraries, indicating that they very rarely colonize the teeth or plaque. CONCLUSIONS: Most VAIs were associated with microorganisms more likely to originate from other body sites than from the oral cavity. The risk of a VAI being caused by microorganisms originating from the oral cavity is very small.

Complications of apheresis.

In general, therapeutic apheresis is a relatively safe procedure with the most commonly seen complications caused by citrate-induced hypocalcemia and urticarial reactions to the protein-containing replacement fluid. Depletion coagulopathy and immunoglobulin depletion must be anticipated when albumin is used as the replacement fluid and becomes more profound as the number of treatment increases. The most serious complications are seen when there is an anaphylactoid reaction to the multiple units of fresh frozen plasma required when used as the replacement fluid. The overall incidence of death is 0.05%, but many of these deaths were in patients with severe preexisting conditions in which the apheresis procedure, itself, may not have been the precipitating cause. As with all extracorporeal treatments requiring large bore vascular access, catheter-related trauma, clotting, infection, and bleeding may also occur.

A proposed approach to the dialysis prescription in severely hyponatremic patients with end-stage renal disease.

Patients with renal failure and severe hyponatremia present a therapeutic dilemma. Conventional hemodialysis is necessary to correct blood chemistries and volume overload, yet it may raise serum sodium (Na) too quickly, potentially resulting in osmotic demyelination syndrome. We present the case of a patient who presented with renal failure requiring dialysis and also with a serum Na of 112 mEq/l. Using a dialysate Na concentration of 130 mEq/l and by limiting the blood flow to 50 ml/minute, we were able to raise her serum Na by only 2 mEq/l/hour during her hemodialysis treatment and thus control both the rate and total change in the patient's serum Na.

Fractional excretion of urea in pre-eclampsia: a clinical observation.

INTRODUCTION: Pre-eclampsia is one of the leading causes of maternal and fetal mortality and morbidity. It occurs in 7% of all the pregnancies and accounts for 80% of the cases of pregnancy-induced hypertension. Diagnosis of pre-eclampsia in patients with pre-existing chronic kidney disease, proteinuria, and hypertension is a dilemma. The fractional excretion of urea has been described as a marker for renal perfusion. Since pre-eclampsia is associated with a marked decline in renal perfusion, we explored the utility of the fractional excretion of urea as a marker for pre-eclampsia. MATERIALS AND METHODS: Urine and serum chemistries were evaluated in 6 pregnant women with pre-eclampsia on their first visit, immediately prior to delivery, and postpartum. For each of these three measurements, the fractional excretion of urea was calculated and proteinuria was assessed by random urine protein-creatinine ratio or 24-hour urine protein studies. RESULTS: In patients diagnosed with pre-eclampsia, the fractional excretion of urea decreased substantially from higher values obtained during the 3rd trimester to values consistent with renal hypoperfusion (< 35%) just prior to delivery, and it rapidly normalized immediately after delivery. CONCLUSIONS: Alterations in fractional excretion of urea, which suggest a decreased renal perfusion, may be a useful tool in supporting the diagnosis of preeclampsia.