Coupled plasma filtration adsorption

Both pro-inflammatory and anti-inflammatory mediators participate in the pathogenesis of sepsis and explain the failure of specific therapies to improve survival. Continuous extracorporeal therapies have been proposed as a therapeutic option in sepsis. We have studied the effects of plasma filtration associated with adsorption in patients with septic shock. We have shown that such treatment may lead to improved survival in a rabbit model of sepsis and to improved hemodynamics, reduced norepinephrine dose and restoration of near-to-normal responsiveness of blood leukocytes to endotoxin in humans. It is anticipated that treatment of plasma, as a device modular to conventional hemofiltration, may pave the way to innovative approaches to the extracorporeal treatment of septic patients.

Effects of novel manufacturing technology on blood and dialysate flow distribution in a new low flux "alpha Polysulfone" hemodialyzer

The main target for low flux hemodialyzers is an efficient low molecular weight solutes clearance. Such efficiency is largely dependent on the optimization of diffusion between blood and dialysis solution. The diffusion process can be impaired if there is a mismatch between blood and dialysate flow distribution in the dialyzer. Thus optimized flow distribution both in the blood and dialysate compartment becomes quintessential for the maximal efficiency of the diffusion process within the hemodialyzer. The present paper describes the distribution of the blood and dialysate flows in a new low flux polysulfone hollow fiber hemodialyzer characterized by a specific undulation of the fibers and a new cutting technology of the fibers for an improved micro-flow condition in the blood compartment headers. Twelve Diacap alpha Polysulfone LO PS 15 (1.5 sqm) (B. Braun Medizintechnologie, Melsungen Germany) were employed for the study. Six were analyzed in vitro and six were studied in vivo. Blood flow distribution was studied in vitro by dye injection in the blood compartment during experimental extracorporeal circulation utilizing human blood with hematocrit adjusted at 33%. Sequential images were obtained with a helical scanner in a fixed longitudinal section of the dialyzer 1 cm thick. Average and regional blood flow velocities were measured utilizing the reconstructed imaging sequence. The method allowed the calculation of single fiber blood flow (SF Qb) and the mass transfer zone (MTR) definition in digitally subtracted images. The patterns 20-10 and 40-30 were utilized. The same technology was used to evaluate flow distribution in the dialysate compartment after dye injection in the Hansen's connector. Regional dialysate flow was calculated in central and peripheral sample areas of 1 cm2. Six in vivo hemodialysis treatments on patients with end stage renal disease were performed at three different blood flow rates (250-350 and 450 ml/min) in order to measure urea, creatinine and phosphate clearance. Macroscopic and densitometrical analysis revealed that flow distribution was homogeneous in the blood compartment while in the dialysate compartment a slight difference between the peripheral and central regions in terms of flow velocity was observed. This however was not generating channeling phenomena. Urea creatinine and phosphate clearances were remarkably high and so were the Kt/V observed in all sessions, especially in relation to the studied blood flows. In conclusion, a significant blood to dialysate flow match with optimized countercurrent flow condition was observed in the studied hollow fiber hemodialyzers. Such optimization might be due both to the improved dialyzer design at the level of the blood header and to the specific fiber undulation that prevents dialysate channeling.

Effects of different doses in continuous veno-venous haemofiltration on outcomes of acute renal failure: a prospective randomised trial

BACKGROUND

Continuous veno-venous haemofiltration is increasingly used to treat acute renal failure in critically ill patients, but a clear definition of an adequate treatment dose has not been established. We undertook a prospective randomised study of the impact of different ultrafiltration doses in continuous renal replacement therapy on survival.

METHODS

We enrolled 425 patients, with a mean age of 61 years, in intensive care who had acute renal failure. Patients were randomly assigned ultrafiltration at 20 ml/h-1/kg(-1) (group 1, n = 146), 35 ml/h(-1)/kg(-1) (group 2, n = 139), or 45 ml/h(-1)/ kg(-1) (group 3, n = 140). The primary endpoint was survival at 15 days after stopping haemofiltration. We also assessed recovery of renal function and frequency of complications during treatment. Analysis was by intention to treat.

RESULTS

Survival in group 1 was significantly lower than in groups 2 (p = 0.0007) and 3 (p = 0.0013). Survival in groups 2 and 3 did not differ significantly (p = 0.87). Adjustment for possible confounding factors did not change the pattern of differences among the groups. Survivors in all groups had lower concentrations of blood urea nitrogen before continuous haemofiltration was started than non-survivors. 95%, 92% and 90% of survivors in groups 1, 2 and 3, respectively, had full recovery of renal function. The frequency of complications was similarly low in all groups.

INTERPRETATION

Mortality among these critically ill patients was high, but increase in the rate of ultrafiltration improved survival significantly We recommend that ultrafiltration should be prescribed according to patient's bodyweight and should reach at least 35 ml/h(-1)/kg(-1).

Choosing new adsorbents for endogenous ultrapure infusion fluid: performances, safety and flow distribution

Adsorption may notably contribute to the removal of uremic toxins and to the efficiency of hemodialysis. We examined different uncoated stationary matrixes, charcoals and synthetic resins to establish their adsorptive capacities in relation to low (urea, creatinine) and high molecular weight (beta2-microglobulin, myoglobin) compounds in in vitro conditions (steady state and flow-through) using isotonic solutions or uremic ultrafiltrate. Trace metal, particle release analyses and scanning electron microscopy of different adsorbents were performed. Dynamic flow-distribution studies were made using 99Technetium and analysing the different regions of interest by single head gamma-camera. We show that adsorbents may differ greatly as to their adsorptive capacity depending on flow rate, nature, and total mass of the compounds to be removed from the ultrafiltrate. These studies suggest a methodological approach for screening stationary matrixes for possible application in hemodialysis.

Practice pattern and treatment options for kidney patients in a single North Italian nephrology center

The experience and the current practice of a single center located in northern Italy is reported. The center of Vicenza is a self-standing nephrologic unit serving a population of about 300,000 individuals. The overall province counts approximately 800,000 individuals and some of them are referred to our center from peripheral hospitals for renal transplantation and/or particular pathologic conditions. The center offers an integrated approach to the treatment of uremia including hemodialysis (HD), peritoneal dialysis (PD), and renal transplantation. In HD and PD, the most peculiar aspect is the treatment personalization that leads to numerous types of applied therapies and technologies. The policy of the center is based on the belief that the nephrology team has a substantial influence on the outcomes of dialysis patients. A large number of treatment options are available. Special care is placed on the delivery of an adequate amount of dialysis, but the fractional clearance of urea in relation to volume (Kt/V) is seen as a prerequisite and other factors are considered important. Reduction in mortality and morbidity is largely dependent on beginning therapy early in the course of renal treatment. The attainment of appropriate hemoglobin concentrations, good nutrition, good control of calcium and phosphorus metabolism, lipids, and blood pressure, is considered of great importance. Beyond all these factors the time spent by the physician with the patient is considered one of the major factors influencing quality of care. The particularly low mortality of the center (6%/yr) may also be ascribed to a lower incidence of diabetes and other comorbidities.

Vascular endothelial growth factor enhances atherosclerotic plaque progression

Vascular endothelial growth factor (VEGF) can promote angiogenesis but may also exert certain effects to alter the rate of atherosclerotic plaque development. To evaluate this potential impact on plaque progression, we treated cholesterol-fed mice doubly deficient in apolipoprotein E/apolipoprotein B100 with low doses of VEGF (2 microg/kg) or albumin. VEGF significantly increased macrophage levels in bone marrow and peripheral blood and increased plaque area 5-, 14- and 4-fold compared with controls at weeks 1, 2 and 3, respectively. Plaque macrophage and endothelial cell content also increased disproportionately over controls. In order to confirm that the VEGF-mediated plaque progression was not species-specific, the experiment was repeated in cholesterol-fed rabbits at the three-week timepoint, which showed comparable increases in plaque progression.

Blood flow distribution in a polymyxin coated fibrous bed for endotoxin removal. Effect of a new blood path design

The analysis of flow distribution in cartridges designed for hemoperfusion is extremely important. Taking advantage of a new imaging technique, based on the analysis of a helical scanner-generated imaging sequence, we studied the blood flow distribution in a series of cartridges for extracorporeal removal of endotoxin. Cartridges with improved design were compared to cartridges with a standard design. The improved design consists in a different structure of the holes of the distributor of the flow within the adsorbent unit. Cartridges were studied in vitro with human blood from voluntary donors at blood flows of 100 and 250 ml/min. The progression of density in specific regions of interest (ROI) was analyzed to detect the distribution of the dye injected in the blood circuit. The study demonstrates that both at 100 ml/min and at 250 ml/min of blood flow, the progression of flow appears more homogeneous in the devices with improved design. In detail, the flow distribution measured by the incremental density values detected in the ROIs of the proximal comers (close to the arterial port) and in the ROIs of the central region of the device (close to the inner wall of the case) displays a significant difference between the standard and the improved device. The ROIs studied in the standard devices display a slower increase in density and significantly lower absolute values expressed in Hounsfield units. The experimental method utilized to analyze flow distribution seems to represent an important means to study the performance and design of this type of device.

Expression of myelin basic protein (MBP) epitopes in human non-neural cells revealed by two anti-MBP IgM monoclonal antibodies

Two monoclonal antibodies (1H6.2 and 45.30) were raised against MBP purified from human brain under experimental conditions that allowed MBP to retain binding to surrounding myelin lipids (human lipid-bound MBP (hLB-MBP)). 1H6.2 and 45.30 MoAbs were selected on the basis of their different binding properties to: hLB-MBP, human lipid-free-MBP (hLF-MBP) and bovine lipid-free-MBP (bLF-MBP). Although the isotype of both MoAbs was IgM, their specificity, as tested in ELISA assays against chemical haptens and unrelated protein antigens, was restricted to MBP. 1H6.2 and 45.30 MoAbs stained MBP from human brain white matter tissue extracts, as well as bLF-MBP, in Western blot assays. Both MoAbs stained oligodendrocytes and myelin in immunohistochemical analysis of white matter from human brain. Tissue sections from human peripheral nerves were labelled by 1H6.2 only, however, demonstrating that the MoAbs recognize two different epitopes. Epitopes recognized by 1H6.2 and 45.30 MoAbs were also expressed by a wide array of human non-neural cells of either normal or pathological origin, as evidenced by cytofluorimetric assays. In particular, MBP epitopes (MEs) were expressed by lymphoid cells as well as by cells which play a pivotal role in immune homeostasis and in the immune response, such as thymic epithelial cells and professional antigen-presenting cells. Both MoAbs were efficiently internalized by cells from a human B cell line, suggesting trafficking of MEs along the endocytic pathways. These findings support hypotheses regarding the role of MEs expressed by non-neural cells in establishing self-tolerance and/or in triggering the immune response against MBP antigen.

Dialysate flow distribution in hollow fiber hemodialyzers with different dialysate pathway configurations

The efficiency of a hemodialyzer is largely dependent on its ability to facilitate diffusion, since this is the main mechanism by which small solutes are removed. The diffusion process can be impaired if there is a mismatch between blood and dialysate flow distribution in the dialyzer. The objective of the paper was to study the impact of different dialysate compartment designs on dialysate flow distribution and urea clearances. Eighteen hollow fiber 1.3 m2 hemodialyzers were studied, 6 each of 3 designs: Type A--standard fiber bundle (PAN 65DX Asahi Medical, Tokyo, Japan); Type B--spacing filaments external to the fibers (PAN 65SF Asahi Medical, Tokyo, Japan); Type C--fibers waved to give Moiré structure (FB130 Nissho-Nipro, Osaka, Japan).

IN VITRO STUDIES

3 dialyzers of each type were studied following dye injection into the dialysate compartment. Dynamic sequential imaging of longitudinal sections of the dialyzer were undertaken, using a new generation helical CT scanner (X-Press/HS1 Toshiba Corporation, Tokyo, Japan). In vivo studies: 3 dialyzers of each type were studied, in randomized sequence, in 3 different patients under standardized dialysis conditions. Blood- and dialysate-side urea clearances were measured at 30 and 150 minutes of treatment. Macroscopic and densitometrical analysis revealed that flow distribution was most homogeneous in the dialyzer with Moiré structure (Type C) and least homogeneous in the standard dialyzer (Type A). Space yarns (Type B) gave an intermediate dialysate flow distribution. Significantly increased urea clearances (p<0.001) were seen with Types B and C, compared to the standard dialyzer. Type C (Moiré) had the highest clearances although these were not significantly greater than Type B (space yarns). In conclusion, more homogeneous dialysate flow distribution and improved small solute clearances can be achieved by use of spacing yarns or waved (Moiré structure) patterns of fiber packing in the dialyzer. These effects are achieved probably as a result of reduced dialysate channeling resulting in a lower degree of mismatch between blood and dialysate flows. The new radiological technique using the helical CT scanner allows detailed flow distribution analysis and has the potential for testing future modifications to dialyzer design.

Effects of a reduced inner diameter of hollow fibers in hemodialyzers

BACKGROUND

The clearance of middle molecules in high-flux hemodialyzers is due to the higher contribution of convection in the overall solute transport. Although net filtration can be maintained low by the machine control, internal filtration in the proximal part of the dialyzer remains high. The final fluid balance is achieved by significant amounts of backfiltration in the distal part of the dialyzer. To increase further middle molecule clearance (MMK), hemodiafiltration has been used. This technique, however, requires complex machines and large amounts of substitution fluid. We present a novel solution to increase the convective transport of middle molecules in high flux dialyzers without the need for substitution fluids. In particular, high-flux dialyzers with a reduced hollow fiber diameter are compared with standard dialyzers in terms of internal filtration and solute clearances.

METHODS

Hemodialyzers with 175 micro inner diameter polysulfone fibers were compared with standard 200 micro polysulfone hollow fiber dialyzers. The study was carried out in vitro using a previously published method to measure internal filtration and backfiltration rates. The method is based on the detection by a gamma camera of segmental variations in concentration along the length of the dialyzer of a nondiffusable Tc99-labeled marker molecule injected in the blood in vitro circuit. At the same time, pressures were detected in the blood and dialysate compartment. The system was operated at zero net filtration maintaining volumetrically constant both dialysate and blood circuits. In vivo clearances were also measured for solutes with different molecular weight.

RESULTS

The pressure drop in the blood compartment at 300 mL/min of blood flow passed from 112 to 159 mm Hg. At the same blood flow, the internal filtration-backfiltration rates increased from 23. 1 to 48.2 mL/min. This resulted in a significant increase of in vivo in clearances of vitamin B12 and inulin of more than 30%. Urea, creatinine, and phosphate clearance did not display any change.

CONCLUSIONS

A reduction of the inner diameter of the hollow fibers in high-flux dialyzers may result in a significant increase of the blood compartment resistance. In turn, this results in increased rates of internal filtration and backfiltration. The practical effect in clinical dialysis is demonstrated on middle molecules. While, in fact, the clearances for small solutes such as urea and creatinine are not affected, the clearances of larger solutes such as vitamin B12 or inulin increase significantly (P < 0.01).

Adsorption in sepsis

The pathophysiology of sepsis offers a highly complicated scenario. In sepsis, endotoxin or other gram-positive-derived products induce a complex and dynamic cellular response, giving rise to several mediators known to be relevant in the pathogenesis of septic shock such as specific mediators, substances responsible for up- or down-regulation of cytokine receptors and cytokine antagonists, inactivators of translational or transductional pathways, and precursor molecules. In this review, we delve into some new concepts stemming up from the use of sorbents in continuous plasma filtration. Nonspecific simultaneous removal of several mediators of the inflammatory cascade have led to improved outcomes in animal models of septic shock and to improved hemodynamics in a pilot clinical study. It seems of great importance to explore all possible treatment techniques that may have a direct impact on circulating mediators of sepsis and that also may interfere with the imbalance between proinflammatory and anti-inflammatory substances in the critically ill patient with multiple organ failure. In this view, the application of sorbents appears to open new and interesting therapeutic options. The search for innovative treatments specifically targeted to the special needs of the critically ill patients seems therefore more important than the attempt to adjust concepts and technologies that are normally applied to patients with chronic renal failure.