Operational characteristics of continuous renal replacement modalities used for critically ill patients with acute kidney injury.

Renal replacement therapy (RRT) is required in a significant percentage of patients developing acute kidney injury (AKI) in an intensive care unit (ICU) setting. One of the foremost objectives of continuous renal replacement therapy (CRRT) is the removal of excess fluid and blood solutes that are retained as a consequence of decreased or absent glomerular filtration. Because prescription of CRRT requires goals to be set with regard to the rate and extent of both solute and fluid removal, a thorough understanding of the mechanisms by which solute and fluid removal occurs during CRRT is necessary. The following provides an overview of solute and water transfer during CRRT and this information is placed in the appropriate clinical context with a discussion of recent clinical trials assessing the relationship between CRRT dose and patient survival. Moreover, the differences between solute removal in CRRT and other dialysis modalities, especially sustained low-efficiency dialysis (SLED) and extended daily dialysis (EDD), along with the potential clinical implications are discussed.

Effect of vitamin E-coated dialysis membranes on anemia in patients with chronic kidney disease: an Italian multicenter study.

BACKGROUND: Increased oxidant stress is increasingly recognized as a crucial factor in anemia in patients with chronic kidney disease. Vitamin E-coated membranes (VECMs) consist of a multilayer membrane with liposoluble vitamin E on the blood surface allowing direct free radical scavenging at the membrane site, which is of potential clinical benefit. Our objective was to examine the effect of VECMs on anemia in chronic hemodialysis (HD). METHODS: We enrolled 172 stable chronic HD patients (94 men, 78 women, age 65.4 +/- 13.4 years) in an open-label multicenter study. They were shifted from their previous dialyzer to VECM for 1 year. Hemoglobin (Hb) levels and recombinant human erythropoietin (rHuEpo) dosage were analyzed after 4, 8, and 12 months on the VECM and compared with baseline values using paired tests. RESULTS: Hb significantly increased from 10.9 +/- 1.2 g/dL at baseline to 11.7 +/- 1.2 g/dL after 12 months (p<0.001) on VECMs. Conversely, the rHuEpo dosage decreased from 7,762 +/- 5,865 IU/week at baseline to 6,390 +/- 5,679 IU/week after 12 months (p<0.001). The proportion of patients who were at target Hb levels (European Best Practice Guidelines) increased from 49.4% at baseline to 80% after 12 months (p<0.001). CONCLUSIONS: Dialysis with VECM in stable chronic HD patients was associated with significantly improved Hb levels and lower rHuEpo requirements. These results suggest that the antioxidant properties of VECMs may impact favorably on anemia management in chronic HD patients. Possible mechanisms include enhanced membrane biocompatibility, reduced oxidative stress and inflammation with VECMs, resulting in improved red blood cell survival and/or rHuEpo responsiveness. This therapy may potentially contribute to more effective anemia management in hemodialysis patients, and merits further rigorous study.

Effect of fiber structure on dialysate flow profile and hollow-fiber hemodialyzer reliability: CT perfusion study.

BACKGROUND: Uniform dialysate distributions in hollow-fiber hemodialyzers facilitate effective solute removal, and the fiber structure inside hemodialyzers plays a significant role in determining dialysate flow distribution and dialysis efficiency. The authors analyzed the effects of undulated fibers on dialysate flow profiles and hemodialyzer reliability using a perfusion CT technique. METHOD: Using a multi-detector row CT unit, perfusion studies were performed on two different types of hemodialyzers: (A) straight fiber configuration; (B) undulated fiber configuration (wavy-shaped fibers). Deconvolution theory was used for image processing to derive dialysate flows, dialysate volumes, and mean transit time distributions. Three-dimensional perfusion maps for the two types of hemodialyzers were reconstructed using high resolution images and these parameters were compared at hemodialyzer midsections. RESULTS: Dialysate maldistributions were observed in both types of hemodialyzer. However, dialysate flow distributions were more uniform in the undulated-fiber hemodialyzer, whereas more complex flow distributions developed in straight-fiber hemodialyzer. Reliability as determined using intraclass correlation coefficients was markedly higher for the hemodialyzer containing undulated fiber (0.968 vs. 0.496 for type A and type B, respectively). CONCLUSIONS: The undulated-fiber type was found to have more uniform, consistent dialysate flow profiles. It is believed that this type of hemodialyzer will be found helpful for measurement and prescription of the delivered hemodialysis dose due to its better consistency.

Dialytic performance evaluation of Rexeed: a new polysulfone-based dialyzer with improved flow distributions.

New dialyzers are designed to optimize the convective and diffusive components of solute transport. Asahi Kasei Medical Co.,Ltd.has developed a new high flux dialyzer series called Rexeed with improved flow distributions. We evaluated the in vivo dialytic performance of two dialyzers of the Rexeed series: Rexeed-18A and Rexeed-25A (1.8 m2 and 2.5 m2 ). We calculated the clearance for urea,creatinine,phosphate and b2-microglobulin both in high flux dialysis (HFD)and in 15 liter postidiluitional on-line hemodiafiltration (HDF)mode. With n = 3 patients in high flux HD at blood flow 450, 400, 350 and 250 ml/min we found remarkably high clearance for urea (347 +/- 4%, 305 +/- 0%, 288 +/- 5%, 230 +/- 3%, for Rexeed-18A and 361 +/- 3%, 329 +/- 0%, 313 +/- 1%, 234 +/- 3%for Rexeed-25A),creatinine (282 +/- 10%, 234 +/- 0%, 221 +/- 8%, 174 +/- 8%, for Rexeed-18A and 276 +/- 6%, 245 +/- 0%, 226 +/- 9%, 172 +/- 13% for Rexeed-25A),phosphate (347 +/- 0%, 316 +/- 0%, 275 +/- 4%, 202 +/- 16%, for Rexeed-18A and 364 +/- 3%, 365 +/- 0%,286 +/- 3%, 224 +/- 2% for Rexeed-25A)and b2-microglobulin (133 +/- 21%, 124 +/- 0%,118 +/- 12%, 98 +/- 11%, for Rexeed-18A and 159 +/- 8%, 169 +/- 0%,157 +/- 8%, 129 +/- 7% for Rexeed-25A) With n = 2 patients in HDF at blood flow 300 ml/min we found remarkably high clearance for urea (268 +/- 2%, for Rexeed-18A and 283 +/- 2% for Rexeed-25A),creatinine (183 +/- 6%for Rexeed-18A and 205 +/- 9% for Rexeed-25A),phosphate (245 +/- 3%, for Rexeed-18A and 270 +/- 2% for Rexeed-25A)and b2-microglobulin (166 +/- 12%, for Rexeed-18A and 192 +/- 4% for Rexeed-25A). Our preliminary evaluation describes the characteristics and the performances of a new polysulfone-based hemodialyzer series called Rexeed. Several innovative features have been implemented by the manufacturer. These constructive approaches seem to have produced a positive effect on the dialyzer performance at the bedside.

CRRT efficiency and efficacy in relation to solute size.

Removal of blood solutes in patients with decreased or absent glomerular filtration is the prime objective of continuous renal replacement therapies (CRRTs). However, because these blood solutes are of different molecular weights, factors such as the porosity and hydrophobicity of the filter membranes and the extracorporeal flow rates determine the CRRT that is the most effective filtration system. This article discusses both small and large solute removal, the interaction of convection and diffusion, and the potential for CRRTs to remove particular inflammatory mediators of acute renal failure.

Continuous plasma filtration coupled with sorbents.

An in vitro system composed of a plasma separation membrane coupled with natural (charcoal) or synthetic (Amberlite, Amberchrome) types of sorbents was evaluated for the simultaneous removal of proinflammatory cytokines (TNF-alpha, IL-1 beta and IL-8) and cytokine antagonists [interleukin (IL)-1 receptor antagonist (IL-1Ra), soluble tumor necrosis factor-alpha (TNF-alpha) receptor I and II (sTNFR I and II)] in whole blood spiked with bacterial lipopolysaccharide (LPS). These studies showed that plasma filtration rather than ultrafiltration significantly increased the clearance of all cytokines, particularly TNF-alpha, and the synthetic (Amberlite-type of resin) but not natural (uncoated charcoal) membrane could extensively absorb almost 100% of plasma filtered IL-Ra, IL-1 beta and IL-8, but only 40% of TNF-alpha. Other synthetic (Amberchrome) membranes could also effectively (80%) remove TNF-alpha. In the complex scenario of sepsis, the simultaneous removal of excess proinflammatory and/or immunomodulatory mediators may play a role in reducing the hemodynamic alterations, thus resulting in enhanced patient survival. Whether this occurs in the human setting awaits the results of an ongoing clinical investigation.

Cellulose triacetate: another membrane for continuous renal replacement therapy.

The evolution of technology and biomaterials has permitted a parallel development of renal replacement therapies in the acute, critically ill patient. From the original continuous artero-venous hemofiltration method new techniques such as continuous veno-venous hemofiltration, hemodiafiltration and high-flux dialysis have been developed and are clinically used. Similar progress has been made with artificial membranes. We investigated the possibility of using a modified cellulosic membrane for continuous therapies, assessing the hydraulic characteristics and clearance performances of high-flux cellulose triacetate hemodiafilter (0.7 m2) in vitro and in vivo. The flowdynamic characteristics of the filter suggest its optimal use in veno-venous pump-drive techniques. Efficiency was excellent, with urea daily clearances as high as 50 liters or more. The high permeability and porosity of the membrane also increased the clearances of larger solutes such as creatinine and inulin. No side effects occurred during treatment and we conclude that cellulose triacetate may be considered a good alternative to synthetic membranes in continuous renal replacement therapies.

Preliminary technical and clinical evaluation of a new hollow fiber dialyzer with a 5 microns thick cuprophan membrane.

In vitro and in vivo studies were performed on 10 dialyzers with 5 microns thick cuprophan membrane to evaluate hydraulic properties and permeability to solutes. Inlet and outlet pressures of the filter were measured at different blood flows to assess the resistance of the device and the end-to-end pressure drop. Hysolated ultrafiltration was performed to evaluate the spontaneous filtration at increasing blood flows, the ultrafiltration rate at different transmembrane pressures and, finally, the sieving coefficients for solutes. Standard hemodialysis was also performed to study the clearances throughout a 4-h session. During hysolated ultrafiltration the UF rate was increased up to 37 ml/min showing a very high hydraulic permeability of the membrane. The spontaneous filtration rates related to blood flow were quite low. Since the end-to-end pressure drop in the filter was also relatively low at high blood flow we may conclude that the geometry of the device is able to dissociate the influence of blood flow on the hydrostatic pressure inside the filter. This results in a easy modulation of the membrane permeability to water. Sievings were surprisingly high and clearances were stable along the dialysis session (BUN = 196 ml/min, creatinine = 161 ml/min and phosphate = 163 ml/min).

Nanoscale modulation of the pore dimensions, size distribution and structure of a new polysulfone-based high-flux dialysis membrane.

Current haemodialysis therapy modalities such as haemodiafiltration enhance the removal of larger uraemic solutes from the blood of patients on end-stage renal disease. A number of clinical investigations have demonstrated the clinical benefits of such therapies in contributing towards better patient survival rates and an improved quality of life. A fundamental prerequisite to the application of convective treatment modalities is the availability of appropriate, technologically-advanced high-flux dialysis membranes that are able to eliminate larger uraemic substances with high efficiency but without causing an excessive leakage of useful proteins. A new membrane, Helixone, has been developed specifically to meet the present-day requirements of high-flux dialysis and haemodiafiltration therapies involving large substitution rates. The application of nanotechnology fabrication principles and procedures has enabled the development of a membrane having highly-defined inner, separating layer surface structures that offer minimal resistance to the removal of large molecular weight substances across the membrane; for the first time, pore size dimensions, pore size distribution and pore geometry have been modulated and controlled at the nanoscale level for Helixone. This paper describes the characterisation of the essential structure- and permeation-related parameters of the new membrane using a number of physical analytical techniques.

Surface topography and surface elemental composition analysis of Helixone, a new high-flux polysulfone dialysis membrane.

Modern dialysis membranes need to fulfil two basic requirements. Firstly, the membrane structure, defined in terms of the size, structure and distribution of the pores at the inner separating layer of the membrane must be such that uraemic solutes of a defined molecular-weight range are selectively removed. Secondly, the physical and chemical properties of the blood-contacting surface must be such that minimal blood-material interactions take place that could either affect the functioning of the membrane, or, cause adverse reactions for the patient. A new polysulfone dialysis membrane, Helixone, has been developed specifically for the elimination of larger uraemic toxins using convective therapy modalities such as haemodiafiltration. The membrane is characterised by the nanoscale modulation of the innermost surface structures that lead to significantly increased sieving coefficients for molecules such as beta2-microglobulin, while maintaining the extremely low albumin removal property of the high-flux Fresenius Polysulfone membrane. A recent publication (Ronco C, Bowry SK. Nanoscale modulation of the pore dimensions, size distribution and structure of a new polysulfone-based high-flux dialysis membrane. Int J Artif Organs 2001; 24: 726-35) described the characterisation of the membrane of Helixone in terms of the membrane wall structure- and permeation-related parameters. In this paper, we describe the analysis of membrane surface parameters that influence the biocompatibility as well as the functioning of a membrane. The degree of roughness and the type of chemical groups of a blood-contacting surface are two of the main determinants of the biocompatibility characteristics of a membrane. The surface elemental composition of Helixone was determined using electron spectroscopy for elemental analysis (ESCA) while the surface topography of the membrane was evaluated using atomic force microscopy (AFM). The analysis showed that Helixone has an improved, smoother blood-contacting surface and retains the essential surface chemistry, and therefore the acknowledged biocompatibility profile, of the Fresenius Polysulfone membrane.

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.

Technical and clinical evaluation of a new synthetic low flux polysulphon membrane for hemodialysis.

New synthetic membranes have been developed to reduce the ultrafiltration coefficient (Kf) maintaining an adequate permeability to medium-large solutes and a good biocompatibility. The new Fresenius F6 Low Flux Polysulphon Membrane is studied in this paper as far as hydraulic and permeability properties are concerned. For this purpose in vitro and in vivo tests have been carried out in a series of different conditions. In vitro sieving coefficients were near 1 for solutes with molecular weight up to 5000 Daltons. The ultrafiltration coefficient of the device was 5.4 ml/h/mmHg while the value of Kf normalized per square meter was lower than 5 ml/h/mmHg. The geometry of the blood path was adequate even operating at high blood flows without excessive resistance and obligate filtration. This resulted in vivo in a good performance during short dialysis schedules with good clearances of small and large molecules and with no risks of backfiltration. In fact, the low permeability to water permits constant operation with positive transmembrane pressures without excessive ultrafiltration rates. The biocompatibility of the membrane was excellent and high capacity of adsorption for beta-2 microglobulin was demonstrated. These results suggest that these membranes seem to be able to join the advantages of the traditional cellulosic membranes and of the newer synthetic membranes reducing their relative disadvantages.

Renal replacement therapy: physical properties of hollow fibers influence efficiency.

INTRODUCTION: Physical properties of filters for continous renal replacement therapy have a great impact on biocompatibility. According to Poiseuille's law, a filter with more and shorter hollow fibers should offer a decreased pressure drop and, therefore, lower transmembrane pressure (TMP). The aim of this study was to study the effect of a new filter configuration in terms of TMP and clotting compared with the standard configuration. METHODS: In a prospective randomized cross-over study 2 polysulphone hollow fiber hemofilters, one handmade, which differed only in length and number of hollow fibers were compared. In each group 12 filters were investigated during continous venovenous hemofiltration in patients with acute renal failure due to septic shock. Pressures were measured every 3 hours and running time until filter clotting was documented. Mediators before and after the filter, at the end of treatment and in filtrate were assessed. RESULTS: The standard filter with longer hollow fibers had significantly lower TMPs (106 vs. 194 mmHg, p=0.02) and longer running times (1276 vs. 851 min, p=0.04). There were no differences in hematocrit, total protein, cellular and plasmatic coagulation or blood temperature. No significant elimination of mediators was shown. CONCLUSION: In contrast to our expectations, the filter with the longer hollow fibers had a better performance, as it ran longer and had lower TMP This may be due to slower blood flow leading to an increase in blood viscosity in a filter with a larger cross section.

Results from EuCliD (European Clinical Dialysis Database): impact of shifting treatment modality.

BACKGROUND: The use of biocompatible high-flux membranes is more efficient than low-flux membranes in controlling a number of hemodialysis-related diseases. The aim of this cooperative study was to evaluate the 6-month effect of a switch from low- to high-flux dialysers on patients treated in 39 Spanish dialysis centres. METHODS: The clinical data used in this analysis were prospectively collected by the EuCliD database, developed to monitor the quality of treatment delivered in a large network of European Dialysis Centres. Inclusion criteria for the study were the condition of end-stage renal disease (ESRD) on chronic hemodialysis and low-flux dialysis for at least six months before the switch to high-flux dialysis. Of 1,543 patients enrolled in the study between 2000 and 2001, 1,046 patients were considered for the analysis. 497 patients were excluded because they did not complete the follow-up. Outcome measures were the reduction of pre-dialysis beta-2 microglobulin, the improvement of anemia or reduction in rHu-EPO dose required to maintain best correction of anemia, reduction of inflammatory parameters (CRP), improvement in lipid profile (Total and HDL cholesterol, tryglycerides), maintenance of nutritional status. Albumin and "dry" (post-hemodialysis) body weight were both evaluated as nutritional indexes. RESULTS: During the six months of high-flux hemodialysis, there was a significant increase in hemoglobin (from 11.55 +/- 1.41 to 11.88 +/- 1.43 g/L; p < 0.001). Considering the temporarily untreated patients on a 0 U/week dose, erythropoietin remained stable (from 5,670 +/- 4,199 to 5,657 +/- 4,411 U/week). During the second part of the follow-up, the lipid profile significantly improved (Fig. 3). Total cholesterol and triglycerides decreased significantly (p < 0.001), while HDL cholesterol increased (p = 0.006). Calculated levels of LDL cholesterol also significantly decreased (p = 0.001). Dry body weight remained stable (64.7 +/- 11.9 vs. 64.7 +/- 12.0 kg) as well as in albumin levels (3.93 +/- 0.43 vs. 3.94 +/- 0.43 g/dL) between the two modalities of treatment. The level of beta2-microglobulin significantly decreased during high-flux dialysis (33.5 +/- 14.4 vs. 26.3 +/- 8.6 mg/dL, p < 0.001). CONCLUSION: All above mentioned results may have as a common denominator an improved blood purification from uremic toxins and a reduced level of chronic sub-clinical inflammation. All together, these results seem to confirm the superiority of high-flux dialysis in terms of clinical and physiological outcomes.

Comparison of four different short dialysis techniques.

The goal of shortening dialysis treatment time has stimulated the development of new, highly efficient dialytic strategies. In this study the Authors compared four different short dialysis treatments in terms of efficiency, clinical tolerance, technological investment and costs: 1) Rapid bicarbonate dialysis with 1.5 sq.m. cuprophane membrane; 2) High flux biofiltration with 1.2 sq.m. AN69S hollow fiber membrane; 3) Hemodiafiltration with 1.2-1.9. sq.m. polysulphonic hollow fiber hemodiafilters, and 4) High flux hemodiafiltration with two serial hemodiafilters with AN69s membrane (total 2.4 sq.m.). Hydraulic properties and solute clearances at different blood flows (300-500 ml/min) were tested for each technique. Once the optimal operative level was established three patients were treated with each technique for at least six months. Since BUN clearance averaged 310 ml/min, the treatment duration varied from 120 to 180 min/session with KT/V always higher than 1. The average protein catabolic rate was 0.9 g/kg/24h. Clinical tolerance was generally good, slightly better in treatments with a high convective component. Despite the greater efficiency of treatment No. 4, the technological requirements and costs are such that the others are currently more feasible and acceptable in clinical routine. The study demonstrates that reduction of dialysis treatment time is possible in all centres in a selected population with adequate blood access. Treatment No. 1 can even be performed with standard equipment and cuprophan membranes, while bicarbonate in the dialysate is mandatory. The real limit to shortening treatment time seems to be related to the maximal rate of ultrafiltration achievable in the patient during dialysis.

Technical and clinical evaluation of a new asymmetric polysulfone membrane (Biosulfane).

First generation asymmetric polysulfone membranes had high hydraulic permeability (kf = 40 ml/h/mmHg/sqm) but a low diffusive permeability due to the hydrophobic nature and wall thickness of 75-100 microns. We have tested a new polysulfone membrane with a wall thickness of 40 microns in a series of in vitro and in vivo dialysis session experiments. The new "Biosulfane" membrane presented a Kf of 45.8 with constant performance up to 240 mins. The koA was 760 and the clearance value at 350 ml/min of Qb in hemodiafiltration was 255 ml/min for urea, 210 for creatinine, 225 for phosphate, 76 for inulin. In high flux dialysis the clearances were similar except for inulin which was 32% lower due to the lower convection amount. Beta-2 microglobulin clearance was 22 ml/min in high flux dialysis and 37 in hemodiafiltration. Solute sieving coefficients were close to 1 for the majority of the studied solutes in a wide range of molecular weights and slight variations were observed for charged solutes due to Donnan's effect. The sieving for Inulin was 0.96 while that for Beta-2 microglobulin was not measurable due to a large molecule adsorption on the inner structure of the fibres. The good performances of this membrane are probably due to reduced wall thickness and a consequent improvement in diffusive permeability to small size solutes.

Technical and clinical evaluation of a new polyamide hollow fiber hemofilter for CAVH.

We carried out an in-vivo and in-vitro evaluation of a new polyamide hollow fiber hemofilter especially designed to operate under conditions of low pressure and low blood flow, such as in continuous arteriovenous hemofiltration (CAVH). The results obtained suggest that this filter is a prototype of a new generation of hemofilters especially designed for CAVH. Its low resistance permits its use even in patients with severe hypotension. The high blood flows achieved at a given pressure reduce the risk of clotting and increase the ultrafiltration rate. When an average ultrafiltration of 20-25 ml/min is achieved in 24 hours CAVH becomes very efficient, and alternative techniques to increase its efficiency are no longer required.

On line filtration of dialysate: structural and functional features of an asymmetric polysulfone hollow fiber ultrafilter (Diaclean).

The endotoxin transfer across dialysis membranes has been investigated using specific in vitro circuits. Backdiffusion and backfiltration have been analyzed and most dialysis membranes have shown to be permeable to LAL positive substances. Synthetic membranes however display the better capacity of retention of these products despite their higher porosity and permeability. For such reason synthetic polysulfone ultrafilters are used as pyrogen filters to obtain ultrapure dialysate. We have investigated the characteristics of a polysulfone ultrafilter named Diaclean and manufactured by Amicon Ireland. The capacity of endotoxin retention has been investigated both in filtration and backfiltration modes on new and used ultrafilters. The capacity of endotoxin adsorption was investigated as well. Used ultrafilters appeared to maintain the retention capacity and the adsorption capacity up to 4 months of use. Only slight differences were noted from the baseline values (p = n.s.). The best adsorption capacity is always displayed by the outer layer of the membrane suggesting its best utilization in back filtration mode with tangential flow. No morphological changes were observed in the used membrane analyzed by scanning electron microscopy.

In vitro and in vivo evaluation of a new polysulfone membrane for hemodialysis. Reference methodology and clinical results. (Part 1: in vitro study).

Different high flux membranes have been recently developed. The present study is aimed at describing the technical features and the clinical performances of a new high flux polysulfone membrane (T-sulfone, Toray, Japan). The study has been carried out on two different dialyzers (surface area = 1.3 and 1.8 m2). The filters have been tested in vitro under definite experimental conditions. The hydraulic flow resistance, the pressure drop in the blood compartment and the hydraulic permeability have been determined in a wide range of in vitro experimental conditions. The in vitro sieving coefficients for various solutes have also been determined utilizing human blood. Hydraulic permeability was found in the range of 28.4 ml/h/mm Hg/m2 and sieving coefficients were between 0.96 and 1.0 for all low molecular weight solutes. The sieving coefficient for inulin was 0.95. The pressure drop in the filter at 300 ml/min of blood flow was 95 mm Hg for the 1.3 m2 and 57 mm Hg for the 1.8 m2. The filters are then designed to operate in the presence of high blood flows without excessive resistance in the blood compartment. The blood compartment analyzed by means of a special radiological sequence obtained with a helical scanner after dye injection confirmed the homogeneous distribution of the blood flow in several cross sections of the bundle. Adequate distribution of dialysate was confirmed with a similar method applied to the dialysate compartment. The new imaging techniques utilized were greatly helpful to determine adequacy of filter design and flows distribution.

In vitro and in vivo evaluation of a new polysulfone membrane for hemodialysis. Reference methodology and clinical results. (Part. 2: in vivo study).

Different high flux membranes have been recently developed. The present study is aimed at describing the technical features and the clinical performances of a new high flux polysulfone membrane (T-sulfone, Toray, Japan). The study has been carried out on two different dialyzers (surface area = 1.3 and 1.8 m2). The filters have been tested in vivo during hemodialysis and hemodiafiltration. The in vivo study was carried out on 12 ESRD patients on regular hemodialysis treatment. The protocol was reviewed and approved by the local ethical committee. The in vivo clearances (K) at 300 ml/min of blood flow are reported in the following Table: [Table in text]. Beta-2-m reduction ratio exceeded 50% in all sessions. Beta-2-m mass balance executed by collection of spent dialysate and elution from the used filters evidenced that removal is obtained mostly by filtration while absorption is negligible. Excellent tolerance and hemocompatibility was observed in all the studied sessions.