Polysulfone Filters Research Articles

Sustained low-efficiency dialysis (SLED) with prostacyclin in critically ill patients with acute renal failure

Prostacyclin is an easy-to-use and safe antihaemostatic drug for continuous renal replacement therapies (RRTs). No study has been performed so far about its use in critically ill patients with acute renal failure (ARF) treated with sustained low-efficiency dialysis (SLED), a hybrid modality between conventional intermittent and continuous RRTs. We studied 35 consecutive ICU patients with ARF, in whom data on safety and efficacy were prospectively collected in a single-centre experience over 15 months since August 2001. There were 25 males and 10 females; mean age, 72.1 (SD 11.4); mean APACHE II score at ICU admission, 24 (range 14-43); at RRT start, 27.4 (20-43); 28 patients (80%) were on mechanical ventilation and 17 (48.6%) had sepsis. SLED was performed using a conventional dialysis machine, with blood flow at 200 ml/min, bicarbonate-based ultrapure dialysate running at 100 ml/min, dialysate temperature 35 degrees C and low-flux polysulfone filters. Prostacyclin, under the form of its synthetic analogue epoprostenol, was infused at 6 ng/kg/min before the filter. Out of 185 daily sessions performed (8-10 h, median 4 per patient, range 1-19), 19 (in 11 patients) were prematurely interrupted (10.3%; 95% CI: 5.4-18.6), after an average 58.5% of the prescribed treatment time (nine sessions in six patients for circuit clotting). This finding compared favourably with the experience we had at our unit using SLED with saline flushes. With the use of prostacyclin, two episodes of upper gastrointestinal bleeding were observed in 2/35 patients during SLED (5.7%; 95% CI: 0.7-19.2), corresponding to 1.1 episodes per 100 person-day on SLED. Therapeutic intervention for hypotension (fluids and/or vasopressor increase) was required in 45/185 (in 20 patients) of the sessions monitored (24.3%; 95% CI: 17.4-32.9); two sessions had to be interrupted because of refractory hypotension. Urea reduction ratio was 0.50 (SD 0.12); mean prescribed and obtained net ultrafiltration were 1.96 l (range 0.5-5.0) and 1.99 l (0.5-5.0), respectively. In-hospital mortality was 46%; mortality predicted by the APACHE II model at ICU admission was 42%; at SLED start, 51%. Prostacyclin is a safe and effective antihaemostatic agent for SLED.

Blood compatibility and filtration characteristics of a newly developed polyester polymer alloy membrane

Many synthetic polymeric membranes have been widely used for blood purification therapies for removing larger solutes and for better blood compatibility. Five different filters with polyester polymer alloy (PEPA) membrane (Nikkiso) that included polyvinylpyrrolidone (PVP), that is, standard-pore-size FLX (PEPA with PVP(-)), standard-pore-size FDX (PEPA with PVP(+)), new FDX (PEPA with PVP(++)), larger-pore-size FDY (PEPA with PVP(+)), and new FDY (PEPA with PVP(++)), were evaluated in terms of in vivo blood compatibility and aqueous in vitro sieving coefficient (s.c.) for albumin. FDY showed excellent small changes in C3a concentration during the treatment right after switching from polysulfone membrane, leaving no significant changes in other blood-compatible indices. New FDY, in contrast, showed less biocompatible characteristics in terms of C3a, which may be caused by increased use of PVP. FLX (no PVP) showed the highest s.c. for albumin. With a hydrophilic agent (PVP), the s.c. was greatly reduced in FDX. By enlarging the pore diameter in FDY, the s.c. increased in accordance with the enlargement. Generally speaking, polysulfone filters with PVP(+++) reach the peak s.c. value approximately 10 min after starting the experiment. The s.c. of the PEPA membrane with no or small amount of PVP, which showed excellent blood compatibility, never showed peaks, whereas the peak s.c. values were found in new PEPA with increased amount of PVP that showed higher C3a changes. The separation characteristics of aqueous albumin may be related to its blood compatibility.

Elimination of linezolid by an in vitro extracorporeal circuit model.

Linezolid is an oxazolidinone antibiotic with activity against important grampositive aerobic bacteria, including nosocomial pathogens. It is not known whether dosage adjustments are necessary in patients treated with continuous renal replacement therapies. This in vitro study was conducted to investigate the elimination of linezolid in an in vitro continuous hemo(dia)filtration model using different filter materials (polysulfone, polyacrylonitrile, polyamide), surface areas, and different modes of renal replacement therapies. Linezolid was measured using HPLC with UV-detection. No adsorption of linezolid to any of the tested membranes was detected. Recovery of linezolid in the ultrafiltrate was 98.2 +/- 10.5% in the filtration mode. During dialysis, recovery was significantly less (87.6 +/- 16.1%; p = 0.02). Linezolid elimination was not altered by filter size, when polysulfone filters with surface areas of 0.7 m2 and 1.3 m2 were tested. In conclusion, the dosage recommendations for linezolid are independent of the filter materials. However, the elimination is significantly higher during hemofiltration compared to dialysis.

Inflammatory response to cardiac bypass in ewe fetuses: effects of steroid administration or continuous hemodiafiltration

Objectives We sought to investigate the effectiveness of glucocorticoid administration or continuous venovenous hemodiafiltration on endothelin and corticotropin-releasing factor release or clearance during prolonged fetal cardiac bypass and on the overall performance of fetuses. Methods Circulating endothelin 1, 2, and 3 and corticotropin-releasing factor levels were measured in fetal ewes during a 60-minute cardiac bypass period performed with an inline axial flow pump. Blood samples were collected before, during, and 90 minutes after cardiac bypass. Animals were divided into 4 groups. The betamethasone group (n = 6) received maternal treatment with 12 mg of betamethasone 1 and 2 days before the experiment. The methylprednisolone group (n = 5) received fetal treatment with 40 mg/kg intravenous methylprednisolone at the beginning of cardiac bypass. The continuous venovenous hemodiafiltration group (n = 4) underwent continuous venovenous hemodiafiltration with a 0.3-m 2 polysulfone filter during cardiac bypass. The final group was the control group (n = 4). Results Maternal steroid pretreatment failed to decrease endothelin or corticotropin-releasing factor production when compared with levels in the control animals. Fetal treatment with methylprednisolone produced a significant decrease in endothelin 2 production during cardiac bypass ( P < .02) and endothelin 1 production at the end of the experiment ( P < .02). Continuous venovenous hemodiafiltration blocked completely the increase of endothelin and corticotropin-releasing factor levels during cardiac bypass ( P < .02), which was maintained 90 minutes after cardiac bypass. Acid-base balance was preserved during cardiac bypass by the continuous venovenous hemodiafiltration but worsened after disconnection of the extracorporeal circuit, whereas animals treated with methylprednisolone had better pH, Pa co 2, and bicarbonate levels by the end of the experiment. The overall tolerance of the procedure was better in the continuous venovenous hemodiafiltration group during cardiac bypass and in the methylprednisolone group at the end of the experiment. Conclusions Continuous venovenous hemodiafiltration provides sustained stability of endothelin levels during fetal cardiac bypass. This technique might help, in association with fetal steroid treatment, to contain the inflammatory response leading to postbypass placental dysfunction.

Total and corrected antioxidant capacity in hemodialyzed patients.

BackgroundOxidative stress may play a critical role in the vascular disease of end stage renal failure and hemodialysis patients. Studies, analyzing either discrete analytes and antioxidant substances, or the integrated total antioxidant activity of human plasma during hemodialysis, give contradictory results.MethodsRecently, we have introduced a new automated method for the determination of Total Antioxidant Capacity (TAC) of human plasma. We have serially measured TAC and corrected TAC (cTAC: after subtraction of the interactions due to endogenous uric acid, bilirubin and albumin) in 10 patients before the onset of the dialysis session, 10 min, 30 min, 1 h, 2 h and 3 h into the procedure and after completion of the session.ResultsOur results indicate that TAC decreases, reaching minimum levels at 2 h. However, corrected TAC increases with t1/2 of about 30 min. We then repeated the measurements in 65 patients undergoing dialysis with different filters (36 patients with ethylene vinyl alcohol copolymer resin filter -Eval-, 23 patients with two polysulfone filters -10 with F6 and 13 with PSN140-, and 6 patients with hemophan filters). Three specimens were collected (0, 30, 240 min). The results of this second group confirm our initial results, while no significant difference was observed using either filter.ConclusionsOur results are discussed under the point of view of possible mechanisms of modification of endogenous antioxidants, and the interaction of lipid- and water-soluble antioxidants.

Congo Red Populates Partially Unfolded States of an Amyloidogenic Protein to Enhance Aggregation and Amyloid Fibril Formation

Congo red (CR) has been reported to inhibit or enhance amyloid fibril formation by several proteins. To gain insight into the mechanism(s) for these apparently paradoxical effects, we studied as a model amyloidogenic protein, a dimeric immunoglobulin light chain variable domain. With a range of molar ratios of CR, i.e. r = [CR]/[protein dimer], we investigated the aggregation kinetics, conformation, hydrogen-deuterium exchange, and thermal stability of the protein. In addition, we used isothermal titration calorimetry to characterize the thermodynamics of CR binding to the protein. During incubation at 37 degrees C or during thermal scanning, with CR at r = 0.3, 1.3, and 4.8, protein aggregation was greatly accelerated compared with that measured in the absence of the dye. In contrast, with CR at r = 8.8, protein unfolding was favored over aggregation. The aggregates formed with CR at r = 0 or 0.3 were typical amyloid fibrils, but mixtures of amyloid fibrils and amorphous aggregates were formed at r = 1.3 and 4.8. CR decreased the apparent thermal unfolding temperature of the protein. Furthermore, CR perturbed the tertiary structure of the protein without significantly altering its secondary structure. Consistent with this result, CR also increased the rate of hydrogen-deuterium exchange by the protein. Isothermal titration calorimetry showed that CR binding to the protein was enthalpically driven, indicating that binding was mainly the result of electrostatic interactions. Overall, these results demonstrate that at low concentrations, CR binding to the protein favors a structurally perturbed, aggregation-competent species, resulting in acceleration of fibril formation. At high CR concentration, protein unfolding is favored over aggregation, and fibril formation is inhibited. Because low concentrations of CR can promote amyloid fibril formation, the therapeutic utility of this compound or its analogs to inhibit amyloidoses is questionable.

Single-step extraction of fluconazole from plasma by ultra-filtration for the measurement of its free concentration by high performance liquid chromatography

High performance liquid chromatography (HPLC) is the reference method for measuring concentrations of antimicrobials in blood. This technique requires careful sample preparation. Protocols using organic solvents and/or solid extraction phases are time consuming and entail several manipulations, which can lead to partial loss of the determined compound and increased analytical variability. Moreover, to obtain sufficient material for analysis, at least 1 ml of plasma is required. This constraint makes it difficult to determine drug levels when blood sample volumes are limited. However, drugs with low plasma-protein binding can be reliably extracted from plasma by ultra-filtration with a minimal loss due to the protein-bound fraction. This study validated a single-step ultra-filtration method for extracting fluconazole (FLC), a first-line antifungal agent with a weak plasma-protein binding, from plasma to determine its concentration by HPLC. Spiked FLC standards and unknowns were prepared in human and rat plasma. Samples (240 μl) were transferred into disposable microtube filtration units containing cellulose or polysulfone filters with a 5 kDa cut-off. After centrifugation for 60 min at 15 000 g, FLC concentrations were measured by direct injection of the filtrate into the HPLC. Using cellulose filters, low molecular weight proteins were eluted early in the chromatogram and well separated from FLC that eluted at 8.40 min as a sharp single peak. In contrast, with polysulfone filters several additional peaks interfering with the FLC peak were observed. Moreover, the FLC recovery using cellulose filters compared to polysulfone filters was higher and had a better reproducibility. Cellulose filters were therefore used for the subsequent validation procedure. The quantification limit was 0.195 mg l −1. Standard curves with a quadratic regression coefficient⩾0.9999 were obtained in the concentration range of 0.195–100 mg l −1. The inter and intra-run accuracies and precisions over the clinically relevant concentration range, 1.875–60 mg l −1, fell well within the ±15% variation recommended by the current guidelines for the validation of analytical methods. Furthermore, no analytical interference was observed with commonly used antibiotics, antifungals, antivirals and immunosuppressive agents. Ultra-filtration of plasma with cellulose filters permits the extraction of FLC from small volumes (240 μl). The determination of FLC concentrations by HPLC after this single-step procedure is selective, precise and accurate.

Quantitative mapping of bacterioplankton populations in seawater: field tests across an upwelling plume in Monterey Bay

Few methods are available for quantifying specific prokaryotic taxa in marine plankton samples. In this study, we report a novel sampling and analysis strategy that circumvents some of the difficulties associated with current methods. This new approach allows for increased spatial, tempo- ral and phylogenetic resolution over what has been achievable in routine bacterioplankton surveys. Picoplankton from small volume samples (30 ml) were collected on polysulfone filters and DNA was extracted with a commercially available DNA purification kit. The contribution of different bacterio- plankton members at the group and subgroup levels was quantified by 5' nuclease assays. Percent- ages of small subunit (SSU) rDNAs from SAR11, SAR86, Roseobacter, Cytophaga and Synechococcus clades in DNA extracted from small samples were compared with SSU rDNA in DNA samples extracted from 6 to 9 l seawater. Only small differences were observed between the methods. The approach was also tested by estimating gene copy numbers in a seawater sample spiked with vary- ing numbers of cells from a cultivated marine Roseobacter strain. Finally we measured SSU rDNAs from the same groups of marine bacterioplankton in samples from a rapid survey of an upwelling plume in Monterey Bay, California, USA. A strong negative correlation between the percentage of Cytophagales and recently upwelled water, and an overlap between higher SAR86 percentages and a chlorophyll a concentration peak was found. The results confirm that rapid mapping of specific bacterioplankton groups is achievable using small samples and 5' nuclease assays.

Optical measurements of lung microvascular filtration coefficient using polysulfone fibers.

Lung fluid balance, which is governed by the product of net transvascular pressure difference and lung filtration coefficient, can be altered in pulmonary diseases. A simple measurement of the lung filtration coefficient (Kfc) would be clinically useful and has been examined by several researchers. Current methods of determining Kfc include gravimetric measurement in isolated lungs and lymph node cannulation, neither of which can be extended to human use. Optical measurements of protein concentration changes in venous blood can be combined with pressure measurements to calculate Kfc. Blood, though, contains red corpuscles, which tend to absorb and scatter light, obscuring these optical measurements. In this study, an optical system was developed in which a polysulfone filter cartridge was used to remove red blood cells before the filtrate was passed through a spectrophotometer. Absorbance changes caused by changes in concentration of albumin labeled with Evans Blue were monitored at 620 nm after venous pressure was elevated by about 13 cm H2O. Optical measurements of Kfc averaged 0.401 +/- 0.074 (ml/min cm H2O 100 g DLW) for an isolated canine lung. Optical measurements of Kfc (0.363 +/- 0.120 ml/min cm H2O 100 g DLW) were made for the first time in an intact, closed chest sheep in which pulmonary pressure was altered by inflating a Foley balloon in the left atrium. We conclude that absorbance and scattering artifacts introduced by red blood cells can be eliminated by first filtering the blood through polysulfone fibers. Kfc measurements using the optical method are similar to values obtained by others using gravimetric methods. Finally, we have demonstrated that the technique can be used to estimate Kfc in an intact animal.

Automatic Continuous Venovenous Hemodiafiltration in Cardiosurgical Patients

Intermittent substitutive treatments in severely ill patients with acute renal failure are difficult or not suitable because of technical problems and/or hemodynamic instability. Continuous venovenous hemodiafiltration allows an adequate, slow removal of fluid, electrolytes, and waste products by combining diffusive and convective solute transport. Eight patients with acute renal failure, after cardiovascular surgery and cardiogenic shock, were treated by continuous venovenous hemodiafiltration. An automatic system (Equaline System, Amicon Division, USA) was employed. Venous accesses (femoral or subclavian) were used with double lumen catheters. A polysulfone filter (0.4 m2) was used in the study. Blood flow was 30 ml/min and dialysate flow rate 16.6 ml/min. Sterile pyrogen-free hemofiltration substitution fluid was used as dialysate. Mean duration of treatment was 10.3 +/- 3.2 days. After 72 hours blood urea nitrogen levels dropped from 136 +/- 46.13 to 53.5 +/- 12.3 mg/dl and creatinine levels dropped from 6.9 +/- 1.7 to 2.6 +/- 0.9 mg/dl. A controlled steady-state was then maintained. Mean urea clearance was 21 +/- 5.3 ml/min; mean ultrafiltration rate was 20.3 +/- 4.1 L/day. Continuous venovenous hemodiafiltration, with the Equaline System, is effective for the clearance of waste products and is able to maintain perfect fluid balance in catabolic patients with acute renal failure and multiple organ failure.

In Search of Sterile, Endotoxin-free Dialysate

Sterile dialysate, free of endotoxin (ET) and other cytokine inducing factors, will probably become a future standard. High-flux dialysis with bicarbonate and reuse has the membrane, the pressures, and bacteriologic potential for ET fragments to pass from dialysate to the blood side of the membrane with activation of monocytes and production of cytokines. Ultrafiltration through polysulfone filters has been shown to remove bacteria, ET, and its fragments and other cytotoxic inducing factors. The authors found that in spite of sterile, ET-free, reverse osmosis (RO) water, ET was usually present at the dialyzer inlet and arose from the RO storage tank water with bacteria < 30 CFU/ml, in spite of repeated disinfection. The authors now remove bacteria, ET, and fragments from RO tank water with a 5 mu cellulose filter followed by ultrafiltration with a Fresenius F-80 polysulfone dialyzer inserted between the wall RO delivery port and each delivery system. At the dialyzer inlet, monthly bacterial counts were < 30 cfu/ml, and ET values (n = 38) were not detectable in 89% and < 0.5 EU/ml in 11%. The F-80 filters were used for 180+ dialyses along with the 5 mu filters, which replaced the frequently endotoxin contaminated 10 mu filters in the Monitral-S delivery systems. The costs did not increase.

Comparison of Sampling Media for Endotoxin-Contaminated Aerosols

Abstract In this study the influence of collection media and sampling method on endotoxin extraction for a variety of endotoxin-contaminated aerosols was examined. A first set of experiments compared endotoxin concentrations on eight different filter media after sampling from a chamber containing a saline endotoxin aerosol. Glass fiber (GF) and cellulose acetate (CA) filters were equivalent and showed significantly higher amounts of extractable endotoxin than any other filter type. Polysulfone, polyvinyl chloride (PVC), and polytetrafluoroethylene (PTFE) filters indicated two-thirds of the endotoxin concentration of GF and CA filters; concentrations on nylon, polycarbonate, and silver membrane filters were significantly lower (one-tenth that of GF and CA filters). The presence of chloride anion was comparable for all filter media from which significant amounts of endotoxin could be extracted, suggesting that extraction of endotoxin, but not chloride anion, was dependent on filter type. In subsequent exper...

Pervaporation membranes for ethanol-water mixture prepared by plasma polymerization of fluorocarbons. II. Perfluoropropane membranes

Pervaporation membranes for ethanol-water binary mixtures were prepared by plasma polymerization of perfluoropropane (PFP). The plasma-polymerized thin films were deposited onto porous polysulfone (PS) filters as substrates with an average pore size from 0.1 to 0.45 μm. By adding argon carrier to PFP system, fluorine/carbon elemental ratios (F/C) of the produced membranes evaluated by X-ray photoelectron spectroscopy (XPS), showed a maximum value, then slightly decreased at higher partial pressure of Ar. This tendency was recognized more clearly by comparing the summation of −CF 3 and −CF 2-peak area percentages based on a whole C 18 peak area. As a measure of hydrophobicity, this value is more intelligible than the direct F/C ratio. The influence of substrate pore-size, plasma-treatment time and hydrophobicity of the membranes on the separation capability were studied. The ethanol-separation coefficient, (α EtOH), of PFP membranes increased slightly with decrease of the average pore-size of the substrates, but treatment time did not apparently affect the α EtOH. We classified the prepared membranes into two classes, i.e. the membranes showing higher and lower permeation fluxes than 0.5 kg/m 2-hr. The α EtOH was more evidently observed to increase with membrane hydrophobicity for the former class of PFP membranes. We suggest that, at least, three separation schemes might be necessary to understand the correlations found in each group.

Continuous Pulse-Oxymetry during Haemodialysis

Continuous, non-invasive measurement of arterial oxygen saturation (SaO2) during haemodialysis was performed in 18 patients with chronic renal failure. They were dialyzed three times for 2 1/2-3 1/2 h weekly using a capillary polysulfone (F60) or a cuprophane (D2) filter. The total number of O2 saturation curves analyzed was 48. The whole group showed a significant mean decline in SaO2 by 1.9% as compared with predialysis values. In 7 patients with three or more recordings, the significant mean decline in SaO2 was 1.5-4.2% and occurred within 15-60 min after onset of haemodialysis. Evaluation of SaO2 during episodes of severe depression of blood pressure was not possible due to loss of the signal as a consequence of peripheral vasoconstriction. Changes in SaO2 which occurred without any clinical signs or symptoms included very short episodes of depression of SaO2 by 3-22%; a decrease in SaO2 by 3-6% occurring towards the end of the treatment and followed by depressed values for a period of 20-60 min; episodes of marked instability of SaO2 values with differences of up to 10%, lasting 20-60 min and occurring towards the end of the treatment. Application of cuprophane instead of polysulfone filter membranes, first use and reuse of dialyzers, and microemboli blood filters were not found to influence the changes in SaO2. There was a significant difference in the initial decrease in SaO2 during acetate as compared with bicarbonate dialysis.

Complement kinetics during continuous arteriovenous hemofiltration: studies with a new polysulfone hemofilter.

Biocompatibility of the Renaflo polysulfone hemofilter was assessed during treatments with continuous arteriovenous hemofiltration. Pre- versus postfilter levels of C3a, C4a, C5a and leukocyte counts were measured prior to and 15, 60 and 90 min after placement of the Renaflo. Results revealed a small, and previously unrecognized, increase in postfilter C3a (1,224 +/- 56 vs. 1,535 +/- 150 ng/ml, mean +/- SEM, n = 15; p less than 0.01). A comparable increase was also found during treatment with an Amicon polysulfone filter. There were no other significant changes in any parameter studied and no patient exhibited symptoms related to complement activation. We conclude that the Renaflo filter is safe for use during continuous arteriovenous hemofiltration. Although clinically insignificant, there is a detectable activation of C3 by polysulfone membranes.

Preparation of reverse osmosis membranes by plasma polymerization of organic compounds

The plasma polymerization of organic compounds was used to prepare a composite reverse osmosis membrane which consists of an ultrathin semipermeable membrane formed by plasma polymerization of an organic compound or compounds and a porous substrate. Many nitrogen-containing compounds (aromatic amines, heteroaromatic compounds, aliphatic amines, and nitriles) were found to yield excellent reverse osmosis membranes by plasma polymerization directly onto porous substrates such as Millipore filters, porous polysulfone filters, and porous glass tubes. Factors involved in the preparation of reverse osmosis membranes by plasma polymerization were investigated and discussed. The plasma polymerized membranes have the following unique features: (1) very stable performance independent of salt concentration and applied pressure (practically no water flux decline was observed with many membranes): (2) salt rejection and water flux both increase with time in the initial stage of reverse osmosis (consequently, the performance of the membrane improves with time of operation); (3) very high salt rejection (over 99%) with high water flux (up to 38 gfd) can be obtained with 3.5% NaCl at 1500 psi (membranes perform equally well under conditions of sea water conversion and brakish water treatment).