A randomized cross-over study with objective quantification of the performance of an asymmetric triacetate and a polysulfone dialysis membrane using different anticoagulation strategies

Background

Different strategies can be used to counteract coagulation of extracorporeal systems. Systemic anticoagulation is most widely used in routine clinical practice, but can be contraindicated in specific settings. The Solacea^™ dialyser, containing the asymmetric triacetate membrane, claims improved biocompatibility, which should result in decreased tendency for coagulation. We quantified the performance of the Solacea^™ versus the FX800CORDIAX dialyser regarding resistance to fibre blocking as assessed by micro-computed tomography (CT).

Methods

This cross-over study with four arms randomized consecutively 10 maintenance haemodialysis patients to a 4-h post-dilution haemodiafiltration session at midweek, using either Solacea^™ 19 H or FX800CORDIAX, with either regular or half dose of anticoagulation (EC2017/1459-NCT03820401). Dialyser fibre blocking was visualized in the dialyser outlet potting using a 3D CT scanning technique on micrometre resolution. Extraction ratios of middle molecules [myoglobin, lambda and kappa free light chains (FLCs)] were determined.

Results

The relative number of open fibres post-dialysis was lower in FX800CORDIAX versus Solacea^™ dialyser, and this was irrespective of the anticoagulation dose used or the threshold for counting open fibres. Extraction ratios of FLCs were not different at regular anticoagulation between Solacea^™ and FX800CORDIAX (21% ± 4% for kappa and 32% ± 8% for lambda with Solacea^™ versus 23% ± 7% and 38% ± 6% for FX800CORDIAX), but were superior with the Solacea^™ (34% ± 12% versus 22% ± 8% with FX800CORDIAX; P = 0.02) for myoglobin in case of halving anticoagulation dose. No clinically relevant albumin loss was detected.

Conclusions

The Solacea^™ dialyser seems to be promising for use in conditions where systemic anticoagulation is contraindicated, as even under conditions of low systemic anticoagulation, virtually no signs of fibre blocking could be observed using the sensitive micro-CT scanning technique. This finding is in line with its presumed good performance in terms of biocompatibility.

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 β2-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.

Heparin-Coated Left Heart Bypass: Renal Function and Hormonal Response

The effect of partial (50 mI/min/kg) left heart bypass (LHBP) on renal function, plasma renin activity (PRA), aldosterone, arginine vasopressin and atrial natriuretic peptide (ANP) response was studied in ten anesthetized, open-chested mongrel dogs (weight 23-50 kg) over a period of 6 h. Standard equipment with systemic heparinization (control), initially 300 IU/kg, was employed in five dogs, and heparin-coated equipment without additional heparin in the other five (heparin coated). Urine was continuously collected through a transurethral catheter. Urine samples and pulmonary artery blood samples for hormonal assays were taken at preset intervals before and during LHBP. The results in each group were summarized as median (25th-75th) and compared using the Mann-Whitney U test. In the control group higher blood loss required higher volume substitution. Urine output was maintained in heparin coated and slightly decreased at 3-4 h in control LHBP. Creatinine clearance at 3-5 h and free-water clearance at 3-6 h were significantly higher with heparin-coated LHBP. PRA, aldosterone and vasopressin peaked at 1-2 h of LHBP similarly in both groups, not exceeding the values before perfusion. PRA and aldosterone response was sustained during 6 h and the percentage changes corrected for hemodilution indicated a stronger response with standard equipment. Vasopressin concentrations were slightly but significantly higher in the control group at 1 and 6 h of perfusion. Corrected for hemodilution, vasopressin percentage changes were not different in the two groups. ANP, despite atrial unloading, rose similarly in both groups. There was a tendency to poorly sustained ANP response (control > heparin-coated) after 6 h of perfusion. In conclusion, preserved renal function and attenuated hormonal response during canine partial LHBP are results of better hemostasis and circulatory integrity of perfusion without systemic heparinization.

Subcutaneous abscess formation around catheters induced by viable and nonviable Staphylococcus epidermidis as well as by small amounts of bacterial cell wall components

The use of catheters is often complicated by infection, mainly due to Staphylococcus epidermidis. Recently, a novel poly(vinylpyrrolidone)-grafted silicone elastomer catheter (SEpvp) was introduced. Less bacteria adhered to SEpvp than to conventional SE catheters in vitro. The frequency of S. epidermidis infection associated with SEpvp and SE was assessed in a rabbit model. Unexpectedly, abscesses were induced by the injection of low numbers of S. epidermidis along subcutaneously inserted SEpvp. No abscesses were seen around SE, even when very high numbers of S. epidermidis were injected. This bioincompatibility reaction observed around the SEpvp was independent of the host, bacterial strain, and method of inoculation. Abscesses were also induced by nonviable S. epidermidis and by bacterial cell wall components. Because these incompatibility reactions were not observed in the absence of bacteria, biocompatibility testing should include experiments in which the inflammatory effects of the combination of catheter and (non)viable bacteria are tested.

The acu-men: a new device for continuous renal replacement therapy in acute renal failure

BACKGROUND

We sought to design a simple machine to safely provide continuous veno-venous hemofiltration to acute renal failure patients.

RESULTS

The acu-men device uses a pneumatic blood pump with tidal blood flow as the driving force. A volumetric balancing system balances the filtrate with the replacement fluid, and the blood-air interface is eliminated by replacing the conventional venous drip chamber with two air-separating membranes. The extracorporeal circuit is integrated in a disposable cartridge, which is inserted into the machine at the beginning of treatment. The priming and rinsing is done automatically.

CONCLUSION

While preliminary data from an ongoing clinic trial on the efficacy of the device are encouraging, further long-term studies are necessary to evaluate its potential to decrease morbidity and mortality in acute renal failure patients.

Assisted circulation without systemic heparinization

The need for improvements in materials and equipment for extracorporeal circulation has been obvious for years. Among the surfaces with biologically active compounds, those with heparin binding have been found sufficiently thromboresistant and particularly suitable for different types of artificial perfusion. Partial left heart bypass (LHBP) was performed in 10 anesthetized, acutely instrumented, and open-chested mongrel dogs (weight 23 to 50 kg) with a servo-controlled roller pump. The pump flow was maintained at 50 mL/kg/min for 6 hours. Heparin surface-coated equipment was used without additional heparin. For LHBP with a standard circuit, the total amount of heparin during the study period was (mean +/- SD) 487 +/- 124 IU/kg. The right atrial, pulmonary artery, and left ventricular end-diastolic pressures, cardiac output, left ventricular output, right and left ventricular stroke work, pulmonary gas exchange, and acid-base balance changed similarly with both systems. Blood loss (204 +/- 78 v 1,240 +/- 586 mL, P < 0.0005), volume substitution requirements (647 +/- 48 v 1,860 +/- 764 mL, P < 0.0025), and oxygen extraction ratio (mean 25.4 to 32.0 v 25.4 to 56.4%, P < 0.025) were significantly lower, and mean aortic pressure (mean 65 to 69 v 62 to 38 mmHg, P < 0.025) and hemoglobin concentration (mean 9.1 to 8.1 v 9.4 to 3.9 g/dL, P < 0.05) were significantly higher during 6 hours of LHBP without systemic heparinization. Low but stable oxygen delivery was provided with heparin-coated LHBP, whereas it showed a descending trend (mean 14.0 to 10.8 v 13.4 to 5.5 mL/kg/min, P < 0.1) with the standard circuit.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyanoacrylate tissue adhesive for closing skin wounds: a double blind randomized comparison with sutures

A comparative double blind randomized study was undertaken in the rat, to compare the external cosmetic and the morphologic aspect of skin wounds, treated by the local application of adhesive glue (ethyl-2-cyanoacrylate-Mediglue) or classical suture technique. Skin incisions were applied and treated by a plastic surgeon, then photographed or biopsied, and evaluated and scored by independent observers, not aware of the initial treatment. Small (1.5 cm) or long (8 cm) incisions were made, on both sides of the back, and treated randomly on one side by glue and on the other side by sutures. Evaluations were performed at 1, 2, 4 and 8 wk. Both small and large wounds scored identically, irrespective of the treatment (overall score 1.5 cm wounds: 8.8 +/- 1.4 for glue versus 8.8 +/- 1.0 for sutures; 8 cm wounds: 8.3 +/- 1.9 versus 8.3 +/- 1.5; P = not significant). A morphological study demonstrated no adverse effects for the adhesive treatment, with a minor inflammatory infiltrate. Sutured wounds had a higher tendency to develop abscesses and/or major inflammation. Adhesive-treated wounds scored better than non-treated wounds (8.9 +/- 1.3 versus 7.4 +/- 3.3, P < 0.01). In conclusion, this controlled comparative study shows no difference in cosmetic aspect between adhesive and suture-treated skin incisions. Morphologically, the glue treatment is not related to any adverse effect or damage to the skin structures.

Developing glucose sensors for in vivo use

The potential uses for in vivo glucose sensors in patients with diabetes mellitus include an alarm for low blood-glucose concentrations, a continuous read-out of glucose levels and as part of a feedback-controlled insulin delivery system (artificial pancreas). Most experience has been with implanted amperometric enzyme electrodes, though sensors based on field-effect transistors (FETs) show promise for the future. Sensing responses at the subcutaneous site correlate with plasma-glucose values, but there are often problems of calibration and drift. Implantable glucose sensors are not therefore in routine clinical use. Non-invasive glucose sensing based on near-infrared spectroscopy is being actively investigated as an alternative strategy.

Biocompatibility issues in hemodialysis

Hemodialysis, as a life-saving treatment modality for uremic patients, implies a repeated and compulsory contact of blood with foreign materials. As a consequence, biocompatibility problems are unavoidable. The same applies for the material used for the creation of vascular access, and for the alternative dialysis method, CAPD (continuous ambulatory peritoneal dialysis), although each system might cause its own and specific problems. Although in early dialysis the focus has been on maintenance of life and elimination of toxins, later on the important morbid implications of this lack of biocompatibility have been recognized. Eight major problems will be discussed, especially in the perspective of recent new findings in this field: (1) coagulation and clotting; (2) complement and leukocyte activation; (3) susceptibility to infection; (4) leaching or spallation; (5) surface alterations of solid materials; (6) allergic reactions; (7) shear; (8) transfer of compounds from contaminated dialysate. After description of the major biochemical and clinical implications of these problems, ways to prevent morbid events and future perspectives will be described.

Leukotriene B4 in hemodialysis

Leukotrienes are eicosanoids arising from arachidonic acid via 5 lipooxygenase, an enzyme essentially present in leukocyte cells. Leukotriene B4 might be an indicator of neutropolymorphonuclear leukocyte activation when there is contact with artificial membranes. The level of plasmatic leukotriene B4 was measured at three different times during the hemodialysis treatment in several patients undergoing dialysis on three different membranes (one cellulosic and two synthetics). A moderate increase of leukotriene B4 was observed early (at 15 min), comparable among the three membranes, but levels returned to baseline at 180 min. Leukotriene B4 production proved leukocyte activation and was probably related to a direct interaction with dialysis membrane. Nevertheless, complement intervention could not be excluded. Leukotriene B4 is one molecule more among the group of inflammatory mediators produced during hemodialysis treatment.