Novel therapies for hemodialysis vascular access dysfunction: fact or fiction!

Patients, healthcare providers, and general population preferences for hemodialysis vascular access: a discrete choice experiment

Background

A patient-centered dialysis treatment option requires an understanding of patient preferences for alternative vascular accesses and nephrologists often face difficulties when recommending vascular access to end-stage kidney disease (ESKD) patients. We aimed to quantify the relative importance of various vascular access characteristics to patients, healthcare providers and general population, and how they affect acceptability for patients and healthcare providers.

Methods

In a discrete choice experiment, patients with maintenance hemodialysis (MHD), healthcare providers, and individuals from the general population were invited to respond to a series of hypothetical vascular access scenarios that differed in five attributes: cumulative patency, infection rate, thrombosis rate, cost, and time to maturation. We estimated the respondents' preference heterogeneity and relative importance of the attributes with a mixed logit model (MXL) and predicted the willingness to pay (WTP) of respondents via a multinomial logit model (MNL).

Results

Healthcare providers (n = 316) and the general population (n = 268) exhibited a favorable inclination toward longer cumulative patency, lower access infection rate and lower access thrombosis rate. In contrast, the patients (n = 253) showed a preference for a 3-year cumulative patency, 8% access infection rate, 35% access thrombosis rate and 1.5 access maturity time, with only the 3-year cumulative patency reaching statistical significance. Among the three respondent groups, the general population found cumulative patency less important than healthcare providers and patients did. Patients demonstrated the highest WTP for cumulative patency, indicating a willingness to pay an extra RMB$24,720(US$3,708) for each additional year of patency time.

Conclusion

Patients and healthcare providers had a strong preference for vascular access with superior patency. While the general population preferred vascular access with lower thrombosis rates. These results indicate that most patients prefer autogenous arteriovenous fistula (AVF) as an appropriate choice for vascular access due to its superior patency and lower complications than other vascular access types.

Optiflow anastomotic device for hemodialysis vascular access creation

The need to have consistent methods and consistent technique to optimize hemodialysis outcomes is behind the concept of the Optiflow™ device. This device was created to allow for consistency in size of the arterial anastomosis and consistency in angle of the vein to the artery at the anastomosis. Early data suggest that allowing these two technical entities can improve outcomes in regards to flow and maturity in arteriovenous fistula creation. This article is a summary of early data that demonstrate the impact the Optiflow device on brachial cephalic fistulas.

Impact of Needles in Vascular Access for Hemodialysis

This article reviews pragmatic aspects of cannulation practice and types of cannulation devices, as well as their impact in vascular access for hemodialysis. Hemodialysis treatment requires successful insertion of two needles for each dialysis treatment. The first needle is the arterial needle; it removes blood with toxin accumulation from the patient and delivers it to the dialysis machine. The second needle, called the venous needle, returns the purified blood from the dialyzer to the patient. Mechanical and hemodynamic trauma related to needle insertions will be discussed.

Arteriovenous Fistula Creation Using the Optiflow™ Vascular Anastomotic Connector: The Open (Optiflow PatEncy and MaturatioN) Study

Purpose

Arteriovenous fistulas (AVFs) are the preferred form of vascular access for hemodialysis. However, non-maturation and patency are major clinical problems. The Optiflow™ device is an implantable anastomotic connector used to standardize the creation of an AVF. Studies have suggested that the geometry of the anastomosis and experience of the surgeon impact patency and maturation rates. The Optiflow serves as a surgical template whereby the geometry and flow path of the anastomosis are predetermined. This prospective study was intended to evaluate maturation, patency and safety of the Optiflow.

Methods

Forty-one upper arm AVFs were created in 41 end-stage renal disease patients using the Optiflow device at two investigational sites. Patients were followed for 90 days with serial Doppler ultrasounds performed at approximately 14, 42 and 90 days to determine AVF maturation. The primary performance endpoint was unassisted maturation, defined as an outflow vein that was equal to or greater than 5 mm in diameter, and with flow equal to or greater than 500 mL/min without the need for any intervention intended to promote or maintain maturation. The primary safety endpoint was the rate of device-related serious adverse events.

Results

Unassisted maturation rates were 76%, 72% and 68% and unassisted patency rates were 93%, 88% and 78%, at 14, 42 and 90 days, respectively. There were no device-related serious adverse events.

Conclusions

The results suggest that the Optiflow is safe for its intended use and could play an important role in enhancing AVF maturation while standardizing the anastomotic technique.

What is happening in the world of vascular access? Research and innovations are flowing through

Vascular access perfectly reproduces myointimal hyperplasia that can be found in coronary or peripheral arteries and has a major advantage that these other sites cannot match: it is quite superficial and not close to a major vital organ and also affects a population that will attend the hospital for dialysis on a very regular basis. It therefore appears obvious to try and develop a tool that will mitigate myointimal hyperplasia and that could later be tested on coronary or peripheral arteries. Over the past few years several trials have been organized and we are now at a stage where some results have become available.

A Novel Technique for Loading of Paclitaxel-PLGA Nanoparticles onto ePTFE Vascular Grafts

The major cause of hemodialysis vascular access dysfunction (HVAD) is the occurrence of stenosis followed by thrombosis at venous anastomosis sites due to the aggressive development of venous neointimal hyperplasia. Local delivery of antiproliferative drugs may be effective in inhibiting hyperplasia without causing systemic side effects. We have previously demonstrated that paclitaxel-coated expanded poly(tetrafluoroethylene) (ePTFE) grafts, by a dipping method, could prevent neointimal hyperplasia and stenosis of arteriovenous (AV) hemodialysis grafts, especially at the graft-venous anastomoses; however, large quntities of initial burst release have remained a problem. To achieve controlled drug release, paclitaxel (Ptx)-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (Ptx-PLGA-NPs) were prepared by the emulsion-solvent evaporation method and then transferred to the luminal surface and inner part of ePTFE vascular grafts through our micro tube pumping and spin penetration techniques. Scanning electron microscope (SEM) images of various stages of Ptx-PLGA-NPs unequivocally showed that micro tube pumping followed by spin penetration effectively transferred Ptx-PLGA-NPs to the inner part, as well as the luminal surface, of an ePTFE graft. In addition, the in vitro release profiles of paclitaxel demonstrated that this new system achieved controlled drug delivery with a reduced initial burst release. These results suggest that loading of Ptx-PLGA-NPs to the luminal surface and the inner part of an ePTFE graft is a promising strategy to ultimately inhibit the development of venous neointimal hyperplasia.

Neointimal hyperplasia associated with synthetic hemodialysis grafts

Stenosis is a major cause of failure of hemodialysis vascular grafts and is primarily caused by neointimal hyperplasia (NH) at the anastomoses. The objective of this article is to provide a scientific review of the biology underlying this disorder and a critical review of the state-of-the-art investigational preventive strategies in order to stimulate further research in this exciting area. The histology of the NH shows myofibroblasts (that are probably derived from adventitial fibroblasts), extracellular matrices, pro-inflammatory cells including foreign-body giant cells, a variety of growth factors and cytokines, and neovasculature. The contributing factors of the pathogenesis of NH include surgical trauma, bioincompatibility of the synthetic graft, and the various mechanical stresses that result from luminal hypertension and compliance mismatch between the vessel wall and graft. These mechanical stimuli are focal in nature and may have a significant influence on the preferential localization of the NH. Novel mechanical graft designs and local drug delivery strategies show promise in animal models in preventing graft NH development. Successful prevention of graft stenosis would provide a superior alternative to the native fistula as hemodialysis vascular access.

In vitro Paclitaxel and Radiation Effects on the Cell Types Responsible for Vascular Stenosis: A Preliminary Analysis

Hemodialysis vascular access dysfunction as a result of venous neointimal hyperplasia in dialysis access grafts and fistulae is currently a huge clinical problem. The aim of this study was to assess the effects of paclitaxel and radiation, both singly and in combination on the proliferation of cell types present within the lesion of venous neointimal hyperplasia (vascular smooth muscle cells, fibroblasts and endothelial cells within the neointimal microvessels). Vascular smooth muscle cells, fibroblasts and endothelial cells were plated onto 96-well plates and exposed to different concentrations and doses of paclitaxel and radiation, respectively (both individually and in combination). Growth inhibition was assessed with an MTT assay. Both paclitaxel and radiation resulted in significant growth inhibition of all three cell types. However, even small doses of paclitaxel appeared to attenuate the antiproliferative effect of radiation on these cell types. Further experiments to elucidate the mechanism behind these findings could result in a better understanding of combination antiproliferative therapies.

Paclitaxel-coated expanded polytetrafluoroethylene haemodialysis grafts inhibit neointimal hyperplasia in porcine model of graft stenosis

BACKGROUND

The main pathology of haemodialysis graft stenosis is venous neointimal hyperplasia at graft-venous anastomoses. Neointimal hyperplasia is also observed in cases of coronary artery in-stent restenosis. Paclitaxel is a chemotherapeutic agent used to treat cancer, and has been proven to inhibit neointimal hyperplasia of coronary artery in-stent restenosis. In this study, we examined whether a paclitaxel-coated haemodialysis graft could inhibit neointimal hyperplasia and prevent stenosis.

METHODS

We dip-coated paclitaxel on expanded polytetrafluoroethylene (ePTFE) grafts at a dose density of 0.59 microg/mm(2). In vitro release tests showed an initial paclitaxel burst followed by a long-term slow release. Using ePTFE grafts with (coated group, n = 8) or without a paclitaxel coating (control group, n = 11), we constructed arteriovenous (AV) grafts connecting the common carotid artery and the external jugular vein in Landrace pigs.

RESULTS

After excluding seven pigs for technical failure, cross-sections of graft-venous anastomoses obtained 6 weeks after placing the AV grafts were analysed. Percentage luminal stenosis, ratios of intima to media in whole cross-sections, areas of intima in the peri-junctional areas (within 2 mm above and 2 mm below the graft-venous junction), and the mean thickness of intima within venous sides of cross-sections, were 60.5% (range, 41.5-60.7), 13.0 (range, 8.6-20.4), 23.7 mm(2) (range, 10.8-32.1) and 2.1 mm (range, 1.1-3.0), respectively, in the control group, whereas corresponding median values in the coated group were 10.4% (range, 1.0-17.8), 1.0 (range, 0.7-5.1), 1.6 mm(2) (range, 0.2-8.0) and 0.3 mm (range, 0.1-2.2). All parameters were significantly different between the two groups (P<0.05 by Mann-Whitney test).

CONCLUSION

Paclitaxel-coated ePTFE grafts could prevent neointimal hyperplasia and the stenosis of AV haemodialysis grafts.