INTRODUCTION The successful creation and maintenance of haemodialysis (HD) vascular access remains of profound importance to patients reliant on regular dialysis. When considering the potential optimal performance of each access type, a natural hierarchy has evolved in which arteriovenous fistulae (AVFs) are favoured over arteriovenous grafts (AVGs), and in which AV access on the whole is favoured over access with central venous catheters (CVCs). Nonetheless, each access method has a specific complication profile that may impart a varying burden of procedures, imaging, complications and hospitalization—all of which may impact upon patients as well as nephrology, surgery and imaging specialties (Figure 1) . In this NDT Digest, we will briefly discuss the current era of HD vascular access provision by describing some of the ‘pearls’ and ‘pitfalls’ associated with each of the main vascular access types. FIGURE 1 View largeDownload slide All vascular access-related procedural activity undertaken within the first year of regular HD. Expressed as new access creation procedures per patient (top panel) and imaging procedures per patient (bottom panel), grouped by those who dialysed through a CVC throughout, those who initiated dialysis on a CVC then switched to an alternative HD access method, those who dialysed on an AVG throughout, those who initiated dialysis on an AVF then switched to an alternative HD access method and those who dialysed on an AVF throughout. Figure reproduced from data courtesy of Murray et al. . USS, ultrasound scan; NTCVC, non-tunnelled central venous catheter. FIGURE 1 View largeDownload slide All vascular access-related procedural activity undertaken within the first year of regular HD. Expressed as new access creation procedures per patient (top panel) and imaging procedures per patient (bottom panel), grouped by those who dialysed through a CVC throughout, those who initiated dialysis on a CVC then switched to an alternative HD access method, those who dialysed on an AVG throughout, those who initiated dialysis on an AVF then switched to an alternative HD access method and those who dialysed on an AVF throughout. Figure reproduced from data courtesy of Murray et al. . USS, ultrasound scan; NTCVC, non-tunnelled central venous catheter. THE AVF The native AVF is regarded as the most reliable and durable of access methods but its utility can be undermined by early primary failure rates of ∼25%, and unsuccessful maturation to a level that cannulation may be reliably achieved that may affect as many as 40–60% of AVF placements . More recent cohorts have been found to exhibit lower patency suggesting that a phenotype of increasing age, diabetes, obesity and vascular disease seen in the dialysis population may be creating more hostile conditions for successful native access creation. These features collectively may explain some of the variation in AVF prevalence, which is between 28% and 93%, in different healthcare systems . Systems of care issues such as vein preservation, multidisciplinary working and robust follow up have been implicated in improving outcomes . Adoption of regional anaesthetic techniques has been shown to improve patency in a randomized controlled trial (RCT) . Targeting arterial juxta-anastomotic and outflow stenosis has demonstrated favourable outcomes, but where AVFs have required such interventions the patency advantage of AVFs over AVGs can be lost . As such, intention-to-treat with an AVF can lead patients down one of two paths: (i) AVFs where successful cannulation is readily achieved without the requirement for intervention and (ii) AVFs in which intervention is required to ensure maturation for successful cannulation and longevity, where high re-intervention rates, vulnerable long-term secondary patency and consequent CVC exposure may be experienced. One study has reported that 25% of patients who successfully start HD with an AVF switch to alternative access within the first year . Being able to confidently predict those patients would be of value as data suggest that the procedure burden they experience is high and the associated impact on radiological and surgical services is costly [1, 7]. Whether this vulnerability may be pre-empted by consideration of alternative strategies, such as more proximal sites for first AVF creation, use of an AVG or peritoneal dialysis, requires to be tested. This issue has been well described in a recent editorial . THE AVG Traditionally, AVGs would be employed where native venous architecture was unfavourable for AVF creation, albeit with a still significant period of healing after surgical placement before use, and higher rates of infection. In recent years, however, the development of early cannulation AVG technology and materials has altered the complexion of advantages and disadvantages seen with their use. A recent RCT of new and established HD patients who required immediate AV access demonstrated superiority of early cannulation arteriovenous grafts (ecAVGs) over tunnelled CVCs in terms of bacteraemia and mortality, while proving cost neutral at 6 months . Within that cost envelope re-intervention made up the largest proportion of costs in the ecAVG arm while infection-related costs made up the largest proportion in the tunnelled central venous catheter (TCVC) arm. The gains offered by ecAVGs in this setting were at the expense of a higher procedure burden required to maintain functional patency—at least in this study population of all-comers requiring urgent access with a 6-month period of follow up. The evidence base around ecAVGs would therefore benefit from further evolution—especially with regard to the maintenance workload that is incurred following ecAVG placement and its associated impact over longer periods on patients and services alike. THE CVC CVCs provide immediate HD vascular access but have been associated with relatively high risks of bacteraemia, catheter malfunction and the long-term effects of central venous stenosis, which may impact upon future access options. CVCs remain the default access for many in the setting of acutely requiring HD, as well as in the longer term. Their vulnerability to infection and failure has been the subject of considerable focus. Catheter-related bloodstream infection (CRBSI) rates sit between 0.56 and 1.60 per 1000 catheter days and there is a strong evidence base behind the use of antimicrobial catheter lock solutions to prevent bacteraemia, as well as a treatment for established bacteraemia alongside catheter replacement . Central vein stenosis (CVS) has been reported in around 25% of prevalent tunnelled CVC users, generally becoming apparent after at least 1.5 years whereafter repeated intervention may be required to maintain central vein patency . In this study, the duration of CVC exposure was independently associated with the risk of CVS. Nonetheless, when considering the absolute event rates of CRBSI and the lag-time before CVS can become apparent and more troublesome to patients, CVC use may provide a viable means of receiving HD for those who face a limited tenure on regular HD either through live donor renal transplantation or reduced life expectancy. CONCLUSION The issues that surround selecting vascular access modality have been well recognized and extensively dealt with in the past. The traditional metrics of access patency, failure and infection are now being seen in a broader context that includes procedure burden, quality of life, morbidity, mortality and cost. What has changed more recently is the recognition of the access journey that many patients experience, as well as the impact of systems in determining selection of vascular access and the level and distribution of resource necessary to support this across different specialties. As such, decision-making around dialysis access is increasingly focusing on the outcome of intention-to-treat strategies as opposed to individual access type. Such data are anticipated to illuminate this further. CONFLICT OF INTEREST STATEMENT P.C.T., D.B.K. and R.K. have all received honoraria from W.L. Gore & Associates for presenting at educational events. D.B.K. has received an investigator-led research grant from W.L. Gore & Associates. P.C.T. has received an investigator-led research grant from Proteon Therapeutics. REFERENCES 1 Murray E , Eid M , Traynor J et al. . The First 365 days on haemodialysis: variation in the haemodialysis access journey and its associated burden . Nephrol Dial Transplant 1 February 2018 ; doi:10.1093/ndt/gfx380 2 Lee T , Allon M. Reassessing recommendations for choice of vascular access . Clin J Am Soc Nephrol 2017 ; 12 : 865 – 867 Google Scholar CrossRef Search ADS PubMed 3 Noordzij M , Jager KJ , van der Veer SN et al. . Use of vascular access for haemodialysis in Europe: a report from the ERA–EDTA Registry . Nephrol Dial Transplant 2014 ; 29 : 1956 – 1964 Google Scholar CrossRef Search ADS PubMed 4 Oliver SW , Campbell J , Kingsmore DB et al. . A national appraisal of vascular access provision in Scotland . 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This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)
Nephrology Dialysis Transplantation – Oxford University Press
Published: Jun 1, 2018
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