In a symposium chaired by Professor Michael Horrocks and Mr Chris Gibbons, four speakers gave their view of the techniques that can be used when trying to secure vascular access in renal failure patients and how best to ensure success.
Mr David Mitchell, Southmead Hospital, Bristol, started the symposium by talking about techniques and training in renal replacement therapy. Of the two types of treatment for kidney failure, haemodialysis accounts for the majority of hospital admissions for those on renal replacement therapy. Mitchell commented that peritoneal dialysis, the more convenient option, works best if the patient has native urine output and doesn’t have adhesions within the abdominal cavity.
In haemodialysis, a practitioner needs access to a patient’s circulatory system. There are three basic ways to achieve this: arteriovenous (AV) fistula, AV graft or a central venous (CV) catheter. Mitchell cited US registry data, which revealed that patients starting haemodialysis with CV lines have a greater risk of mortality. For diabetics, both grafts and CV lines have poor outcomes, mainly owing to risk of sepsis. In general terms, in haemodialysis, the AV fistula technique is preferred. It lasts the longest and has a low revision rate; it is the least likely to become infected or develop clots and, at one year, around half of AV fistulas are still open. This is despite the fact that it is often difficult to establish and can take at least six weeks to mature.
Mitchell opined that the upside to using an AV graft, on the other hand, is that it is not necessary for a patient to have a good vein next to an artery. It is easy to place a graft and they can be ready for use almost immediately. And while they are less durable than an AV fistula, with revision rates of 80%+ per year, over time the patency rates are roughly equivalent.
However, Mitchell observed that the big question is what to do if the patient has poor vessels in the wrist. In an attempt to answer this, a randomised control trial compared the autogenous radial-cephalic AV fistula to a prosthetic PTFE graft. The results showed that 98% of PTFE grafts were useable for haemodialysis; the equivalent figure for radial-cephalic AV fistulas was only 59%. Patency figures were also better for the prosthetic grafts: primary patency was 44% vs 33% for PTFE graft; assisted patency was 63% vs 48%; and secondary patency was 79% vs 52% (all at p<0.05). It was only the intervention rate that was in AV fistula's favour: each patient required on average 0.5 interventions per year, compared to 0.94 for prosthetic grafts. From this, the conclusion is that those with poor forearm vessels benefit from prosthetic access (Rooijens et al. 2005). Mitchell also raised the issue of vascular surgeon training. Renal replacement therapy is a core part of both the vascular surgical and transplant training curricula, but currently transplant centres cannot meet demand. However, Mitchell claimed that renal replacement therapy is not seen as a priority for vascular surgeons and it is often poorly resourced. He told Vascular News: “Vascular access has not been in favour because many vascular surgeons worked short handed and could not manage the extra work. It was seen as the preserve of transplant surgeons. However with an ageing population and an increasing uptake of patients onto dialysis, the problems in providing access are becoming greater. Vascular surgeons are the specialist group with the skills to provide this service and we should encourage them.” He concluded by saying that the demand for vascular access surgery (VAS) is rising and vascular surgeons could meet this demand, provided they have access to day theatres for both service and training purposes. Going deeper into patient specifics, Professor Michael Nicholson, Leicester, spoke about patient and operation selection. He started with four guiding principles for vascular access:
When faced with a patient with kidney failure, the decision tree runs as follows:
Is a live donor kidney transplant planned?
Yes – Use a cuffed tunnelled catheter
No – Is the patient suitable for continuous ambulatory peritoneal dialysis (CAPD)?
Yes – CAPD
No – Try wrist AV fistula, followed by brachio-cephalic AV fistula, then brachio-basilic AV fistula, arm AV graft and then thigh AV graft.
However, choosing a procedure is one thing; assessing its adequacy and maintaining it are another. But they are just as important.
According to Professor Mitch Henry, Columbus, Ohio, “the five things in life that you don’t want to have to deal with are: lawyers, malpractice, alimony, college tuition fees, and vascular access”.
Henry said that, given that the fifth item is necessary, and in order to avoid the second (and thus the first!), there are certain practices that can be undertaken to monitor vascular access. A physical examination, which should be undertaken by the same examiner each time and include the patient, should look at the change in character of thrill and pulse and where that transition takes place.
In addition, he claimed that bloodflow should also be measured and this can be done directly – using duplex ultrasound or magnetic resonance angiography – or indirectly, using indicator dilution techniques such as flow dilution, timed ultrafiltration, glucose infusion, differential conductivity and ionic dialysance.
According to the Disease Outcomes Quality Initiative, for AV grafts, intra-access flows, duplex ultrasound and static venous pressures are preferred studies, while dynamic venous pressures and recirculation measures are to be avoided. Henry commented, “For the AV fistula, measuring recirculation is also acceptable, although the jury’s out on dynamic venous pressures.”
Henry also presented his reference list of abnormalities for definitive assessment of a vascular access in order to avoid thrombosis:
It is important that the data measured should be tabulated and analysed, so that organised and regular assessments can be made of the function and adequacy of the dialysis, he concluded.
Finally, Dr Jan Tordoir, Maastricht, Holland, gave a flavour of the magnitude of the renal replacement therapy situation. In Europe, the number of people on haemodialysis is around 346,000. However, each year 94,000 people need new vascular access, 41,480 people need AV fistula replacements, and 110,720 require fistula maintenance; a total of 246,200 operations. Issues that can arise with these operations include non-maturation of fistulae, the need to maintain access, and the need to salvage complicated access to prevent ischaemia, thrombosis, central venous obstruction, infection or aneurysm.
Tordoir emphasised that much can be done to monitor and manage these issues. Functioning fistulae can be enhanced using percutaneous transluminal angioplasty or through surgery. Monitoring and pre-emptive radiological or surgical intervention can prevent thromboses forming, and radiology is the first treatment option for obstructions. However, ischaemia is a major problem that defies intervention.