ReDVA

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Overcoming problems around vascular access Patients suffering from kidney failure depend on peritoneal or haemodialysis to purify their blood, yet the failure of renal dialysis vascular access is a significant and serious problem. The ReDVA project is a joint industry-academia research programme that aims to overcome the scientific and technical barriers associated with the failure of vascular access, as Dr Shona Matthew explains

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All haemodialysis patients need some

Multi-disciplinary

form of vascular access. An arteriovenous fistula (AVF) is the preferred choice, as it reduces the risk of subsequent complications and serious infections in comparison to the other options; arteriovenous grafts and central venous catheters. AVF’s are created by surgically joining an artery to a vein so that the fast flowing blood from the artery is fed directly into the vein, causing the vein to dilate and the vein walls to thicken over a period of weeks or months. This process is known as maturation. A mature fistula provides the high flow rates required to ensure that the patient receives adequate dialysis clearance within a standard 3-4 hour dialysis session and is robust enough to withstand repeated cannulations. “Because of the high failure rates and limited number of suitable sites on the body, surgeons prefer to create the first AVF in the wrist. This is not always possible as the patient’s vessels may be too small; so two potential fistulae sites are lost straight away,” says Dr Shona Matthew of the ReDVA project. “It is not uncommon for all suitable AVF sites in the body to be ‘used up’ and once that happens there’s very little else that can be done.” Repeated AVF failure impacts on patient morbidity and mortality. It also costs healthcare services a large amount of money each year as patients require an immediate and often temporary form of vascular access, and further surgery to create a new AVF. The ReDVA project was formed to investigate the problems associated with renal dialysis vascular access, bringing together partners from industry and academia with the shared goal of improving clinical understanding in this challenging area.

The multi-disciplinary nature of the project means that the problems around haemodialysis vascular access are being approached from several different angles. A lot of attention was initially devoted to analysing the existing guidelines for vascular access. “In the first year of the project, partners worked together on literature reviews, looking at existing guidelines for vascular access across the world. Several members of the ReDVA team worked with European Renal Best Practice, to update their guidelines, and one of our fellows had a Cochrane systematic review title accepted,” says Dr Matthew. Single slice image through a patient’s arm acquired using MRI scanner.

Imaging ReDVA clinicians, physicists and engineers looked at pre-operative AVF vein mapping. “Before a patient goes for surgery, the surgeon will use ultrasound (US) to ‘map’ the patient’s vein and artery to ensure that they are suitable, as recommended in all the current guidelines,” explains Dr

Matthew. Very few centres offer more than one post-operative US scan to check on the maturation process, preferring a more ‘hands on’ assessment until a problem arises. However, Dr Matthew says that her NHS colleagues apply a highly pro-active imaging approach. “In Dundee we have a system where we use US to scan our patient’s vessels before their surgery and then again at regular intervals after surgery.” This allows problems to be picked up and hopefully resolved before they affect the maturation process, or the patient’s dialysis treatment. “We are trying to encourage other centres to be more proactive with US imaging and so we developed optimised imaging protocols, which we shared with other centres,” says Dr Matthew. Researchers from the University of Dundee, the University of Limerick and Vascular Flow Technologies also looked at Magnetic Resonance Imaging (MRI) as a tool for pre-surgical vein mapping and post-surgical surveillance, as they believe that MRI may offer additional information, which cannot be obtained with US. For example, many renal patients require a central venous catheter (CVC) at some point, perhaps as a form of temporary vascular access or as a conduit for administering drugs and fluid during surgery. Central vein stenosis is a common complication of using a CVC and needs to be considered when planning further AVF surgery, as it can lead to post operative complications. “This type of stenosis cannot be detected using US, but can be imaged with MRI, ” says Dr Matthew. However, MRI is not routinely used as it’s quite expensive, not easy to access

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