Vascular access in hemodialysis: an ongoing search for improvement

Abstract

Current guidelines promote the use of native arteriovenous fistulas (AVF) as first choice access over ePTFE grafts and central venous catheters, because of favourable complication and patency rates. However, prevalent AVF use shows enormous differences among national and regional practice surveys, even after adjusting for demographics. ePTFE grafts are characterized by stenosis formation at the venous anastomosis. However, due to the global diabetes epidemic and the abundant presence of cardiovascular disease in the ageing hemodialysis population, ePTFE grafts are likely to play an increasingly important role in the future. In a review, (inter)national practice pattern differences were discussed and actions were presented that potentially increase AVF use and improve vascular access outcomes. In 11 dialysis facilities, a guidelines implementation program, CIMINO (Care Improvement by Multidisciplinary approach for Increase of Native vascular access Obtainment) demonstrated that prevalent AVF use was increased quicker in comparison to a 22 center control group. These changes were predominantly observed in clinics where AVF use was less than 75% at the start of the observation period. Furthermore, AVF use displayed a wide range among the participating centers but these ranges narrowed during the project. In 395 hemodialysis patients, a 33% primary AVF failure rate was observed. Female gender, duration of renal replacement therapy prior to access placement, diabetes mellitus, and AVF placement at the wrist (in comparison to the elbow) were associated with the risk of primary failure. Primary failure varied from 8-50% between participating hospitals and was strongly related to the hospital of vascular access placement. In 491 AVFs, we showed that AVF patency (from surgical creation date) and functional patency (from date of first cannulation) are markedly different. This difference appears to be caused by high primary failure rates. Primary functional patency was decreased in diabetics. Secondary failure varied from 0-38% among participating hospitals and was not related to patient characteristics or cardiovascular risk factors. Compared to eight hospitals with a low secondary failure rate combined, three hospitals had a significantly higher risk for secondary failure. After achieving adequacy for hemodialysis, baseline access blood flow was lower in AVFs that failed during follow up. These values were different for forearm and upper arm AVFs. In untreated AVFs access blood flow (Qa) did not change from five months after creation. Forearm AVF Qa was inversely associated with diabetes mellitus and decreasing BMI. In upper arm AVFs, no relations with risk factors were found The 6-month primary patency rate of 20 helical Swirlgrafts™ was similar to standard ePTFE AV-grafts, but assisted primary (84%) and secondary patency (100%) rates are at the highest end of reported series. Angiographic examination in a limited number of grafts suggested reduction of helical geometry at or after implantation, implying a function like conventional ePTFE prostheses. Compared to conventional angioplasty alone, a single treatment with cryoplasty reduced the intima-media ratio at the venous anastomosis of bilateral arteriovenous grafts in 4 pigs, without obvious signs of adverse effects on graft flow or venous remodeling.