Increasing AV Fistulae

The pathways to increased AV fistula prevalence are now clearly delineated in the K/DOQI recommendations and Fistula First change concepts [11, 12]. Patients should be referred for evaluation for access placement approximately 6 months before dialysis initiation. Arterial and venous mapping, typically by ultrasound is performed to identify appropriate vessels for AV fistula creation [13]. This provides visualization of arteries and veins including the approximately 50% of vessels that are not apparent on physical examination. To minimize early AV fistula failure, arteries should be 6 2 mm in diameter, without dampening of the waveform and without a significant pressure differential between the arms. Veins should be

62.5 mm in diameter, have continuity with the deep venous system and have no evidence of segmental stenosis [8]. An AV fistula is then surgically created in the most appropriate site. These sites may be in the forearm, upper arm, or require transposition of deep vessels in the upper or lower arm to more superficial locations. The fistula should be examined approximately 4 weeks after creation and referred for imaging and correction of identified lesions if not maturing by 6 weeks. Blood flow and vessel diameter increase rapidly following AV fistula creation with no significant change noted after 1 month [14]. Most non-maturing fistula have identifiable lesions that can be corrected by percutaneous techniques. In a series of 100 AV fistulae with early failure, 78% had a venous stenosis, 38% anastomotic stenosis and 46% accessory veins that were preventing adequate maturation. After treatment, 92% became usable for hemodialysis and 84% remained functional at 3 months, 72% at 6 months and 68% at 12 months [15]. Even a thrombosed AV can generally be salvaged. With the advent of percutaneous techniques often including thrombolytics, initial success rates of 78-94% with a 6-month unassisted patency of up to 67% have been reported. This is a significant improvement over previous surgical thrombectomy and has allowed continued fistula use after the development of stenosis or thrombosis [16].

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