Minimizing hemodialysis vascular access trauma with an improved needle design

The maintenance and longevity of hemodialysis vascular access remains one o f the most problematic topics in the care of dialysis patients. Although mu ch attention has focused on neointimal hyperplasia, the repetitive trauma t o vessel walls by dialysis needles causes significant cumulative damage tha t has undergone little investigation, Commercial needles have beveled tips with intentional cutting surfaces to ease insertion. It was hypothesized th at a pencil-point conical-shaped needle would cause less damage by taking a dvantage of the elasticity of native fistulae and produce an improved hole configuration in synthetic materials with minimal ability to stretch. A nee dle was subsequently designed with a removable pencil-point trocar and a si de arm for the dialysis tubing. Once the trocar is removed, the blunt-ended cannula can be advanced or can be subject to inadvertent motion without ca using damage to the luminal surface of the access. The new design as well a s standard 15-gauge hemodialysis needles were tested on GoreTex(R) graft ma terial and two bovine carotid artery preparations. Scanning electron micros copy was used to study the hole patterns. For all materials, the commercial needle holes had typical crescent shapes, and the cuts sliced sequentially through the various layers. For grafts, the new design caused a linear def ect parallel to the axis of the graft that may preserve longitudinal streng th. Interestingly, that tear line was nearly perpendicular to the linear ho le in the thin polytetrafluoroethylene overwrap, which would be consistent with maintenance of hoop integrity. It is believed that these nonoverlappin g defects would also improve hemostasis. The bovine specimens tested the im portance of tissue stretching: Fresh carotid artery had experimental holes dramatically smaller than those from standard needles. In the denatured tis sue, the experimental needle provided less benefit than that observed in fr esh tissue, which is likely due to limited elasticity of the preserved arte ry. Improvement in needle design thus provides distinct advantages for nati ve vessels and unique less traumatic holes in current synthetic materials. Pencil-point needle designs may be particularly applicable to the developme nt of new elastomeric graft material.