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Minimizing hemodialysis vascular access trauma with an improved needle design.

The maintenance and longevity of hemodialysis vascular access remains one of the most problematic topics in the care of dialysis patients. Although much attention has focused on neointimal hyperplasia, the repetitive trauma to vessel walls by dialysis needles causes significant cumulative damage that has undergone little investigation. Commercial needles have beveled tips with intentional cutting surfaces to ease insertion. It was hypothesized that a pencil-point conical-shaped needle would cause less damage by taking advantage of the elasticity of native fistulae and produce an improved hole configuration in synthetic materials with minimal ability to stretch. A needle was subsequently designed with a removable pencil-point trocar and a side 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 causing damage to the luminal surface of the access. The new design as well as standard 15-gauge hemodialysis needles were tested on Gore-Tex graft material and two bovine carotid artery preparations. Scanning electron microscopy 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 defect parallel to the axis of the graft that may preserve longitudinal strength. Interestingly, that tear line was nearly perpendicular to the linear hole in the thin polytetrafluoroethylene overwrap, which would be consistent with maintenance of hoop integrity. It is believed that these nonoverlapping defects would also improve hemostasis. The bovine specimens tested the importance of tissue stretching : Fresh carotid artery had experimental holes dramatically smaller than those from standard needles. In the denatured tissue, the experimental needle provided less benefit than that observed in fresh tissue, which is likely due to limited elasticity of the preserved artery. Improvement in needle design thus provides distinct advantages for native vessels and unique less traumatic holes in current synthetic materials. Pencil-point needle designs may be particularly applicable to the development of new elastomeric graft material.