Madalyn S. Berns, Elizabeth Y. Tsai, Jesse Austin-Breneman, James C. Schulmeister, Edward Sung, Dr. Charles K. Ozaki, Dr. Conor J. Walsh

Abstract

This paper describes the design of the single entry tunneler (SET), devised to create a loop-shaped path in forearm subcutaneous tissue prior to placement of a vascular graft for hemodialysis access. Existing tunnelers are almost universally rigid and require high forces and multiple incisions to complete even the most simple path geometries. Furthermore, they are guided from the handle with limited tip-location feedback. This paper presents a three-stage tunneler design consisting of concentric nested tubes. The first stage is a straight stainless steel tube; the second is a smaller pre-curved nitinol tube and the third is a straight inner nitinol tube. By deploying the stages in this order, SET is able to produce an approximately 180◦ looped path in tissue. A tip that is illuminated via a fiber optic cable provides visual feedback of the tip location. The SET outer diameter is limited to ensure that the pre-curved nitinol will not exceed its yield strain and not require an excessive force to be deployed from the straight outer stage. Therefore, a custom dilator was designed to increase the size of the tunnel to one suitable for the intended graft. A prototype of the SET tunneler and dilator system was manufactured. The device was shown to achieve the desired path in ballistics gel and was capable of at least 100 repeated-use cycles. By reducing the number of required incisions and improving ease of use during graft insertion procedures, the SET has the potential to greatly reduce the risk of infection and degree of unnecessary tissue trauma while increasing tunneling accuracy.