Clinical Sonography III Practice Exam

The main idea is that the size of the venous lumen in a hemodialysis access graft must be large enough to allow sufficient blood flow and to tolerate repeated needle cannulation. If the lumen is too narrow, resistance to flow becomes high, making it hard to achieve the required dialysis blood flow and increasing the risk that the graft will clot. A small lumen also complicates cannulation, increasing the chance of needle damage or graft injury with repeated punctures. Therefore, the minimum diameter is defined by the smallest size that still provides practical flow and safe cannulation; while larger diameters are easier to cannulate and tend to have better long‑term patency, there is a threshold below which the graft is not suitable for use. In practice, that minimum is described as a small, but usable, diameter—larger sizes are preferred for ongoing use.