This is a minimally invasive procedure in which a small tube known as a sheath is inserted into the fistula. Through this sheath, we are able to administer sedative medication and perform diagnostic and therapeutic interventions. X-rays are taken to identify narrow areas (stenoses) within your fistula/graft. If stenoses are identified a balloon can be used to widen the narrowing (angioplasty) to restore improved flow in your fistula/graft.