Assessment of stenosis in vascular access grafts

The major complication that occurs with grafts used as vascular access for hemodialysis, is stenosis at the venous anastomosis or in the draining vein. 75% area stenosis is considered significant as thrombotic occlusion may occur. The aim of this experimental study was to evaluate invasive and noninvasive indices to detect significant stenoses in a vascular access graft. A compliant underarm loop graft in vitro model was built and studied with 50, 65, 80, and 90% stenosis at flow rates of 500, 1000, and 1500 mL/min. Flow in the system was pulsatile. Velocity was measured with ultrasound Doppler and the pressure was measured invasively. The resistance index (RI), p(venous line)/MAP, and the newly introduced pressure ratio (PR) were calculated and compared. A stenosis can be suspected when a high frequency ultrasound velocity signal develops at the venous anastomosis. RI > 1 confirms a very severe stenosis (90%). The parameter PR < 8% confirms significant stenoses showing its clinical relevancy.