Techniques for prospective detection of venous stenosis.

Abstract

The vascular access device continues to be a bottleneck in the quest for improved dialysis efficiency and cost reduction. Stenotic lesions occur frequently in synthetic arteriovenous fistulas (AVFs), usually at the venous end, and less often in native AVFs. The reduction in blood flow and other thrombogenic effects of the stenosis, such as local turbulence, eventually lead to loss of the access. Before thrombosis occurs, reduced blood flow through the AVF limits inflow to the dialyzer and predisposes to local recirculation. Recirculation decreases the effective solute clearance of the dialyzer, jeopardizing the adequacy of treatment. Regular evaluation of the access using methods such as routine physical examination, measurement of recirculation, measurement of venous dialysis pressure, and radiographic or ultrasonic imaging when combined with percutaneous or surgical interventions have been shown to prolong access life and eliminate recirculation. Physical examination includes inspection and palpation to detect edema, palpation and auscultation to detect local increases in the intensity of a thrill or bruit, and optional occlusion of the fistula during dialysis to detect recirculation. Recirculation can be measured directly using classical solute dilution techniques or indicator dilution methods provided by a variety of devices now appearing on the market. Recirculation may also be detected indirectly from the results of urea modeling. The difference between modeled and expected urea clearance is a measure of recirculation provided no other error (eg, in blood flow) contributes to the difference. Pressure monitoring has proven useful in many centers. A strict protocol is required to normalize other influences such as blood flow and needle size that may alter pressure independently of access stenosis. Duplex Doppler ultrasonography has been evaluated and found useful in several studies but suffers from relatively high cost and operator dependency. Controlled studies of these screening techniques are needed, especially for those that incur high costs.