Blood flow surveillance of hemodialysis grafts and the dysfunction hypothesis

It is widely recommended that hemodialysis graft surveillance programs should be implemented and that significant stenosis should be corrected when it is accompanied by graft dysfunction. The rationale for surveillance depends on the dysfunction hypothesis, which states that stenosis causes graft dysfunction [such as a decrease in graft blood flow (Q_a)], and this dysfunction reliably precedes and accurately predicts thrombosis. The usefulness of Q_a surveillance depends on accurate prediction of thrombosis so that stenosis can be corrected prior to thrombosis. An analysis of the dysfunction hypothesis indicates that some or all of its underlying assumptions are invalid. Most importantly, the presence of wide hemodynamic variation during Q_a measurements makes Q_a a relatively inaccurate predictor of throm-bosis. A number of studies have evaluated the value of surveillance with intervention in reducing thrombosis rates and prolonging graft life. Review of these studies show that few have been prospective and randomized, and many have included historical control groups. It is debatable whether these studies have established that Q_a surveillance with intervention should be applied to all grafts. Data from several studies suggest that severity of stenosis may be at least as accurate as Q_a in predicting thrombosis. Consequently, inclusion of stenosis measurements (e.g., by duplex ultrasound) may improve the results of surveillance. These unresolved issues indicate it is premature to recommend routine Q_a surveillance with intervention of all hemodialysis patients with grafts.