Pressure or flow recordings for the surveillance of hemodialysis grafts

Venous pressures (VP) measured by the dialysis machine are widely used for access surveillance and have significantly improved outcomes. VP reflect the resistance in the venous outflow tract, which will rise in the presence of stenosis. Low graft flow caused by high graft resistance predicts thrombosis. In this study we investigated whether high VP coincides with low graft flow (measured by ultrasound dilution technique). Of 70 forearm bridge grafts in 42 chronic hemodialysis patients, 31 had an angiographically proven outflow stenosis. VP at 200 ml/min blood flow (VP200), total graft resistance and venous outflow resistance were higher whereas graft flow was lower in patients with venous outflow tract stenosis as compared to patients without stenosis. Diagnostic power of the tests for identifying patients with venous stenosis showed no important differences. However, arterial inflow resistance, which is not reflected in VP measurements, represented a substantial and, more importantly, a highly variable percentage of total graft resistance. As a result graft flow showed no correlation with VP measurements. In conclusion, although patients with venous outflow stenosis may be identified accurately using venous pressure assessments, graft flow measurements seem to be more suitable for selecting patients at risk for thrombosis.