Given the task definition and input, reply with output. Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.

Abstract: Residual arteriovenous fistulas are a potential source of morbidity after femorodistal bypass operation has been performed with the in situ great saphenous vein graft. A review of our initial experience with 155 operations in which various methods of intraoperative detection were used showed that fistulas were overlooked in 27 cases (17.4%), causing graft thrombosis in 10 cases (6.4%). After the introduction of a rapid and simple intraoperative test that used retrograde irrigation of the graft, only three superficial fistulas were overlooked in 70 operations (4.2%), with no associated graft thrombosis. The test had no detectable deleterious effects and graft distension pressures were within acceptable limits.
Angiography