Does postoperative surveillance with duplex scanning identify the failing distal bypass?

Duplex scanning used to determine graft flow velocities is an effective means of identifying lower extremity bypass grafts at risk for failure before they occlude. We implemented a graft surveillance protocol using duplex scanning and over a two-year interval evaluated fifty-four lower extremity bypasses utilizing graft flow velocities, ankle/brachial indices, and toe pressure measurements. Three patients were identified with grafts at risk for thrombosis. Of these patients, one had no evidence of arteriographic stenosis, one patient had clinical symptoms of reduced flow velocity measurements, and one's graft subsequently occluded during follow-up. Eight patients with graft flow velocities of greater than 45 cm/sec subsequently developed occlusion or were noted to have a severe associated stenosis. Six patients developed unheralded graft occlusion less than three months following determination of the graft flow velocity. Four of these patients (67%) had bypasses to the dorsalis pedis artery. Graft flow velocity measurements do not always predict an impending graft failure, and other factors may contribute to the sudden occlusion of patent distal bypasses, especially to the pedal arteries. Although the concept of hemodynamic monitoring to identify impending graft failure is an attractive one, more sensitive or refined measurements (especially to the pedal vessels), are required.