Friday, July 11, 2008

Physical Exam for AV Fistulas & Grafts

We all realize that maintaining vascular access is a dialysis patient's life-line. Many patients must undergo multiple interventional radiology or surgical procedures in order to sustain fistula or graft patency over a prolonged period of time.

The physical exam can be a useful tool in the examination of vascular access. Stenoses--often the culprit for a malfunctioning fistula or graft--can be characterized as either inflow or outflow stenoses, with outflow stenoses being the most common. Both may occur in the same access.

Inflow stenosis--the definition for which is debatable but one reasonable one is a narrowing of >50% when compared to the native artery--can be detected by an abnormal pulse augmentation exam. In a normal fistula, occlusion of the access several centimeters beyond the arterial anastamosis should lead to a detectable increase in the magnitude of the distal fistula pulse. When there is substantial inflow narrowing, no such increase will be observed. In addition, a weak pulse or lack of continuous thrill may also be indications of inflow stenosis.

Outflow stenosis can best be detected by an abnormal arm elevation test. In a normal fistula or graft, having the patient raise their arm should allow venous collapse and flattening of the fistula; if there is significant outflow stenosis the fistula may remain plump with arm elevation. In addition, a water-hammer pulse, a loud systolic thrill, or prolonged post-dialysis bleeding may also be signs of outflow stenosis.

A relatively recent study (Asif et al, CJASN 2007) confirmed that a good physical exam correlates well with angiographic data.

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