Page 187 - Libro 2

11
Ultrasound Assessment of Arterial Bypass Grafts
Peter W. Leopold and Ann Marie Kupinski
OBJECTIVES
KEY TERMS
arteriovenous fistula | autogenous vein | bypass | distal anastomosis | graft | hyperemia | in situ bypass | orthograde vein bypass | prosthetic graft | proximal anastomosis | reverse vein bypass
GLOSSARY
anastomosis a connection created surgically to connect two vessels that were formerly not connected
arteriovenous fistula a connection between an artery and vein that was created as a result of surgery or by other iatrogenic means
bypass a channel that diverts blood flow from one artery to another; usually done to shunt flow around an occluded portion of a vessel
Duplex ultrasound evaluation of arterial bypass grafts has become a well-recognized fundamental compo- nent in postoperative follow-up and management. Careful monitoring of patients with infrainguinal by- passes has clearly shown to improve long-term pa- tency rates.1 There are several methods that can be used to evaluate bypass function including clinical assessment, indirect assessment with systolic pres- sure measurements and plethysmographic wave- forms, and lastly, direct assessment with ultrasound. Clinical assessment of patient symptoms and physical examination of the limb often fails to identify prob- lems early. Prior studies have shown that ultrasound can detect significant pathology in asymptomatic pa- tients and before a measureable change in physiolog- ic testing results.2 However, there is a complementary
graft a conduit that can be prosthetic material or autogenous vein used to divert blood flow from one artery to another
hyperemia an increase in blood flow; this can occur following exercise; it can also occur following resto- ration of blood flow following periods of ischemia
in situ bypass the great saphenous vein is left in place in its normal anatomical position and used to create a diversionary channel for blood flow around an occluded artery
role for ultrasound and indirect physiologic testing. Combining duplex ultrasound with physiologic test- ing provides both direct assessment of the bypass conduit itself as well as indirect assessment of global limb perfusion. This chapter will focus on the use of duplex ultrasound to evaluate lower extremity bypass grafts. Using these methods, disease can be detected early, prior to bypass graft thrombosis, and will thus aid the long-term maintenance of graft patency.
TYPES OF BYPASS GRAFTS
The types of bypass grafts can be categorized by the components of the graft and the surgical techniques employed. There are two main types of bypass graft
Describe the types of common arterial bypass grafts
Define the essential components of an arterial bypass scan including B-mode, color, and spectral Doppler requirements
Describe the normal hemodynamic profiles of arterial bypass grafts
List the diagnostic criteria employed for identifying a bypass stenosis, occlusion, and other pathology
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