Peripheral resistance measurement in the assessment runoff in femorodistal bypass grafting.

Vascular reconstruction beyond the inguinal ligament is a well established technique but the results are poor compared with more proximal reconstructions. The state of the vessels distal to the site of graft insertion is a major factor in determining the outcome. Arteriography, the main means of assessment of this runoff, is subjective and unreliable. Using the analogy to Ohm's law a quantitative assessment of runoff has been made by calculation of peripheral resistance from measurement of pressure created by a known flow of blood infused into the vessel under study. Resistance was measured in two groups of dogs, and in three groups of patients undergoing amputation, femorotibial or femoropopliteal reconstruction. Both constant pressure and constant flow measurements were applied with blood, saline and Dextran. The dog work showed that resistance fell with increasing flow, so that to make comparisons between individuals necessitated measurement at a fixed flow. Results were very reproducible despite the varying sizes of the animals. The concentric cannula technique for pressure mesurement was shown to be more accurate than direct stab or sidearm measurement. The constant pressure technique, whilst correlating well with the constant flow technique, was cumbersome and impractical. Saline and Dextran were both suitable for resistance measurement but neither carried any specific advantages over blood. Resistance in the amputation, femorotibial and femoropopliteal groups correlated with; severity of disease defined by type of operation; level of graft insertion in the leg; and runoff defined by a comprehensive assessment of the arteriogram. Resistance was significantly higher in failed grafts than patent grafts upto six months after operation, and a cutoff level of resistance of 1200mPRU was a highly significant predictor of outcome. Similar results were achieved after drug induced vasodilatation. Resistance measurement has proved a useful predictor of outcome in femorodistal reconstruction.