Does the in situ technique improve flow characteristics in femoropopliteal bypass?

A postulated advantage of in situ over reversed vein bypass is improved flow characteristics. This study compares Doppler frequency analyses in 22 patients with reversed veins and in 21 patients with in situ femoropopliteal vein grafts. Signals from the common femoral artery, the femoral anastomosis, and the vein in the mid thigh were analyzed and the pulsatility index (PI) and flow disturbance index (FDI) calculated (FDI = maximum frequency divided by median frequency). The two groups were similar clinically and common femoral artery PI showed inflow to be similar and satisfactory. Marked turbulence occurred at the femoral anastomosis where peak FDI rose from 1.67 ± 0.19 (mean ±SD) to 2.96 ± 0.69 in the in situ vein group and from 1.74 ± 0.51 to 3.11 ± 0.64 in the reversed vein group (p < 0.001). This turbulence was much reduced at mid thigh level where peak FDI had fallen to 1.45 ± 0.17 in the reversed vein grroup and 1.51 ± 0.23 in the in situ vein group (p < 0.001). Comparison of the signals from the femoral anastomosis and from the vein at mid thigh showed that the amount of flow disturbance was no different in the in situ vein group from that in the reversed vein group (unpaired t test). In this study flow patterns were not improved by use of the in situ bypass technique.