The effect of different factors on the hemodynamics of extra-anatomic bypass.

Extra-anatomic bypass is an extremely useful procedure under certain clinical situations. However, it has been suggested that it may steal blood from the peripheral distribution of the donor artery. The hemodynamics of extra-anatomic bypass under basal and maximal flow, hypotensive state and inadequate inflow and outflow of donor artery were studied in twelve mongrel dogs. A right external iliac artery to left external iliac artery bypass with ligation of left external iliac artery proximal to the anastomosis was used as an experimental model. The hemodynamic situation of axillo-femoral bypass where the flow through the graft is several times the normal flow in the donor artery was simulated by increasing the graft flow by creating an A-V fistula on the recipient side. Following bypass, the increased demand of flow was met by a proportional increase of inflow into the donor artery and in supra-renal aortic flow. The "steal" of blood from the peripheral distribution of the donor artery was observed only when inflow into the donor artery was restricted beyond a critical point (60% in basal flow and 40% in a maximal flow). Restriction of outflow in the donor artery had no adverse effect on the hemodynamics of the bypass grafts. Neither steal nor redistribution of blood was observed in the hypotensive state. The result of this study suggests that the fear of "stealing" blood from other areas following an extra-anatomic bypass is ill-founded in the presence of normal inflow.