Saphenous vein (SV) interposition grafts are often used for high-flow extracranial-intracranial bypass procedures. During these procedures, it is essential to remove air and debris from the graft and to evaluate blood flow through the graft after it has been anastomosed to other cortical vessels. In this paper, the authors describe the preservation of a large side branch on the proximal end of the SV. This side branch can be used to flush out air and debris from the graft and to evaluate blood flow during revascularization.