Abstract: An introducer sheath for inserting a catheter into a circulatory vessel, such as the femoral artery. The introducer sheath is in the form of a tube having an open proximal end, an open distal end, and a lumen through which a device such as a catheter can be passed. The introducer sheath is provided with at least one, preferably multiple, fenestration through the tube wall, preferably at the outer radius of curvature of the introducer sheath where the sheath bends to transition from lying parallel to the femoral artery to being at an angle so as to exit the femoral artery, tissue and skin, such that blood can flow through the introducer sheath and continue to the extremities after the introducer sheath is inserted.