The Global Vascular guidelines 'GVG proposes a new Global Anatomic Staging System (GLASS), GLASS incorporates two novel and important concepts, the target arterial path (TAP) and estimated limb-based patency (LBP). Based on appropriate angiographic imaging, the TAP is defined by the treating surgeon or internationalist as the optimal arterial pathway to restore in-line (pulsatile) flow to the ankle and foot. LBP allows more direct comparison of anatomic outcomes across revascularization strategies in CLTI. The complexity of disease traversed by the TAP is integrated in the GLASS. Femoropopliteal (FP) and infrapopliteal (IP) arterial segments are individually graded on a scale of 0 to 4.(2)(3) Using a consensus based matrix, these segmental grades are combined into three overall GLASS (I-III) stages for the limb, reflecting the complexity of the disease with a proposed likelihood of immediate technical failure ' ITF  and 1 year LBP  after endovascular intervention of  TAP ' (1)
Critical limb threatening ischemia CLTI 'is not a separate local disease but also it is a part of generalized vascular disorder. A clinical syndrome that can be presented by many symptoms and signs as rest pain, gangrene and chronic ulceration more than 2 weeks (1).