Critical limb ischemia occurs when the ankle brachial index falls to below

Ankle Brachial Index ABI= Systolic BP at the ankle/systolic BP in the arms Compared to the arm, lower blood pressure in the leg is an indication of blocked aeries (peripheral vascular disease) ABI is calculated by dividing the systolic blood pressure at the ankle by the systolic blood pressures in the arm ABI is calculated by dividing the systolic blood pressure at the ankle by the systolic blood pressures in the arm ABI Interpretation >1.2 Non-compressible, severely calcified vessel (in DM & ESRD) 1.0-1.2 Normal vessels 0.5-0.9 Intermittent claudication (mild to moderate ischaemia) 0.1-0.4 Critical limb ischaemia (Ischaemic ulceration, gangrene) Ref: Sabiston 20th edition Pgno :1758