Ischaemic foot. Darkened skin and blood blisters on the toes and top of a foot caused by ischaemia. Ischaemia is a low oxygen condition caused by an insufficient supply of blood to the limbs that starves tissues of oxygen. This may result from constriction or blockage of a blood vessel, or inadequate pumping of the heart. An ischaemic limb is usually painful and pulseless. Ischaemia may be treated with vasodilator drugs or angioplasty, but if the tissue has suffered necrosis (tissue death) or gangrene, surgical amputation may be necessary.