Acute limb ischemia results from a blood supply that is inadequate to meet tissue oxygen and nutrient requirements. If allowed to persist, it will lead to cell death and irreversible tissue damage. Even after perfusion is partially or completely restored, reperfusion injury can occur as oxygen radicals form and cause further cell injury. Perfusion may not be fully attainable with prolonged arterial obstruction due to distal edema and thrombi forming in the microcirculation. The extent of injury depends on the duration and location of the arterial blockage, the amount of collateral flow, and the previous health of the involved limb. Also, some tissues are more susceptible to anoxia than others, presumably on the basis of differences in cellular respiration and oxygen requirements. Peripheral nerves and skeletal muscle are very sensitive to ischemia; in them, irreversible changes occur within 4 h of anoxia at room temperature.
Nonembolic limb ischemia is secondary to atherosclerosis in the vast majority of patients.12 Plaque formation within the intima of an artery results from lipid accumulation, proliferation of smooth muscle cells, and fibrogenesis. Narrowing of the vascular lumen occurs with progression of the atheromatous plaque. Complete or high-grade obstruction can occur at this site of stenosis secondary to plaque rupture, hemorrhage, or thrombus formation. An atherosclerotic vessel can give rise to an aneurysm because of its weakened walls. A true aneurysm, involving dilatation of its entire wall, can present clinically with thrombosis, rupture, and hemorrhaging or by its mass effect on adjacent structures.
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