What is it?
Acute limb ischemia happens when there is a sudden interruption of the blood supply in the arteries of the limb, with no time for collateral blood circulation to form.
There are three main causes of Acute Limb Ischemia:
- Thrombosis — 85%
- Embolus — 15%
- Vascular Trauma — <1%
Thrombus can form in atherosclerotic arteries in the limbs or in patients in hypercoagulable states, such as with leukemia, polycythemia, Factor V Leiden, or pregnancy.
15% of Acute Limb Ischemia cases are caused by emboli. Among cases caused by emboli, 90% of the emboli come from the heart, 9% come from arterial sources, and 1% come from others.
- Heart — 90% — clots can form in the heart of patients with arrhythmia (particularly atrial fibrillation), valvular heart disease, prosthetic heart valves, MI, and very rarely, atrial myxoma. This can dislodge to form an emboli, which travels to the limb and subsequently obstructs the blood flow in the limb.
- Arteries — 9% — clots can also form in atherosclerotic vessels as well as aneurysms. These would then dislodge as emboli then obstruct blood flow to the limb.
- Other — 1% — other causes of emboli are malignant tumors, as well as the risks from certain medications (i.e. oral contraceptives)
Emboli often lodge at branching points in the arterial tree, like the bifurcation of aorta, common femoral bifurcation, or the popliteal trifurcation.
Vascular trauma is a very rare cause of acute limb ischemia. These include anything that would cause artery damage, like in penetrating trauma from arterial catheterization angioplasty, blunt trauma, or in limb fractures, particularly supracondylar fractures, which can occlude arteries.
Remember the 6 P’s:
- Pain — sudden and severe. leads to numbness.
- Pallor — early stage
- “Perishingly” Cold
- Paraesthesia — late stage
- Paralysis — late stage
- CBC — look for polycythemia
- U&E (urea and electrolytes) — check renal impairment before doing arteriography, because you need to make sure your kidneys can handle the contrast used.
- Clotting Screen — check for any clotting diseases
- Arteriography — find areas of occlusion
- EKG — look for MI, atrial fibrillation, or any other cardiac anomalies that could have caused the emboli.
- Cardiac enzymes (troponin, CK-MB) — another way to look for signs of MI.
- Duplex imaging — check flow and rhythm of the pulse. Duplex consists of a still grayscale ultrasound image of the tissue, overlayed with a color doppler image of the flow of blood in the area. Any area of stenosis in the arteries would cause blood to flow faster, resulting in a different color.
Heparin — prevent pregression of thrombus
Immediate surgical management is necessary otherwise the patient may risk losing the limb.
Embolectomy — You use a Fogarty balloon catheter in which a catheter is inserted into the effected artery, passing the clot. Then the balloon is inflated inside the artery (with the clot in front of it). When you withdraw the catheter, you pull the clot out with you.
Thrombolytic therapy — give percutaneously into the arteries effected. It takes 12-72 hours to dissolve the clot. tPA is probably the most popular thrombolytic medication to use. tPA converts plasminogen to plasmin, which would then lyse the fibrin that is holding the clot together.