ACUTE ARTERIAL OCCLUSION OF A LIMB
Acute arterial occlusion is one of the most devastating diseases in vascular surgery, resulting in limb loss, long-term morbidity, and death. Early recognition of symptoms of limb ischemia is necessary in order to salvage limb function and prevent an increased risk of mortality.
Patients with acute limb ischemia often present soon after the onset of symptoms and are able to describe the exact moment symptoms began. This process should be differentiated from chronic limb ischemia, which occurs over a prolonged period of time with progression of symptoms. Severity of symptoms is dependent on the amount of arterial collateralization around the site of occlusion which can often reflect underlying chronic vascular disease.
Symptoms and Signs
The sudden onset of extremity pain, with loss or reduction in pulses, is diagnostic of acute arterial occlusion. This often will be accompanied by neurologic dysfunction, such as numbness or paralysis in extreme cases. With popliteal occlusion, symptoms may affect only the foot.
With proximal occlusions, the whole leg may be affected. Signs of severe arterial ischemia include pallor, coolness of the extremity, and mottling. Impaired neurologic function progressing to anesthesia accompanied with paralysis suggests a poor prognosis.
Immediate revascularization is required in all cases of symptomatic acute arterial thrombosis. Evidence of neurologic injury, including loss of light touch sensation, indicates that collateral flow is inadequate to maintain limb viability and revascularization should be accomplished within 3 hours. Longer delays carry a significant risk of irreversible tissue damage. This risk approaches 100% at 6 hours.
As soon as the diagnosis is made, unfractionated heparin should be administered (5000–10,000 units) intravenously, followed by a heparin infusion to maintain the activated partial thromboplastin time (aPTT) in the therapeutic range (60–85 seconds) (12–18 units/kg/h). This helps prevent clot propagation and may also help relieve associated vessel spasm. Anticoagulation may improve symptoms, but revascularization will still be required.
Catheter-directed chemical thrombolysis into the clot with tissue plasminogen activator (TPA) may be done but often requires 24 hours or longer to fully lyse the thrombus. This approach can be taken only in patients with an intact neurologic examination who do not have absolute contraindications such as bleeding diathesis, gastrointestinal bleeding, intracranial trauma, or neurosurgery within the past 3 months. A sheath is used to advance a TPA-infusing catheter through the clot. Heparin is administered systemically to prevent thrombus formation around the sheath. Frequent vascular and access site examinations are required during the thrombolytic procedure to assess for improved vascular perfusion and to guard against the development of a hematoma.
General anesthesia is usually indicated; local anesthesia may be used in extremely high-risk patients if the exploration is to be limited to the common femoral artery. In extreme cases, it may be necessary to perform thrombo-embolectomy from the femoral, popliteal and even the pedal vessels to revascularize the limb. The combined use of devices that pulverize and aspirate clot and intraoperative thrombolysis with TPA improves outcomes.