Chapter 28. Occlusive Arterial Disease

Peripheral arterial disease is defined as an ankle-brachial index (ABI) of <0.9 (see ABI definition below). The disease prevalence is 4.3% in Americans under age 40 years; prevalence climbs to 15.5% in those over 70 years of age. High-risk individuals (such as those over 70 years, or those over 50 years with risk factors such as diabetes or tobacco use), should be evaluated carefully when complaints are indicative of possible occlusive arterial disease. This time-sensitive condition can lead to irreversible changes in peripheral nerves and skeletal muscle tissue in 4 to 6 hours. The most frequently involved arteries, in descending order, are the femoropopliteal, tibial, aortoiliac, and brachiocephalic.

Clinical Features

Patients with acute arterial limb ischemia typically present with one of the “six Ps”: pain, pallor, poikilothermia (coldness), pulselessness, paresthesias, and paralysis. Pain is the earliest symptom and may increase with elevation of the limb. Changes in skin color with mottling, splotchiness, and cool temperature are common. One of the early signs of ischemic limb pain may present as muscle weakness. Limb viability may be in question when there is acute anesthesia progressing to paralysis. A decreased pulse distal to the obstruction is an unreliable finding for early ischemia, especially in patients with peripheral vascular disease and well-developed collateral circulation. Claudication refers to a cramplike pain, ache, or tiredness that is brought on by exercise and relieved by rest. It is reproducible, resolves within 2 to 5 min of rest, and reoccurs at consistent walking distances. The pain of acute limb ischemia is not well localized, is not relieved by rest or gravity, and can be a worsening of chronic pain (if it is caused by a thrombotic event).

Diagnosis and Differential

Although thromboembolic disease is the most common cause of acute arterial occlusion, the differential diagnosis may include: catheterization complications, vasculitis, Raynaud disease, thromboangiitis obliterans, blunt or penetrating trauma, or low-flow shock states such as sepsis. Most commonly, a history of an abruptly ischemic limb in a patient with atrial fibrillation or recent myocardial infarction is strongly suggestive of an embolus. A history of claudication suggests a thrombosis.

For more objective testing, a handheld Doppler can document blood flow or its absence in the affected limb. Duplex ultrasonography can detect an obstruction to flow with sensitivity greater than 85%. In addition, the ABI can be easily measured in the emergency department. Using a blood pressure cuff, place a Doppler US at the brachial artery and record the pressure of occlusion. Repeat the procedure on the leg, measuring the occlusion pressure of the posterior tibial and dorsalis pedis arteries. The ABI is the leg occlusion pressure divided by the arm occlusion pressure; normal ABI is >0.9. With arterial occlusion with a blood pressure cuff, the ABI usually is markedly diminished with a ratio between 0.9 and 0.41. A ratio lower than 0.41:1 is usually found in limbs with critical ischemia. A pressure difference greater than 30 mm Hg between any two adjacent levels of the limb can localize the site of obstruction. The diagnostic gold standard is the arteriogram, which can define the anatomy of the obstruction and direct treatment of the limb.

Emergency Department Care and Disposition

1. Patients with acute arterial occlusion should be stabilized. Fluid resuscitation and pain medications should be administered as needed. Dependent positioning can increase perfusion pressure. Obtain an ECG and consider echocardiography to assess for conditions associated with embolism.

2. It is standard procedure to initiate anticoagulation with unfractionated heparin. Dosing is weight-based: 80 units/kilogram intravenous bolus followed by infusion of 18 units/kilogram/h. The activated partial thromboplastin time should be maintained between 55 and 80 seconds (1.5 to 2.5 times normal). Aspirin should also be administered. Use of thrombolytics is controversial, with no clear benefit.

3. Definitive treatment should be performed in consultation with a vascular surgeon and an interventional radiologist. Catheter-directed embolectomy is the preferred approach for occlusion caused by an embolus. Other options include thrombolysis and surgery.

4. All patients with an acute arterial occlusion should be admitted to a telemetry bed or to the intensive care unit, depending on the stability of the patient and the planned course of therapy.

5. Reperfusion injury after revascularization of the injury can result in myoglobinemia, renal failure, hyperkalemia, and metabolic acidosis, these complications account for one-third of deaths from occlusive arterial disease.

6. Chronic peripheral arterial disease patients who lack comorbidities and have no immediate limb threat, can be discharged on aspirin (75 milligrams daily), with close vascular surgical follow-up for reassessment and further care.