LOWER EXTREMITY REVASCULARIZATION

Lower extremity arterial insufficiency, or peripheral arterial disease, is a common condition affecting as many as 10 million people in the United States, and its incidence is increasing annually.^[472] Because individuals with lower extremity peripheral arterial disease are most often asymptomatic^[473] or present with symptoms other than classic intermittent claudication,^[474] the true prevalence of the disease is unknown. In a population-based study of individuals 55 years old or older, the prevalence of peripheral arterial disease was 19.1% (16.9% in men and 20.5% in women).^[473] The prevalence of peripheral arterial disease in primary care practices in the United States is high (29%), and the condition is often unrecognized (44%).^[475] Arterial disease of the upper extremity occurs, but it is much less common than lower extremity involvement.^[476]

Atherosclerosis is the most common cause of peripheral arterial disease. Risk factors for atherosclerosis of the lower extremity are the same as for other vascular areas and include advanced age, male sex, hypertension, smoking, hyperlipidemia, and diabetes. Infrainguinal atherosclerosis may involve the femoral artery, popliteal artery, and any of the infrapopliteal arteries. The superficial femoral artery is the most common site of major atherosclerotic involvement below the inguinal ligament. Nonatherosclerosis causes of peripheral arterial disease include embolism, thromboangiitis obliterans (i.e., Buerger's disease), immune arteritis, radiation arteritis, giant-cell arteritis, adventitial cystic disease, fibromuscular dysplasia, and homocystinemia.

Peripheral arterial disease is a very strong indicator of generalized atherosclerosis and is a risk marker for other vascular conditions, including CAD, cerebrovascular disease, and aneurysmal disease. For example, patients with concomitant CAD and peripheral arterial disease have a higher prevalence of triple-vessel coronary disease than patients with CAD alone.^[477] More than 20% of patients with peripheral arterial disease have a 70% or greater carotid artery stenosis.^[478] It is well documented that patients with peripheral arterial disease are at an increased risk of cardiovascular morbidity and mortality compared with individuals without peripheral arterial disease. ^{[479] [480] [481] [482] [483] [484]} The increased cardiovascular risk may not be entirely due to atherosclerosis, because these patients may have an enhanced prothrombotic state resulting from platelet activation ^[485] and a high prevalence of diverse hypercoagulable states.^[486]

Acute Arterial Occlusion

Acute peripheral arterial occlusion occurs primarily as a result of embolism and thrombosis. Pseudoaneurysm after invasive procedures in which the femoral artery is cannulated is a much less common cause of acute ischemia. Most emboli to the lower extremity originate in the heart, with intermittent atrial fibrillation and MI being the most common causes of emboli. Although rheumatic heart disease is now a rare cause of embolic occlusions, prosthetic heart valves may be a source of emboli. Other causes of embolization include bacterial endocarditis, atrial myxoma, paradoxical venous emboli, and

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Thrombotic occlusions likely outnumber embolic occlusions by a ratio as high as 6:1.^[487] Acute arterial thrombosis of native vessels almost always occurs in the setting of severe and long-standing atherosclerosis. It can be viewed as the terminal event in the progression of atherosclerosis. Thrombosis of vascular bypass grafts is common and may result in acute ischemia. The high prevalence of diverse hypercoagulable states in patients with peripheral arterial disease may predispose such patients to thrombosis.^[486]

The clinical presentation of acute arterial occlusion depends on the location of the obstruction and extent of collateral circulation. In patients with a sudden onset of acute extremity ischemia, the occlusion often occurs abruptly and without the preexisting development of collateral pathways. Although ischemic symptoms are often more severe in patients with embolic occlusion compared with patients with thrombotic occlusion, differentiation between embolic and thrombotic occlusions may be difficult. Acute occlusion of a previously patent extremity artery is a dramatic event characterized by pulselessness, pain, pallor, paresthesia, and paralysis (i.e., the five Ps). Absent pulses and pallor are early manifestations. The sudden onset of pain is very common and may be intense. Motor weakness and paresthesia are usually late manifestations of severe ischemia.

Acute ischemia needs to be rapidly evaluated because irreversible tissue injury can occur within 4 to 6 hours.^[488] The initial management usually involves immediate anticoagulation to prevent propagation of thrombus, stabilization and control of coexisting medical conditions, and arteriography. Immediate surgical revascularization is usually indicated in the profoundly ischemic extremity. Patients with embolization to a nonatherosclerotic extremity are often managed with femoral thromboembolectomy under local anesthesia. Management of patients with peripheral arterial disease suspected of having thrombotic occlusion requires arteriography to determine severity and anatomic location of the occlusion. Angioplasty and thrombolytic therapy are occasionally performed in conjunction with arteriography. Intraarterial thrombolysis is often used as an initial intervention in an effort to unmask the culprit lesion responsible for the occlusive event. Patients are frequently scheduled for lower extremity bypass surgery the following day, pending evaluation of lower extremity blood flow. The frequent use of heparin anticoagulation and thrombolytics has significant implications for the anesthesiologist because regional anesthesia is not an option in the anticoagulated patient. Morbidity and mortality rates for this patient population is high, particularly for patients requiring significant operative intervention.^{[489] [490] [491]}