Anesthesia for Vascular Surgery

Anesthesia for Vascular Surgery

PERIPHERAL VASCULAR DISEASE

Atherosclerosis is the most common cause of peripheral vascular occlusive disease. This degenerative process involves the formation of atheromatous plaques that may obstruct the vessel lumen resulting in a reduction in distal blood flow. The pathophysiologic process is systemic, progressive, and primarily affects the arteries due to plaque formation, which can lead to stenosis and potentially occlusion of the vascular lumen; thrombosis from hypercoagulability, resulting in acute organ ischemia; embolism from microthrombi or atheromatous debris; and weakening of the arterial wall, resulting in aneurysm formation. Atherosclerosis is an inflammatory condition that is partially caused by cholesterol plaques, which occur within arteries. In response to cholesterol plaques, immune cells such as macrophages and monocytes liberate proinflammatory cytokines, which leads to a progressive increase in the size of plaques. The lipid cap that envelops the plaque can rupture, resulting in intraluminal thrombosis or plaque emboli. The most common risk factors associated with atherosclerosis are shown in Box twenty-eight point one. Endothelial dysfunction is a potential cause of increased hemodynamic variability during anesthesia. Smoking, elevated proinflammatory mediators, and diabetes mellitus are major risk factors in the pathogenesis of atherosclerosis in the arterial tree. Typical symptoms associated with peripheral occlusive disease include claudication, skin ulcerations, gangrene, and impotence. The extent of disability is primarily influenced by the development of collateral blood flow. The mortality rate in patients with vascular disease is two- to sixfold higher than in the general population. Hypercoagulability resulting from platelet interaction with leukocytes and other cells that modulate the immune response plays a major role in the development of atherosclerosis. Researchers have discovered heritable genetic factors that predispose patients to developing vascular disease.

Treatment for peripheral occlusive disease may range from pharmacologic therapy to surgery. Surgical therapy includes transluminal angioplasty, endarterectomy, thrombectomy, endovascular stenting, and arterial bypass. Some common surgical maneuvers used to bypass occlusive lesions are aortofemoral, axillofemoral, femorofemoral, and femoropopliteal procedures. Bypass techniques may be classified as inflow or outflow procedures depending on the level of the obstruction, with the dividing axis occurring at the level of the groin. Temporary occlusion of the operative artery is mandatory during surgical bypass, as this temporarily further reduces blood flow and oxygen delivery. The development of collateral circulation provides alternative vascular blood flow in patients with occlusive disease. Initially, angiogenesis or the development of new vessels supplies collateral blood flow that is sufficient to meet tissue oxygen demands. As the disease progresses, the blood flow is decreased, and the oxygen supply is unable to meet the tissues' demand, which could result in myocardial dysfunction, neurologic dysfunction, renal dysfunction, and/or limb ischemia.

Preoperative Evaluation

The atherosclerotic process in occlusive disease is not limited to peripheral arteries and should be expected to be present in the coronary, cerebral, and renal arteries. More than half of the mortality associated with peripheral vascular disease results from adverse cardiac events. There is a clear association between the development of aortic aneurysms and coronary artery disease. It has been estimated that forty-two percent of patients presenting for abdominal aortic aneurysm repair have significant coronary artery disease. Preoperative cardiovascular evaluation and treatment are beneficial for reducing not only perioperative risk but also late cardiovascular events. After elective abdominal aortic aneurysm repair, the five-year survival rate and incidence of major adverse cardiovascular events is eighty-six percent. Cardiac pathology, which often occurs in this patient population, must be managed aggressively to optimize cardiac functioning and decrease morbidity and mortality from cardiac causes.