Ultrasound-Guided Peripheral Nerve Block in the Anesthetic Considerations for Vascular Surgery – An Alternative Choice for Neuroaxial Anesthesia Techniques

Abdominal aortic aneurysm, with its incidence approaching approximately 8% in the population, accounts for more than 8,000 deaths annually in the United States. It is a multifactorial disease associated with atherosclerosis. Age, male gender, smoking, and the family history of abdominal aortic aneurysm are thought to be the risk factors for the disease (Ashton et al., 2002, Fleming et al., 2005). The natural history of abdominal aortic aneurysm is characterized by the progressive enlargement of the aneurysm, which ultimately leads to the rupture and the subsequent death of the patient. The aorta wall consists of a thin intima, a thick tunica media, and an adventitia, composed of endothelium for a thin intima, smooth muscle layers for a thick tunica media, and a connective tissue including the vasa vasorum and nervi vascularis for the adventitia, respectively. The wall of aorta is particularly vulnerable to an injury owing to the continuous exposure to high pulsate blood pressure and shear stress. Once degenerated which most commonly occurs by atherosclerosis, cystic medial necrosis, a condition in which the collagen and elastic fibers in the tunica media of the aorta are degenerated and replaced by the mucoid connective tissues, will immediately take place. It will subsequently result in the circumferential weakness, dilatation, and as a consequence, the development of aneurysm. The other etiological conditions that lead to the development of aneurysm include some hereditary basis such as Marfan’s and Ehlers-Dnlos syndromes, the infection including syphilis and tuberculosis, and vasculitis associated with autoimmune diseases such as Takayasu’s arteritis and rheumatoid arthritis (White et al., 1993, Shah et al., 1997). The prognosis of abdominal aortic aneurysm is strongly correlated with the size of aneurysm, and the risk of rupture is 1-2% for 5 years for an aneurysm less than 5cm in diameter, whereas it is more than 20-40% for those more than 5cm in diameter. Hence, an elective operation is indicated if the diameter of aneurysm is >5.5cm (Sakalihasan et al., 2005).