AAA represents a dilatation of the abdominal aorta which can extend above the renal arteries. If the aneurysm extends above the diaphragm, it is classified as a thoracoabdominal aortic aneurysm (TAAA). Adventitial degradation is a central feature of the disease. Factors promoting development of the disease are shear stress, inflammation and hypercoagulability, potentiated by oxidized LDLs. The aorta and peripheral vessels affected by the atherosclerotic process become susceptible to aneurysm development and dissection. Dissection may lead to intramural hematoma formation. True aneurysm affects all layers of the aortic wall, and pseudoaneurysm is an intimal expansion through a damaged muscularis layer. The natural history of the disease is a continuous progression of atherosclerosis [1].

Smoking, hypertension, familial predisposition, advancing age (greater than 40), low HDL, high LDL, increased fibrinogen, and atherosclerosis. Low platelet count may result from a consumptive process in patients with aneurysms. Currently, it is recommended to screen males older than 65 who have smoked.

There are more than 45,000 patients with abdominal aortic aneurysm undergoing surgical repair each year. A population-based study from Norway in the late 1990s found a prevalence of 8.9 and 2.2% in males and females respectively. In the US, approximately 1% of males between 55 and 65 years of age have a clinically significant aneurysm and the prevalence increases by 2–4% for each decade of life thereafter. Women are affected four times less frequently than males and about a decade later in life [2].

AAA are most often found incidentally, and if electively repaired, the risk of all-cause mortality is less than 8%. Acute dissection will present with abdominal, back or groin pains, pulsatile mass and possible hemodynamic compromise. A patient with these findings must be immediately evaluated to prevent further dissection or rupture.

Risk of rupture depends on the diameter of the internal lumen and increases with growth of the aneurysm. An important dimension to keep in mind is a diameter of 4.5 cm. A study following patients with AAA showed that on average the size increased by 0.3 cm/year and the cumulative 6 year risk of rupture was less than 2% when the size was less than 4.5 cm. Risk of rupture increased to above 20% in AAA greater than 5 cm in diameter. Rupture carries high mortality; approximately 23–69%, compared to 1.4–6.5% if not ruptured [3].

One time ultrasound screening is recommended in patients ages 65–75 with known risk factors and followed by active monitoring of a detectable aneurysm. No benefit has been found in screening of women or men over 75 with negative previous screening. Life style modification and medical therapy may slow growth and delay the need for repair. When the internal diameter of the aneurysm reaches 5.5 cm the risk of rupture is equal to the operative mortality risk and thus aneurysm sizes greater than 6.0 cm or lumen size twice the normal aortic diameter should be repaired [4].

When a patient presents for elective aortic aneurysm repair, the surgeon will recommend one of two approaches to manage the AAA; open repair versus endovascular aortic repair (EVAR). The 2005 ACC/AHA Guidelines recommend open surgical repair for patients with low-to-moderate risk of surgical complications and endovascular repair for high surgical risk individuals [5].

Classification of AAA is based on the relationship of the aneurysm to the renal arteries, with suprarenal, juxtarenal and infrarenal AAA as typical labels. An infrarenal AAA will have at least 10 mm of a normal aortic segment adjacent to the most cephalad end of the aneurysm [4]. A suprarenal AAA may involve the celiac arteries. Thus it is important to understand the implications of vessel involvement and possible additional surgical interventions. This information plays a significant role in deciding open surgical repair versus EVAR, and profoundly influences intraoperative anesthetic management.

Additionally, aneurysms may be classified as fusiform, involving all layers of the aortic wall, saccular or pseudoaneurysms when they are more focal and localized and do not involve all mural layers, and inflammatory, which are prone to significant intraoperative bleeding.

Patients who are deemed low or average risk of perioperative surgical complications may undergo open repair. Octogenarians have an operative mortality rate less than 10% and may be appropriate open repair candidates. Some studies have shown that preoperative management of coronary artery disease (diagnostic tests followed by an intervention) has helped reduce the rate of perioperative major adverse cardiac event (MACE) to about 2%. Other studies were not so optimistic [2]. An association between presence of renal plus cardiac disease and mortality has been established. Patients with advanced cardiac and renal disease may benefit from EVAR.

Patients who represent high risk of postoperative surgical complications and patients with favorable anatomical and clinical attributes may be suitable for EVAR.

Anatomic Factors influencing decision for EVAR versus open repair.

A scoring system has been set up based on the aortic angle and tortuosity, and the presence of intraluminal thrombus. The scores are 1 through 3 points with higher total number of points signifying poorer EVAR outcomes [4].

Clinical factors:

The short-term outcomes of EVAR have been found to be superior to open repair with regard to 30-day mortality, hospital length of stay, and number of blood transfusions. However, these advantages disappeared in the long term where the mortality from either procedure was equal at 6 years. Other differences between groups related to dye exposure and fluoroscopy, occurrence of endoleaks and the need for re-intervention which were higher in the EVAR group. Thus cost savings from the short-term EVAR advantages were lost. Current literature does not support EVAR for small AAA [6]. Ruptured AAA can successfully be managed by EVAR [7].

Obese and frail patients can benefit significantly from EVAR with regard to short-term outcomes. Continuous improvement of endograft technology and design with availability of branched and fenestrated grafts, as well as total percutaneous access has helped shift the risk–benefit balance toward EVARs [6].

In the open group, organ ischemia and humoral changes due to cross-clamping have been identified as major reasons for perioperative mortality and morbidity. The open approach has also been associated with higher blood product and fluid utilization, protracted ICU stay and early morbidity, including acute kidney injury and pneumonia.

Stable patients with a suspected ruptured AAA, should undergo a CT angiography to determine AAA morphology. Unstable patients should be taken immediately to the operating room. A hybrid operating room allows more flexibility for on-the-table decision to maximize control of dissection and bleeding. Sometimes a supraceliac balloon can be inserted to stabilize hemodynamics initially and give the anesthesiology team time to catch up with fluids and blood products.

Patients with significant fluid or blood product resuscitation, and those with coagulopathy are more prone to developing this condition. A high degree of vigilance is needed for early recognition before it impacts other organs. ACS may cause liver or renal failure, interrupt venous return, induce coagulopathy and may quickly become lethal.

Open repair is considered a high-risk vascular procedure with regard to cardiac morbidity and mortality. The pooled prevalence of myocardial infarction and death in the perioperative period in vascular surgery patients is 4.9% and 2.4% respectively. In the long term they approach 8.9 and 11.2%. A detailed understanding of the cardiac status, in terms of ischemic potential and ventricular function is important.

Unstable angina, uncontrolled heart rhythm and chronic heart failure symptoms should prompt immediate evaluation and optimization of therapy prior to surgery. This follows the latest recommendations from the American Heart Association and American College of Cardiology for perioperative evaluation of the cardiac patient presenting for noncardiac surgery. This guideline-based approach should not simply target clearance for the surgical procedure but give the patient and caregivers the ability to make informed decisions, help optimize the current therapy and provide recommendations for the perioperative management of the cardiac problems. Emergency procedures should focus on resuscitation of the patient and stratification of cardiac risk should occur in the postoperative phase.

There is a significant prevalence of coronary artery disease and carotid artery disease in patients with AAA. The Coronary Artery Revascularization Prophylaxis (CARP) trial did not find improvement of short-term outcome or long-term survival despite aggressive revascularization prophylaxis. Patients with the absence of multiple preoperative cardiac risk variables experienced the best long-term survival after vascular surgery [8]. Similar results were established by the Dutch Echocardiographic Cardiac Risk Evaluation Applying Stress Echo (DECREASE) in high-risk patients. This is also reflected in the current AHA/ACC recommendations for CABG, recommending only those patients who experience unstable angina symptoms benefit from revascularization despite the higher incidence of periprocedural complications in those patients. Patients who underwent prophylactic revascularization did exhibit 5.5% mortality from the CABG itself thus reducing the actuarial benefit from the procedure.