AAA is a full-thickness dilatation of a segment of the abdominal aorta located between the diaphragm and the bifurcation of the aorta to the common iliac arteries. Approximately 200,000 AAAs are diagnosed annually resulting in about 13,000 deaths per year in the United States. Risk factors for AAA include older age, male sex, family history of AAA, smoking, hypertension, hyperlipidemia, atherosclerotic occlusive disease, and obesity. Lifestyle factors reducing risk for AAA include regular exercise, smoking cessation, and favorable diet (includes fruits, vegetables, and nuts). Diabetes mellitus is also associated with decreased risk of AAA. The prevalence of AAA is lower in Blacks, Hispanics, and Asians in comparison to Whites and Native Americans.

The major pathologic cause of aneurysmal disease is atherosclerosis. In addition, hypertension (55%), heart disease (73.5%), peripheral vascular disease (21%), stroke and transient ischemic attacks (22%), diabetes mellitus (7%), and renal insufficiency (10%) are the most common comorbid illnesses. It is worth noting that in some studies, smoking history has been reported in as many as 80% of patients presenting for AAA repair. A recent study demonstrated an association of current smoking with AAA rupture in younger patients. However, hypertension had a greater association than smoking with AAA rupture in older patients. These risk factors, combined with advanced age (greater than 60), are exacerbated by the extreme physiologic changes that occur during aneurysmal surgery.

Morbidity in this patient group is most commonly due to cardiovascular, pulmonary, and renal complications. Perioperative mortality for elective open AAA repair is 2% to 5%. Increased postoperative mortality was associated with older age, elevated serum creatinine, a lower forced expiratory volume in 1 second (FEV1), and gender. One retrospective study demonstrated higher mortality in women in comparison to men: 7% versus 5% for open repair and 2% versus 1% for endovascular repair. Despite the increasing fraction of patients undergoing endovascular repair, numerous large studies have not shown significant long-term differences in mortality between open and endovascular repair. The major cause of death in the nonsurgically treated patient is rupture with a mortality of up to 80%. Ruptured AAAs account for approximately 9,000 deaths per year in the United States. In one study, resection of AAAs doubled life expectancy. The incidence of rupture within 5 years of diagnosis of an AAA is 80%. The incidence of rupture increases with aneurysmal size: 25% for lesions of 4 to 7 cm in diameter, 45% for lesions 7 to 10 cm, and 60% for lesions larger than 10 cm. Repairing aneurysms smaller than 5.5 cm has not been shown to improve survival. Thus, only patients with aneurysms 5.5 cm or larger should be considered for surgical intervention.

After 10 years, graft patency is worse for patients with disease in distal vessels. Mortality is also increased for patients with diseased distal vessels. Survival rate is 28% in patients with isolated aortoiliac disease and increases to 41% in patients with femoral popliteal or tibial disease.

Physical examination and screening, either by abdominal ultrasound or CT scan, uncover many patients with aortic aneurysms less than 5.5 cm in diameter. One study compared patients with smaller aneurysms that were followed until the aneurysm reached 5.5 cm, enlarged by more than 0.7 cm in 6 months, 1.0 cm in 1 year, or were symptomatic from their aneurysm. Mortality was the same in patients randomized to immediate repair or followed closely with no intervention. Aneurysm repair was delayed 4 years in patients who received close monitoring instead of surgical intervention. The U.S. Preventive Services Task Force
(USPSTF) 2015 update on screening recommendations for AAA reinforces that early surgical intervention of smaller AAAs <5.5 cm (open or endovascular) does not reduce mortality. USPSTF recommends repeat ultrasonography every 3 to 12 months for AAAs 3 to 5.4 cm with surgical referral for rapid growth (>1 cm per year) or when the aneurysm reaches 5.5 cm or larger. Therefore, watchful waiting is suggested for aneurysms that are smaller than 5.5 cm.

A retrospective analysis confirmed that cardiac mortality is high for patients who undergo vascular surgery and experience postoperative myocardial ischemia. Key factors that determine perioperative morbidity and mortality rates include the stress of surgery (aortic, peripheral vascular, emergency surgery), increased blood loss, poor preoperative cardiac functional status, history of congestive heart failure (CHF), a low ejection fraction, known coronary artery disease (CAD), and preoperative history of coronary artery bypass grafting.

The occurrence of a recent MI is an important independent predictor of perioperative morbidity and mortality. In a group of patients studied prospectively for perioperative reinfarction by Rao et al., the statistical rate of reinfarction was related to the length of time since the initial MI, decreasing to less than 2% if the infarction occurred more than 6 months earlier. Patients were monitored with PACs and arterial lines and were aggressively treated and monitored in an intensive care unit setting for 3 to 4 days postoperatively. Currently, the acute care for MI has improved and subsequent risk stratification with noninvasive testing allows for a more tailored approach to the timing of surgery in these patients.

Special consideration needs to be given to patients who have recently undergone percutaneous coronary intervention procedures for revascularization of stenotic lesions and are being treated with platelet inhibitors. Depending on the type of intervention undertaken, bare metal stent (BMS) or drug-eluting stent (DES) placement, surgery may need to be delayed for a period of 1 month, 6 months, to 1 year. This is due to the significant risk of acute stent restenosis or thrombosis in these patients if antiplatelet therapy is terminated prematurely. Caring for patients with coronary stents in the perioperative period requires input from a team consisting of anesthesiologists, surgeons, and cardiologists. The management of the dual antiplatelet therapy regimen should be customized to each patient depending on the type and urgency of surgery, type of coronary stent, time since the coronary intervention, and complexity of the coronary intervention. The current recommendations for perioperative management of patients with stents are shown in Figure 10.1. For patients identified at high risk for stent thrombosis, surgery should be planned in a hospital with cardiac catheterization facilities. Postoperatively, these patients require a monitored setting and their antiplatelet agents restarted immediately. Signs and symptoms of stent thrombosis should be promptly recognized and aggressively treated with percutaneous coronary intervention.

In most studies, the morbidity following a perioperative MI approaches 50%. The risk after an MI may be best linked to the ongoing risk of ischemia. Patients who have survived a non-Q-wave infarction are potentially at great risk for further ischemia. Badner et al. reported a 17% post-MI mortality rate after noncardiac surgery. The mortality rate was higher if the ST-segment and T-wave changes occurred during the intraoperative period. These patients should be evaluated by symptom-limited exercise testing and/or cardiac catheterization. The prevention of perioperative myocardial ischemia is the goal of the anesthesiologist regardless of the technique chosen. The basic goal is to reduce myocardial oxygen demand by avoiding tachycardia and hypertension while increasing oxygen supply by preventing hypotension and anemia. Oxygen demand on the left ventricle is dependent on heart rate, contractility, and the ventricular loading conditions. Of the three, the increase in heart rate imposes the greatest demand and should be readily controlled by the anesthesiologist. Left ventricular
preload and afterload also affect oxygen demand by end-diastolic and systolic wall tension. Other factors, such as coronary collateral blood flow, hematocrit, and blood rheology also may influence myocardial ischemia.

β-Adrenergic antagonists are a well-established class of drugs effective in reducing myocardial oxygen consumption. Some studies suggest that β-blockers reduce perioperative ischemia and may reduce the risk of MI and cardiovascular death in patients undergoing high-risk procedures such as vascular surgery. The mechanism of reduction of myocardial oxygen consumption with β-antagonism is related to decreases in heart rate and myocardial contractility, counteracting the deleterious effects of sympathetic stimulation. In addition, this class of drugs has antiarrhythmic qualities. However, results of recent trials have not shown efficacy of high-dose, acutely administered, perioperative β-blockers to reduce overall mortality in patients undergoing noncardiac surgery. The largest of these trials, the 2008 Perioperative Ischemic Evaluation (POISE) trial, did show better perioperative cardiac outcomes with β-blocker use; however, increased mortality and stroke rate were also noted in the β-blocker group. Interestingly, the sub-analysis of vascular surgery patients in the study demonstrated efficacy of perioperative β-blockers. Currently, the only class I recommendation for perioperative β-blockers use by the American Heart Association (AHA) is to continue their use in the patients who are already on β-blockers. Patients undergoing vascular surgery who have multiple risk factors or have reversible ischemia on preoperative testing may benefit from perioperative
β-blockers (class IIa). Although there are some differences between the European Society of Cardiology and the AHA guidelines, they both agree that if β-blockers are used for prophylactic purposes, they should be slowly titrated (at least a week prior to elective surgery) and acute administration of high-dose β-blockers in high-risk population is not recommended.

Nitrates also can reduce myocardial oxygen demand by decreasing preload and by dilating large epicardial coronary arteries and collateral conduit vessels. However, the benefit of perioperative nitroglycerin prophylaxis has not been proven.

The use of statins in patients with cardiovascular disease is increasingly supported by multiple studies that display a reduction in the risk of MI, stroke, and mortality. Furthermore, accumulating data suggests that continuation of statin therapy in the preoperative period reduces the risk of postoperative death and acute coronary syndromes. The mechanisms by which statin medications attenuate cardiovascular disease extend beyond their lipid-lowering properties. In addition to anti-inflammatory and antioxidant actions, they also improve endothelial function and stabilize plaques. Thus, current American College of Cardiology (ACC)/AHA guidelines recommend continuation of statin therapy in the perioperative period (see also Chapter 14, sections A.7 and A.8).

The overall mortality for a ruptured aortic aneurysm is greater than 50%. One study showed an overall survival rate of 19.8% as compared with an elective surgical survival rate of 95%. The worst prognosis occurred in patients older than 80 years; a systolic blood pressure of less than 80 mm Hg on admission; a prior history of hypertension, angina, or previous MI; and an operating time of greater than 4 hours. Other risk factors include a systolic blood pressure less than 100 mm Hg at the end of surgery and blood loss greater than 11,000 mL. Retroperitoneal rupture was more likely to be associated with a higher rate of survival. Elective surgical intervention should be considered if the size of the aneurysm changes rapidly or if its diameter is greater than 5.5 cm.

The patient should have the following laboratory tests as part of the preoperative evaluation: complete blood count and platelet count, serum electrolytes, BUN, creatinine, and coagulation profile. ABG analysis may be useful, but pulse oximetry can give similar information and PaCO₂ may be inaccurate if the patient is hyperventilating or sedated prior to obtaining the test. Chronic hypercarbia may be gleaned from the serum bicarbonate value. A chest radiograph will help ascertain whether signs of heart failure, pulmonary disease, or acute pneumonia are present. Spirometry should be considered in the patient with severe disease and those in whom an adequate medical history is not available. In addition, spirometric data may be useful in assessing the effects of inhaler therapy.

An ECG should be obtained because this patient displays multiple risk factors for ischemic disease. The ECG is a sensitive and simple screening test for active cardiac conditions, such as unstable coronary syndromes and significant arrhythmias, which necessitate further management prior to proceeding to surgery. Additionally, preoperative laboratory tests should be defined by positive findings on history and physical exam.

The patient’s preoperative ECG is consistent with a prior inferior wall MI. Patients with a history of a prior MI or angina in conjunction with an abnormal ECG have a fivefold increase in postoperative mortality when compared with those with no clinical indication of CAD. This patient’s history of claudication suggests peripheral vascular disease. Peripheral artery disease is associated with a fourfold increase in risk for MI and a twofold to threefold increase in risk of stroke. In selected patients with severe or unstable cardiac ischemia, evaluation may be needed to assess if prior myocardial revascularization is indicated.

When coronary angiography was performed on 1,000 patients undergoing elective peripheral vascular surgery, it was revealed that more than half of the patients had significant CAD (greater than 50% stenosis), and 33% had severe stenosis (greater than 70%). Of the asymptomatic patients with no history or electrocardiographic evidence of ischemic heart disease, 15% had severe CAD, and 22% of these seemingly normal patients had impaired left ventricular function. Hertzer et al. found that only 8% of patients undergoing elective vascular surgery had normal coronary arteries.

A comparison of this patient’s current ECG with a prior ECG may aid in assessing the timing of the previous infarction if the history alone is not helpful. The 2014 update to the joint AHA/ACC guidelines concerning perioperative cardiovascular assessment suggest incorporating clinical risk factors, exercise tolerance, and surgical risk when determining whether further testing is necessary. Vascular surgeries, such as AAA repair, are categorized as high-risk procedures. In addition, clinical risk factors include a history of ischemic disease, compensated or prior heart failure, cerebrovascular disease, diabetes mellitus, and renal insufficiency. The algorithm for the cardiac assessment of patients undergoing surgical procedures associated with a high perioperative cardiac risk is shown in Figure 10.2.

Many vascular surgery patients are unable to undergo exercise stress testing because of limitations presented by their cardiac, pulmonary, or peripheral vascular disease. A dipyridamole-thallium stress test or a dobutamine stress echocardiogram is a pharmacologic test to assess ischemic potential. Dipyridamole causes vasodilation of normal coronary arteries. This results in a “steal” of blood flow from the area beyond a coronary stenosis. Blood flow redistributes as the drug dissipates.

Positive results on preoperative stress testing may not always necessitate revascularization. There is evidence to suggest that vascular patients who undergo coronary revascularization have an increased risk of periprocedural and long-term complications. The decision to perform coronary revascularization procedures, rather than employ medical management, should be undertaken in close consultation with a cardiologist and a cardiac surgeon.

Recent evidence also suggests that patients at significant risk for ischemic heart disease may benefit from an endovascular approach, if anatomically feasible.

The patient’s smoking history and the chronic changes present on his chest radiograph are evidence of chronic obstructive pulmonary disease (COPD). Provided the patient is minimally symptomatic and has good functional status, a detailed history and thorough physical exam can provide significant information regarding pulmonary status. A chest radiograph can be particularly useful at detecting underlying lung infection. If the radiograph displays the absence of acute pulmonary processes, as in this patient, further pulmonary testing may not be indicated. In the patient with severe signs and symptoms of COPD, an ABG analysis can be particularly helpful. ABG analysis can evaluate the patient’s ability to oxygenate and ventilate. Patients with severe COPD tend may be chronically hypercarbic and hypoxic. A preoperative ABG is particularly helpful at guiding perioperative ventilatory management and predicting the likelihood of postoperative mechanical ventilation in these patients.

In those patients with severe disease, particularly those with poor functional status and significant findings on physical exam and chest radiograph, pulmonary function testing may be indicated. Preoperative pulmonary function testing evaluates baseline forced vital capacity (VC) and FEV1. Maximum midexpiratory flow rate (MMEFR) is an effort-independent value that is a sensitive index of small airway obstruction. Peak expiratory flow rate is related to the FEV1 and MMEFR, although often it is less reproducible. These tests should be performed before and after bronchodilator therapy to assess reversibility of airway obstruction. A 15% improvement is considered a positive response.

This patient is a two pack-per-day smoker with dyspnea on exertion, and the anticipated surgery required an upper abdominal incision. These factors likely affect his baseline pulmonary function and presage postoperative ventilatory problems. A VC less than 50% of predicted, or less than 2 L total, is an indicator of increased risk of pulmonary complications as a VC at least three times the tidal volume is necessary for an effective cough. FEV1 less than 2 L, maximum breathing capacity less than 50% of predicted, and MMEFR less than 50% of predicted are also values associated with increased risk of postoperative mechanical ventilation.