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Outline the preoperative evaluation of the patient with an AAA.
Patients presenting for aortic surgery almost always have coexisting medical conditions that can significantly affect anesthetic management. These include diseases of the cardiovascular, pulmonary, renal, and central nervous systems. The goal of preoperative evaluation is to detect coexisting diseases, assess the risk of adverse outcomes, optimize the patient’s medical status, and devise an anesthetic technique that minimizes complications. It is not always possible to obtain a complete preoperative evaluation when surgery is required on an urgent basis, thus preoperative optimization of medical problems is not always feasible.
It is imperative to evaluate the patient’s myocardial reserves prior to aortic surgery. Risk factors for myocardial ischemia include previous myocardial infarction, angina, congestive heart failure, male gender, smoking, hyper-cholesterolemia, diabetes mellitus, and limited exercise tol-erance. Patients at low risk for myocardial ischemia may proceed to surgery without further evaluation; however, this represents a very small group of patients. Additionally, those who have had a negative stress test within 2 years of surgery or who have had coronary artery bypass surgery within 5 years of surgery without postoperative symptoms most likely do not require further investigation for myocardial ischemia. While stress testing is probably most appropriate for patients with moderate risk, coronary angiography is recommended for patients at high risk for myocardial ischemia.
There are two components to stress testing: the “stress-ing” of the myocardium and the detection of myocardial ischemia or infarction. The “stressing” can be performed by either mechanical means (such as exercise via treadmill or hand-crank) or pharmacologic means. The pharmacologic stress may involve drugs such as dobutamine that increase myocardial oxygen demand or drugs that cause “myocar-dial steal” such as dipyridamole. Detection of myocardial ischemia may be performed by electrocardiogram (ECG), nuclear studies, or echocardiography. Ischemic myocardium is characterized by a lack of uptake of nuclear tracers with stressing and uptake of nuclear tracers with rest; this is known as a reversible defect. Fixed defects, i.e., no uptake during stressing or rest, is consistent with old infarction. Echocardiography reveals ischemic myocardium as signifi-cant changes in wall motion during stressing. In each of these studies it is important to determine whether there is myocardium at risk, i.e., myocardium that may become ischemic with stress, as opposed to myocardium that is infarcted. If patients have significant areas of myocardium at risk, further optimization (either pharmacologic or interventional) is warranted prior to surgery.
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