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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