Special Feature: ED Management of the Unstable Patient with Abdominal Aortic Aneurysm
September 1, 2002 6 minutes read
ED Management of the Unstable Patient with Abdominal Aortic Aneurysm
By Michael A. Gibbs, MD
The emergency department diagnosis and management of the patient with a ruptured abdominal aortic aneurysm (AAA) poses several unique challenges. The clinical presentation is seldom "classic" and, as a result, the diagnosis often is delayed or may be overlooked completely. Once a ruptured AAA is suspected, important diagnostic imaging decisions must be made. The emergency physician should be familiar with the strengths and weaknesses of each of these testing modalities. Coincident urgent resuscitation needs make the situation even more demanding. Lastly, and perhaps most importantly, this is a condition for which time is clearly not on our side. Even short delays in definitive management may dramatically increase both morbidity and mortality. This special feature will review the epidemiology of AAA, and provide a logical management framework that I hope will address these issues
Epidemiology of a Potentially Lethal Disease
Ruptured AAA is the 13th most common cause of death in the United States. About 3-5% of patients older than 65 years harbor an asymptomatic AAA. The male-to-female ratio is approximately 4:1. There have been several different criteria employed to define AAA. The most widely used definition is any aortic diameter greater than 3.0 cm. AAA is the most common type of aneurysm. Ninety-five percent arise below the origin of the renal arteries. Coexistent iliac artery aneurysms are found in 50% of cases. Major risk factors are advanced age, male gender, smoking, hypertension, chronic obstructive pulmonary disease, and peripheral vascular disease. The incidence of AAA in patients with a first-degree relative with the disease is 11-28%. A family history of AAA is an important component of the history in the elderly patient with abdominal pain.1
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Population-based studies suggest that an untreated AAA increases in diameter by about 0.2 cm annually. Larger aneurysms—those more than 5-6 cm—expand more rapidly than smaller ones. Table 1 illustrates the relationship between aortic diameter and the risk of rupture. Because of the striking increase in rupture-risk with size, some recommend that all asymptomatic aneurysms larger than 5 cm undergo elective repair. The prognosis of aortic rupture is dismal. Up to 60% of patients with ruptured aneurysms die before ever reaching the hospital. Of those who "arrive alive," the operative mortality is greater than 50%; i.e., the overall mortality of ruptured AAA is nearly 90%. When contrasted with a 1-5% mortality for patients undergoing elective operative repair, the priority clearly should be early detection of symptomatic AAA prior to rupture.1,2
A Challenging Clinical Diagnosis
Clinical diagnosis in symptomatic AAA is neither sensitive nor specific. It has been well demonstrated that unless the AAA is large, even experienced clinicians cannot rely solely on the physical examination.2,3 In patients with a rapidly expanding or ruptured AAA, the classic triad of abdominal or flank pain, hypotension, and a pulsatile abdominal mass is only present in 30-50% of cases. In addition, since the majority of aneurysms rupture into the retroperitoneum, the expanding hematoma may be contained and patients may have "normal" vital signs on presentation.4 Moreover, the differential diagnosis of a patient with hypotension, syncope, abdominal pain, flank pain or back pain is quite broad.1
It is prudent to consider the diagnosis of AAA in all patients older than age 50 with abdominal, flank, or back pain. This certainly does not mean the emergency physician should work up everyone with those complaints for the disease; but it should be given thought. If the patient is sick, AAA should move up a few notches on the differential diagnosis.
Making a Definitive Diagnosis
A definitive diagnosis of AAA can be made by either computed tomography (CT) scanning or ultrasound (or laparotomy, of course). Each modality has important strengths and weaknesses. (See Table 2.) The central question then becomes: Which test is best? There is no blanket answer, and decisions should be based primarily on the hemodynamic stability of the patient at hand. In the clinically unstable patient with a leaking or ruptured AAA, every minute saved will improve outcome. If available, immediate ED bedside ultrasound should be performed. The accuracy of ultrasound in this setting is well-established, and the technology is portable and readily available.1,5 The ultrasonographic detection of AAA in the unstable patient is an indication for immediate surgical consultation. Sending these patients to the bowels of the radiology department for CT scanning can be a perilous mistake.
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As ultrasound moves into emergency medicine, emergency physicians have taken the imaging of the abdominal aorta as one of its key applications.6,7 Recent studies have shown that well-trained emergency physicians can diagnose AAA with a sensitivity that approaches 100%.8-10 If you have ED ultrasound available, learn how to image the abdominal aorta. If you don’t have ED ultrasound available, get it.
In the stable symptomatic patient, the decision to obtain a CT scan or formal ultrasound should be based on an understanding of the strengths and weaknesses of each test, their availability, and the preference of consulting surgeons. Be cautious with over-reliance on plain film radiographs. These may demonstrate aortic calcification with dilatation as an indirect marker of AAA, but never should be used to exclude the diagnosis.
A special note of caution: Up to 30% of patients with symptomatic AAAs are misdiagnosed on initial presentation. In one study, common erroneous diagnoses included: renal colic (23%); gastrointestinal hemorrhage (13%); diverticulitis (12%); and back pain (9%).11 Be especially cautious when evaluating the elderly patient with flank pain (with or without hematuria) for presumed renal colic. A helical CT scan, rather than an intravenous pyelogram, is especially useful in this setting, as both diagnostic possibilities can be explored. An alternative is sonographic evaluation of the kidneys for hydronephrosis and the aorta for AAA.
Management Essentials
The following algorithms are suggested for evaluation and treatment of the patient with suspected symptomatic AAA:
Resuscitative efforts should focus on: 1) early, aggressive airway management, especially prior to interfacility transfers; 2) the establishment of adequate intravenous access; 3) early blood transfusion; 4) prevention of coagulopathy and hypothermia; and 5) early surgical consultation.
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Common Management Pitfalls
Immediate surgery is the only intervention that will save an unstable patient with a ruptured or leaking AAA. We resuscitate dying patients better than anyone else in the hospital, but remember, what these patients need is a surgeon and a knife.
Common ED pitfalls include:
• Failure to suspect the diagnosis on clinical grounds alone;
• Failure to obtain immediate surgical consultation and/or interfacility transfer;
• Failure to obtain the right diagnostic test for the right patient; and
• Failure to secure the airway and initiate appropriate resuscitation.
Summary
Ruptured AAAs represent one of the most lethal conditions in emergency medicine. Most of these patients, unfortunately, will not survive the experience. As emergency physicians, our prime directive should be to suspect the diagnosis in the right patient, move quickly to see if we are right, and to get the patient to the operating room. We have all the tools to do this, and to do it well. v
Dr. Gibbs, Chief, Department of Emergency Medicine Maine Medical Center Portland, Maine, is on the Editorial Board of Emergency Medicine Alert.
References
1. Ernst CB. Abdominal aortic aneurysm. N Eng J Med 1999;328:1167-1172.
2. Lederle FA, et al. Does this patient have abdominal aortic aneurysm? JAMA 1999;281:77-81.
3. Fink HA, et al. The accuracy of physical examination to detect abdominal aortic aneurysm. Arch Intern Med 2000;160:833-836.
4. Zimmers T. Absence of back pain and tachycardia in the emergent presentation of abdominal aortic aneurysm. Amer J Emerg Med 1988:6:316.
5. Hojer J. Diagnosis of acute symptomatic aortic aneurysm—Ultrasonography is an important tool. J Intern Med 1992;232:427-431.
6. American College of Emergency Physicians. ACEP emergency ultrasound guidelines—2001. Ann Emerg Med 2001;38:470-481.
7. American College of Emergency Physicians. Use of ultrasound imaging by emergency physicians. Ann Emerg Med 2001;38:469-470.
8. Miller J, et al. Small ruptured abdominal aneurysm diagnosed by emergency physician ultrasound. Amer J Emerg Med 1999;17:174-175.
9. Kuhn M, et al. Emergency department ultrasound scanning for abdominal aortic aneurysm: Accessible, accurate, and advantageous. Ann Emerg Med 2000; 36:219-223.
10. Graf C, et al. Prospective study of accuracy and utility of emergency ultrasound for AAA over a two-year period. Acad Emerg Med 2002;9:451-452.
11. Martson WA, et al. Misdiagnosis of ruptured abdominal aortic aneurysm. J Vasc Surg 1992;16:17-22.
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