The Clinical Challenges of Abdominal Aortic Aneurysm: Rapid, Systematic Detection and Outcome-Effective Management
The Clinical Challenges of Abdominal Aortic Aneurysm: Rapid, Systematic Detection and Outcome-Effective Management
Part II: Diagnosis, Management, and Post-Operative Complications
Authors: Gary Hals, MD, PhD, Attending Physician, Department of Emergency Medicine, Palmetto Richland Memorial Hospital, Columbia, SC; Michael Pallaci, DO, Department of Emergency Medicine, Palmetto Richland Memorial Hospital, Columbia, SC.
Peer Reviewer: Dawn Demangone, MD, Assistant Professor of Medicine, Assistant Residency Director, Temple University Hospital, Philadelphia, PA.
Even with the current arsenal of ultrasonic and computerized tomographic modalities, all the diagnostic tools available to the ED physician have limitations. For example, bedside ultrasound (US) is an excellent screening tool to identify patients with an abdominal aortic aneurysm (AAA), but is less reliable for detection of vascular rupture. Because of its rapidity of execution, however, US is the better tool for rapid identification of an AAA in an unstable patient.
On the other hand, strong suspicion that an unstable patient has an AAA may be all that is required to transport the patient to the OR for definitive treatment. In contrast, computed tomography (CT) is accurate for both detection of an AAA and identifying leak or rupture; its diagnostic advantages must be weighed against that fact, but the scanning suite is often the last place one wants to put an unstable patient. Accordingly, CT is most useful in evaluation of symptomatic but stable patients.
The alert physician will be aware of post-surgical complications, which are associated with an increased risk of rupture and arteriovenous complications.
With these diagnostic and management issues in mind, this concluding part of our two-part series outlines the diagnostic and management strategies for patients with AAA. The sequencing of diagnostic testing is highlighted, and the role of stabilization prior to surgical intervention is emphasized.
— The Editor
Diagnostic Pathways for AAA: Sequencing, Strategy, and Execution
The appropriate test and sequencing for ED evaluation of patients with a suspected AAA depends on several factors: 1) the stability of the patient; 2) the time delay in performance of the test; and 3) the disposition options available to the ED physician. In the small ED, where limited surgical back up is available, transfer of the patient to more appropriate facilities should take precedence over completing the work-up or even making the diagnosis. When high-risk patients need to be evaluated for a symptomatic AAA, they should be taken to the nearest ED where they can be rapidly taken to the OR if the diagnosis is confirmed.
As a rule, time should not be wasted ordering an evaluation if the patient will be transferred for surgery anyway. In those EDs where adequate surgical consultation is readily available, the question is: "Which test do I order first?" More often than not, the answer is: Order whichever test (US or CT) can be obtained most rapidly.
Overview. Given equal availability of US and CT, bedside US is the test to obtain in order to answer the question of whether there is an aneurysm. It is nearly 100% sensitive for diagnosing the presence of an AAA, it can be executed in a matter of minutes, and it does not require unstable patients to leave the department.1 While much less accurate than CT in detecting actual rupture, if the patient has the symptoms of rupture and presence of an AAA, this usually is all the information required for the consultant to take the patient to the OR.
CT scanning, on the other hand, is much more accurate for defining the anatomy of the aneurysm; moreover, it can detect involvement of other major arteries (i.e., renal or mesenteric), the presence of hematoma or thrombus, and involvement of retroperitoneal structures. As an overarching approach to modality selection, the following is true: If it is simply a matter of determining whether the patient has an AAA, then bedside US (if available without delay) will give the best response. If the questions to be answered are, "How does this patient’s AAA need to be managed, is there a rupture, and what will be required in the OR?" then CT will provide the best characterization of the management plan.
Plain Films. Unlike the case for most causes of acute abdominal pain, plain radiographs do represent a reasonable initial screening test for the ED physician who is evaluating a patient with suspected AAA. In this case, evidence of AAA is seen in about 60-75% of abdominal films.2,3 The clinician should attempt to identify a calcified aortic wall, which can be seen on cross-table lateral films in up to 68% of patients.4 Cautious interpretation is required since the outer rim of the aneurysm may not be calcified, leading the physician to assume the aortic diameter is much smaller than it is in reality.
Other signs that are suggestive of AAA include: paravertebral soft tissue mass, loss of psoas or renal outlines, and rarely, erosion of vertebral bodies from long-standing AAAs.5 Advantages of plain films for evaluation of these patients primarily are rapid availability of the test and results. Radiographs can be performed at the bedside, preventing the unstable patient from leaving the department. The major disadvantage of plain films is that a negative study cannot exclude the diagnosis. In patients for whom there is a high suspicion for AAA, one should not use plain films unless other options (US or CT) are not rapidly available. If the physician is forced to wait for US or CT, a plain x-ray should certainly be obtained during the waiting period, since confirmation of AAA on plain film may obviate the need for further radiographic evaluation.
Ultrasound. As previously mentioned, US has been shown to be nearly 100% accurate for detecting the presence of AAA.6 The appearance of an AAA as seen on US is shown in Figure 1. The primary advantages of US is its rapidity, non-invasiveness, and that it can be used in nearly all patients who present with suggestive symptoms. Perhaps the most useful aspect of US is that unstable patients can be evaluated in the ED without interruption of resuscitation and stabilization efforts. Although the study is still in abstract form, one current study demonstrates potential advantages of US over CT. When comparing bedside US to CT scan, the average time to diagnosis was 5.4 minutes for US and 83 minutes for CT. The average time to OR was similarly reduced: 12 minutes in US patients and 90 minutes in those diagnosed by CT scan.7 Another author found that use of bedside US in the ED was 95% accurate in identifying patients who needed emergency surgery.6 These patients were hemodynamically unstable and had abdominal pain; the US was used to confirm presence of an aneurysm.
Drawbacks of the US also should be noted. First, US cannot accurately identify rupture in an aneurysm; one study evaluating only 60 patients yielded a sensitivity for extraluminal blood of only 4%.6 Although failure to identify rupture is a disadvantage, oftentimes identification of the presence of an aneurysm is sufficient to refer the patient for urgent consultation. US can be used to recognize relatively small volumes of intraperitoneal fluid (several hundred ccs), and it has recently been reported that this modality can diagnose AAA rupture in an ED patient.8
The fact that most AAAs rupture into the retroperitoneal space—an area that is less accessible to the US—compromises the usefulness of this modality. Abdominal cavity hemorrhage, which is associated with AAA, carries a much higher mortality rate, presumably from unrestricted hemorrhage. Secondly, it is technically difficult to visualize the aorta with US in obese patients, or in those with excessive, overlying bowel gas. Finally, US does not provide the complex data that CT scan can show concerning the relationship of the aneurysm to other vascular structures.
These disadvantages notwithstanding, immediate bedside US is an appropriate modality for rapid and safe identification of AAA in ED patients suspected of having an AAA. One team of investigators has identified three specific situations where limited bedside US should be used in evaluation of the aorta in ED patients: 1) in the presence of abdominal pain and hypotension, where demonstration of normal aorta excludes AAA as the diagnosis early in the work-up; 2) in the stable patient with unexplained abdominal or back pain, in which AAA is one of the few life-threatening diagnoses that needs to be ruled-out early in the patient’s course; and 3) every elderly patient with abdominal or back pain with risk factors such as peripheral vascular disease, hypertension, tobacco use, etc.1
Computed Tomography (CT). As with US, CT is virtually 100% accurate in detection and measurement of an AAA.9 Visualization of an AAA as seen by CT is shown in Figure 2. Unlike US, it can also provide accurate characterization of the entire aorta and identify involvement of surrounding vascular or intestinal structures. Obesity or presence of bowel gas does not limit the ability to perform the study. It is also much more accurate than US in identifying rupture.10 As little as 10 mL of blood can be identified outside the aortic lumen.11
CT has even been reported to identify signs of impending rupture in patients with symptomatic AAA. A "high-attenuating crescent" in the aneurysm wall was shown to be indicative of imminent AAA rupture in one recent study.12 Newer helical CTs can produce three-dimensional reconstructions of an AAA. Typically, IV contrast is given for elective studies, but these are not absolute requirements for emergency scans. IV contrast will help the radiologist identify mural thrombus and periaortic fibrosis, but acute hemorrhage and aneurysm size can still be measured without IV contrast. Withholding IV contrast also will be of benefit to patients with baseline renal insufficiency, as many patients experience renal dysfunction after AAA repair. Oral contrast will aid precise identification of bowel loops, but the time delay required for its use can be a liability for some patients.13
While CT provides a wealth of information in the patient being evaluated for symptomatic AAA, it does have several distinct disadvantages. The most important is that the patient must leave the ED to obtain the study, or if the scanner is in the department, the patient must still enter a room where he or she is not accessible for continued resuscitation or treatment. Therefore, use of CT should be reserved only for evaluation of stable patients.
Even though the CT scan is extremely accurate, it still can produce false-negative results. In other words, in some cases, an AAA will be identified but the CT will be negative for acute rupture. Patients have been reported to have a negative CT scan for rupture, but then soon decompensate and a ruptured AAA is found at surgery.14 These cases emphasize that one should not be lead into thinking a patient’s symptoms are not from impending rupture if the CT shows an AAA but no hemorrhage. From a practical, sequencing perspective, if the patient has an AAA and symptoms consistent with possible rupture, the patient should have emergent consultation by a vascular surgeon regardless of whether the CT scan shows the presence of hemorrhage.
In one four-year study, only 8% of patients taken to the OR for an AAA rupture had evidence of hemorrhagic leakage upon surgical evaluation in the OR.15 Nevertheless, 75% of these patients required surgical repair for AAA or another nonvascular surgical procedure at the time of their laparotomy. Consequently, it is beyond the purview of the emergency physician alone to "make the final call" on whether the AAA is leaking and what kind of surgical procedure is required. This assessment should always be undertaken in collaboration with a surgical consultant. One recent article by a vascular surgeon suggested "that CT has little additional diagnostic value" in the work-up of patients with suspected AAA rupture.16 He suggested that "if the patient has no medical contraindications to AAA repair, the patient should be taken directly to the OR."
Angiography. Angiography represents another option for evaluation of patients with symptomatic AAA, but this modality should not be used by emergency physicians to screen patients for AAA. It often underestimates aortic diameter, as the presence of mural thrombus is common in AAAs and this can produce a normal sized aortic lumen in the presence of a larger aneurysm. Its primary function is for consulting surgeons who may obtain anatomic information that will aid in the surgical plan.
Many vascular surgeons still routinely order arteriography before aneurysm resection, although there is considerable debate in the surgical literature as to whether the information obtained justifies the cost, discomfort, and potential risk to the patient.11 Currently, the reported indications for arteriography as articulated in the surgical literature include: 1) symptoms of mesenteric ischemia; 2) hypertension or renal dysfunction (i.e., suspicion of renal artery stenosis which could also be repaired at time of surgery); 3) horseshoe kidney; and 4) claudication or other signs/symptoms of coexistent lower extremity occlusive disease.11 Newer helical CTs with the ability to produce three-dimensional reconstructions have been evaluated for replacement of conventional arteriography. One study found that CT angiography can provide all the necessary imaging for elective aneurysm repair, but it requires twice the radiation dose and three times the amount of contrast dose.17
Magnetic Resonance Imaging. Magnetic resonance imaging (MRI) offers the advantages of US and CT in that it is accurate for detecting the presence of an AAA. It is even better than CT for defining three-dimensional views of the aorta and surrounding vascular structures. At present, though, the disadvantages prevent its routine use in the ED for evaluation of patients for symptomatic AAA. Most importantly, MRI does not accurately identify acute hemorrhage.18 Furthermore, the limitations placed by the inability to scan patients with metallic foreign objects (i.e., pacemakers, surgical clips), the lack of accessible monitoring equipment in the MRI room, and the high cost all relegate the use of MRI scans in the setting of AAA to primarily for elective pre-operative evaluation.
Management
The emergency management of patients with AAA requires a systematic and methodical approach, which will be determined by various factors, including the patient’s symptoms, co-morbid conditions, and aneurysm size. The resources of each institution (surgical back-up, access to US/CT) also need to be taken into consideration. As mentioned previously, if a patient presents with symptoms strongly suggestive of AAA rupture and with a physical exam consistent with this condition (i.e., palpable pulsatile abdominal mass), the clinician does not need additional information to justify transfer of the patient to the nearest appropriate center if adequate surgical back-up is not available.
Management strategies are identified for three categories of patients: 1) Those with an incidental AAA; 2) patients with a ruptured AAA who are stable; and 3) patients with an AAA who are unstable.
Incidental AAA. With the frequent use of US and CT scans, AAAs are found in increasing numbers in ED patients who are being evaluated for other disease processes. Furthermore, it is estimated that 50% of these "new," previously undetected aneurysms are small (i.e., < 5 cm), and therefore, the approach to the treatment of asymptomatic aneurysms in this size range is controversial.19
What is not a matter of debate, however, is that symptomatic AAA requires surgical intervention. Therefore, the burden of proof falls on the emergency physician when an AAA is detected; specifically, one must be certain that the patient’s presenting symptoms are not the result of the aneurysm detected in the ED. As mentioned before, appropriate consultation may be necessary to establish this relationship. Once it is confirmed that the AAA is not symptomatic, the patient will need referral to a vascular surgeon. While the ED physician will not be in the position of making the decision of whether to operate, it is important to know the general approach to elective AAA repair taken by most vascular surgeons.
Asymptomatic patients should have serial US to follow growth of the aneurysm. Recent recommendations from a prospective study suggest an interval of one year between US for patients with aneurysms less than 4 cm in size, and every six months for those with aneurysms 4 cm or greater.20 Since coronary artery disease (CAD) is clinically evident in at least 50% of patients with AAAs,19 AMI is one of the most common cause of death during or after surgery for these patients.
To provide clinical guidance for managing these patients, one author has suggested three preoperative classes, or risk categories, for patients that are based on their CAD status. Class 1 patients are those at lowest risk, i.e., without evidence of CAD and normal exercise tolerance. These patients may have elective repair without further cardiac evaluation. Class 2 patients represent individuals with known CAD or those with significant risk factors (diabetes, hypertension, etc.). It is recommended that these patients have a preoperative cardiac evaluation with subsequent catheterization and angioplasty if needed. Class 3 patients have significant CAD and are acutely symptomatic or unstable. He suggests these patients undergo cardiac catheterization for evaluation and treatment prior to elective surgery. Relative contraindications to AAA, as recommended by the Joint Council of the Society for Vascular Surgery, include patients with life expectancy of less than two years, recent MI, severe angina, severe pulmonary insufficiency with dyspnea at rest, severe renal dysfunction, intractable congestive heart failure, and advanced dementia.21 Finally, patients should be given clear discharge instructions concerning who to follow up with and when, as well as specific symptoms that should prompt them to seek immediate medical treatment (abdominal/back pain, GI bleeding, etc).
Ruptured AAA in the Stable Patient. Patients with symptomatic AAA who are able to maintain their cardiovascular status should be treated aggressively. They can decompensate at any time and are likely to give the physician little warning before doing so. Once the diagnosis of ruptured AAA has been established, they should be taken to the operating room as quickly as possible. However, as the mortality for emergency surgery on intact aneurysms is 20-25% compared to 5% for elective repair (primarily from lack of time to address co-morbid conditions), it is not unreasonable for the surgeon to request verification of rupture prior to surgery.21,22
In other words, if a bedside US demonstrates the presence of an AAA in a stable patient, the surgeon may appropriately request CT scan for proof of rupture and delineation of anatomy prior to surgery. Although this maneuver is associated with some risk for the patient, as it does delay time to definitive treatment and the patient has a significant risk for sudden, catastrophic collapse at any point, many surgeons will obtain a CT prior to surgery. The decision must weigh the potential benefits of decreased surgical mortality from improved definition of the case vs. increased mortality from delay of surgery. Accordingly, the ED physician should contact the consulting surgeon as soon as the presence of an AAA is established (even from physical exam) and he or she should be closely involved in decisions from that point on. After the presence of an AAA is established, the ED physician should never send the patient for additional studies (such as CT scan) without surgical consultation.
In addition, the patient should have someone at his or her bedside at all times who is capable of resuscitation while the patient is being transported to the OR should he or she suddenly decompensate. Two large bore IVs should be placed as soon as possible and laboratory tests, such as type and crossmatch (for at least 10 units of blood), hemoglobin and hematocrit, chemistry panel for renal function, coagulation studies, urinalysis (UA), and electrocardiogram (ECG), are all indicated. However, no laboratory test should delay transport of the patient.
Finally, the patient may be hypertensive on presentation to the ED. One may be tempted to treat the blood pressure as in patients with thoracic aortic dissection, and reduce it with beta-blockers and nitroprusside. While it "makes sense" that reducing stress on the aortic wall would help slow or prevent further rupture, this approach has not been shown to improve outcomes in any studies. Furthermore, development of hypotension is a risk and this may confuse the clinical picture. Therefore, antihypertensive treatment is not generally recommended, and should not be initiated without discussion with the consultant.
Ruptured AAA in the Unstable Patient. Patients with ruptured AAA are not considered "stable" until the aorta is cross-clamped in the OR. Consequently, these patients should have a rapid ED course and all delays should be avoided prior to transport to the OR. Emergency surgical intervention is the procedure providing definitive benefits in this patient subgroup. At least one study evaluating patients who were taken to emergency surgery who did not have an AAA rupture found that 75% of these patients still required emergency surgical intervention.23 Use of the MAST (military antishock trousers) suit has been suggested for ED patients with ruptured AAA, but it has not been shown to be beneficial.5 Therefore, general use in the ED is not recommended, but the suit may be helpful while transporting patients to another facility. These patients should have two large bore IVs and/or central IV access initiated as soon as they arrive. At least 10 units of blood should be ordered, as these patients often require a large volume of blood.24 Preoperative hypotension is strongly correlated with risk of death in these patients.25
Patients with ruptured AAA may develop hypotension and tachycardia secondary to blood loss, or from a combination of hypovolemia and depressed cardiac function. Accordingly, the appropriate degree of volume resuscitation in these critically ill patients is debatable. Some argue that preoperative hypotension slows bloods loss and allows clot formation, much as has been suggested in trauma patients with penetrating injuries.26 Giving the patient a large volume of crystalloid can promote a dilutional coagulopathy as well.27 On the other hand, prolonged hypotension in these elderly patients can contribute to end organ problems, such as renal failure and cardiac ischemia. Indeed, most patients who undergo emergent repair of ruptured AAAs die in the early postoperative stage from MI or respiratory or renal failure, which may represent complications of inadequate organ perfusion.24,25
As no studies on varying resuscitation strategies in these patients have been published, there is no blood pressure "number" to aim for when caring for a patient with a ruptured AAA. Adequate blood pressure should be maintained to preserve mental status and prevent cardiac ischemia, and the blood pressure required will vary from patient to patient. Blood products should be used early in the resuscitation efforts in order to reduce dilutional coagulopathy.
Few diagnostic studies are necessary in unstable patients with ruptured AAA. One author reported a significantly increased mortality rate in patients with symptomatic aneurysms who underwent more extensive preoperative evaluation.28 If the physical exam reveals a pulsatile abdominal mass, the patient should be taken to the OR directly. If the physical exam is not diagnostic, bedside US will often demonstrate the presence of an AAA. Documentation of the aneurysm and symptoms consistent with rupture are usually all that is required to take unstable patients to the OR. These patients should not be taken out of the department for any other reason; tests such as CT scan are too risky and time consuming in hypotensive patients. Baseline labs, including chemistry panel, CBC, coagulation studies, UA, and ECG, are all indicated, but none of these values is likely to impact the treatment of the ED patient. Although these patients can be in considerable pain, their low blood pressure usually precludes use of narcotics for pain relief.
At this time, surgery is the only definitive treatment for AAA rupture; endovascular repair currently is being used only in elective repairs. Although the risk of emergent repair remains high (around 50%), without surgery the process is almost certainly fatal.21,29 Even so, debate is under way in the literature as to whether emergent repair should be withheld from certain patients based on risk factors. Several retrospective studies have attempted to identify prognostic indicators for mortality in patients undergoing emergent AAA repair.25,30-34
The following factors have been suggested as preoperative factors that characterize the patient as being in a "higher risk" category: hypotension or shock on admission; age older than 76 years; creatinine greater than 0.19 mmol/L; loss of consciousness after arrival to the ED; hemoglobin less than 9 g/dL; evidence of cardiac ischemia on ECG; history of COPD; and history of transient ischemic attack (TIA) or stroke.30,34 Intraoperative factors affecting survival include increased cross-clamp time, need for a bifurcated graft, presence of saccular aneurysm, and persistent hypotension in the OR.31-33 Postoperative events associated with increased risk include renal failure requiring dialysis, mesenteric infarction, and respiratory failure. The results of these studies vary. One group found that patients with three or more of five selected risks (age > 76, creatinine > 0.19 mmol/L, loss of consciousness after arrival, hemoglobin less than 9 g/dL, or ECG ischemia) had 100% mortality.30 With two factors, the mortality was 72%, and with one it was 37%. This compared to a mortality of 16% with zero risk factors. Based on these results, they suggest that one should consider withholding surgery from the highest risk groups.
On the other hand, another study found that while increased age was indeed a risk factor for death, there was a survival rate of 44% in patients older than 80 years of age operated on in a 10-year period.25 Furthermore, they also reported that 28% of patients who experienced cardiac arrest before surgery still survived repair.25 Therefore, no clear criteria have yet been established for withholding surgery from patients with acute rupture. Currently, the only absolute contraindication to surgery is a competent patient who refuses the procedure, which is not a common occurrence. All patients presenting with AAA rupture should be referred to a vascular surgeon for evaluation; even if he or she initially refuses surgery, the patient may change his or her mind after speaking with the surgeon.
Late Complications of AAA Repair
AAA repair, whether elective or emergent, improves the life expectancy of those who survive the surgery. The five-year survival rate after repair is reported to be 76%.35 However, the presence of CAD or cerebral vascular disease in these patients is correlated with a much lower survival rate of 30-40% over eight years, compared to 60% survival in those without CAD.19 In one series, 60% of patients had either sustained a MI in the eight years since repair or died from complications of their MI.19
Connective tissue disorders associated with aneurysmal disease makes recurrence of a new aneurysm possible. Up to 5% of patients with one aortic aneurysm will eventually develop a new one requiring surgery.19 The most common sites for new aneurysm after repair are above the original graft or in the thoracic aorta. These patients are also at risk for femoropopliteal aneurysms; 5-15% will develop an aneurysm in this location.19 Two other significant complications that the ED physician needs to be aware of are graft infection and aortoenteric fistula. These two complications can occur together, with infection leading to fistula. In one recent series, 38% of patients with aortic graft infection also had a graft-enteric fistula.36 Approximately 3-5% of patients surviving aneurysm repair will experience one of these problems.19
Graft Infection. Symptoms of graft infection can occur soon after repair, resulting from contamination during surgery, or they can occur years later, when they are caused by spread of contiguous infection or hematogenous spread. The infected portion may be localized (most commonly the inguinal section), or it may involve the entire graft.37 As with AAA rupture, the mortality of graft infection is also high. Mortality rates range from 33% in one series of infected grafts without intestinal fistula formation, to 50% in a British series.38,39 Another recent series found that 100% of 24 patients with graft infection alone presented with symptoms of sepsis.40 Infection was suspected in an additional 31% of patients diagnosed with aortoenteric fistula (AEF).
Staphylococcus epidermidis is the most common organism isolated from graft cultures, and is thought to enter as a result of contamination during the healing process or later seeding from skin ulcers at distant sites.39 Presenting symptoms can be divided into two groups of patients: those with sepsis and perigraft infection, and those with graft infection leading to aortoenteric fistula (AEF). Those patients found to be infected with S. epidermidis presented with more subtle symptoms of low grade fever, malaise, elevated erythrocyte sedimentation rate, and elevated white blood cell (WBC) count. Signs of graft infection seen on CT scan include perigraft fluid, gas and soft tissue swelling, or false aneurysm formation.39 A small prospective series comparing CT with indium-labeled WBCs found CT to be more sensitive as a marker for infection.41
Unfortunately, the treatment for aortic graft infection requires not only antibiotic therapy, but also graft excision and extra-anatomic bypass. The bypass is typically performed by the axillofemoral route, and leads to a high risk for lower extremity amputation (5-year limb loss rate of 33%) as some bypasses fail or the patient is not a candidate for this surgery at all.42 Consequently, all patients with a post AAA repair status that includes systemic infections of unknown etiology or those with GI bleeding will need to be evaluated for possibility of graft infection. As will be stressed below, it is wise to assume that the cause of GI bleeding in patients with AAA repair is graft-enteric fistula until proven otherwise. In one series, 75% of patients with GI bleeds were found to have a cause other than an AEF.39 The converse means that 25% of patients being evaluated for GI bleed after AAA repair did have an AEF.
Aortoenteric Fistula. While fistulae can form between an AAA and intestine prior to repair, these are much more commonly seen after aneurysm repair. The most common site of development is between the proximal aortic anastomosis and the distal duodenum, as this is the nearest intestinal structure and it is fixed in the retroperitoneum. However, fistulas can be formed at any site in the GI tract and may cause upper or lower GI tract bleeding.43
Although one could expect the patient to present with massive GI bleeding, the blood loss from an AEF can be acute or chronic, minimal or extensive. As mentioned above, graft infection is thought to be a significant cause of AEF formation. One series of 22 patients with AEF found blood cultures were positive for enteric organisms in 85% of cases.44 The mean interval in their series from surgery to presentation with AEF was 36 months, but AEF has been reported in patients as long as 14 years after surgery.44 A significant minority of these patients (22%) presented with a "herald hemorrhage;"44 i.e., a sudden, brisk bleeding episode leading to hypotension, that ceases spontaneously and is followed by rebleeding hours to days later.
Accordingly, all patients with previous AAA repair and GI bleeding require evaluation for possible AEF. The precise approach depends on the patient’s hemodynamic condition. Unstable patients with limited response to resuscitation should be taken to the OR for exploratory surgery to stop bleeding and identify its source. In stable patients, upper GI endoscopy is the recommended initial test, but it is not 100% accurate and its main value may lie in identifying another cause of bleeding.45 CT scan is also useful, not because it will identify the fistula, but because it can recognize evidence of graft infection. Unfortunately, graft fistulas are only recognized with certainty, at best, 50% of the time, and exploratory surgery is often required in patients with suspected AEF and major GI bleeding to rule-out the diagnosis.45
When identified, an AEF requires high-risk, graft replacement surgery. A recent review suggests that surgery for AEF carries a higher mortality than for graft infection alone; only 25% of patients were alive at 18 months after surgery, compared to 60% surviving graft infection alone.40 Therefore, when a patient with an aortic graft presents to the ED with GI bleeding, consultation with a GI specialist or vascular surgeon is essential to rule-out AEF.
Summary
Patients with AAA are presenting in ever increasing numbers in EDs across the country, due to both an increase in incidence and an increase in the number of elderly patients in the population. Ruptured AAAs account for at least 15,000 deaths per year and represent the 10th leading cause of death in men older than 55 years of age.46 With these increasing numbers, ED physicians will encounter more patients with symptomatic aneurysms, as well as patients with complications of AAA repair.
Patients with AAA have always been a challenge for emergency physicians because these individuals are often unaware of their disease until the sudden, catastrophic presentation of acute rupture. When patients present with AAA rupture, diagnosis of this condition is often difficult. Any patient older than 50 years of age who presents to the ED complaining of back or abdominal pain and has any of the risk factors (family history, hypertension, vascular disease, tobacco use) should be evaluated with either US or CT for the possibility of AAA.
If an AAA is confirmed, consultation with a vascular surgeon will be required to rule-out acute rupture as the cause of the complaints. Ultimately, the take-home message is: 1) remember to look for an aneurysm in patients with risk factors; 2) keep in mind the best approach for care of patients in the three general conditions encountered (incidental finding, stable rupture, and unstable rupture; and 3) do not assume the patient’s complaints are not related to the AAA until proven otherwise. With these points in mind, the ED physician can improve the patient’s chances of survival.
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Physician CME Questions
89. All of the following are advantages of US over CT for emergency department evaluation of patients for possible AAA except:
A. US will show presence of rupture more consistently than CT.
B. Bedside US can be done on unstable patients without interfering with their resuscitations.
C. US is equally accurate when compared to CT in diagnosing presence of an AAA.
D. CT is contraindicated in patients not responding to resuscitative efforts.
90. When managing patients in the ED with newly found AAAs, all of the following are correct except:
A. When an AAA is discovered in an ED patient, the ED physician must be certain the AAA is not the cause of the patient’s presenting symptoms.
B. Appropriate consultation should be obtained in an unstable patient with pulsatile abdominal mass by physical exam after additional tests are obtained to verify the presence of an AAA.
C. Patients with a history of CAD are at higher risk of mortality with emergency surgical AAA repair.
D. At least 10 units of blood should be crossmatched, as these patients often require large transfusion volumes.
91. Angiography for AAA detection:
A. often underestimates the size of the aorta from the presence of mural thrombus.
B. is not useful when suspicion of mesenteric ischemia is high.
C. is contraindicated when the patient has a horseshoe kidney.
D. All of the above
92. When AAAs are discovered as an incidential finding:
A. the ED physician must prove that the patient’s presenting complaints are not because of the AAA.
B. the ED physician should refer patients to a vascular surgeon for follow-up.
C. Both A and B
D. Neither A nor B
93. In management of ruptured AAAs:
A. mortality is higher for elective repair than for emergent repair.
B. patients should be resuscitated to restore and maintain mentation and prevent cardiac ischemia, not to a certain BP number.
C. Both A and B
D. Neither A nor B
94. Which of the following is true?
A. All patients who have had AAA repair who present with GI bleeding need to have evaluation for aortoenteric fistula (AEF).
B. AEFs most commonly arise from aortic graft infections.
C. Bleeding from AEFs is often small and not catastrophic.
D. All of the above
95. In the stable patient with a ruptured AAA, which of the following tests are recommended?
A. Chemistry panel for renal function
B. Urinalysis
C. Electrocardiogram
D. All of the above
96. The most common site for new aneurysm after repair is:
A. above the original graft.
B. in the thoracic aorta.
C. Both A and B
D. Neither A nor B
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