Abdominal Aortic Aneurysm (AAA)
An abdominal aortic aneurysm (AAA) is defined as an aortic aneurysm >3.0cm in diameter.
AAA may present as:
- Symptomatic - ruptured or non-ruptured.
- Asymptomatic - an incidental finding on physical examination or imaging.
AAA should be considered in the patient aged >60 who presents with abdominal, flank or back pain. The symptoms of a ruptured aneurysm may mimic those of renal colic, diverticulitis, gastrointestinal haemorrhage or other intra-abdominal conditions.
Risk factors for developing AAA include:
- Male gender
- Advancing age
- Caucasian race
- Family history of AAA
- Other peripheral artery aneurysm (iliac, femoral, popliteal)
Asymptomatic as an incidental finding
Incidental AAAs found on physical examination or bedside ultrasound should be confirmed by formal ultrasound or CT which may be done as an outpatient.
The management of AAAs found on formal imaging is determined by size:
- 3.0-3.9cm: Refer to GP to arrange for 2-3 yearly surveillance and cardiovascular risk reduction management
- 4.0-4.9cm: Refer to GP to arrange for 6-12 monthly surveillance and cardiovascular risk reduction management
- >4.9cm: Consultation with a vascular surgeon for possible elective repair
Fluoroquinolones should be avoided in patients with known AAA, as they have been shown to increased the risk of aneurysm progression and dissection. See here.
B Pasternak et Al: Fluoroquinolone use and risk of aortic aneurysm and dissection: nationwide cohort study BMJ 2018 Mar 8;360:k678. doi: 10.1136/bmj.k678.
A symptomatic AAA may be ruptured or non-ruptured. A ruptured abdominal aortic aneurysm is a life threatening and time critical emergency. A patient who presents with a symptomatic AAA is at increased risk of rupture. If the diagnosis is suspected, early notification of a surgeon is indicated.
In patients with previous AAA endoluminal repairs the possibility of endoleaks leaks from the graft should always be considered. The risk of endoleak following endovascular aneurysm repair (EVAR) is 24% and they can be detected via postoperative surveillance or after ED presentation. Treatment varies dependent on the type of endoleak.
ED Treatment Summary
Place two large-bore IVs in place for rapid administration of crystalloids, blood, or medication.
As soon as the diagnosis is suspected, consult vascular or general surgery or transfer to an institution capable of emergency repair.
Blood and fluids
Targets unclear; restoring normal blood pressure may worsen outcomes; permissive hypotension, a systolic blood pressure of 80–90 mm Hg, is recommended.14
Level of consciousness (responds appropriately) is another target for volume replacement.15
Avoid severe hypotension and respiratory depression.
Hypertension control in suspected expanding aneurysm and severe hypertension
In the event of suspected expanding aneurysm and severe hypertension, esmolol (half-life, 9 minutes) is recommended for its ability to be titrated to a target systolic blood pressure of 120 mm Hg. Esmolol can be quickly stopped if the patient’s blood pressure drops suddenly.
ED Treatment in detail
Step 1: Pathway Entry
- Pain - abdominal, flank, back
- Less commonly pain may be pelvic or radiate to the thigh or groin
- Pain suggestive of AAA in combination with limb ischaemia
- Shock (if ruptured)
- Pulsatile abdominal mass
- Patient may be known to have an abdominal aortic aneurysm
- Classic triad of severe acute pain, a pulsatile abdominal mass, and hypotension occurs in about 50 percent of patients with ruptured AAA
Less common presentations:
- Fever, malaise, vague abdominal symptoms, which may be chronic-infected AAA
- Chronic abdominal pain and weight loss in association with AAA-inflammatory aneurysm
- DIC-associated with large or extensive AAAs
- Myocardial infarction related to acute blood loss (25% of patients)
- Heart failure, haematuria or massive leg swelling and lower extremity cyanosis without distal ischemia-aortocaval or aortovenous fistula
- GI bleeding-aortoenteric fistula
Risk of aneurysm rupture is increased with:
- Large initial aneurysm diameter (>5.5 cm)
- Current smoking
- Elevated blood pressure
- Greater aortic expansion rate (>0.5 cm/year)
- Female gender
Step 2: Is the Patient Stable?
- In the unstable patient (hypotension, reduced GCS, chest pain), low volume resuscitation is indicated, titrate fluids to alert and orientated around a MAP 65 mmHg and not "normal for patient".
- Activate local institution’s massive transfusion protocol, immediate blood given from "Trauma Pack" or similar source of O-negative blood.
Step 3: Initial Assessment
Obtain a focused history and physical examination. Assess for limb ischaemia. Send bloods for FBC, EUC, Coagulation profile, Cross-match 4 units (meanwhile obtaining O negative or type specific blood if immediate transfusion required). Perform a 12 lead ECG and CXR.
Physical examination has a moderate sensitivity to detect a large abdominal aortic aneurysm. The sensitivity of abdominal palpation increases with aortic aneurysm diameter. Tenderness to palpation of an aneurysm is commonly interpreted as a sign of aneurysmal expansion or rupture. However, a lack of tenderness does not exclude this. It is difficult to identify an aneurysm on physical examination in an obese patient. Very thin patients may have an aorta that is easily palpable, but is not aneurysmal.
Step 4: Imaging
The hemodynamically unstable patient with known AAA who presents with classic symptoms/signs of rupture (hypotension, flank/back pain, pulsatile mass) should be taken emergently to the operating room for immediate control of hemorrhage, resuscitation, and repair of the aneurysm. Imaging confirmation of the presence of AAA in hemodynamically unstable patients suspected but not known to have the disease is ideal prior to intervention but is not required.
Bedside ultrasound has >90% sensitivity for detecting AAAs and is the investigation of choice in the unstable patient. A useful resource has been produced by ACEP and can be accessed here.
The diameter of the AAA is measured between both outer walls at its largest transverse diameter. However a bedside AAA scan will not be able to diagnose rupture. A FAST may be performed to look for intraperitoneal free fluid. The absence of free fluid does not exclude a rupture, as blood may track into the retroperitoneum.
A patient who presents with a symptomatic AAA who is haemodynamically stable should have a CT abdomen. A CT provides anatomical information to aid surgical planning and is able to diagnose rupture or impending rupture. The CT is able to identify other pathologies which may be the cause of symptoms.
Step 5: Risk assessment for AAA repair
Factors associated with poor prognosis following open repair include:
- hypotension with a systolic blood pressure < 90 mmHg
- advanced age (>80 years)
- cardiac arrest
- loss of consciousness
- creatinine >110 umol/L on admission
- ischemic heart disease
- female sex
- Low haemoglobin
The presence of multiple risk factors for poor outcome in a patient of advanced age, especially those with an advanced directive or a history of AAA repair refusal should lead to consideration for comfort care. It is unclear whether endovascular repair decreases mortality in patients with ruptured AAA. A decision must be made according to the wishes of the patient (if known) and family whether to proceed with repair or provide comfort measures.
An interesting article discussing perioperative risk assessment is linked here:
J Vasc Surg. 2009 August ; 50(2): 256–262 Risk prediction for perioperative mortality of endovascular versus open repair of AAA using medicare population.
Step 6: Management
If the decision is made for surgical intervention, the surgeon, anaesthetist and intensivist should be notified. AAAs which have ruptured or are at risk of imminent rupture should have emergent repair, and symptomatic non-ruptured AAAs should have urgent repair. Repair of AAA may be open or endovascular, depending on the patient’s perioperative risk assessment and local surgical expertise. If there is no local surgical expertise to undertake AAA repair, proceed to step 7.
Step 7: Decision for Patient Transfer
For patients who present to a facility where local surgical expertise is not available, transfer is appropriate. The number of general surgeons in the community experienced with open repair of ruptured AAA is declining due to the shift towards endovascular repair of AAAs. If transfer is chosen, the patient and their family should be informed of the risk of deterioration during transfer, and the transfer should be accomplished as soon as possible.
Further References and Resources
BMJ Best Practice - abdominal aortic aneurysm tools
Textbooks and Journal Articles
- Anderson JL et al, 'ACC/AHA Practice Guidelines: Management of Patients with Peripheral Artery Disease (Compilation of 2005 and 2011 ACCF/AHA Guideline Recommendations)', Circulation. 2013;127:1425-1443.
- Tintinalli, Judith E, 'Tintinalli's Emergency Medicine : a comprehensive study guide', 9TH edition, Chapter 59: Aortic Dissection and Related Aortic Syndromes
- J Vasc Surg. 2009 August ; 50(2): 256–262 Risk prediction for perioperative mortality of endovascular versus open repair of AAA using medicare population.
- B Pasternak et Al: Fluoroquinolone use and risk of aortic aneurysm and dissection: nationwide cohort study BMJ 2018 Mar 8;360:k678. doi: 10.1136/bmj.k678.