Mount Carmel Health Partners Clinical Guidelines Abdominal Aortic Aneurysm | Page 3

Diagnostic Imaging
Patients with suspected AAA generally require immediate imaging. CT scanning without contrast, recommended by some as the first
diagnostic test in the evaluation of a potentially ruptured AAA, may be used as a confirmatory test after ultrasound (US) has been
performed, either in the ED or by radiology when the patient is stable.
In unstable patients, focused ED bedside US permits continued resuscitative efforts, without the need to transport patients out of the ED.
Ultrasound findings consistent with an AAA include an enlarged abdominal aorta greater than 3 cm (i.e., a 50% increase in its normal
diameter) or focal dilatation of the aorta. When there are no contraindications, contrast-enhanced CT scanning is useful in identifying the
entire aorta, the retroperitoneum, and the branch and end arteries, which allows for surgical planning. US is insensitive for retroperitoneal
bleeding from rupture, and its sensitivity in detecting extraluminal blood flow is as low as 4% in some studies. AAAs typically rupture into
the retroperitoneum and are best diagnosed with a CT scan.
MRI has high accuracy and provides excellent anatomical detail, but MRI availability and the stability of patients often preclude its use.
Vascular Surgery Considerations
For intact AAAs, aneurysms greater than 5.5 cm in diameter warrant surgery. Those less than 4 cm are followed with regular imaging. The
AAAs that are between 4 cm and 5.5 cm in diameter are in an ambiguous zone for surgical intervention and thus need urgent evaluation by
a vascular surgeon. Many institutions use a cut-off of 5 cm for vascular surgery evaluation.
Elective surgery is recommended due to the risk of rupture if the AAA is greater than 5.5 - 6.0 cm in men or greater than 5.0 cm in
women, or if diameters between 4.5 and 5.9 cm increase greater than 1 cm/year, or for any increase in diameter over 5 mm in any
6-month period (regardless of initial or baseline size). A recommendation for early elective repair may also be made in patients with a
familial history of AAA, local outpouchings of the aneurysm, or eccentric or saccular aneurysms.
Abdominal Aortic Aneurysm Management
Symptomatic AAA Management:
The most critical management step is notifying the surgical and anesthesia team, especially if the patient is hemodynamically unstable.
Large bore IV access (x2) should be established and blood sent for cross match. Attempts to resuscitate a hypotensive patient with fully
normalized vital signs in the ED should be avoided and patient should be taken to the operating room or endovascular suite immediately
if leaking or ruptured aneurysm is suspected with minimal diagnostic testing.
Preoperative hypotension is a strong predictor of mortality in patients with a ruptured AAA; correction of hypotension before the aorta
is clamped may not improve mortality and may even be harmful. Hypotension may slow the bleeding in patients with AAA and allow
local clot formation and tamponade of the rupture site. Raising intravascular volume and blood pressure before occluding the aorta may
dislodge clots and cause further bleeding. Large volumes of crystalloid solution may contribute to further bleeding by causing a
delusional coagulopathy. Blood pressure should be raised with crystalloid or blood products to a level that maintains adequate cerebral
and myocardial perfusion with a reasonable target of a systolic blood pressure of 90 to 100 mmHg. Patients with a leaking or ruptured
AAA rarely present with hypertension induced by pain or associated with chronic hypertension; no evidence exists that lowering the
blood pressure is beneficial; lowering the blood pressure puts the patient at risk for developing precipitous hypotension.
Asymptomatic AAA Management:
In asymptomatic patients, the surgical risk of complications from endovascular or open AAA repair is greater than the risk of rupture
until the aneurysmal diameter exceeds 5.5 cm. Aneurysms of 5.5 cm or greater are associated with a high risk of rupture and therefore
surgical intervention is generally recommended. The 2009 guidelines from the Society for Vascular Surgery recommend observation for
asymptomatic AAA less than 5.5 cm in diameter. Other factors may influence the timing of AAA repair which includes coexistent
peripheral artery disease, advanced age, ongoing smoking, rapid aneurysm expansion rate, or additional peripheral artery aneurysms
such as iliac or femoral aneurysms.
A small (<4.0 cm) or medium (4 to 5.5 cm) AAA that expands ≥0.5 cm over six months at follow-up is considered to be at high risk for
rupture. A small to medium-sized AAA (less than 5.5 cm) expands at an average rate of 2 - 3 mm/year, while larger aneurysms expand
at approximately 3-4 mm per year. Aneurysm expansion tends to be more rapid for smokers and it has been estimated that smoking
increases the aneurysm expansion rate 20 - 25 percent per year. Comparatively, expansion occurs less rapidly in patients with diabetes
mellitus or peripheral artery disease.
(continues next page)

Abdominal Aortic Aneurysm - 3