REBEL Core Cast 82.0 – Abdominal Aortic Aneurysm

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Definition: An abdominal aortic aneurysm (AAA) is localized dilation (> 3 cm) of the aorta caused by a weakening involving all three layers (intima, media and adventitia) of the aortic wall. It most commonly develops distal to the renal arteries.

Epidemiology: 

• Uncommon in patients < 50 yo
• Found in 2-5% of men > 50 yo
• It is more common:
  • In men than women
  • In patients with coronary artery disease (CAD) or peripheral arterial disease (PAD)
  • Patients with a family history of AAA
  • Smokers
• Up to 50% of AAA in patients < 65 occur in women
• Mortality
  • 30-40% with open aortic repair
  • 20-25% with endovascular repair

Presentation

Unruptured Aneurysm

• Signs and Symptoms
  • Most AAAs are asymptomatic until expansion or rupture occurs
  • Pain is a common symptom when symptoms are present
    • Abdominal, back and/or flank pain
    • Acute pain associated with a AAA can mimic renal colic
    • Acute pain may be an ominous sign of impending rupture
• Physical Exam
  • Large aneurysms may be found on routine abdominal examination as pulsatile abdominal masses
  • May be limited secondary to patient body habitus and size of aneurysm
  • Abdominal bruits are uncommon findings
• Complications of unruptured AAAs
  • Thromboembolic: lower extremity ischemia
  • Direct compression of adjacent structures (duodenum, ureters etc)

Ruptured Aneurysm

• Classic Triad: Pain, hypotension and a pulsatile abdominal mass. Often will only see one or two features of the triad
• Symptoms
  • Pain is the most common symptom
    • Abdominal, back and/or flank
    • Typically acute in onset, severe and can radiate to the chest, back or groin
    • Acute onset of pain in a patient with a AAA should be assumed to be secondary to rupture
  • Syncope (or near-syncope) is common though hemodynamic compensation may result in near-normalization of blood pressure
• Physical Exam
  • Large, palpable abdominal mass
  • Aortic pulsation may be felt (may be absent if blood pressure is low)
  • Hypotension
    • Seen in 50% of ruptures on presentation (Gaughan 2009, Rose 2001)
    • Late finding suggestive of impending hemodynamic collapse and death
  • Tachycardia may be variably present
    • Many patients are on beta-blockers at baseline
    • Blood in the abdomen can stimulate vagal responses leading to lower than expected heart rate
• AAA Variants
  • Aortoenteric fistula
    • Definition: AAA rupture into the GI tract that can be either primary (from an unrepaired AAA) or secondary (after prior aortic repair)
    • Consider diagnosis in any patient with a known AAA or prior repair who presents with GI bleeding
    • Can see both hematemesis and melena as the aortoenteric fistula commonly connects the AAA to the duodenum
    • Patients will typically experience rapid, massive exsanguination. Aortoenteric fistula has a very high morbidity and mortality
  • Aortocaval fistula
    • Definition: Periaortic inflammation leads to a connection between the AAA and the adjacent vena cava.
    • Free rupture of the AAA will present in same way as any ruptured AAA
    • Formation of a large arteriovenous (AV) fistula may occur if there is no external AAA leak
    • Signs and Symptoms (Cinara 2005)
      • Palpable mass (80-90%)
      • Abdominal bruit (75%)
      • Palpable thrill (25%)

Differential Diagnosis

• Aortic Dissection
• Ureteric Colic
• Pancreatitis
• Intestinal ischemia
• Bowel obstruction
• Diverticulitis

Diagnostics

• Patients with ruptured aneurysms will often be diagnosed based on clinical presentation alone.
• Ultrasound (INSERT IMAGES HERE)
  • Sensitivity for detecting AAA approaches 100% (Lederle 2003)
  • Detection of AAA rupture
    • Presence of free intraperitoneal fluid confirms rupture
    • Rupture may be retroperitoneal or small leading to a false negative US for free fluid
  • Advantages
    • Allows for rapid evaluation of the aorta as a cause for shock in the undifferentiated patient while resuscitation is ongoing
    • Obviates the need for the patient to be transported to the radiology department for imaging
    • Can provide alternative explanations for the patient’s presentation
  • Limitations
    • Prone to both technical (ultrasonographer skills) and interpretive error
    • Visualization of the aorta can be limited by obesity or the presence of bowel gas
    • Not as sensitive for detecting rupture
• CT Scan
  • Abdominal CT has a sensitivity and specificity approaching 100% for both diagnosis of AAA as well as rupture (Hermsen 2004)
  • Addition of IV contrast can delineate the patent lumen of the AAA from the mural thrombus but is not necessary for identification of aneurysm or hemorrhage
  • More sensitive than US for detecting retroperitoneal hemorrhage of AAA
  • CT also helpful in identifying alternative diagnoses

Management

Regardless of vital signs, patients with ruptured AAA should be considered unstable and should be aggressively resuscitated. A ruptured AAA has a mortality rate > 80%. (Adam 1999)

Basics: ABCs, Large bore (> 16 gauge) IV X 2, Supplemental O₂ (if needed), Cardiac 

Monitor + Immediate Surgical Consultation for repair

Aggressive Volume Resuscitation in Hypotensive patients

• Target systolic blood pressure of 90-100 mm Hg pre-operatively
  • Exact target unknown
  • Over-resuscitation may contribute to increased bleeding from dilutional coagulopathy
  • Under-resuscitation harmful as prolonged hypotension can lead to end-organ damage (myocardial infarction, renal failure) and cardiac arrest
• Start with administration of uncrossmatched blood
• Activate massive transfusion protocol as patients often have large transfusion requirements
• Consider administration of a 1:1:1 (PRBC:FFP:Platelets) ratio of blood products
• Administer reversal agents for anticoagulant use if indicated

Take Home Points

• Consider ruptured AAA in patients (especially those > 50 years of age) with unexplained hypotension, back or abdominal pain
• All ruptured AAAs should be considered unstable regardless of vital signs as rapid deterioration is common
• A ruptured AAA is 100% fatal without surgical or endovascular intervention. Mobilize your surgical colleagues early

Read More

• Bessen HA, Poffenberger CM: Abdominal Aortic Aneurysm, in Marx JA, Hockberger RS, Walls RM, et al (eds): Rosen’s Emergency Medicine: Concepts and Clinical Practice, ed 8. St. Louis, Mosby, Inc., 2010, (Ch) 86: p 1129-1140.

References

1. Adam DJ et al. Community and hospital outcome from ruptured abdominal aortic aneurysm within the catchment area of a regional vascular surgical service. J Vasc Surg 1999; 30:922-928. PMID: 10550191
2. Cinara IS et al: Aorto-caval fistulas: A review of eighteen years experience. Acta Chir Belg 2005; 105:616-620. PMID: 16438071
3. Gaughan M et al. Emergency abdominal aortic aneurysm presenting without haemodynamic shock is associated with misdiagnosis and delay in appropriate clinical management. Emerg Med J 2009; 26:334-339. PMID: 19386866
4. Hermsen K, Chong WK. Ultrasound evaluation of abdominal aortic and iliac aneurysms and mesenteric ischemia. Radiol Clin North Am 2004; 42:365-381. PMID: 15136022
5. Lederle FA: Ultrasonographic screening for abdominal aortic aneurysms. Ann Intern Med 2003; 139:516-522. PMID: 24957320
6. Rose J et al. Ruptured abdominal aortic aneurysms: Clinical presentation in Auckland 1993-1997 ANZ J Surg 2001; 71: 341-4. PMID: 11409018

Post Peer Reviewed By: Salim R. Rezaie, MD (Twitter: @srrezaie)