Abdominal aortic aneurysm

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Background

  • Infrarenal diameter >3cm or >50% increase in size of diameter
    • 98% of cases are infrarenal
  • M to F ratio is 4:1
  • Rupture Risk
    • <4cm: low risk for rupture
    • 4-5cm: 5 year risk 3-12%
    • >5cm: 25-41%
    • Rupture possible at any size, most commonly >5cm

Risk Factors

  • Smoking
    • Risk factor most strongly associated with AAA
    • Also promotes the rate of aneurysm growth
  • Age (prevalence is negligible in age <50yrs)
  • Family history
  • Hypertension
  • Diabetes mellitus
  • Hyperlipidemia

Clinical Features

  • Classic triad is pain + hypotension + pulsatile mass
    • Pain often described as sudden, severe, radiating to back
  • Syncope (10%)
  • Signs of Retroperitoneal hemorrhage
  • Massive GI bleed from erosion into intestines
  • Pain + AAA = rupture until proven otherwise
  • Acute abdomen + hypotension = possible rupture
  • Gross Hematuria can be caused by an aortocaval fistula (very rare)

Differential Diagnosis

Diffuse Abdominal pain

Lower Back Pain

Evaluation

AAA
  • Ultrasound
    • ~100% sensitive for increased diameter
    • Cannot reliably visualize rupture
  • CT
    • ~100% sensitive for increased diameter and rupture
    • IV contrast is preferred but not essential

Management

Rupture

  • Do not waste time in ED trying to "stabilize" patient
  • Immediate surgery consultation/ go to OR
  • Crossmatch 6 units of pRBC
  • Pain control (avoid hypotension)
  • Antihypertensives (use with caution, goal SBP 110-120 mmHg or MAP 70-80)[1]
    • Labetalol: 20mg IV, then 40-80mg IV q10 min (max 300mg)
    • Esmolol: Bolus 500 mcg/kg, then 50-200 mcg/kg/min
    • Nitroprusside: 0.3 - 0.5 mcg/kg/min, titrate to max 10 mcg/kg/min
  • Controversial
    • Too little (ischemia), too much (increased bleeding)
      • Consider allowing for permissive hypotension (SBP 80-100) in conscious patient
    • Pressors
      • Norepi 0.05mcg/kg/min IV; titrate by 0.02mcg/kg/min q5min
      • Phenylephrine 100-180mcg/min; titrate by 25mcg/min q10min
      • Dopamine 5mcg/kg/min; titrate by 5mcg/kg/min q10min

Asymptomatic

  • Prompt vascular surgery outpatient follow-up appt
  • Screening frequency:
    • 3-4 cm diameter: 12 months
    • 4-5 cm diameter: 6 months
    • 5-6 cm diameter: 1 month
  • Elective Surgery indicated if:
    • AAA > 5.5 cm in men
    • AAA > 5 cm in women
    • increase in size > 1 cm/year
    • increase in size > 5 mm/6 months

Complications

Disposition

  • Admit to OR in cases of ruptured OR
  • Vasc surgery follow up in asymptomatic cases

References

  1. Reed, K. Aortic Emergencies, EB Medicine. 2006.