Abdominal aortic aneurysm

Background

• Infrarenal diameter >3cm or >50% increase in size of diameter
  • 85% 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
  • Mortality with rupture: 85-90%

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

• Abdominal aortic aneurysm
  • Aortocaval fistula
• Acute gastroenteritis
• Aortoenteric fisulta
• Appendicitis (early)
• Bowel obstruction
  • Large bowel obstruction
    • Ogilvie's syndrome
  • Small bowel obstruction
• Bowel perforation
• Gastroparesis
• Diabetic ketoacidosis
• Inflammatory bowel disease
• Mesenteric ischemia
• Pancreatitis
• Peritonitis
• Sickle cell crisis
• Spontaneous bacterial peritonitis
• Volvulus

Lower Back Pain

• Spine related
  • Acute ligamentous injury
  • Acute muscle strain
  • Disk herniation (Sciatica)
  • Degenerative joint disease
  • Spondylolithesis
  • Epidural compression syndromes
    • Spinal cord compression (non-traumatic)
    • Cauda equina syndrome
    • Conus medullaris syndrome
    • Epidural abscess (spinal)
    • Epidural hematoma (spinal)
  • Spinal fracture
  • Cancer metastasis
  • Spinal stenosis
  • Transverse myelitis
  • Vertebral osteomyelitis
  • Ankylosing spondylitis
  • Spondylolithesis
  • Discitis
• Renal disease
  • Kidney stone
  • Pyelonephritis
  • Nephrolithiasis
• Intra-abdominal
  • Abdominal aortic aneurysm
  • Ulcer perforation
  • Retrocecal appendicitis
  • Large bowel obstruction
  • Pancreatitis
• Pelvic disease
  • PID
• Other
  • Retroperitoneal hemorrhage/mass
  • Meningitis

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)
  • 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
    • Norepinephrine 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
  • Endovascular (75%) vs open repair
• 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

• Aortoenteric fistula
• Aortocaval fistula
• Inflammatory abdominal aortic aneurysm
• Acute limb ischemia - embolism to lower extremities

Disposition

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

References

Authors

Ross Donaldson