Surgery - EVAR (Endovascular aneurysm repair)





EVAR = Endovascular aneurysm repair

Goal: To insert a stent graft which will act as an artificial lumen for blood flow

  • Takes pressure off the aneurysm wall
  • Aneurysm wall will thrombose in time

Procedure can take 2 to 12 hours

Compared to open aneurysm repairs

EVAR has the advantages of:

  • Less blood loss
  • Complications of laparotomy avoided
  • Complications of aortic cross clamping avoided
    • Balloon would be inflated to deploy the stent, but duration is short

The procedure

Location and operator

Carried out in special theatres with fluoroscope
... by vascular surgeons and/or interventional radiologists

Choice of stents

EVAR can involve different types of stent:

  • Standard
  • Special custom-made stents
    • Fenestrated stents
      • Has fenestrations that allows flow to the side branches
        • i.e. Renal, visceral vessels
    • Branched stent grafts
      • Branches already attached
  • Chimney stent grafts
    • Off-the-shelf covered stents are used
      • Used when custom-made stent is NOT available due to design issue or urgency
    • Involves
      • Stent deployed to the side vessels from left axillary or brachial artery
        • Proximal end goes UP into the aorta
      • Then followed by a conventional stent which goes over the chimney
        • i.e. Chimney stent goes between the aneurysm wall and the conventional stent
    • Allows perfusion of side-vessels

Standard EVAR stent graft

  • Requires 1.5 cm neck length both proximally and distally
    • i.e. landing zone
      • e.g. Distance from the renal arteries to the aneurysm sac
    • To ensure adequate sealing
    • Approx 20% of patient would not have an adequate aneurysm neck
  • Should also have 1.5 to 3 cm clearance from major branches like celiac or left subclavian

Difference between thoracic and abdominal EVAR

Thoracic aortic aneurysm stents

  • Requires adequate proximal and distal neck of 1.5 cm to ensure adequate sealing
  • Conduit vessel needs to be ≥ 8mm diameter
    • Due to the size of the stent-introducer system
    • May need retroperitoneal approach to access aorta or the common iliac artery directly
  • May need slight right decubitus positioning
  • May need to be prepped for left thoracotomy

Abdominal aortic aneurysm

  • Commonly arise inferior to renal arteries
  • 80 to 90% involves either one or both iliac arteries
  • If bilateral iliac arteries involved → Needs two-stage procedure
    • An iliac limb first
    • Then an aorto-iliac module
    • Both femoral arteries will be cannulated

Complications

  • Stent migration
  • Detachment
  • Aortic rupture
  • Stenosis / kinking of stent
  • Blockage of important arteries
    • Organ failure
      • esp renal, gut
    • Spinal ischaemia
      • Higher risk with thoracic stent grafts
      • Paraplegia = 2 to 3%
  • Thromboembolism esp to liver or bowel
  • Infection (< 1%)
  • Endoleaks
  • Blood loss and coagulopathy
  • Femoral artery dehiscence
  • Post-implantation syndrome

Migration

MAP may need to be lowered to 50 to 60 mmHg
... to reduce risk of inadvertent downstream deployment

Rapid deployment also minimises distal migration

Acute kidney injury

➤ Risk factors include:

  • Age > 70 yr
  • DM
  • Cardiac failure
  • Preop eGFR < 60 mL/min
  • Periop dehydration
  • Drugs
    • ACE inhibitors and AIIRAs
    • Aminoglycosides
    • Diuretics
    • NSAIDs
  • Repeated exposure to contrast within 7 days
  • Complex EVAR (fenestrated, chimney, branched)

➤ Prevention:

  • Avoid potentially nephrotoxic drugs
  • Minimise contrast exposure
  • Appropriate fluid therapy
  • Also consider:
    • N-acetylcysteine (NAC)
      • Possible benefit
      • Minimal risk
    • Sodium bicarbonate
      • Reduce contrast-induced nephropathy
      • But have not been shown to reduce mortality ... or unanticipated renal replacement therapy

Endoleaks

Leakage into the aneurysm sac after endovascular repair

➤ 4 different types:

  • Type 1
    • Seal failure at the graft ends
  • Type 2
    • Filling via a branch vessels
  • Type 3
    • Leak through graft fabric ... due to stent graft separation
  • Type 4
    • Porosity of the graft

➤ Implications:

  • Type 1 and 3 endoleak leaves aneurysm at risk ... of continued expansion and rupture
  • Type 2 endoleaks are common (10 to 25%)

Blood loss and coagulopathy

Constant leakage from arterial access sites (instead of acute haemorrhage)

➤ Risk of coagulopathy, due to:

  • Intraop heparin
  • Concurrent antiplatelet agents
  • Inadvertent periop hypothermia

Post-implantation syndrome

➤ S&S:

  • Pyrexia
  • Leucocytosis
  • Elevated CRP
  • NO sepsis

Usually mild and self-limiting

Lasting 2 to 10 days

➤ Rx:

  • Exclude an infective cause
  • Symptomatic Rx with antipyretics and IV fluids