Elective Open Abdominal Aortic Aneurysm Repair

Airway: ETT
Access: 14G IVC (two) or RIC line, CVC, arterial line.
Pain: Substantial, often in comorbid indivduals. Strongly consider thoracic epidural.
Position: Supine, arms out.
Time: 2-4 hours.
Blood loss: Extensive, with possibility of exsanguination. Cell saver, cross-match at least 4 units.
Special: ICU/ required post-op.

Removal of an aneurysmal aorta and replacement with a synthetic graft. May be:

• Infra-renal
• Supra-renal
  Requires a supra-renal cross-clamp, and therefore is associated with significantly greater peri-operative AKI.

High risk of perioperative morbidity and mortality. Discuss:

• 1-6% perioperative mortality
• Requirement for ventilation post-operatively
• Post-operative respiratory compromise
• Bleeding and transfusion requirement)

Considerations

• B
  • Respiratory reserve
• C
  • Optimise co-existing CVS disease
    • 40% of patients will have coexisting disease
    • Particularly cardiac function and presence of inducible ischaemia
    • Prevent and control SNS stimulation
    • Defend coronary perfusion pressure
  • Invasive monitoring
    • Arterial line pre-induction
    • CVC can be placed post-induction
    • Consider PAC in complex disease
  • Prepare for surgical maneuvers that will affect BP Vasoactives:
    • Vasodilators
      For the cross-clamp phase.
    • Vasopressors
      For the ischaemic wash-out phase.
    • Inotropes
• D
  • Analgesic plan
    Consider thoracic epidural.
  • Spinal cord ischaemia and spine protection
    Thoraco-lumbar portion of the anterior spinal artery receives the majority of its blood supply from the intercostal arteries and the artery of Adamkiewicz, and may be impaired during cross-clamping.
• E
  • Warming devices
    • Upper body warmer
      Do not warm legs during cross clamp - there is a risk of worsening ischaemia, as well as causing burns due to absence of circulation.
    • Fluid warmer
• F
  • Pre-existing renal impairment
    Especially in supra-renal AAA.
• H
  • Rapid transfusion set available

Preparation

• Standard ANZCA monitoring
• 5-lead ECG
• Large-bore IV access
• Arterial line
  Pre-induction, in the arm with the higher pre-operative BP.
• CVC
  Generally post-induction, unless required. Transduce CVP.
• Consider thoracic epidural
  
  • Place at T6-T11
  • Place immediately after IV, to give maximal time for haemostasis prior to intraoperative heparinisation
  • Consider not using immediately, instead only initiating after the ischaemic washout phase is complete.
    Limits haemodynamic instability if haemorrhage is significant.
• Temperature monitoring
• Fluid warming

Induction

Haemodynamically stable induction required:

• Consider
  • Fentanyl
    4-6, up to 10μg/kg.
  • Remifentanil infusion
    0.1-0.3μg/kg/min.

Intraoperative

Surgical Stages

The AAA can be divided into 3 phases:

Pre-Cross Clamp

• Send baseline ABG
• Maintain stable haemodynamics
• Prepare vasodilators
• Draw up heparin
  100 U/kg.

During Cross-clamp

• SVR ↑, leading to an ↑ in BP
  BP typically ↑ 7-10% during cross clamp.

  • Begin vasodilators immediately prior to crossclamp
  • Magnitude of this effect is reduced if occlusive aortoiliac disease is present
    As SVR is already high prior to clamping.

• VR reduces as ischaemia of lower limbs occurs.

• Maintain MV to induce respiratory alkalosis

• Optimise circulation:

  • Give volume
  • Prepare vasopressors
  • Avoid negative inotropes

• Protect renal function

  • Some surgeons will request mannitol 0.25-0.5g/kg prior to cross-clamp

• Ensure lower limbs are not actively warmed

Post-Cross Clamp

Ischaemic washout of lower limbs occurs, leading to haemodynamic instability due to:

• Immediate fall in SVR
  ↑ size of arterial tree.

• Relative hypovolaemia
  ↑ size of venous bed.

• Myocardial irritation
  Metabolic waste irritating the ventricles.

• Aim to release one limb at a time, reducing instability Consider:

  • Volume
  • Vasopressors
  • Reduce anaesthesia

Postoperative

ICU or HDU:

• One or the other is required
  
• HDU acceptable if the patient can be extubated

Post-operative complications:

• C
  • Major bleeding
  • Abdominal compartment syndrome
    Incidence relates to blood loss volume.
  • MACE
    ~7%.
• D
  • Stroke
• F
  • AKI
• G
  • Mesenteric ischaemia

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References

1. Al-Hashimi M, Thompson J. Anaesthesia for elective open abdominal aortic aneurysm repair. Contin Educ Anaesth Crit Care Pain. 2013;13(6):208-212. doi:10.1093/bjaceaccp/mkt015