FRCA Notes

Ruptured AAA

Resources

  • The strongest predictors of AAA rupture are maximum diameter and annual expansion rate
  • Once >5.5cm in diameter, the risk of rupture is 12% (men) - 18% (women)
  • Ruptured AAA carries a high overall mortality of 65 - 90%
    • 75% of those with ruptured aneurysms die before reaching surgery
    • Of those who undergo surgery, a further 40 - 65% die

Factors affecting mortality in ruptured AAA

  • Mortality is most closely linked to the degree of pre-operative hypotension
  • Other factors include:
Non-modifiable Modifiable Surgical
Female gender Delayed diagnosis Prolonged surgery
Increasing age Low intra-operative urine output Inexperienced surgeon
Site of rupture (see below)
Pre-operative loss of consciousness (~100% mortality)

  • 88% of bleeds are retroperitoneal and 'contained', which is associated with better outcome
  • 12% of bleeds are intra-peritoneal, aorto-caval or aorto-enteral and are associated with higher mortality

  • A rapid, targeted pre-assessment should take place although the ultimate goal is to provide adequate resuscitation and avoid delays to surgery
  • Priorities include:
    • Rapid diagnosis (if not already)
    • Mobilisation of theatre staff
    • Mobilisation of blood products via major haemorrhage protocol and/or cross-matching 10 units
    • Insertion of wide-bore IV access

Pre-clamp resuscitation

  • There are conflicting views about whether permissive hypotension or aggressive resuscitation in the pre-clamp phase is better
  • Arguments against fluid resuscitation include:
    • Increased BP may cause further haemorrhage
    • Use of fluids causes dilutional coagulopathy, further increasing haemorrhage
    • Further haemorrhage increases need for major blood transfusion and impairs the surgical field

  • Arguments against permissive hypotension include:
    • Longer duration of shock increases risk of cardiac and other major organ complications
    • SBP at presentation is the most important factor influencing survival; SBP ≤90mmHg is associated with a >60% mortality

  • Without definitive evidence either way, short periods of hypotension may be tolerable but any surgical delay should prompt resuscitation with blood (products)
  • Fluid loading with crystalloids/colloids while the cross-clamp is being applied may help reduce post-clamping hypotension

  • Speed is of the essence; the abdomen should be cleaned and draped whilst awake and the surgeons should be scrubbed and ready

Monitoring

  • AAGBI monitoring, as standard
  • Although invasive monitoring will be required, it may be instituted post-cross-clamping and its insertion should not delay start of surgery

Haemodynamics

  • Induction in patients with ruptured AAA may cause cardiovascular collapse due to:
    • Cardio-depressant effects of anaesthesia
    • Reduced tamponade effect following relaxation of abdominal muscles
    • Reduced sympathetic tone
    • Reduced venous return following instigation of PPV
  • Most will use a 'cardio-stable' induction technique, typically one incorporating heavy amounts of opioid and ketamine
  • Naturally these patients are in the throes of major haemorrhage, the management of which is similar to that of other haemorrhagic emergencies

  • Patients will require ITU care post-operatively, although early extubation is preferable

Complications

  • Prolonged periods of hypotension and inadequate perfusion pressures can cause:
    • A global ischaemic insult
    • Lower limb ischaemia; regular lower limb neurovascular observations should take place
    • Intra-abdominal organ ischaemia, particularly kidneys and colon
    • Spinal cord ischaemia

  • Coagulopathy due to major haemorrhage and massive transfusion
  • Hypothermia