Abdominal Aortic Aneurysm
These are the commonest form of arterial aneurysm, and occur in 2-10% of patients
over the age of 50, with a 5:1 male:female ratio
It’s defined as a prolonged abnormal dilatation of the artery to greater than 1.5 times
its normal diameter (in an adult, normal diameter is 2cm). 95% are due to
atherosclerotic disease.
They can be fusiform (diffusely dilated) or saccular (like a berry aneurysm) most
commonly. 95% are infrarenal and 30% will also involve the iliacs. This is thought to
be due a decreased elastin content in the arterial wall as you move away from the
heart.
The aorta is retroperitoneal, located just to the left of midline (left of the IVC).
Important branches include:
- Paired visceral – supra-renal, renal and gonadal
- Unpaired visceral – coeliac, SMA, IMA
- Paired somatic – inferior diaphragmatic, numerous lumbar spinal
- Unpaired somatic – median sacral
Risk Factors
- Smoking
- HTN
- Hyperlipidaemia
- COPD
- Age
- Gender
- Collagen disorders
- Family history
Presentation
Can be found incidentally on abdominal US, on CT or calcifications may be seen on
x-ray
While 75% are asymptomatic, symptomatic AAA will present with:
- Deep, boring abdominal pain, radiating to the back, or may be solely back pain
- May be aware of an abdominal pulsation
The other presentation is either due to rupture, or from a complication – e.g. embolic
disease of the lower limb (ischaemic leg, trash foot)
With a rupture they will have:
- Sudden collapse
- Nausea & vomiting
- Abdominal pain
- Pulsing sensation in the abdomen
- May have signs of shock
- Abdominal rigidity
- Abdominal mass
- Tachycardia
- Bruising in the flanks
- Check peripheral perfusion as an indicator of status and check distal pulses
If a patient makes it to hospital with a rupture there is still a 50% mortality rate
Very rarely, patients may present with symptoms of local compression
Differential diagnosis of a rupture
-
MI
Perforated DU
Pancreatitis
Renal colic
Mesenteric ischaemia
Indications for surgery
-
Aneurysm >/= 5.5cms in men (>/= 5cm in women), with or without symptoms
Aneurysm < 5.5cms which is symptomatic
Any rupture
4cm aneurysm has a 10% 5yr rupture risk
8cm aneurysm has an 80% 5yr rupture risk
Investigations
-
FBC – look for low Hb
U&E – check renal status
Amylase
Group and cross-match - 6 units
Coags
Urinalysis
ABG (if there’s time)
ECG +/- cardiac enzymes
Erect CXR
CT – only if stable (they might die inside if they’re not)
If you’re comfortable with the diagnosis, call ahead to theatre
Acute treatment
-
-
IV access and fluids – keep systolic below 100mmHg – if the patient has
formed a temporary clot around a rupture, raising their BP could make them
blow it off. Hypotension will keep them alive!
Urinary catheter
Oxygen
May need central line
Arterial line if you have time
Try to get consent
In the emergency situation an open AAA repair is indicated. In elective cases, an
EVAR may be more appropriate
Open AAA repair
This is done by a midline laparotomy using a PTFE (polytetrafluoroethylene) graft or
a Dacron graft, which is stitched into the artery. The graft may be bifurcated to treat
iliac disease as well. Important medications during surgery are antibiotics at induction
and heparin when the aorta is clamped.
Early complications:
- Bleeding
- Infection – wound, intra-abdominal, graft and LRTI
- Ileus – most will have an ileus for up to 48 hours due to handling of the bowel
- 15% will have a cardiac event of some sort
- Mesenteric ischaemia
- Lower limb ischaemia
- Renal impairment
- Paraplegia – due to damage to some spinal arteries – this is more common in
emergencies
- Stroke
Late complications:
- Graft rupture or leak
- Erectile dysfunction – due to sympathetic nerve damage
- Rarely there can be a fistula between the graft and the bowel causing massive
haematemesis
There is no follow up required with open repairs.
EVAR
This is pretty much the same idea as above except – uses a graft to bypass the
aneurysm. The differences are that:
- The access is through the femorals – if the iliacs are very diseased, EVAR
may not be possible due to the size of the deployment devices. Also, can’t do
if very tortuous iliacs.
- Both femorals have to be cannulated
- The graft isn’t stitched in, it’s just deployed
- It can be done under spinal
- Isn’t rarely used in emergencies
Advantages of open repair
-
Less follow up
Available to more patients
Longer follow up research data
Advantages of EVAR
-
Doesn’t need a GA
Don’t clamp the aorta
Less invasive – no post-op ileus
Less post-op pain
Less ICU time
Can be used in riskier patients – i.e. those who may be unsuitable for open
surgery
Disadvantages of EVAR
-
No long-term data about the longevity of the operation
The graft can migrate
The patients require serial CT to watch for endoleak – because the graft isn’t
stitched in, blood can leak around into the aneurysm
Mr McGreal’s notes
Mortality rate in ruptured AAA
- 90% in the community
o If don’t die immediately, will bleed retroperitonealy and become
hypovolaemic. This will cause the bleeding to stop.
Management: patient should be minded, kept calm, oxygen,
and don’t give fluids. Hypotension will keep the patient alive!
- 50% if make it to hospital
The big causes of death in general surgery are ruptured AAA and big GI bleed.
Risk of rupture depends on
- diameter
- sex – women are actually more likely to rupture an aneurism at a smaller
diameter. Hence, in men repair AAA when >5.5cm, but in women when >5.
Mortality of EVAR – 1-2%
Mortality of open repair – 5%
Why do patients die after repair? – renal failure, MI, pneumonia, bowel ischaemia,
graft infection (1%)