Abdominal aortic aneurysm

Notes

Definition

Abdominal aortic aneurysm (AAA) is defined as an abnormal dilatation of the abdominal aorta with a diameter greater than 3 cm.

It is a relatively common aortic pathology that results in significant amounts of morbidity and mortality. Between 1-2% of men undergoing NHS screening (over the age of 65) will be found to have a AAA. The vast majority are infrarenal (i.e below the origin of the renal arteries).

AAA Facts

Risk factors

AAA may be considered a degenerative condition of the aorta though its aetiology is not fully understood. 

A number of risk factors have been shown to be associated with AAA:

  • Age
  • Male gender
  • Atherosclerotic disease
  • Family history
  • Smoking
  • Hypertension
  • Diabetes
  • Connective tissue disorders

Uncommonly an aneurysm may be secondary to infection, inflammatory diseases or trauma.

AAA

Clinical features

AAA’s are frequently asymptomatic, the presence of symptoms often indicates rupture or impending rupture.

Unruptured AAA’s tend to be asymptomatic. Local mass effect may result in back pain or ureteric obstruction. AAA may be found incidentally on imaging or clinical examination. It may also present due to complications such as distal embolisation.

Ruptured AAA's frequently present with pain, the patient may also exhibit signs of haemodynamic compromise.

Symptoms

  • Abdominal pain
  • Back/loin pain

Signs

  • Hypotension
  • Tachycardia
  • Collapse
  • Pulsatile abdominal mass

Screening

The NHS has introduced screening for AAA for men aged 65 and over in England. It consists of an abdominal USS.

USS is a relatively cheap, non-invasive test with a high sensitivity for detecting AAA. Further management is dependent on the USS findings:

  • < 3cm: No further follow-up required
  • 3cm - 4.4cm: Follow-up with yearly USS and lifestyle modification advice
  • 4.5cm - 5.4cm: Follow up with 3 monthly USS and lifestyle modification advice
  • > 5.4cm: Urgent referral (2 weeks) to vascular surgery

AAA Management

Investigations

AAA may be diagnosed with an abdominal USS or axial imaging.

Bedside

  • Observations/Monitoring
  • ECG
  • Urine dip

Bloods

  • FBC 
  • UE
  • LFT
  • Clotting screen 
  • ABG/VBG
  • Group and Save / Crossmatch

Imaging

  • AXR: Though not a sensitive test an AXR may be ordered in the work-up of a patient presenting with abdominal pain. May reveal a dilated aorta if aortic wall calcification is seen.
  • Abdominal USS: A simple non-invasive test, standard modality readily available in emergency departments. 
  • MRI/CT:  Used for pre-operatively in the elective setting to allow for surgical planning. May be used in the acute setting in suitably stable patients.

Management

Management of AAA depends on the patients presentation, co-morbidities and anatomical considerations.

Conservative

Patients with stable AAA not requiring surgical input should be advised to follow a healthy lifestyle and diet. They should be evaluated for hyperlipidaemia and hypertension and treated if necessary. 

Their AAA should be monitored based on its diameter (see screening chapter above).

Surgical

Open surgical repair has long been the main-stay of management of patients with AAA. Elective surgery is indicated in:

  • Diameter > 5.4cm
  • Symptomatic aneurysms
  • Rapid expansion

Acute rupture represents a medical emergency. Fluid resuscitation / blood transfusion (BP targets vary, many advocate 100-120 systolic) and analgesia are key. Emergency surgery is indicated in suitable patients in acute rupture.

Endovascular Aneurysm Repair

EVAR is a minimally invasive technique that utilises endovascular iliofemoral access to deploy an aortic graft. It may be used either in the elective or emergency setting. It should be noted that the in the draft for the latest NICE guidelines EVAR appears likely to be removed from most clinical pathways.

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