Abdominal Aortic Aneurysm

Introduction

Abdominal aortic aneurysm (AAA) is a permanent pathological dilation of the aorta with a diameter >1.5 times the expected anteroposterior (AP) diameter of that segment, given the patient's sex and body size. The most commonly adopted threshold is a diameter of 3 cm or more.

Prevalence

More than 90% of aneurysms originate below the renal arteries. Patients are usually asymptomatic and their AAA is detected incidentally.

Management Approach

For AAA detected as an incidental finding, surveillance is preferred to repair until the theoretical risk of rupture exceeds the estimated risk of operative mortality.

Repair Indications

Repair is indicated in patients with large asymptomatic AAA or those with symptomatic or ruptured AAA.

Identifying Symptomatic or Ruptured AAA

Emergency Situation

Rupture of abdominal aortic aneurysm causes a large number of deaths, many of which occur suddenly out of hospital. Even when the patient reaches hospital alive, there is significant mortality. The best chance of survival lies with early diagnosis, prompt resuscitation, and rapid transfer to theatre.

Clinical Suspicion

Think about the possibility of ruptured AAA in people with new abdominal and/or back pain, cardiovascular collapse, or loss of consciousness.

Be aware that ruptured AAA is more likely if they also have any of the following risk factors:

An existing diagnosis of AAA
Age over 60
They smoke or used to smoke
History of hypertension
Female sex (although AAAs are 4-6 times more prevalent in men than women, risk of rupture is greater in women than in men)

The abdomen can be palpated for a pulsatile abdominal mass and abdominal tenderness. Aneurysm palpation on clinical examination has only been shown to be sensitive in thin patients and those with AAA >5 cm, with an overall sensitivity and specificity of 68% and 75%, respectively.

Imaging Technique

Appropriate imaging is crucial for diagnosing AAA and determining the appropriate management approach.

Offer an immediate bedside aortic ultrasound to people in whom a diagnosis of symptomatic and/or ruptured AAA is being considered.

Discuss immediately with a regional vascular service if:

The ultrasound shows an AAA or
The ultrasound is not immediately available or it is non-diagnostic, and an AAA is still suspected.

Consider further imaging with thin-slice contrast-enhanced arterial-phase CT angiography for people with a suspected ruptured AAA who are being evaluated for AAA repair.

Initial Management

Emergency Resuscitation

Prompt and appropriate initial management is critical for patients with suspected ruptured AAA.

Airway management (supplemental oxygen or endotracheal intubation and assisted ventilation if the patient is unconscious).

Obtain venous access with two large-bore venous cannulae.

Send blood for FBC, U&E, glucose, baseline coagulation screen, LFTs, and emergency cross-matching, as per the hospital's massive transfusion protocol.

Give IV analgesia (e.g. morphine titrated according to response).

Provide IV antiemetic (e.g. cyclizine 50mg).

Avoid excessive IV fluid resuscitation. Treat major hypovolaemia, but accept moderate degrees of hypotension (systolic BP >90 mmHg). In general, patients who are conscious and passing urine require minimal IV fluid therapy until theatre.

Ensure blood product (packed red cells, platelets, and fresh frozen plasma) availability and transfusion for resuscitation, severe anaemia, and coagulopathy.

Obtain a CXR.

Insert a urinary catheter and a radial arterial line, and record an ECG.

Call the vascular team early to consider open or endovascular aneurysm repair (EVAR).

Ensure that other relevant staff (e.g. ICU, emergency theatre staff) are informed.

Emergency Transfer to Regional Vascular Services

Appropriate and timely transfer to specialized vascular services is crucial for optimal patient outcomes.

Be aware that there is no evidence that any single symptom, sign or prognostic risk assessment tool can be used to determine whether people with a suspected or confirmed ruptured abdominal aortic aneurysm (AAA) should be transferred to a regional vascular service.

When making transfer decisions, be aware that people with a confirmed ruptured AAA who have a cardiac arrest and/or have a persistent loss of consciousness have a negligible chance of surviving AAA repair.

For people with a suspected ruptured or symptomatic unruptured AAA who have been accepted by a regional vascular service for emergency assessment, ensure that they leave the referring unit within 30 minutes of the decision to transfer.

Emergency departments, ambulance services and regional vascular services should collaborate to:

Provide a protocol for the safe and rapid transfer of people with a suspected ruptured or symptomatic unruptured AAA who need emergency assessment at a regional vascular service.
Train clinical staff involved in the care of people with a suspected ruptured or symptomatic unruptured AAA in the transfer protocol.
Review the transfer protocol at least every 3 years.

Complications

Potential Complications

Complications after AAA treatment can be serious and require careful management.

Immediate Complications

Abdominal compartment syndrome
Ileus, intestinal obstruction and ischaemic colitis
Acute kidney injury
Post-implantation syndrome

Vascular Complications

Amputation due to limb ischaemia
Spinal cord ischaemia
Anastomotic pseudoaneurysm
Aortic neck dilation
Graft infection
Graft limb occlusion
Distal embolisation
Endoleak

Other Complications

Impaired sexual function
Ureteric obstruction
Functional gastric outlet obstruction

AAA Summary

Definition

Risk Factors

Clinical Features

Management

Abdominal Aortic Aneurysm: Diagnosis and Management