Abdominal Aortic Aneurysm
Introduction
An abdominal aortic aneurysm (AAA) is a pathological dilatation of all 3 layers of the aorta to > 3cm. They are generally thought to increase in size by approx. 5 mm per year and risk of rupture is greatest once they are > 5.5cm in diameter. They can be fusiform (entire circumference of the vessel) or saccular (only part of the circumference is involved) and 90-95% are infra-renal in location.
AAA can present to the ED in a variety of ways.
Incidental finding while performing imaging on an ED patient for other reasons
Abdominal, back of leg pain due to acute expansion or a contained leak
Shocked patient secondary to un-contained rupture
Ruptured AAA has a mortality rate of about 80%, including anywhere from 25 - 60% of those patients who undergo emergency surgical repair
Risk factors include;
Male gender
Advanced age
Family history
Hx connective tissue disorders
Marfans disease
Ehlers Danlos syndrome
Smoking
Athersclerotic disease
Clinical Features
The classic triad described in most text books of, abdominal pain, hypotension and a pulsatile abdominal mass is found in <50% of patients with a ruptured AAA
Symptoms
AAA is often asymptomatic prior to acute rupture
Acute onset of epigastric, abdominal or back pain
NB: new back or abdominal pain in the elderly is a AAA until proven otherwise
Sciatica type back pain radiating to the legs
Patients may experience radicular pain secondary to expanding AAA causing pressure on retroperitoneal nerve roots
Collapse / dizzyness associated with rupture
Signs
Hypotension
Tachycardia
Pallor
Tachypnoea
Altered consciousness
Abdominal distension
Presence of a pulsatile abdominal mass
Differential Diagnosis
Ruptured AAA is a life threatening diagnosis. Consider differential diagnoses but the priority should be to rule out AAA first
Ruptured hollow abdominal viscus
Acute MI
Acute Pancreatitis
Acute Biliary Pathology
Ureteric colic
Musculoskeletal back pain
Clinical Investigations
Bedside
Immediate bedside point of care ultrasound looking for a AAA (sens + spec >95%) in trained hands
ECG - looking for other causes
Venous blood gas - low pH and high lactate - shocked patient
Finger prick blood glucose
Laboratory
Group and crossmatch at least 6 units
FBC
U&E
Co-ag
Looking for alternative diagnoses
Amylase
LFT’s
CRP
Radiology
Unstable patients
Convincing clinical scenario and bedside ultrasound is sufficient to take patient to theatre directly
Stable patient
CT angiogram aorta is the gold standard and shows
size
location
any leak
any other complications
Management and Disposition
Initial Resuscitation
Manage in resus
Multiple wide bore cannulas
Activate Massive Transfusion Protocol if patient is shocked
Hypotensive Resuscitation. Aim for systolic BP of approx 80mmHg
Resuscitation fluid of choice is blood
Consider RSI in ED if low GCS and pt is not protecting airway.
Most experienced operator as high risk of arrest at induction.
Specific Treatment
Unstable patient
The priority is not fluid resuscitation but urgent transfer to theatre with a vascular surgeon for operative repair
Patient will need
invasive BP monitoring
central venous catheter
indwelling urinary catheter and urine output monitoring.
None of this should delay transfer to theatre
Stable patient with incidental finding of AAA
refer to vascular surgeon for ongoing surveillance or consideration of operative management depending on size
Symptomatic Treatment
Analgesia as clinically indicated
Keep pt as warm as possible
High flow O2
Disposition
Urgent transfer to theatre for operative repair under a vascular surgeon for patients with a ruptured AAA
Anaesthetics / ICU and the blood bank will need to be urgently notified as their input will be necessary
References
1. Chung J et al. Epidemiology, risk factors, pathogenesis and natural history of abdominal aortic aneurysm. Uptodate.com
2. Cameron et al. Textbook of Adult Emergency Medicine: 5th Edition. Chapter 5.11. Aneurysms.
This blog was written by Dr. Deirdre Glynn and was last updated in October 2020