AAA_flashcards
Definition
An abdominal aortic aneurysm (AAA) is a permanent dilatation of the aorta, usually in the infrarenal portion, to 1.5 times its normal diameter. A diameter over 3 cm is the accepted threshold.
Major Complication
Rupture of an AAA is the major complication with a high mortality rate. It occurs when the mechanical stress on the wall of the aorta exceeds the wall’s strength, leading to a tear through all the layers of the wall and massive internal haemorrhage.
Risk of Rupture
Risk of rupture increases significantly as the size of an aneurysm increases, for example AAAs under 5.5cm have a 3% risk of rupture per year, compared to a 10% risk in AAAs which are 6-6.4cm and a 33% risk in AAAs which are over 7cm in diameter.
Epidemiology
Prevalence of AAAs is six times as high in men as in women, and so the NHS national screening programme offers all men aged 65 an ultrasound of the aorta. Around 1 in 70 men screened have an AAA; 1.4% of men screened have a small or medium aneurysm; 0.1% have a large aneurysm; Approximately 3000 deaths a year occur due to ruptured AAAs.
Aetiology
Risk factors for AAAs include: Male sex, Older age, Family history of AAA, Hypertension, Smoking, Hyperlipidaemia, Chronic obstructive pulmonary disease (independently of smoking status), Connective tissue diseases. Additional risk factors for AAA rupture include: Larger diameter aneurysms, Rapid expansion (>1cm per year), Saccular aneurysms.
Signs and Symptoms
The classic triad of a ruptured AAA comprises hypotension, sharp and severe flank, abdominal or back pain and a palpable pulsatile abdominal mass (the aneurysm). Other signs include collapse, tachycardia, clammy skin, lightheadedness, lower limb ischaemia, fistulation into other organs e.g. the bowel causing PR bleeding.
Differential Diagnosis
Renal colic, Diverticulitis, Bowel ischaemia, Gastrointestinal perforation - each with specific symptoms distinguishing them from AAA.
Investigations - Bedside Tests
ECG in preparation for surgery and to investigate for arrhythmias. Blood gas to rapidly check haemoglobin, lactate and acid-base status (may be deranged due to haemorrhage).
Investigations - Blood Tests
FBC to check haemoglobin. U&Es which may be deranged due to haemorrhage. Amylase which may be raised in AAA rupture and is considered a poor prognostic marker. Troponin to look for myocardial injury. Clotting screen. Cross-match for blood transfusions.
Investigations - Imaging
Bedside ultrasound to visualise an AAA and evidence of rupture. CT or CT angiography in stable patients to confirm diagnosis and help plan surgical management.
Management - Conservative
Take an A to E approach, ensure wide-bore IV access, keep patients nil by mouth, and transfer urgently to a vascular centre. Palliative management may be considered for patients with significant comorbidities.
Management - Medical
Resuscitation with IV fluids and blood, targeting a systolic blood pressure of 90-120mmHg. Inotropes may be required. Provide adequate analgesia for pain.
Management - Surgical
Emergency surgery required to repair the rupture - this may be with endovascular aneurysm repair (EVAR) or open surgery.
Complications
Distal embolism causing limb ischaemia, Aorto-caval fistulation causing heart failure, Aorto-enteric fistulation causing gastrointestinal haemorrhage, Hydronephrosis secondary to left ureteric obstruction, Death.
Prognosis
Prognosis is very poor if an AAA ruptures, with 80% of patients dying either before reaching hospital or not surviving surgery. Patients undergoing surgical repair have a 50% mortality rate.
