Chapter 16 Aortic and vascular emergencies
ABDOMINAL AORTIC ANEURYSM
Abdominal aortic aneurysm (AAA) affects approximately 2% of the population with a peak incidence between 70 and 75 years of age and a significant male predominance. Ninety-five percent of AAAs occur below the level of the renal arteries. The most common life-threatening complications of AAA seen in the emergency department are rupture or threatened rupture.
The risk of rupture increases with aneurysmal size. The 5-year risk is 1–2% when the aneurysm is less than 5 cm in diameter and rises to 20–40% when the diameter is greater than 5 cm.
History, examination
Ruptured AAA typically presents with severe abdominal and/or back pain which may radiate to the groin (thus mimicking renal colic). Examination reveals a patient who looks unwell, with tachycardia, hypotension and an acutely tender abdomen (without guarding or rigidity). A tender, pulsatile abdominal mass is felt in approximately 50% of cases only. Absent femoral pulses and an aortic bruit may sometimes be detected.
Investigation, diagnosis
In the unstable patient, the diagnosis must be made on history, examination and by use of emergency department ultrasound. Misdiagnosis and delayed diagnosis can occur in up to 30% of cases. The differential diagnoses include renal colic, pancreatitis, diverticulitis and acute myocardial infarction.
In the stable patient, imaging will help clarify the diagnosis. CT scanning confirms the diagnosis of AAA including the site, the extent and the presence or absence of rupture. Its disadvantage is the requirement for the patient to move to the radiology suite. Ultrasound is portable, safe and increasingly available in the emergency department. It allows easy diagnosis of AAA but cannot reliably diagnose rupture. Plain abdominal X-ray has a limited role as only 60% of AAA show significant aortic calcification and it cannot detect rupture.
All patients suspected of AAA rupture require bloods for emergency crossmatch (10 units) and estimation of haemoglobin, electrolytes, renal function, troponin and lipase. An ECG and chest X-ray should be performed if the patient is haemodynamically stable.
Management
Management of acute rupture is rapid resuscitation while simultaneously organising immediate surgery. Patients should be monitored in an acute resuscitation area and two wide-bore intravenous cannulae inserted. Resuscitation involves oxygen, crystalloid fluids such as normal saline and early blood transfusion. Universal donor O negative blood may be required. The endpoint of fluid resuscitation is a systolic blood pressure of approximately 90 mmHg in a strategy termed ‘hypotensive resuscitation’. Higher resuscitation blood pressures may increase bleeding and have been associated with worse outcomes in several studies. Incremental doses of IV morphine should be administered to control pain.
Ninety percent of patients with ruptured AAAs die without surgery although the mortality with surgery is still 50%. Surgical options include open repair of the rupture with insertion of a prosthetic graft or, more recently, percutaneous endoluminal repair and stenting.
The management of a painful, non-ruptured AAA larger than 5 cm is urgent surgical repair, as the risk of death from rupture outweighs that of elective repair (10%). Surgery is performed as soon as adequate CT imaging and rapid stabilisation of concurrent medical conditions have occurred.
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