Abdominal Aortic Aneurysm (AAA): Clinical Findings and Complications AAA = Abnormal, irreversible dilation of a focal area of abdominal aorta (area of aorta between
diaphragm & aortic bifurcation) to twice the diameter of adjacent normal artery segments
Asymptomatic, non-ruptured aneurysm:
Most AAAs are asymptomatic until rupture or days before impending rupture
Asymptomatic AAAs are only detectable on imaging or by palpation
Given their structural weakness, AAAs are at risk of rupture (risk ↑ with ↑ size of aneurysm)
Ruptured AAA: a medical emergency
Aorta lies in between the peritoneal and retroperitoneal space
Symptomatic, non-ruptured aneurysm: rarely, an unruptured AAA can cause symptoms or complications (0.1%-1% of AAAs)
Authors: Olivia Genereux, Davis Maclean, Yan Yu* Reviewers: Jason Waechter*, Amy Bromley*, Sandeep Aggarwal*, Gregory Samis* *MD at time of publication
Posterior aortic wall rupture
Retroperitoneal hemorrhage
Sudden and severe abdominal and/or back pain
Anterior aortic wall rupture
Peritoneal hemorrhage
Peritoneal space is larger and holds larger volumes of blood
Peritoneal hemorrhages are large (entire blood volume can pool in the peritoneal space in minutes)
Prior to rupture, the adventitia (thin outermost collagenous layer of the aorta) may dilate significantly
Adventitia is the only layer of the aorta that contains sensory innervation à nociceptors there can be activated by adventitia dilation
Very rarely (0.1%), areas of stagnant blood flow within the AAA allow for blood & clotting factors to accumulate
Thrombi (blood clots) develop in these aneurysms
Thrombi may dislodge and travel (embolize) to distal vasculature, cutting off blood- flow to these areas
This process (referred to as tamponade) is crucial in preventing catastrophic blood loss, allowing for a window of opportunity for treatment
Compensated Hypovolemic Shock: Low blood pressure &
poor organ perfusion, but blood loss has temporarily stopped. This state of shock is compatible with life if patient is otherwise healthy (e.g. no coronary artery disease)
↓ space for blood to accumulate in the retroperitoneal space (compared to the peritoneal space)
Rapid pressure ↑ in retroperitoneal space overcomes the pressure in aorta
Since blood will only travel from areas of ↑ pressure to areas of ↓ pressure, this pressure gradient prevents further blood loss from ruptured aorta
Massive hemorrhage due to high blood flow volume through aorta
Hypotension and rapid progression to hypovolemic shock
Abdominal and/or àorgan ischemia
back pain
The most common symptom of a symptomatic non- ruptured aneurysm, and may be the first sign of an impending aneurysm rupture
Death within minutes
(rare)
If low blood pressure is now (inappropriately) treated with fluid resuscitation, the blood pressure will ↑
Differential pressure gradient is reversed (aortic blood pressure > pressure in retroperitoneal space)
Bleeding into retroperitoneal space resumes
Decompensation of hypovolemic shock Possible death
Kidney ischemia
Lower limb ischemia
Time exists to transfer patient to tertiary care center for surgical treatment
Legend:
Pathophysiology
Mechanism
Sign/Symptom/Lab Finding
Complications
Re-Published February 28, 2021 on www.thecalgaryguide.com