Abdominal Aortic Aneurysm (AAA)

Author: Michael D. Parsa, MD,Texas Tech University Health Sciences Center El Paso

Editor: Doug Franzen, MD, M.Ed

Last Update: Sept 2019


Case Study

CASE 1:  72 yo male presents to the ED with low back pain and diaphoresis that began two hours ago. He has never had anything like this before and can’t move due to the pain. PMH - MI with cardiac stent two years ago, hypertension and hyperlipidemia. SH- 50 pack-year tobacco history. On exam - HR 118, BP 78/40, appears diaphoretic and in distress due to the discomfort. He has vague diffuse abdominal tenderness with rebound and guarding in the lower abdomen. He denies back tenderness but notes low back pain with movement.

CASE 2:  68 yo male presents to the ED with lower abdominal pain, dysuria and right flank pain with vomiting and fever. Labs and CT are consistent with pyelonephritis. The radiologist also notes a fusiform infra-renal abdominal aortic aneurysm of 4.5cm. There is no free intra-abdominal fluid. He has no prior imaging for comparison.


Objectives

Upon finishing this module, the student will be able to:

  1. Describe the clinical presentation of a ruptured abdominal aortic aneurysm (AAA)
  2. Discuss imaging modalities for diagnosis of AAA
  3. Describe the ED management of ruptured AAA
  4. Determine which patients diagnosed with AAA can be safely discharged


Introduction

Ruptured AAA is fatal unless treated surgically, and even with surgical intervention mortality is approximately 50%. Overall survival is less than 25% as many ruptured AAA patients die before making it to surgery. This is why early diagnosis in the ED is of vital importance.

The most common chief complaints in patients presenting to the ED who are found to have ruptured AAA are abdominal, back, or flank pain. Common misdiagnoses of patients with ruptured AAA include renal colic, pyelonephritis, pancreatitis, bowel ischemia, diverticulitis, appendicitis, bowel obstruction or perforation, GI bleeding, myocardial infarction, and musculoskeletal back pain. 

AAA prevalence increases with age and rises quickly after age 60. Other risk factors include male sex, Caucasian race, tobacco use and atherosclerotic disease. Interestingly, diabetic patients have a lower risk of developing AAA.

An unruptured, asymptomatic AAA may be an incidental finding on CT or ultrasound. If the AAA is <5.5cm, outpatient referral, rather than emergent consultation is all that is required.

AAA most typically are found between the renal and iliac arteries. They can be more superior and the renal arteries can extend from the aneurysm and they can be present in the iliac arteries as well. Mycotic aneurysms can originate anywhere along the aorta and have a unique pathophysiology and are managed differently.


Initial Actions and Primary Survey

Patients with a ruptured AAA will typically be hypotensive, tachycardic and diaphoretic. The cause of their shock physiology is often initially unknown. Resuscitation of these patients is critical while proceeding with a workup for evaluation of their presenting symptoms. The ABCs are always our top priority. Typically in these patients the airway and breathing portions are not compromised, however, circulation will be our greatest concern. Initial management includes starting two large bore IVs and initiating IV crystalloid. While stabilizing the patient, you will need to work to narrow a broad differential.

In the awake and oriented patient it is crucial to obtain an accurate history. Patients  may describe an acute onset of severe pain in the back, flank and/or abdomen. However, since this is visceral pain, it can be quite vague and difficult to localize, so patients may complain of chest, thigh, inguinal or scrotal pain. Pertinent past medical history targeted toward risk factors and comorbidities should also be obtained.

Physical exam can also offer important findings that will help the clinician to establish the diagnosis. Since often these patients are presenting in undifferentiated shock your differential      should remain broad and include all the diagnoses listed in the introduction.

Below are some quick action points in a primary survey:

  • Assessment of mental status: an altered level of consciousness (LOC) may indicate poor cerebral perfusion and may accelerate the need for immediate intervention, such as intubation. 
  • Perform a cardiopulmonary exam:check for signs of cardiac tamponade or pulmonary edema. 
  • Examine the abdomen and back, check for abdominal distention, peritoneal signs, flank tenderness or ecchymosis (may be seen in retroperitoneal hemorrhage) or a pulsatile mass. 
  • Evaluate the extremities, checking for pulses and adequate perfusion. 

A quick bedside ultrasound can also give valuable information. A RUSH exam can evaluate for various causes of shock and includes sonographic views of the aorta. AAA is not difficult to identify with ultrasound with the appropriate training,but can be challenging in an obese patient or with overlying bowel gas. Presence of a >5.5 cm AAA on ultrasound and a hypotensive patient in shock, should confirm the diagnosis of ruptured AAA. Keep in mind that if a AAA has ruptured into the retroperitoneum, there may not be overwhelming free intraabdominal fluid and may only be faintly positive on FAST exam. If the diagnosis of AAA has been made on bedside exam we should expedite further management quickly.


Presentation

The classic presentation of ruptured AAA is abdominal pain, back or flank pain with associated shock physiology. Atypical presentations may include limb ischemia due to thrombosis occluding an iliac or femoral artery, or massive GI bleeding due to an aortoenteric fistula.

AAA can also be an incidental finding on a CT or ultrasound study. If the patient is asymptomatic and the AAA is <5.5cm in diameter, the patient can be discharged with close follow-up with vascular surgery for monitor of the AAA with serial ultrasounds and discussions regarding elective repair.

If a AAA is >5.5 cm in diameter, further consultation with vascular surgery in the ED is warranted. Vascular surgery should also be consulted in the ED if the AAA is unruptured but symptomatic (i.e. abdominal or back pain not explained by other pathology). 


Diagnostic Testing

Imaging: This is the key to diagnosis of AAA.CT is the imaging modality of choice and gives precise details to establish the diagnosis. In an unstable patient, bedside ultrasound can be utilized (such as the RUSH examdiscussed above)should be your initial diagnostic imaging test. If this is inconclusive and the patient has been stabilized, a CT of the abdomen/pelvis with IV contrast can be obtained. If definitive diagnosis by ultrasound cannot be made and the patient is too unstable for CT, we may need to consult general or vascular surgery with the limited information to determine whether the patient should be taken for emergent surgery. Remember that an unstable patient should not be sent for diagnostic imaging before being adequately resuscitated. 

An in depth review of the use of ultrasound in AAA can be found in the Bedside Ultrasound AAA Examination in the CDEM M3 Curriculum. 

Lab: There are no lab tests to establish the diagnosis of ruptured AAA. However, labs will help guide your resuscitation. Labs to consider sending will be the same for this patient as for any patient in undifferentiated shock. Obtaining a blood gas, CBC, CMP, UA, coagulation studies, lipase, troponin and type and crossmatch. In a patient with a ruptured AAA,the blood gas will likely show a metabolic acidosis, the CBC may have a leukocytosis and anemia, the CMP may show azotemia and a low serum bicarbonate level, and a troponin may also be mildly elevated. However, all of these abnormalities may be caused by a wide variety of disease processes and none are specific for AAA.


Treatment

ED management is aimed at resuscitation, establishing the diagnosis and getting the patient to surgery. Shock in ruptured AAA is due to hypovolemia. Hypovolemic shock should be corrected with IV fluids and blood products - transfusion should be initiated in the ED. Do not wait fora crossmatch if the patient is in shock, give uncrossmatched blood. If available, a mass transfusion protocol should be activated. Aim for a systolic BP of 90-100. A BP higher than this may cause clot dislodgement and exacerbate bleeding. Vasopressors should be a last resort.

As soon as the diagnosis is established or strongly considered, emergently consult vascular surgery. Survival is greater when patients get prompt surgery. The standard procedure is an open surgical repair.

Unruptured patients can be managed as discussed above under presentation. Many of these patients can have an endovascular graft placed. This is a procedure done in the interventional radiology suitewith far lower morbidity and mortality than open repair.

Limiting treatment to comfort care may be appropriate in patients with a ruptured AAA who are very elderly and frail or with multiple comorbidities. These patients are unlikely to survive the surgery and honest discussion with the patient and family members regarding the best course of action is important. 


Pearls and Pitfalls

  • AAA should be in the differential diagnosis for any patient over 50 with abdominal, back, or flank pain, especially those with undifferentiated shock.
  • In a patient with a known AAA who develops acute pain, assume rupture is imminent or has already occurred.
  • Perform a RUSH exam to attempt to establish the diagnosis.
  • The patient with a ruptured AAA who is hemodynamically stable can deteriorate at any time.
  • Consider limiting treatment to comfort care under appropriate circumstances.


Case Study Resolution

CASE 1: Two large bore IVs are established, and a one liter IV normal saline bolus is initiated in each arm. His abdominal exam reveals distention with diffuse tenderness and peritoneal signs. A RUSH exam is performed which reveals an infrarenal aortic diameter of 9cm with a large amount of free intra-peritoneal fluid. A massive transfusion protocol is initiated with uncrossmatched blood and urgent vascular surgery consult placed.  The BP is now 94/50. Vascular surgery responds promptly and the patient is taken immediately to surgery for an open surgical repair from which he has a full recovery.

CASE 2: This patient is treated for pyelonephritis and told about the incidental finding of the AAA. He is instructed to follow-up with both his PCP as well as vascular surgery and counseled on the importance of smoking cessation.


References and Further Reading

Carino D, Sarac TP, Ziganshin BA, Elefteriades JA. Abdominal aortic aneurysm: Evolving controversies and uncertainties

Int J Angiol. 2018 Jun;27(2):58-80. doi: 10.1055/s-0038-1657771.

Chaikof EL, Dalman RL, Eskandari MK, et al. The Society for Vascular Surgery practice guidelines on the care of patients with an abdominal aortic aneurysm. J Vasc Surg. 2018 Jan;67(1):2-77.e2. doi: 10.1016/j.jvs.2017.10.044.

Golledge J. Abdominal aortic aneurysm: update on pathogenesis and medical treatments
Nat Rev Cardiol. 2018 Nov 15. doi: 10.1038/s41569-018-0114-9. 

Sakalihasan N, et al. Abdominal aortic aneurysms
Nat Rev Dis Primers. 2018 Oct 18;4(1):34. doi: 10.1038/s41572-018-0030-7.

RUSH protocol link https://www.aliem.com/2013/06/rush-protocol-rapid-ultrasound-shock-hypotension/