Abdominal, back, and flank pain are some of the more common presenting complaints of patients for whom an emergency physician cares. In such cases, the physician must consider abdominal aortic aneurysm (AAA) in the differential diagnosis.
Competence in evaluating for an AAA is a core emergency ultrasound application as outlined by the 2008 American College of Emergency Physicians Policy Statement on Emergency Ultrasound. Studies demonstrate that emergency physicians are able to perform bedside ultrasound of the abdominal aorta with a high sensitivity and specificity for an abdominal aortic aneurysm.
Clinical Indications for Performing An Aortic Ultrasound Exam
The main indication for bedside aortic ultrasound examination is the rapid identification an AAA.
Patients older than 50 years with the classic presentation of abdominal, back, or flank pain, a pulsatile abdominal mass, and hypotension should have a bedside aortic ultrasound examination.
Pain can be referred to the scrotum, buttocks, thighs, shoulders, or chest, and many patients are misdiagnosed with renal colic, diverticulitis, or musculoskeletal pain. Any patient with unexplained hypotension, dizziness, or syncope should have a bedside aortic ultrasound.
Also consider that patients presenting in cardiac arrest may have a ruptured AAA. Patients with pulseless electrical activity may be in a state of severe hypotension that could be reversed if the cause is rapidly identified and aggressively treated.
Performing an Abdominal Aorta Ultrasound
Patient positioning: Place the patient in the supine position. When bowel gas or adipose tissue prevents adequate visualization, the patient can be placed in the lateral decubitus position. Consider bending the patient’s knees to decrease tension on the rectus muscles.
Anatomic landmarks: The abdominal aorta is a retroperitoneal structure beginning at the aortic hiatus of the diaphragm and then coursing anterior to the vertebral spine before dividing into the iliac arteries. The inferior vena cava (IVC) runs along the right side of the aorta, and sonographically the two structures must be distinguished from each other.
The IVC is thin walled, varies in size with respiration, and may be flattened with minimal pressure by an ultrasound probe. The aorta does not change in size with respiration and is non-compressible, thick-walled, and pulsatile.