On exam Mr. Jones appears in mild distress. Vital signs are stable. Head and neck are unremarkable. Lungs and heart are normal to auscultation with a well-healed sternotomy from a "Cabbage" he had 15 years ago. His abdomen is rotund with mild, non-focal tenderness without rebound or guarding. You note mild CVA tenderness on the right side. As you finish examining his back, the nurse brings you his urine dipstick results, which are unremarkable except for 1+ hematuria. While you are looking at the UA printout you hear the overhead page that you have a phone call from the PMD of one of your other patients. After the call, you order some labs and a CT-urogram on Mr. Jones. You are about to order him some morphine, but the nurse needs you in room 1 STAT for "a bad trauma". Forty-five minutes later you ask yourself, "Now where was I?" and just as you remember, Mr. Jones’ nurse asks if you can order him "something for pain." You do, but before you have time to see how he is doing, you remember you have a few patients that were waiting not so patiently to be discharged home. It takes you an hour to finally get caught up and recheck your patients. Mr. Jones states his pain is down to a "4" after 5mg of morphine. His labs are normal except for a hemoglobin of 10.4 g/dL and 5-10 RBC’s on his UA. He is next on the CT queue.
About a half-hour later, Mr. Jones’ nurse tells you his blood pressure is 80/40 and he feels nauseated. You ask him to give Mr. Jones a 500cc bolus of normal saline and recheck the BP in both arms to make sure it is accurate. Meanwhile you role the ED ultrasound machine to the bedside and get this image (above). Your patient is starting to look a bit pale and diaphoretic. His nurse tells you that his best blood pressure is now 68/44 and he checked it in both arms. Panic sets in. You ask the secretary to phone the on-call vascular surgeon and the OR and to order 6 units cross-matched blood and two units O-positive blood for Mr. Jones STAT. Just then the radiologist calls to inform you that Mr. Jones has a leaking 6.6cm infra-renal aortic aneurysm. By this time, you are looking a little bit pale yourself. You give the O-positive blood. You convince the vascular surgeon to come in and start to get the patient ready for the OR, but the blood pressure is dropping. His second hemoglobin comes back at 6.2 g/dL. You note new ST-elevation on the monitor. Mr. Jones becomes unresponsive. You shock V-fib and get PEA. You ask for CPR. You intubate. The team does what it can, but it’s too late. You ask the unit secretary to call the family and the PCP while thinking to yourself if only you would have done that ultrasound earlier things might have gone differently.
In this day and age, it is unlikely that an emergency physician will miss the diagnosis of an abdominal aortic aneurysm (AAA). In the rare instance that this occurs, confounding factors often preclude the appropriate work-up and diagnosis (e.g. inability to obtain a CT scan, an extremely atypical clinical presentation, or premature diagnostic closure based on a red herring in the work-up). Making the diagnosis is not the problem; delaying the diagnosis and succumbing to a bad patient outcome has now become the fear that fuels the fire. Pitfalls in management may include sending an unstable patient to the CT scanner instead of to the OR, or allowing a seemingly "stable" patient detract you from advocating for a timely study or intervention when you suspect a AAA. With reasonable suspicion, perform a bedside ultrasound as soon as possible. If your ED has neither a dedicated ultrasound machine that you know how to use or a tech that can be at the bedside in 10 to 15 minutes, you may one day find yourself "behind the eight ball".
Pearls & Pitfalls For Imaging The Aorta
•Use the curved array 2.5 to 3.5 MHz transducer on most patients. If increased patient body habitus prevents adequate visualization, switch to a lower frequency probe for greater penetration.
•Place the probe in a transverse plane just below the xiphoid with the probe indicator directed towards the patient’s right. Make sure the indicator dot on the ultrasound screen is oriented to the left side of the projected image.
•In this view, orient yourself by finding three distinct landmarks: the large, hypoechoic vertebral body casting a dark shadow farfield (posterior), the compressible, thin-walled, almond-shaped IVC near-field (anterior) to the spine on the patient’s right, and the non-compressible, pulsatile, round aorta near-field (anterior) to the spine on the patient’s left.
•Once you find the aorta, maintain a transverse view and begin scanning down the entire length of the aorta from the xiphoid to the umbilicus where it should eventually bifurcate. Visualize the aorta running directly anterior/near-field to the spine along the length of the scan (image 2: AAA Labeled).
•As you scan inferiorly, bowel gas may intermittently occlude your view. Apply gentle pressure to displace the bowel to the left or right until you can clearly visualize the aorta again.
•Remember that the IVC can also appear pulsatile due to its proximity to the aorta. When in doubt, obtain an image that allows you to directly compare both structures side-by-side and utilize color Doppler.
•View the entire aorta in at least two planes: transverse and longitudinal.
•Take your measurements in the transverse plane, outer wall to outer wall. Obtaining measurements in the longitudinal view may lead to underestimation of the diameter if the aorta is visualized tangentially. Normal diameter is up to 2 cm with distal tapering. An aneurysm is defined as a diameter >3 cm or lack of tapering. Any sized aneurysm in a symptomatic patient is an emergency. In an asymptomatic patient, elective surgery is usually considered once the diameter exceeds 5cm.
•Intraluminal clot will appear hypoechoic with a mixed density similar to that of the liver. Vascular calcifications will appear bright white and hyperechoic. Do not be misled by these findings during measurement of the aortic diameter.
•A pulsatile white structure within the aortic lumen may represent a dissection. Aortic dissections propagate into the abdomen in approximately 90% of cases.
•If you can’t find the aorta try starting the longitudinal plane just below the xyphoid, slightly to left of midline.
•Look carefully for sacular aneurysms. If you are not on the lookout for them, they may be easily missed.