PAH EMERGENCY Department Aortic Scanning module Abdominal Aorta Scan is a goal directed ultrasound examination to detect the presence of an Abdominal Aortic Aneurysm (AAA). The Abdominal Aorta scan is a scan of the aorta in both transverse and longitudinal planes such that the aorta is visualised from the diaphragm to the aortic bifurcation. The study should include measurement of the maximum aortic diameter, in two planes. The role of the Abdominal Aorta Scan in the hypotensive patient is to rapidly identify or exclude the presence of an AAA. Becoming Credentialed for AAA Scan in PAH ED To become credentialed to perform AAA Scans independently in the Emergency Department you must: 1) Attend an accredited course 2) Complete the AAA Competency logbook Perform 15 supervised AAA scans - half of which are clinically indicated - 5 positives Ongoing Credentialing Ongoing credentialing within the department is required biannually and involves performing 15 AAA scans, half of which are clinically indicated, including 5 positive scans. Alternatively an accredited refresher AAA scanning course can be attended to meet ongoing credentialing requirements. Accredited Courses Qld Faculty Introductory Ultrasound Course Australian Institute of Ultrasound (AIU) www.aiu.edu.au Australian School of Medical Imaging (ASMI) www.asmi.edu.au Ultrasound Training Solutions (U-T-S) www.u-t-s.com.au Emed Ultrasound www.emedultrasound.com.au
Abdominal Aorta Scanning Like FAST, Abdominal Aorta Scanning is a goal directed examination to detect the presence of an abdominal aortic aneurysm. The examination involves imaging the abdominal aorta from the epigastrium to the aortic bifurcation in both the longitudinal and transverse plane. The sensitivity of ED ultrasound in diagnosing a AAA is 97-100%. 1 The aorta should taper as it travels distally that is it is at its largest as it enters the abdomen through the diaphragm and smallest just prior to bifurcation. An aorta is considered aneurysmal if it is more than 3cm at any point or if there is a focal dilation more than 50% normal calibre. Rupture is more likely in aneurysms greater than 5cm. 1 Most aneurysms are infra-renal. The entire abdominal aorta must be imaged to exclude a AAA. Anatomy of Abdominal Aorta 2
Transverse View of Aorta Starting with the curvilinear probe in the epigastrium. Identify the aorta sitting on the vertebra which you can identify by its bright outline with posterior shadowing. Carefully follow the aorta down to the bifurcation ensuring it tapers uniformly. Take a measurement in the transverse plane of the widest point you have visualised. The measurement should be taken from outer wall to outer wall. vertebra
Longitudinal View of Aorta Turn the probe clockwise 90 0 so it overlies the aorta in the longitudinal plane. It is important in this plane to identify the origin of the SMA. Given the L renal artery reliably arises within an inch of the SMA. It is worth practising taking your longitudinal measurement 3cm distal to the SMA origin. Aneurysm which arise after this point deemed infra-renal ultrasonographically. Coeliac axis SMA vertebrae
Abnormal Scans 6cm AAA in Transverse Plane Same AAA in Longitudinal Plane It is possible to sometimes visualise complications of aortic aneurysms including intramural clot, dissection flaps and haemoperitoneum. Clot True lumen Intramural clot within AAA
Dissection flap Aortic Dissection with visible flap Haemoperitoneum Disadvantages of Abdominal Aorta Scanning o Suboptimal images in some populations Obese Ileus o An aortic ultrasound only tells you if a AAA is present, not if it is responsible for the patient s presentation o Does not adequately visualise retroperitoneal rupture o Operator dependant Tips & Tricks Significant pressure can be required to displace bowel gas and minimise artifact Similarly jiggling the probe can encourage peristalsis and clearing offending bowel out of the image If you are really struggling go back to the beginning and find the vertebrae to orient yourself and start again
Suggested Algorithm for Assessment of the Patient with a suspected AAA Indications for AAA scan 1 Shock Syncope Hypotension Abdominal/Flank/Back Pain AAA present AAA absent Unstable patient Stable patient Urgent Vascular referral & likely OT CT imaging & Vascular Referral Look for alternative causes Further Reading Kuhn M et al. Emergency Department ultrasound scanning for abdominal aortic aneurysm: accessible, accurate and advantageous. Annals of Emergency Medicine 2000; 36 (3): 219-23 References 1. Cameron et al. Textbook of Adult Emergency Medicine 2 nd ed 2008, Churchill Livingstone, Sydney 2. http://www.vascularultrasound.net/abdominal-arteries-and-pelvicarteries