1. FOCUSED EMERGENCY ULTRASOUND: EVALUATION OF THE ABDOMINAL AORTA
MARY BETH PHELAN, MD, RDMS
DEPARTMENT OF EMERGENCY MEDICINE
FOREDTERT MEMORIAL HOSPITAL

2. Lecture Objectives
Describe clinical role of bedside ultrasound in screening for AAA
Describe the technique of acquiring sonographic images of the aorta
Describe the sonographic appearance of the normal aorta
Describe the sonographic appearance of AAA
SAEM

3. Case History

4. Case History
A 62-year-old man comes to the emergency department at 11PM complaining of left flank pain for approximately 2 hours. He has a history of hypertension.
His initial vital signs are: HR 98, RR 24, BP 190/105, Temp 98.0.
SAEM

5. Case History
The emergency medicine resident equipped with the latest in emergency medicine ultrasound technology and training, IMMEDIATELY performs an abdominal ultrasound on the patient. This exam reveals the following:
SAEM

6. SAEM

7. Case History
The patient is taken to the OR after only 30 minutes in the ED.
SAEM

8. OVERVIEW Epidemiology Clinical presentation Anatomy US exam
Sonographic anatomy
Scanning techniques
Pitfalls

9. Epidemiology AAA present in 2-4% of the population > 50
Incidence increasing
Male > female
10,000 deaths/yr
Rupture has a > 80% mortality rate

10. Epidemiology: Risk Factors
Cardiovascular disease
Family History increases risk 10-20%
Age > 50
Smoker

11. Clinical Perspective Settings in which to perform US in the ED
Abdominal/back/flank pain and hypotension
Stable elderly patient with abdominal or back pain
SAEM

12. Clinical Perspective Rate of expansion variable
4-4.9 cm AAA has a 3.3% risk of rupture
5cm AAA has a 14% risk of rupture
> 5cm has a 20-40% risk of rupture

13. Clinical Perspective 4cm or less: annual US examinations
Between 4-5 cm: US every 6 months
Greater than 5cm: Elective repair
Mortality rate for elective repair is 5%

14. Clinical Presentation
Highly variable
Classic triad:
Abdominal/Back pain
Pulsatile mass
Hypotension
Less than 1/3 of patients will have the triad

15. Clinical Presentation
Diagnosis
A formidable clinical challenge
Notorious for masquerading as renal colic
May be mistaken for:
Diverticullitis
GI bleed MI
Musculoskeletal back pain
SAEM

16. Clinical Presentation
Stable vital signs
Back or flank pain, left side > right
Testicular or leg pain
Hypertension
Mortality rate same as elective repair

17. Clinical Presentation
Vast majority are retroperitoneal
% intraperitoneal
GI bleeding most often seen in patients with aortic grafts
Mortality 50%

18. Does this patient have an abdominal aortic aneurysm?LEDERLE, JAMA 99
2 groups
Sensitivity of examination for ruptured AAA
Sensitivity of exam with increasing size of AAA
CONCLUSION:Cannot be relied on to exclude AAA

19. Misdiagnosis of Ruptured Abdominal Aortic Aneurysms MARSTON W ET AL J OF VASCULAR SURG 1992
Misdiagnosis= delay >6hr or other diagnosis
Most common physical findings in misdiagnosed group: ABD PAIN, SHOCK, BACK PAIN
Pulsatile mass present more often in correctly diagnosed group

20. SUSPECTED LEAKING ABDOMINAL AORTIC ANEURYSM:USE OF SONOGRAPHY IN THE EMERGENCY ROOM SHUMAN WP, ET AL, RADIOLOGY 88
US IN ED FOR SUSPECTED AAA
1 MIN EXAM
CORRECTLY IDENTIFIED 31/32 AAA
DECISION TO OPERATE BASED ON 3 CRITERIA CORRECT 21/22
DX EXTRALUMINAL BLOOD BY SONOGRAPHY POOR 4% (1/24)
NO FALSE NEG EXAMS

21. Diagnosing AAA Palpation of the abdomen alone Plain radiographs
Computed tomography
ULTRASOUND

22. Diagnosis: PE Absence of mass does not R/O AAA Obesity
Bleeding into retroperitoneum may create doughy abdomen.
Hypotension minimizes pulsations

23. Diagnosis: Plain Radiographs
AAA can be seen in 60-75% of cases
Calcification of aortic wall
Paravertebral mass
Cross table lateral most helpful view
Negative study not helpful

24. Diagnosis: CT Scan Near 100% accuracy
Better demonstration of extent of aneurysm
Will detect complications of the aneurysm
Retroperitoneal blood
Dissection
Drawbacks
Contrast
Patient has to leave the ED
Delays time to diagnosis

25. Diagnosis: US Ultrasound Best test for detection of AAA in the ED
Sensitivity 97% to 100%
Small percentage can not be imaged due to bowel gas
6% in one study
SAEM

26. Diagnosis: US Ultrasound In some studies as accurate as CT
Measurements within 3 mm of surgical specimens
Angiography may underestimate AAA diameter
SAEM

27. Diagnosis: US
Emergency department ultrasound scanning for abdominal aortic aneurysm: accessible, accurate and advantageous
Kuhn et al. Ann Emerg Med 2000
“Relative neophytes can perform aortic ultrasound scans accurately. These scans appear useful as a screening measure in high-risk emergency patients; they may also aide in rapidly verifying the diagnosis in patients who require immediate surgical intervention”
SAEM

28. Diagnosis: US
ED Ultrasound Improves Time to Diagnosis and Survival in Ruptured AAA
Plummer D, et al: Abstract at 1998 SAEM, Chicago, IL.
Average time to diagnosis by bedside US = 5.4 minutes
Average time to diagnosis by CT = 83 minutes
Average time to OR for diagnosis by US = 12 minutes
Average time to OR for diagnosis by CT = 90 minutes
SAEM

29. US EXAM Transducer is 2.5-3.0MHz curvilinear
Place the transducer in the subxiphoid area, using the left lobe of the liver as an acoustic window
Pressure must be applied to displace bowel gas
The aorta must be examined in both the longitudinal and transverse planes

30. Longitudinal Orientation
Marker

31. Transverse Orientation
Marker
Orientation is similar to that of a CT scan
Position probe is perpendicular to long axis of body or to long axis of object that is being studied
Aorta
IVC,Liver
SAEM

32. US EXAM
The aorta appears as an anechoic, pulsatile tubular structure to the left of the spine
After the longitudinal scan, the transducer is rotated 90 degrees to the aorta to obtain transverse views.
The key landmark in the transverse view is to locate the spinal column as a hypoechoic area at the bottom of the screen.
The aorta is located above and to the left of the spine

33. AORTA IVC Left sided structure Thick vascular wall Not compressible
Pulsatile
Right sided structure
Thin wall
Will collapse
“Sniff”
Valsalva
May pulsate from aortic transmission

34. US EXAM Measure from outside wall to outside wall
An aneurysm is identified as any measurement of 3 cm or greater
Measure at:
Epigastric region
Take off of SMA
3-4 cm intervals to bifurcation
Measure any aneurysm

35. US EXAM Obesity or excessive bowel gas may obscure the aorta
A coronal view of the aorta may be a reasonable alternative
The patient is supine
The transducer is placed in the mid-axillary line (probe indicator toward the patient’s head)
The aorta is visualized adjacent to the vena cava

36. SONOGRAPHIC APPEARANCE OF THE NORMAL AORTA: LONGITUDINAL

37. SONOGRAPHIC APEARANCE OF THE NORMAL AORTA: TRANSVERSE
Mid portion
Bifurcation

38. SONOGRAPHIC APPEARANCE OF THE NORMAL AORTA (L LATERAL DECUB/CORONAL)

39. ABDOMINAL AORTIC ANEURYSM
90% of AAA are infra-renal
70% involve the renal vessels
Thrombus is common, and usually forms on the antero-lateral walls of the aneurysm
Two forms
Sacular
Fusiform – most common

40. ABDOMINAL AORTIC ANEURYSM
First sign may be loss of normal taper
AP diameter > 3CM
Focal dilitation even if less than 3 cm
Thrombus
Intimal flap

41. AORTIC ANEURYSM

42. Large fusiform AAA
SAEM

43. AAA with clot
SAEM

44. Another AAA with clot
SAEM

45. ULTRASOUND EXAM: PITFALLS
Bowel gas can be a major problem
Apply pressure
Roll the patient on their left side ( use the liver as an acoustic window)
Does not detect complications of AAA
Retroperitoneal rupture
Dissection
CT/MRI/angiography for stable patients is still recommended

46. Pitfalls in Technique
Failure to acquire high resolution images due to bowel gas
Inaccurate measurements – do not measure what you cannot see!
Distinguishing the IVC from the aorta
Not identifying extraluminal fluid
Failing to distinguish the normal “tortuous” aorta from an abdominal aortic aneurysm.