FOCUSED EMERGENCY ULTRASOUND: EVALUATION OF THE ABDOMINAL AORTA

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FOCUSED EMERGENCY ULTRASOUND EVALUATION OF THE
ABDOMINAL AORTA

• MARY BETH PHELAN, MD, RDMS
• DEPARTMENT OF EMERGENCY MEDICINE
• FOREDTERT MEMORIAL HOSPITAL

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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

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Case History
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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.

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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

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Case History

• The patient is taken to the OR after only 30
  minutes in the ED.

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OVERVIEW

• Epidemiology
• Clinical presentation
• Anatomy
• US exam
• Sonographic anatomy
• Scanning techniques
• Pitfalls

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Epidemiology

• AAA present in 2-4 of the population gt 50
• Incidence increasing
• Male gt female
• 10,000 deaths/yr
• Rupture has a gt 80 mortality rate

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Epidemiology Risk Factors

• Cardiovascular disease
• Family History increases risk 10-20
• Age gt 50
• Smoker

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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

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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
• gt 5cm has a 20-40 risk of rupture

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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

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Clinical Presentation

• Highly variable
• Classic triad
• Abdominal/Back pain
• Pulsatile mass
• Hypotension
• Less than 1/3 of patients will have the triad

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Clinical Presentation

• Diagnosis
• A formidable clinical challenge
• Notorious for masquerading as renal colic
• May be mistaken for
• Diverticullitis
• GI bleed
• MI
• Musculoskeletal back pain

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Clinical Presentation

• Stable vital signs
• Back or flank pain, left side gt right
• Testicular or leg pain
• Hypertension
• Mortality rate same as elective repair

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Clinical Presentation

• Vast majority are retroperitoneal
• 10 -30 intraperitoneal
• GI bleeding most often seen in patients with
  aortic grafts
• Mortality 50

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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
• CONCLUSIONCannot be relied on to exclude AAA

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Misdiagnosis of Ruptured Abdominal Aortic
Aneurysms MARSTON W ET AL J OF VASCULAR SURG 1992

• Misdiagnosis delay gt6hr or other diagnosis
• Most common physical findings in misdiagnosed
  group ABD PAIN, SHOCK, BACK PAIN
• Pulsatile mass present more often in correctly
  diagnosed group

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SUSPECTED LEAKING ABDOMINAL AORTIC ANEURYSMUSE
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

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Diagnosing AAA

• Palpation of the abdomen alone
• Plain radiographs
• Computed tomography
• ULTRASOUND

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Diagnosis PE

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

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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

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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

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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

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Diagnosis US

• Ultrasound
• In some studies as accurate as CT
• Measurements within 3 mm of surgical specimens
• Angiography may underestimate AAA diameter

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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

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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

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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

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LongitudinalOrientation
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Transverse Orientation

• 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
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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

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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

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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

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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 patients head)
• The aorta is visualized adjacent to the vena cava

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SONOGRAPHIC APPEARANCE OF THE NORMAL AORTA
LONGITUDINAL
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SONOGRAPHIC APEARANCE OF THE NORMAL AORTA
TRANSVERSE
Mid portion
Bifurcation
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SONOGRAPHIC APPEARANCE OF THE NORMAL AORTA(L
LATERAL DECUB/CORONAL)
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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

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ABDOMINAL AORTIC ANEURYSM

• First sign may be loss of normal taper
• AP diameter gt 3CM
• Focal dilitation even if less than 3 cm
• Thrombus
• Intimal flap

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AORTIC ANEURYSM
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Large fusiform AAA
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AAA with clot
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Another AAA with clot
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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

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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.