focused emergency ultrasound: evaluation of the abdominal aorta

FOCUSED EMERGENCY ULTRASOUND: FOCUSED EMERGENCY ULTRASOUND: EVALUATION OF THE ABDOMINAL AORTAEVALUATION OF THE ABDOMINAL AORTA

MARY BETH PHELAN, MD, RDMS

DEPARTMENT OF EMERGENCY MEDICINE

FOREDTERT MEMORIAL HOSPITAL

SAEM 2

Lecture ObjectivesLecture 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 4

Case HistoryCase 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 HistoryCase 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 HistoryCase History

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

OVERVIEWOVERVIEW

Epidemiology Clinical presentation Anatomy US exam Sonographic anatomy Scanning techniques Pitfalls

EpidemiologyEpidemiology

AAA present in 2-4% of the population > 50

Incidence increasingMale > female10,000 deaths/yrRupture has a > 80% mortality rate

Epidemiology: Risk FactorsEpidemiology: Risk Factors

Cardiovascular disease

Family History increases risk 10-20%

Age > 50

Smoker

SAEM 11

Clinical PerspectiveClinical Perspective

Settings in which to perform US in the ED

– Abdominal/back/flank pain and hypotension

– Stable elderly patient with abdominal or back pain

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

Clinical PerspectiveClinical 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%

Clinical PresentationClinical Presentation

Highly variableClassic triad:

– Abdominal/Back pain– Pulsatile mass– Hypotension

Less than 1/3 of patients will have the triad

SAEM 15

Clinical PresentationClinical Presentation

Diagnosis– A formidable clinical challenge– Notorious for masquerading as renal colic– May be mistaken for:

Diverticullitis GI bleed MI Musculoskeletal back pain

Clinical PresentationClinical Presentation

Stable vital signs

Back or flank pain, left side > right

Testicular or leg pain

Hypertension

Mortality rate same as elective repair

Clinical PresentationClinical Presentation

Vast majority are retroperitoneal

10 -30 % intraperitoneal

GI bleeding most often seen in patients with

aortic grafts

Mortality 50%

Does this patient have an abdominal Does this patient have an abdominal aortic aneurysm?aortic aneurysm?LEDERLE, JAMA 99LEDERLE, JAMA 99

2 groupsSensitivity of examination for ruptured

AAASensitivity of exam with increasing size

of AAACONCLUSION:Cannot be relied on to

exclude AAA

Misdiagnosis of Ruptured Abdominal Misdiagnosis of Ruptured Abdominal Aortic AneurysmsAortic Aneurysms

MARSTON W ET AL J OF VASCULAR SURG 1992MARSTON 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

SUSPECTED LEAKING ABDOMINAL AORTIC SUSPECTED LEAKING ABDOMINAL AORTIC ANEURYSM:USE OF SONOGRAPHY IN THE ANEURYSM:USE OF SONOGRAPHY IN THE

EMERGENCY ROOMEMERGENCY ROOM SHUMAN WP, ET AL, RADIOLOGY 88SHUMAN 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

Diagnosing AAADiagnosing AAA

Palpation of the abdomen alone

Plain radiographs

Computed tomography

ULTRASOUND

Diagnosis: PEDiagnosis: PE

Absence of mass does not R/O AAA

Obesity

Bleeding into retroperitoneum may create

doughy abdomen.

Hypotension minimizes pulsations

Diagnosis: Plain RadiographsDiagnosis: 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

Diagnosis: CT ScanDiagnosis: 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

SAEM 25

Diagnosis: USDiagnosis: 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: USDiagnosis: 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: USDiagnosis: 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: USDiagnosis: USED 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 = Average time to diagnosis by bedside US = 5.4 minutes5.4 minutes•Average time to diagnosis by CT = 83 Average time to diagnosis by CT = 83 minutesminutes•Average time to OR for diagnosis by US = 12 Average time to OR for diagnosis by US = 12 minutesminutes•Average time to OR for diagnosis by CT = 90 Average time to OR for diagnosis by CT = 90 minutesminutes

US EXAMUS 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

LongitudinalLongitudinalOrientationOrientation

Marker

SAEM 31

Transverse Transverse OrientationOrientation

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 IVC,Liver Aorta

US EXAMUS 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

AORTA IVCAORTA IVC

Left sided structure Thick vascular wall Not compressible Pulsatile

Right sided structure Thin wall Will collapse

– “Sniff”– Valsalva

May pulsate from aortic transmission

US EXAMUS EXAMMeasure from outside wall to outside

wallAn aneurysm is identified as any

measurement of 3 cm or greaterMeasure at:

– Epigastric region– Take off of SMA– 3-4 cm intervals to bifurcation

Measure any aneurysm

US EXAMUS 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

SONOGRAPHIC APPEARANCE OF SONOGRAPHIC APPEARANCE OF THE NORMAL AORTA: LONGITUDINALTHE NORMAL AORTA: LONGITUDINAL

SONOGRAPHIC APEARANCE OF SONOGRAPHIC APEARANCE OF THE NORMAL AORTA: THE NORMAL AORTA:

TRANSVERSETRANSVERSE

BifurcationMid portion

SONOGRAPHIC APPEARANCE OF THE SONOGRAPHIC APPEARANCE OF THE NORMAL AORTANORMAL AORTA

(L LATERAL DECUB/CORONAL)(L LATERAL DECUB/CORONAL)

ABDOMINAL AORTIC ANEURYSMABDOMINAL 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

ABDOMINAL AORTIC ANEURYSMABDOMINAL AORTIC ANEURYSM

First sign may be loss of normal taperAP diameter > 3CMFocal dilitation even if less than 3 cmThrombus Intimal flap

AORTIC ANEURYSMAORTIC ANEURYSM

SAEM 42

Large fusiform AAALarge fusiform AAA

SAEM 43

AAA with clotAAA with clot

SAEM 44

Another AAA with clot Another AAA with clot

ULTRASOUND EXAM: PITFALLSULTRASOUND 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

Pitfalls in Technique 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.