Emergency Ultrasound
Mary Ann Edens, M.D.
Assistant Professor, Dept. of EM
Director of Emergency Ultrasound

Physics
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Sound waves with frequencies greater than 20 kHz are called ultrasound
Medical ultrasound waves have frequencies between 1 – 20 MHz
Sound waves are mechanical waves
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Created in the transducer by back and forth displacement

Physics and Knobology

Physics
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Ultrasound transducers send out sound waves and then “listen” for returning echoes
Most transducers at this time send out waves only approximately 1% of the time

Physics
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Acoustic impedance determines the amount of sound waves transmitted and reflected by tissues
Reflection occurs when the ultrasound beam hits two tissues (areas) having different acoustic impedance
Large differences in impedances inhibit useful information

Terms
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Hyperechoic
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Structure reflects most sound waves
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Structure appears white on screen

Terms
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Anechoic
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Structure allows most sound waves through
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Structure appears black on screen

Terms
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Echogenic
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Tissues in between
Allow some sound waves through and reflect others
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Structures appear in various shades of gray depending on amount of reflection

Terms
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Homogeneous
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Tissue has uniform texture

Terms
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Heterogeneous
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Various degrees of echogenicity present

Terms
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Isoechoic
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Two tissues with same amt of echogenicity

Transducers
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The higher the frequency, the better the resolution
The better the resolution, the better you can distinguish objects from each other

Transducers
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Lower frequency

Transducers
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Higher frequency

Transducers
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Linear
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Gives rectangular image
Generally has higher frequency
Good for looking at a smaller area and for gauging depth
Gives more of a one dimensional view
Sometimes referred to as the vascular probe

Transducers
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Linear

From Heller & Jehle. Ultrasound in Emergency Medicine
W.B. Saunders, 1995, p. 202.
. Philadelphia:

Transducers
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Curvilinear
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Uses same linear orientation but arranged on a curved surface
Generally lower frequency
Gives a wider angle of view

Transducers
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Curvilinear

Transducers
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The footprint refers to the portion of the transducer that contacts the patient
Curvilinear transducers come with different footprints for different purposes

Transducers
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Transducers have a marker that corresponds to a mark on the screen
Helps with spatial orientation

Knobology
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Power
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Controls the strength or intensity of the sound wave
Use ALARA principle
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As low as reasonably acheivable

Knobology
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Gain
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Degree of amplification of the returning sound
Increasing the gain, increases the strength of the returning echoes and results in a lighter image
Decreasing the gain, does the opposite

Knobology
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Too much gain

Knobology
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Too little gain

Knobology
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Optimal gain

Knobology
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Time gain compensation
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Used to equalize the stronger echoes in the near field with the weaker echoes in the far field
Should be a gentle curve

Knobology
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Focal zone
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Where the narrowest portion of the beam is
Gives the optimal resolution

Knobology
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Focal zone off
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Focal zone right

Knobology
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Depth
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Each frequency has a range of depth of penetration
Decrease the depth to visualize superficial structures
May need to increase the depth of penetration to visualize larger organs

Knobology
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Zoom
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Can place zoom box on a portion of a frozen image to enlarge that portion of the image
May lose some resolution because pixels are enlarged

Basic OB/Gyn Ultrasound

Goals
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To perform a focused examination on patients with complicated first trimester pregnancies
To rule in an intrauterine pregnancy
(not to rule out an ectopic)

Scanning Techniques
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Transabdominal
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Supine position
A full bladder will provide sonographic window
3.5 MHz curvilinear transducer
Place transducer in the sagittal plane just above the pubic bone

Scanning Techniques
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Transabdominal
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Locate the long-axis of uterus and sweep from side to side
Turn transducer 90 degrees counterclockwise

Scanning Techniques
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Transabdominal
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Locate the short-axis of the uterus and angle cephalad and caudad
Goal is to see the entire uterus

Scanning Techniques
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Transvaginal
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Supine lithotomy position
5.0-7.5 MHz intracavitary transducer
Need to apply gel to the transducer and transducer cover
Have assistant to chaperone

Scanning Techniques
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Transvaginal
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With locator anterior, scan the long-axis of the uterus
Transducer does not need to be inserted all the way to the cervix

Scanning Techniques
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Transvaginal
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Turn transducer 90 degrees counterclockwise to scan the short-axis of the uterus
Goal is to see the entire uterus

Sonographic Findings
Nonpregnant Uterus
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May see endometrial stripe

Sonographic Findings
Normal Intrauterine Pregnancy
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Gestational sac
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First indication of pregnancy but not a reliable sign of an IUP
Transabdominal scanning
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5.5 – 6 weeks gestation
B -HCG of 6500

Sonographic Findings
Normal Intrauterine Pregnancy
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Gestational sac
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Transvaginal scanning
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4.5 – 5 weeks gestation
B -HCG of 1000-2000

Sonographic Findings
Normal Intrauterine Pregnancy
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Gestational sac
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Features of normal sac
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Round or oval in shape
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Central position in uterus
Smooth contour

Sonographic Findings
Normal Intrauterine Pregnancy
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Yolk sac
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First reliable sign of an intrauterine pregnancy
Should be seen by 5 – 6 weeks gestation

Sonographic Findings
Normal Intrauterine Pregnancy
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Fetal pole
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Should be seen by TV when mean gestational sac diameter is > 16 mm
Cardiac activity usually detected by TV by 6 weeks gestation
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Use M-mode to confirm activity

Sonographic Findings
Ectopic Pregnancy
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Detection of ectopic pregnancy outside uterus < 20%
Suggestive findings
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No IUP with high B -HCG
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Pseudogestational sac
Complex adnexal mass
Free fluid in cul-de-sac

Basic Trauma Ultrasound
The FAST Scan

Goals
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Bedside screening test for the detection of hemopericardium and hemoperitoneum
Not a formal study to detect pathology

Scanning Techniques
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Four standard views
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Pericardial
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Subxiphoid (parasternal if cannot obtain subxiphoid view)
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Perihepatic
Perisplenic
Pelvic
3.5 MHz curvilinear transducer

Scanning Techniques
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Pericardial views
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Subxiphoid view
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Place transducer in midline and aim towards the patient’s left shoulder

Scanning Techniques
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Pericardial views
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Parasternal view
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Place transducer oriented between ribs on the patient’s left

Scanning Techniques
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Perihepatic view
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Place the transducer on the patient’s right in the midaxillary line between the 8 th and
11 th intercostal spaces

Scanning Techniques
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Perisplenic view
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Place the transducer on the patient’s left in the midaxillary line between the 8 th and
11 th intercostal spaces

Scanning Techniques
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Pelvic view
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Place the transducer in midline just above the pubic symphysis

Sonographic Findings
Pericardial Views
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Subxiphoid view
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Four chamber view
The visceral and parietal pericardium are adherent

Sonographic Findings
Pericardial Views
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Subxiphoid view
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Pericardial fluid will show as a dark layer in between the visceral and parietal pericardial layers
Tamponade is diagnosed by circumferential fluid collection with diastolic collapse of the right atrium or ventricle

Sonographic Findings
Perihepatic View
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Normal view
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The kidney and liver will be adjacent to each other
Morrison’s pouch will not be visible
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Morrison’s pouch is the space between the liver and the right kidney

Sonographic Findings
Perihepatic View
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Abnormal view
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Intraperitoneal fluid will appear as anechoic area in Morrison’s pouch
Be careful not to misinterpret a fluid filled structure (i.e. gallbladder, colon, duodenum) as free fluid

Sonographic Findings
Perisplenic View
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Normal view
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The left kidney and spleen are normally adjacent to each other

Sonographic Findings
Perisplenic View
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Abnormal view
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Intraperitoneal fluid will appear as anechoic area in the subphrenic space or splenorenal fossa
Be careful not to misinterpret a fluid filled structure (i.e. stomach, colon) as free fluid

Sonographic Findings
Pelvic View
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In female patients, intraperitoneal fluid will appear in the pouch of Douglas just posterior to the uterus
In male patients, intraperitoneal fluid will appear in the retrovesicular pouch or cephalad to the bladder

Interpretation of FAST
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Positive pericardial view
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Patient should go to the OR
Positive perihepatic, perisplenic or pelvic view
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The stable patient should go to CT to further define injuries
The unstable patient should go to the OR

Basic Abdominal Ultrasound

Gallbladder
Goals
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Evaluation of RUQ abdominal pain for diagnosis of
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Cholelithiasis
Cholecystitis

Gallbladder
Scanning Technique
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Supine or left lateral decubitus position
Ideally patient should be NPO for 4-6 hours
3.5-5.0 MHz curvilinear transducer
Start with transducer in sagittal plane in the midclavicular line at the lower costal margin

Gallbladder
Scanning Technique
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Slide and angle through liver to find gallbladder
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Look for main lobar fissure to lead to the gallbladder
Having patient take a deep breath may help
Once gallbladder is visualized, turn transducer slightly to find long-axis of the gallbladder

Gallbladder
Scanning Technique
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Sweep from side to side to evaluate for stones
Turn the transducer 90 degrees counterclockwise to find short-axis of the gallbladder
Angle the transducer to evaluate the entire gallbladder

Gallbladder
Sonographic Findings
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Normal gallbladder
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Anechoic
Wall thickness < 3 mm
Transverse diameter < 4 cm
May see folds or valves within the gallbladder

Gallbladder
Sonographic Findings
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Abnormal gallbladder - cholelithiasis
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Stones > 3mm in size will cause shadowing
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Smaller stones and “sludge” will not
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May see wall-echo sign in a gallbladder full of stones
Evaluate neck of gallbladder carefully for an impacted stone

Gallbladder
Sonographic Findings
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Abnormal gallbladder - cholecystitis
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Wall thickening > 3 mm
Gallbladder enlargement
Pericholecystic fluid
Sonographic Murphy’s sign
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Pressing with transducer directly over the gallbladder elicits pain

Renal
Goals
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Detection of obstructive uropathy (i.e. hydronephrosis) in patients with
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Suspected renal colic
Acute renal failure

Renal
Scanning Techniques
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Left lateral decubitus or right lateral decubitus for each respective kidney
3.5–5.0 MHz curvilinear transducer
Use intercostal oblique technique described for the FAST scan
May also use subcostal approach in the sagittal plane at the midclavicular line

Renal
Scanning Techniques
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Once kidney is found turn transducer slightly to find long-axis
Scan through entire kidney
Then turn transducer 90 degrees counterclockwise to find the short-axis
Scan through entire kidney

Renal
Sonographic Findings
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Normal kidney
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The renal pelvis appears echogenic
The surrounding renal cortex is hypoechoic
The size is ~ 9-13 cm in length

Renal
Sonographic Findings
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Abnormal kidney - hydronephrosis
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Appears as anechoic dilatation of the renal pelvis
Marked thinning of the cortex implies longstanding hydronephrosis
The degree of hydronephrosis does not correspond with the degree of obstruction
May be present uni- or bilaterally

Renal
Sonographic Findings
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Abnormal kidney – renal cysts
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Appears as anechoic areas within the cortex with a normal renal pelvis

Aorta
Goals
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Evaluation of abdominal or back pain to rule out AAA

Aorta
Scanning Technique
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Supine position
2.5-5.0 MHz curvilinear transducer
Start with transducer in sagittal plane in the midline just below the xiphoid process
Angle the transducer slightly to the patient’s left to locate the aorta

Aorta
Scanning Technique
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Slide and rock the transducer caudally down the abdomen to follow the aorta all the way to the bifurcation
Then move the transducer back to the subxiphoid space and relocate the aorta
Turn the transducer 90 degrees counterclockwise to visualize the shortaxis of the aorta (transverse view)

Aorta
Scanning Technique
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Again slide the transducer caudally down the abdomen to follow the aorta all the way to the bifurcation
Any measurements of the aorta should be taken in this transverse view
Pressure may be placed to distinguish the aorta from the IVC
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The IVC will collapse, the aorta will not

Aorta
Sonographic Findings
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Normal aorta
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Diameter no greater than 3 cm at any point
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Be careful not to measure obliquely
Should taper distally
Lumen should appear anechoic

Aorta
Sonographic Findings
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Abnormal aorta - aneurysm
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Diameter greater than 3 cm at any point
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Be careful not to measure obliquely
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Most aneurysms are found infrarenally
Mural thrombus may be seen as areas of low to medium echogenicity within the wall

Aorta
Sonographic Findings
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Abnormal aorta - dissection
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Aorta may be greater than 3 cm, but not always
Diagnosed when an intimal flap is visualized within the vessel lumen

Ascites
Goals
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Evaluation of the patient with liver failure
May be helpful in deciding the most appropriate needle placement for paracentesis

Ascites
Scanning Techniques
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Same general technique as described with FAST scan

Ascites
Sonographic Findings
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Same general findings as described with
FAST scan

Basic Cardiac Ultrasound

Goals
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To evaluate the patient with cardiac failure for
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Pericardial fluid/tamponade
Cardiac activity

Scanning Technique
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Same general technique as described with FAST scan
Best way to document the presence of cardiac activity is with the M-mode

Sonographic Findings
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Pericardial fluid as described with FAST scan
M-mode shows good movement with normal cardiac activity

Sonographic Findings
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In cardiac arrest, four-chamber view may be difficult to see
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M-mode shows no movement in area of heart

Central Line Placement
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US can be used for placement
Easiest line to use for is IJ
Place patient in Trendelenberg position if able
Place linear probe on neck