Emergency Ultrasound

Mary Ann Edens, M.D.Assistant Professor, Dept. of

EMDirector of Emergency

Ultrasound

Physics 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 Created in the transducer by back and

forth displacement

Physics and Knobology

Physics 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 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 Hyperechoic

Structure reflects most sound waves

Structure appears white on screen

Terms Anechoic

Structure allows most sound waves through

Structure appears black on screen

Terms Echogenic

Tissues in between Allow some sound

waves through and reflect others

Structures appear in various shades of gray depending on amount of reflection

Terms Homogeneous

Tissue has uniform texture

Terms Heterogeneous

Various degrees of echogenicity present

Terms Isoechoic

Two tissues with same amt of echogenicity

Transducers The higher the frequency, the

better the resolution The better the resolution, the

better you can distinguish objects from each other

Transducers Lower frequency

Transducers Higher frequency

Transducers Linear

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 Linear

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

Transducers Curvilinear

Uses same linear orientation but arranged on a curved surface

Generally lower frequency Gives a wider angle of view

Transducers Curvilinear

Transducers The footprint refers to the portion

of the transducer that contacts the patient

Curvilinear transducers come with different footprints for different purposes

Transducers Transducers have a marker that

corresponds to a mark on the screen

Helps with spatial orientation

Knobology Power

Controls the strength or intensity of the sound wave

Use ALARA principle As low as reasonably acheivable

Knobology Gain

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 Too much gain

Knobology Too little gain

Knobology Optimal gain

Knobology Time gain compensation

Used to equalize the stronger echoes in the near field with the weaker echoes in the far field

Should be a gentle curve

Knobology Focal zone

Where the narrowest portion of the beam is

Gives the optimal resolution

Knobology Focal zone off Focal zone right

Knobology Depth

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 Zoom

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 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 Transabdominal

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 Transabdominal

Locate the long-axis of uterus and sweep from side to side

Turn transducer 90 degrees counter-clockwise

Scanning Techniques Transabdominal

Locate the short-axis of the uterus and angle cephalad and caudad

Goal is to see the entire uterus

Scanning Techniques Transvaginal

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 Transvaginal

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 Transvaginal

Turn transducer 90 degrees counter-clockwise to scan the short-axis of the uterus

Goal is to see the entire uterus

Sonographic FindingsNonpregnant Uterus May see endometrial stripe

Sonographic FindingsNormal Intrauterine Pregnancy Gestational sac

First indication of pregnancy but not a reliable sign of an IUP

Transabdominal scanning 5.5 – 6 weeks gestation B-HCG of 6500

Sonographic FindingsNormal Intrauterine Pregnancy Gestational sac

Transvaginal scanning 4.5 – 5 weeks gestation B-HCG of 1000-2000

Sonographic FindingsNormal Intrauterine Pregnancy Gestational sac

Features of normal sac Round or oval in shape Central position in uterus Smooth contour

Sonographic FindingsNormal Intrauterine Pregnancy Yolk sac

First reliable sign of an intrauterine pregnancy

Should be seen by 5 – 6 weeks gestation

Sonographic FindingsNormal Intrauterine Pregnancy Fetal pole

Should be seen by TV when mean gestational sac diameter is > 16 mm

Cardiac activity usually detected by TV by 6 weeks gestation

Use M-mode to confirm activity

Sonographic FindingsEctopic Pregnancy Detection of ectopic pregnancy

outside uterus < 20% Suggestive findings

No IUP with high B-HCG Pseudogestational sac Complex adnexal mass Free fluid in cul-de-sac

Basic Trauma Ultrasound

The FAST Scan

Goals Bedside screening test for the

detection of hemopericardium and hemoperitoneum

Not a formal study to detect pathology

Scanning Techniques Four standard views

Pericardial Subxiphoid (parasternal if cannot obtain

subxiphoid view) Perihepatic Perisplenic Pelvic

3.5 MHz curvilinear transducer

Scanning Techniques Pericardial views

Subxiphoid view Place transducer in midline and aim

towards the patient’s left shoulder

Scanning Techniques Pericardial views

Parasternal view Place transducer oriented between ribs

on the patient’s left

Scanning Techniques Perihepatic view

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

Scanning Techniques Perisplenic view

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

Scanning Techniques Pelvic view

Place the transducer in midline just above the pubic symphysis

Sonographic FindingsPericardial Views Subxiphoid view

Four chamber view The visceral and parietal pericardium

are adherent

Sonographic FindingsPericardial Views Subxiphoid view

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 FindingsPerihepatic View Normal view

The kidney and liver will be adjacent to each other

Morrison’s pouch will not be visible Morrison’s pouch is the space between

the liver and the right kidney

Sonographic FindingsPerihepatic View Abnormal view

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 FindingsPerisplenic View Normal view

The left kidney and spleen are normally adjacent to each other

Sonographic FindingsPerisplenic View Abnormal view

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 FindingsPelvic View 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 Positive pericardial view

Patient should go to the OR Positive perihepatic, perisplenic or

pelvic view The stable patient should go to CT to

further define injuries The unstable patient should go to the

OR

Basic Abdominal Ultrasound

GallbladderGoals Evaluation of RUQ abdominal pain

for diagnosis of Cholelithiasis Cholecystitis

GallbladderScanning Technique 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

GallbladderScanning Technique Slide and angle through liver to

find gallbladder 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

GallbladderScanning Technique 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

GallbladderSonographic Findings Normal gallbladder

Anechoic Wall thickness < 3 mm Transverse diameter < 4 cm May see folds or valves within the

gallbladder

GallbladderSonographic Findings Abnormal gallbladder - cholelithiasis

Stones > 3mm in size will cause shadowing

Smaller stones and “sludge” will not May see wall-echo sign in a gallbladder

full of stones Evaluate neck of gallbladder carefully

for an impacted stone

GallbladderSonographic Findings Abnormal gallbladder -

cholecystitis Wall thickening > 3 mm Gallbladder enlargement Pericholecystic fluid Sonographic Murphy’s sign

Pressing with transducer directly over the gallbladder elicits pain

RenalGoals Detection of obstructive uropathy

(i.e. hydronephrosis) in patients with Suspected renal colic Acute renal failure

RenalScanning Techniques 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

RenalScanning Techniques 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

RenalSonographic Findings Normal kidney

The renal pelvis appears echogenic The surrounding renal cortex is

hypoechoic The size is ~ 9-13 cm in length

RenalSonographic Findings Abnormal kidney - hydronephrosis

Appears as anechoic dilatation of the renal pelvis

Marked thinning of the cortex implies long- standing hydronephrosis

The degree of hydronephrosis does not correspond with the degree of obstruction

May be present uni- or bilaterally

RenalSonographic Findings Abnormal kidney – renal cysts

Appears as anechoic areas within the cortex with a normal renal pelvis

AortaGoals Evaluation of abdominal or back

pain to rule out AAA

AortaScanning Technique 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

AortaScanning Technique 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 short-axis of the aorta (transverse view)

AortaScanning Technique 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 The IVC will collapse, the aorta will not

AortaSonographic Findings Normal aorta

Diameter no greater than 3 cm at any point

Be careful not to measure obliquely Should taper distally Lumen should appear anechoic

AortaSonographic Findings Abnormal aorta - aneurysm

Diameter greater than 3 cm at any point

Be careful not to measure obliquely Most aneurysms are found

infrarenally Mural thrombus may be seen as areas

of low to medium echogenicity within the wall

AortaSonographic Findings Abnormal aorta - dissection

Aorta may be greater than 3 cm, but not always

Diagnosed when an intimal flap is visualized within the vessel lumen

AscitesGoals Evaluation of the patient with liver

failure May be helpful in deciding the

most appropriate needle placement for paracentesis

AscitesScanning Techniques Same general technique as

described with FAST scan

AscitesSonographic Findings Same general findings as

described with FAST scan

Basic Cardiac Ultrasound

Goals To evaluate the patient with

cardiac failure for Pericardial fluid/tamponade Cardiac activity

Scanning Technique Same general technique as

described with FAST scan Best way to document the

presence of cardiac activity is with the M-mode

Sonographic Findings Pericardial fluid as described with

FAST scan M-mode shows good movement

with normal cardiac activity

Sonographic Findings In cardiac arrest, four-chamber

view may be difficult to see M-mode shows no movement in area

of heart

Central Line Placement 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