Emergency Ultrasound Mary Ann Edens, M.D. Assistant Professor, Dept. of EM Director 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 Findings Nonpregnant Uterus May see endometrial stripe

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

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

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

Sonographic Findings Normal 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 Findings Ectopic 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 3.5 MHz curvilinear transducer 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 Findings Pericardial Views Subxiphoid view Four chamber view The visceral and parietal pericardium are adherent

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

Sonographic Findings Perisplenic 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 Findings Pelvic 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

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

Gallbladder Scanning 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

Gallbladder Scanning 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

Gallbladder Scanning 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

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

Gallbladder Sonographic 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

Gallbladder Sonographic 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

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

Renal Scanning 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

Renal Scanning 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

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

Renal Sonographic 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

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

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

Aorta Scanning 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

Aorta Scanning 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)

Aorta Scanning 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

Aorta Sonographic 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

Aorta Sonographic 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

Aorta Sonographic 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

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

Ascites Scanning Techniques Same general technique as described with FAST scan

Ascites Sonographic 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

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