Dave Spear, M.D., F.A.C.E.P
The first practical use of
sound wave reflection was in world war II in searching for German
submarines. If you were scuba diving near an underwater wall and
began striking your air tank with a wrench, the sound would travel
to the wall and bounce back as an echo. The time it took would tell
you the distance it took to travel to the wall and back. If you knew
the speed of sound in water you could determine the distance to the
underwater wall. This is the same principle used by bats and
Back to the scuba diver � if a dolphin
appears it would also be sending echoes to the wall. Because
dolphins rely on this method as another sense, they send many more
waves and analyze the reflections with their brain. By analyzing
this data the dolphin can �see� the wall.
have a "brain" like the dolphin and translate sound wave into images
we can see on a screen. Whether the machine is called an ultrasound
machine, a sonogram machine or and echocardiography machine, the
same process is going on.
Some important characteristics
of the waves we use to image humans:
Scatters these US Waves and you lose the image
& Fluid transmit waves - appear black
between two high fluid content structures gives sharp
delineation � for example liver next to kidney gives a "line"
between the two.
Characteristics of Thorax vs
The thorax is mostly air.
There are fewer places to place a sonogram probe on the chest in
which air is not getting in the way. When US waves hit air they
scatter and the image is lost.
The abdomen has many more
areas to approach which don�t have air.
with US in Trauma Patients
The liver happens to be an
excellent structure to sonogram. There is no overlying air and its
high water contenttransmits ultrasound waves very well. If the
ultrasound probe is placed on the patient's side "laterally" you can
see liver and kidney next to each other.
We don�t desire to do an official abdominal
ultrasound like a radiologist would want done. Our use is to confirm
what we already may suspect. If a blunt trauma patient is
hypotensive, we want to do a US screening exam just to look for
suspected blood in the abdomen.
Note that water, blood, urine and other fluids
look identical with ultrasound. Therefore, it is the fact that we
suspect blood in the belly of a trauma patient that leads us to
equate fluid with blood in these cases.
As stated previously, if
the ultrasound probe is placed on the right lateral side of the
abdomen, the liver and kidney are easy to visualize. This happens to
also be the area where blood would collect in the supine
Hepatorenal (Morison�s) Pouch
If a surgeon were to
open you mid abdomen and pour in fluid into the peritoneal space it
would collect or �puddle� in the deepest (most dependent) part of
the supine abdomen. This happens to be between the liver and the
kidney and is called Morison�s Pouch.
Blood (fluid) in
the abdomen of a trauma patient:
Notice that the liver in this US is "floating" or
surrounded by blood!
Blood (fluid) in the abdomen
of a trauma patient:
you point out the blood? (more subtle on this one)
� True Positive (Blood
truly is in the peritoneum)
� Needs exploratory surgery or
� True Negative (No blood in the
� Can place patient in Trendelenberg or repeat
Study q 30 min to 60 min
� False Positive (See fluid
� but it is not blood)
� Bladder Rupture, Ascities
False Negative (There is blood � but not enough to
� Takes 500cc-1000cc of blood to
The Role of
the Ultrasound Machine in a Trauma Patient
� Where?: the field ultrasound should be
done en route
should be part of the secondary survey
� Why?: will let you know the patient has a
serious problem if there is blood in the
Shortcomings of Ultrasound in Trauma
Air is the enemy and
scatters waves losing the image
Needs to be 500cc -
1000cc to be able to image
Does not evaluate for a
retro peritoneal hematoma
Diagnostic Studies in Blunt Abdominal Trauma
Hemoperitoneum (blood in the abdomen) can
be diagnosed by any of the following ways:
� Diagnostic Peritoneal
� CT Scan of Abdomen & Pelvis
Ease of Use
"The sooner EMS Ultrasound use
becomes widespread, the more lives that will be