Advanced Trauma Life Support ATLS Student Course Manual 2018

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BIOMECHANICS OF INJURY
••
A male falls 15 feet (4.5 m) from the roof of a
house, landing on his feet.
••
A male falls 15 feet (4.5 m) from the roof of a
house, landing on his back.
••
A male falls 15 feet (4.5 m) from the roof of a
house, landing on the back of his head with his
neck in 15 degrees of flexion.
In the first example, the entire energy transfer occurs
over a surface area equivalent to the area of the male’s
feet; energy is transmitted through the axial skeleton
from the lower extremity to the pelvis and then the
spine. The soft tissue and visceral organs decelerate
at a slower rate than the skeleton. In addition, the
spine is more likely to flex than to extend because
of the ventral position of the abdominal viscera. In
the second example, the force is distributed over a
much larger surface area. Although tissue damage may
indeed occur, it is less severe. In the final example, the
entire energy transfer is directed over a small area and
focused on a point in the cervical spine where the apex
of the angle of flexion occurs. It is easy to see how the
injuries differ in each of these examples, even though
the mechanism and total energy is identical.
Among the elderly population, osteopenia and
overall fragility are important factors in determining
the severity of injury even with “low impact” falls.
Blast Injury
Explosions result from the extremely rapid chemical
transformation of relatively small volumes of solid,
semisolid, liquid, and gaseous materials into gaseous
products that rapidly expand to occupy a greater volume
than that occupied by the undetonated explosive. If
unimpeded, these rapidly expanding gaseous products
assume the shape of a sphere. Inside this sphere, the
pressure greatly exceeds atmospheric pressure.
The outward expansion of this sphere produces a
thin, sharply defined shell of compressed gas that acts
as a pressure wave at the periphery of the sphere. The
pressure decreases rapidly, in proportion to the third
power of the distance, as this pressure wave travels
away from the site of detonation. Energy transfer
occurs as the pressure wave induces oscillation in the
media it travels through. The positive-pressure phase
of the oscillation may reach several atmospheres in
magnitude (overpressure), but it is of extremely short
duration, whereas the negative-pressure phase that
follows is of longer duration. This latter phase accounts
for the phenomenon of buildings falling inward.
Blast injuries may be classified into primary,
secondary, tertiary, and quaternary. Primary blast
injuries result from the direct effects of the pressure
wave and are most injurious to gas-containing organs.
The tympanic membrane is the most vulnerable to the
effects of primary blast and can rupture if pressures
exceed 2 atmospheres. Lung tissue can develop
evidence of contusion, edema, and rupture, which
may result in pneumothorax caused by primary blast
injury. Rupture of the alveoli and pulmonary veins
produces the potential for air embolism and sudden
death. Intraocular hemorrhage and retinal detachments
are common ocular manifestations of primary blast
injury. Intestinal rupture also may occur. Secondary
blast injuries result from flying objects striking an
individual. Tertiary blast injuries occur when an
individual becomes a missile and is thrown against
a solid object or the ground. Secondary and tertiary
blast injuries can cause trauma typical of penetrating
and blunt mechanisms, respectively. Quaternary blast
injuries include burn injury, crush injury, respiratory
problems from inhaling dust, smoke, or toxic fumes, and
exacerbations or complications of existing conditions
such as angina, hypertension, and hyperglycemia.
Penetrating Trauma
Penetrating trauma refers to injury produced by foreign
objects that penetrate tissue. Weapons are usually
classified based on the amount of energy produced by
the projectiles they launch:
••
Low energy—knife or hand-energized missiles
••
Medium energy—handguns
••
High energy—military or hunting rifles
The velocity of a missile is the most significant
determinant of its wounding potential. The importance
of velocity is demonstrated by the formula relating
mass and velocity to kinetic energy:
Velocity
Kinetic Energy = mass × (V 2
− V
1 22
)
2
where V1 is impact velocity and V2
is exit or remaining velocity.
The wounding capability of a bullet increases markedly
above the critical velocity of 2000 ft/sec (600 m/
sec). At this speed a temporary cavity is created by
tissue being compressed at the periphery of impact,
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