WOUNDING EFFECTS OF BLAST OVERPRESSURE
Physics of Blast Waves - blasts produce two separate
types of waves. Each wave does specific forms of damage to the human body.
Stress waves are supersonic,
longitudinal pressure waves. These waves create high potential for injuries,
especially in gas-filled organs such as the lungs, ears, and intestines.
Sheer waves
are lower velocity transverse waves with longer duration than stress waves.
These waves cause tissue in the body to move back and forth.
Lung Injuries occur when the victim experiences
overpressure of greater than 40 pounds per square inch (PSI). Increases in
pressure of 200 PSI in an open-air environment are almost universally fatal.
Lung injuries are the most common cause of death related to the primary blast
effect.
Signs and Symptoms may appear
immediately or they may be delayed for up to 48 hours, depending on the severity
of the wound. Internal hemorrhage in the pulmonary region, along with alveolar
edema will lead to frothy, bloody secretions from the mouth. The casualty will
also exhibit signs of labored breathing and appear hypoxic.
Treatment
is difficult in a tactical environment. The patient should be monitored for the
appearance of dyspnea and/or frothy sputum. Oxygen should be administered as
soon as it is available. IV fluids should be used with extreme caution to avoid
overloading the lungs with fluid.
Ear
Injuries can occur from as little as 5-15 PSI of
overpressure. It is imperative that all blast injury casualties be examined for
possible tympanic membrane (TM) rupture. Since it takes a far greater amount of
pressure to rupture lungs or abdominal organs, the absence of ruptured
tympanic membranes can help rule out other injuries, provided the patient is not
experiencing any other symptoms related to organ damage. Blast induced deafness
may heighten the patients anxiety. The hearing loss may be permanent or resolve
in a matter of hours.
Signs and Symptoms will be
noticeable upon examination. The patient will have a noticeable loss of
hearing, along with some bleeding from the ear(s). Visualizing the eardrum with
an otoscope can positively identify a ruptured TM.
Treatment
of a ruptured TM is relatively conservative and is not a priority
on the battlefield. Although 50-80% of TM ruptures will heal on their own,
patients should still be referred to a medical officer within 24 hours. Until
then, avoid probing or irrigating the ear canal.
Gastrointestinal Injuries are more likely to occur in
patients of blasts detonated inside a building than those exposed to explosions
in an open-air environment. Of all abdominal blast injuries, intestinal
perforation is the most common. While the blast may induce the intestinal
perforation which is considered a closed injury, other aspects of the blast may
produce open injuries as well.
Signs and Symptoms include pain in
the abdomen, rectum, and testes and may be difficult to appreciate early in the
care of the casualty.
Treatment
of gastrointestinal injuries is covered in Block two of this text
and will be based on the extent of the injury.
Solid Organ
injury is rare in open-air blasts but has been reported in underwater blasts.
All abdominal injuries should be treated symptomatically as discussed in Block
two.
Central Nervous System Injuries,
to include Traumatic Brain Injuries (TBI), are significant issues associated
with blast injuries. Moderate to severe TBI accounts for 71% of the early
deaths associated with explosions and 52% of later deaths. Mild TBI is
associated with long term issues such as memory loss, irritability, and
decreased cognitive functions. For this reason, ALL
PERSONNEL INVOLVED IN AN EXPLOSIVE ATTACK SHOULD BE REFERRED TO A MEDICAL OFFICER
FOR DOCUMENTATION AND EVALUATION.
Mutitple-Etiology Injuries. Explosions create
different injury patterns based on various factors. Among these are the size of
the explosion, the location of the explosion, and the proximity of the casualty
to the explosion. These events often lead to the casualty experiencing
multi-etiology injuries. In this case the patient has injuries to more than one
body part or system. To determine the correct intervention, you must be able to
perform a systematic casualty assessment to identify and treat life threatening
injuries first.
REFERENCE
Pre-hospital Trauma Life
Support, Medical Edition, 6th Edition, Chapter 25
Rev: July 2008
Blast Review
1.
What types of injuries can you expect from the secondary effects of a blast.
2.
