The Physics of a Gun Shot Wound

Anatomy and Physics of a Gunshot Wound (GSW)

Gunshot wounds can be devastating. From the immediate impact on the organs of the body to their long-term consequences and lengthy recovery time, no GSW follows the exact same wound pattern. Knowing some basic ways in which bullets tend to operate can help us better prepare for their effects on the human body, and can lead us to be better prepared to assess the ENTIRE body system rather than focusing on the immediate presentation of the individual bullet wound.

A bullet’s damage is directly related to its kinetic energy.

KE = 1/2mv^{2             (}½ mass*velocity^Squared)

What does that mean? It means a small standard 11.9g, 5.56mm (.223) round, fired at 2800fps can cause MASSIVE damage.

What happens as a bullet passes through the body?

- Tissue damage

- Secondary shock wave

- Cavitation

The faster a bullet goes, the more damage it has the potential to do.

How much damage it causes varies by its velocity, where it enters, trajectory, weight and design (7.62 vs 5.56 vs hollow point, .45 vs .9mm etc.)

As a bullet enters the body, it forms a cavitation, or expansion, of the surrounding tissue. It also lacerates the tissue it encounters. The bullet may yaw, or tumble, as it slows, further lacerating the tissue and causing the bullet to follow often unpredictable pathways within the body.

High velocity bullets create a pressure wave, pushing the tissue away from it on entry. The acceleration of tissue away from the pressure caused by the velocity of the bullet will often leave a secondary cavity, often larger than the entry wound. 

This is why you do NOT USE TAMPONS FOR BLEEDING CONTROL!! They do a ‘soft expand’ which does NOTHING for controlling bleeding except soak up blood.

Pic from TriadMedical

So how does a bullet effect some of our major systems?*

Skin and Muscle

These tissues are relatively elastic and therefore tolerate the temporary stretching effect of the cavitation relatively well with limited tissue necrosis. Functionally, injuries to these tissues are well tolerated.

Neurovascular Structures 

Nerves and vessels are often relatively fixed anatomically and therefore are vulnerable to the temporary distorting effect of cavitation. They can remain macroscopically intact away from the permanent cavity; however, intimal damage in vessels and axonal damage in nerves can result in functional failure even some distance from the path of the bullet. 

Bone

The unique strength of this tissue means that it exerts a significant retarding effect on projectiles that strike it. This results in considerable energy transfer, often with extensive fragmentation of both bone and bullet. This follows the potential for these fragments to be accelerated as secondary missiles.

*Breakdown comes from NIH breakdown on GSW, and can be found at following link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4596205/

So what can we do about it?

Understand that bullet wounds can affect multiple systems. If someone is shot, FIND THE EXIT WOUND. If you find what you believe is the exit wound, find the entrance wound. Finding both (if both exist) will help you trace the path of the bullet and begin to figure out where the bullet may have traveled, and what organ systems it may have affected.

Let’s go over SMARCH really quickly, but in direct relation to systems a bullet would affect.

Security/Scene Safety: Make sure the scene is safe and that you do not become a victim.

Massive hemorrhage: Look for heavy venous and/or arterial bleeds. Extremities can receive tourniquets if necessary, inguinal and non-tourniquet areas should be packed and secured immediately. Understand the path of the bullet. For instance, placing TQ on a leg is great, but if you find an exit wound near the hip or higher, you must take into account the possibility of additional bleeding in the hip, intestines, etc.

Airway: Damage to the mouth, nose, or airway cavity is a severe concern, and must be addressed immediately after severe bleeding. A pneumonic we used in the medical course was ‘teeth and tongue intact, no blood or mucous’. If the mouth is severely damaged, teeth are broken, and there is significant blood or debris in the mouth, upgrade their airway asap. If you have the capability of giving a cricothyroidotomy, do so. If not, figure out a way for them to be able to draw in breath, either through positioning, NPA, OPA, etc.

Respirations: GSW’s in the torso are very likely to damage your pleural cavity, lungs, etc. Delay formation of Tension Pneumothorax by placing chest seals on any penetrating injuries, from the top of the hip bone (top of the ischium) to the base of your chin, front and back of your torso. Support breathing as necessary.

Circulation: Bandage remaining bleeds, even if they are only minor. Keeping as much blood in the body as possible can have profound consequences on recovery time and overall outcome. Initiate IV access at this time, but do NOT begin pumping with fluids. Make a plan for fluids and medication based on presentation of patient.  

Hypothermia/Head Injury: Patients with significant blood loss are at a risk for hypothermia, regardless of outside temperature. Keep patient warm and monitor vitals q 5 minutes minimum. GSW’s causing head injury are extremely serious, and noting patient’s condition and any deterioration is vital to follow-on care. Be prepared to position the patient, bag the patient, etc. Always assume a neck injury until cleared.

There are MANY additional steps that were not covered here in the interest of time and information overload. PLEASE continue to research the steps in TCCC.

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