Prehospital Academy Lesson 29.1
Trauma: An Introduction to Kinematics and Energy Transfer
Trauma is a disease of Physics. To provide effective prehospital care, the EMT must look beyond the visible injury and analyze the Kinematics the process of predicting injury based on the forces involved. By understanding how energy is dissipated through human tissue, the provider establishes an Index of Suspicion that guides life-saving interventions before the patient's physiology collapses.
Newtonian Physics: The Law of Energy Conservation
Energy cannot be created or destroyed; it can only be transformed. In a traumatic event, Kinetic Energy (KE) is transformed into the Energy of Work the work of crushing bone and tearing soft tissue.
KE = 1/2 Mass x Velocity
The Velocity Factor: Because velocity is squared, it is the most lethal variable in trauma. A vehicle traveling at 70 mph has four times the destructive energy of a vehicle traveling at 35 mph, even if the mass remains identical.
The Three-Collision Rule in Blunt Trauma
Every motor vehicle collision (MVC) involves three distinct energy transfers:
The Vehicle Collision: The car strikes an object. The damage to the vehicle indicates the amount of energy involved.
The Body Collision: The occupant strikes the interior of the car (e.g., chest vs. steering wheel). This causes external injuries like contusions and fractures.
The Organ Collision: The internal organs strike the inside of the body cavities. This is the "hidden killer" responsible for aortic shearing, brain contrecoup injuries, and liver lacerations.
Mechanisms of Organ Shearing
Internal organs are not all attached to the body with equal rigidity. During a sudden stop (deceleration), "fixed" organs stop instantly, while "mobile" organs continue forward.
The Ligamentum Arteriosum: The heart is relatively mobile, but the descending aorta is fixed to the spine. In high-speed deceleration, the heart moves forward, creating a "shear force" at the Ligamentum Arteriosum. This can result in a partial or complete **Aortic Rupture**, which is fatal in 80-90% of cases.
Blast Injuries: A Complex MOI
Explosions present a unique, four-phase mechanism of injury:
Primary (Pressure): Caused by the Overpressure Wave. Affects hollow, gas-filled organs (lungs, eardrums, GI tract).
Secondary (Projectiles): Caused by flying debris or shrapnel striking the body.
Tertiary (Displacement): The patient is physically thrown by the "blast wind" against a hard object.
Quaternary (Miscellaneous): Includes burns, toxic gas inhalation, or crush injuries from collapsing buildings.
The Platinum 10 Minutes vs. The Golden Hour
Trauma survival is a race against Anaerobic Metabolism.
The Golden Hour: The time from injury to definitive surgical repair.
The Platinum 10 Minutes: The maximum time an EMS crew should spend on scene with a critical trauma patient. Scene time is for "Life-or-Limb" interventions only (SABC: Stop Massive Hemorrhage, Airway, Breathing, Circulation).
Assessment: Critical Thinking Questions
Using the KE formula, explain why a 10lb bowling ball dropped from 5 feet is less dangerous than a 1oz bullet traveling at 1,000 feet per second.
Describe the "Third Collision" in a head-on MVC. Which specific organs are most at risk for shearing?
A patient is found near an explosion with ruptured eardrums but no external bleeding. Which "Phase" of blast injury caused this, and what other internal organ should you be highly concerned about?
Define the **Index of Suspicion**. Why might a patient with a "normal" blood pressure after a 40mph crash still be considered high-acuity?
Compare **Blunt Trauma** to **Penetrating Trauma** in terms of energy dissipation. Which one typically involves "Temporary Cavitation"?