Wilderness and Rescue Medicine 8th Edition

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Section IV: Trauma

than a skier moving at half the speed. It explains why a fall from two meters in height may be no big deal, but four meters can be fatal. Deceleration The rate of change in speed is called acceleration. Because injuries are usually caused by a sudden decrease in speed, or negative acceleration, we use the term deceleration. Deceleration requires the transformation or dissipation of energy over time. When you step on the brakes, your truck does not decelerate instantly. There must be time for the brakes to absorb and diffuse the truck’s kinetic energy without damage to the vehicle or its occu- pants. If your truck were to decelerate instantly, against a bridge abutment, for example, massive deformation would result as the kinetic energy was absorbed instantly by the vehicle and the occupants. The difference between braking and crashing is the rate of deceleration. Deceleration causes injury due to inertia, the tendency of a moving body to keep moving until acted on by an outside force. If a skier’s head is suddenly stopped by a maple tree, their brain will continue to move forward until it strikes the inside of the skull. This causes direct injury to the front of the brain from the impact, and indi- rect injury to the back of the brain as suspended arteries and veins tear away from the brain tissue (known as a contra-coup injury). The heart and great vessels in the chest can experience the same forces, resulting in a torn aorta. Rapid deceleration concentrates energy and magnifies its effect. High kinetic energy with rapid deceleration causes the most damage. A good helmet and body armor can reduce trauma by decreasing the rate of deceleration, but if your patient was moving fast and stopped quickly you still have a lot to worry about. This would be a good time to use the Generic to Specific Principle in assessment.

Rapid deceleration offers a high probability of multi-system trauma. The shoulder dislocation was obvious on exam in the field, the pneumo- thorax (collapsed lung) was not. Be sure to look beyond the most obvious injuries. By contrast, slow deceleration can dissipate the same amount of energy without deforming struc- ture. The high-speed skier who falls on a steep, open slope can dissipate their kinetic energy while sliding several hundred meters to a stop. They might even emerge uninjured. Ski patrollers call this a yard sale because ski equipment and cloth- ing tend to dissipate as well. The skier’s kinetic energy is absorbed by the snow as the skier slides along, and by the flexion and compression of body tissues and clothing at the points of contact. If the energy of each impact is low enough, the skier’s body can accept the momentary deforma- tions without lasting damage. Cavitation High-velocity trauma can cause injuries remote from the point of impact due to an effect called cavitation. This is the sudden displacement of internal organs creating a shock wave that can dis- tribute energy throughout the body. Low-density organs like the gut and lungs are elastic, like foam rubber, and they can move and compress as they absorb the energy transmitted by cavitation. It is unusual to see rupture of hollow organs from blunt trauma. High-density solid organs and bones are less elastic; they are more like watermelon and tend to split and fracture as energy is absorbed. This