Wilderness and Rescue Medicine 8th Edition

Chapter 11: General Principles of Trauma

Energy can be neither created nor destroyed. It can change form, but it must go somewhere. The faster an object is moving and the more massive a moving object is, the more energy there is to be transformed and dissipated as the object is slowed or stopped. The faster this transformation takes place, the higher the risk of damage to the object or person gaining or losing the energy. The more you can dissipate energy over time and area, the less energy any structure must con- tend with at any point in time. This is the principle behind crumple zones in cars, helmets on skiers, and body armor on bull riders. It also explains why some impacts are just annoying and others produce significant trauma. The problems associated with trauma tend to be cumulative, especially in the backcountry. Patients are often cold or hot, dehydrated, calorie deplet- ed, and dirty as well as injured. This explains an important part of the Generic to Specific Principle discussed in the chapter on general principles of wilderness rescue, and the reasons that you need to look well beyond the immediate event and spe- cific complaint to consider the whole patient and all the influences on their health.

Energy and Injury Kinetic energy is the energy of motion. When a moving object stops moving, its kinetic energy must be converted into another form or absorbed by the object and whatever stops it. The brakes on your truck, for example, slowly transform the vehicle’s kinetic energy into heat as you slow down. Potential energy is possessed by an object wait- ing to fall. When the frost finally dislodges the rock above you, its potential energy is converted into kinetic energy. When the rock strikes you, the foam lining in your helmet absorbs the energy as it deforms, reducing the amount of energy trans- mitted to your head. Trauma happens when the human body absorbs too much kinetic energy too quickly, resulting in damage to its structure, just like the foam in your helmet. K = 1/2 mv 2 Kinetic energy is equal to mass times veloc- ity squared, divided by two. This formula tells us that velocity contributes substantially more than mass to the kinetic energy possessed by a moving object. This explains how a very small high-velocity bullet can do so much damage. It also tells us that a fast-moving skier stopped by a large maple tree will dissipate a lot more energy