Visiting Skid Row

      We have all been trained to look for bent steering wheels and dashboards and cracked windshields in motor vehicle collisions (MVCs), which is very helpful in suspecting injuries, but we can benefit from new research in MVC reconstruction to help us and the ED identify life-threatening injuries quickly. For example, after you determine a MVC scene is safe, look for skid marks and deformity of the vehicles involved. Clues in the wreckage can help you begin assessing your patient for specific injuries prior to making patient contact.

SKID MARKS AND DAMAGE

   The skid marks on the road can tell you speed loss, direction of energy, place of impact and deceleration time, and can give you clues to what happened at the time of impact. It would be unreasonable to ask healthcare providers to measure the skid marks; however, as you approach the scene, you can gather a few clues that will help your assessment. Determine if the skid marks are long or short. Consider road conditions. Note the direction of the skid marks and if there is any radical change in the marks. With this quick evaluation of the scene, you can get a general idea of how much energy was absorbed and where it went. Your patient's injuries will mimic the vehicle they were in. Imagine what path the energy took as it traveled through your patient's body and what injuries it caused along the way. We do not have all of the tools available in the ED, but if we relay our suspicions to the ED physician, there can be faster recognition and treatment of a possibly life-threatening injury. Of our many roles in trauma care, one of the most important is to paint a picture of the scene for all those involved in the patient's care.

SPEED LOSS

   When you arrive on the scene of a pedestrian vs. car incident, note the number of skid marks prior to the point of the suspected patient impact. Skid marks can indicate speed loss prior to impact. Skid marks can vary, depending on road surface, condition and changes in elevation. Note whether the skid marks are long or short, which can determine if it was a high-speed collision. Asking the patient how fast he was traveling is only part of the story. If the patient struck a tree and both he and bystanders report an approximate speed of 55 mph, but you note 25 feet of skid marks on dry blacktop, this indicates an approximate speed of 31 mph at the time of impact. If you note only 5 feet of skid marks and all other circumstances are the same, the approximate impact speed is 44 mph. Remember, as velocity doubles, energy quadruples, so a small increase in speed suggests a large increase in energy. If there are no skid marks, the question of why the patient did not attempt to stop indicates a possible pre-event condition like hypoglycemia, CVA, ETOH use, etc. Medical causes of a MVC are often recognized late in patient care.

   The speed loss chart (Figure 1) is only an estimation. All road surfaces, make and model of vehicles and direction of the vehicle must be considered to make an exact calculation. Do not use this chart in a court of law.

MOMENTUM

   Momentum is the energy transferred to the patient and objects involved in a MVC. Momentum is more than simply how fast an object is traveling; it is a combination of speed and mass (momentum = velocity x mass). This means that, due to its mass, an 18-wheeler has more momentum at 5 mph than a small two-door vehicle traveling at 20 mph. If you double the mass of an object, you double the energy; if you double the speed, you quadruple the energy. A small car traveling at 60 mph has more momentum than a large truck traveling at 25 mph. The vehicle with the most momentum generally has less energy absorption and transfers most of its energy to the object with less momentum. Determining the amount of momentum, where the energy was absorbed and what direction it traveled can be a good indicator of possible injuries

DECELERATION