The overall goal of the emergency medical services (EMS) system is to reduce overall mortality and morbidity at nominal or reduced costs. To accomplish this goal an EMS system uses many subcomponents, each with specialized skills, integrated so as to insure a competent continuum of care. Questions inevitably arise about the ability of EMS systems to deliver the intended results. While discussions of mortality and morbidity tendencies are meaningful measures of outcomes and, perhaps, the “bottom line,” these two criteria are a total system measurement. They are not subsystem measures, and, therefore, offer little insight into the reasons for success or failure of the EMS system.

As a field commander attacks an emergency medical incident, his thought processes depend upon information gathered during the incident and information about the effect of resources and competencies upon past incidents. The decisions which determine treatment and patient survival, as well as rescuer safety, are a direct function of this tactical thought process. This paper examines how this thought process is formed and how it may be improved through the use of a mechanistic system evaluation model.

In 1966, the first major step toward a systematic delivery system for EMS was taken when a U.S. government report recommended that a nationwide program be established that would form non-traditional “EMS regions.” These regions would be the foundation for a comprehensive systematic approach to the problem of unnecessary death and disability in the prehospital setting (1).