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The emergency medical services (EMS) system is a complex combination of various providers and facilities that provide three basic medical functions: stabilization, evacuation, and redistribution. Although organizational structures and resources vary worldwide, the fundamental components of any EMS system are essentially the same. This chapter will provide the EMS physician with a vital understanding of the organization of EMS systems and how such design considerations provide ­challenges and opportunities for patient-centered emergency medical care.


  • Define the EMS system in terms of the overall medical response to emergencies.

  • List the original 14 components of an EMS system.

  • List and describe the components of an EMS system as defined by NHTSA.

  • Describe the basic types of emergency medical service agencies.

  • Describe the main differences between urban and rural EMS systems.

  • Discuss how community groups, corporations/businesses, patient advocacy groups, and health care facilities affect EMS system design.

  • Define mutual aid and describe how it is employed in EMS system design.

  • Discuss state, regional, and local EMS councils and/or administrations.

  • Discuss state, regional, and local medical oversight committees.


The entry of a patient into the emergency health care system brings with it a complex cascade of events, with a number of possible outcomes. Figure 12-1 displays a simplified look at the emergency health care system from the time of entry to the time of exit. Most striking to this flow diagram is its serial nature, and therefore, input to one process is limited by its output. This input-throughput-output conceptual model of the emergency health system is essential to consider as one examines the design of EMS systems, as an output limitation such as unstaffed ambulances or hospital crowding will progressively limit the system's ability to function and respond to the demands placed on it.1,2

FIGURE 12-1.

Patient flow within the emergency health care system.

The majority of patients who enter the emergency health care ­system do so by making a telephone call to the 9-1-1 system. The Medical Priority Dispatch System (MPDS) or the Association of Public-Safety Communications Officials (APCO) Emergency Medical Dispatch Program are specifically designed to abstract this caller information through a question-driven protocol and direct appropriate resources based on that information. Although a complete discussion of Emergency Medical Dispatch will be covered in Chapter 15, it is important to recognize that nearly all public safety answering points (PSAPs) are able to begin rendering care for the patient over the phone by using prescripted, postdispatch, and prearrival instructions.3-6 The instructions could include directing a bystander to perform CPR, assist with the delivery of a newborn, or direct self-care such as hemorrhage control or aspirin administration. Further, the prioritization of requests for EMS service through any call-taking program ...

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