While it is clear that ALS saves lives after sudden cardiac arrest, the number of lives saved and the cost are often debated. 56 Since sudden cardiac death (SCD) is the number one cause of out-of-hospital death in the United States, the potential benefit of treatment is enormous. Some have argued that the successful treatment of out-of-hospital cardiac arrest alone by EMS systems justifies their existence.6 Population studies with an age distribution of the entire US population find that the annual incidence of out-of-hospital cardiac arrest is about 1 per 1000. 6 In regions with a higher concentration of elderly persons, the annual incidence is higher.
Without treatment at the scene, the survival rate of out-of-hospital cardiac arrest is virtually zero. Early studies by groups in Seattle and King County, Washington, have demonstrated that as many as 26 percent of patients may be successfully resuscitated from out-of-hospital cardiac arrest. 5 Resuscitation rates in other communities are not as high. The overwhelming majority of survivors of out-of-hospital sudden cardiac arrest were those whose cardiac arrests were witnessed and who had an initial cardiac rhythm of ventricular fibrillation (VF). Multiple studies have shown that survival is clearly related to the time from the collapse of the patient to the delivery of defibrillation and that survival rates decline dramatically with delays of only a few minutes. 7
These findings have lead a number of physicians to train FRs or EMT-Bs, who usually arrive first at the scene of an emergency, to recognize and treat VF. Systems in King County, Washington, and in Iowa have documented that this approach improves survival from cardiac arrest if the interval between collapse and defibrillation is short. That observation has lead to the wide proliferation of automated external defibrillators (AEDs). The American Heart Association has identified AED defibrillation as the standard of care for vehicles that respond to emergencies and transport patients. However, there is conflicting evidence concerning whether equipping FRs or EMT-Bs with AEDs incrementally improves survival in an existing EMS system with paramedics.2 Clearly, a cost-benefit analysis should be undertaken in individual systems, and, if implementation of AEDs by police or fire FRs can significantly decrease the time to defibrillation in a system, this modality should be part of the system. Automatic defibrillation is clearly efficacious, but for maximum benefit (more survivors in the community) the local system must optimize the "chain of survival": early access, early CPR, early defibrillation, and early ALS. 7 Citizen awareness of the signs of cardiac arrest, quick access to the system, and rapid and appropriate dispatch of units are all critical links to maximizing survival. Pilot programs are being conducted to test whether laypersons, or targeted FRs, such as casino security guards, can effectively utilize AEDs to treat SCD patients.
Despite the emphasis on cardiac arrest during the development of EMS systems, such cases make up less than 5 percent of the volume of an EMS system. The most common clinical entities seen in EMS systems are the manifestations of cardiac disease, usually ischemic chest pain and its complications. Common treatment includes relief of ischemic chest pain with nitrates and narcotic analgesics, control of cardiac arrhythmias with antiarrhythmics, treatment of symptomatic bradyarrhythmias with external pacemakers, and treatment of congestive failure with diuretics and, if necessary, endotracheal intubation. While most EMS authorities agree that such treatment to prevent a cardiac arrest is the true benefit of an ALS system, there is a lack of research to document this assertion.
Many EMS systems are now also facilitating emergency department care through the field use of 12-lead electrocardiography (ECG). Either paramedics interpret the initial rhythm or a computer-generated algorithm is used to diagnose an AMI and contact an intended receiving facility. Limited studies have found that field ECG decreases the time to initiate thrombolysis or to perform angioplasty in patients with AMI. Some EMS systems have used field 12-lead ECG to triage AMI patients to "cardiac centers" that have been prospectively identified to provide emergency angioplasty.
Early administration of thrombolytics has been shown to significantly reduce mortality and morbidity. Logistical obstacles to field thrombolytic therapy include the difficulty in diagnosing myocardial infarction in the field, identification of contraindications by paramedics, and management of complications by the limited resources available in the field. Studies of field administration of thrombolytics by paramedics have identified that this therapeutic approach is feasible, but it does not improve outcome when compared to patients who are diagnosed in the field (by 12-lead ECG) and are treated promptly on arrival in the emergency department. 8
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