13 Public Access Defibrillation
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Chapter 13 / Public Access Defibrillation 229 13 Public Access Defibrillation Vincent N. Mosesso, Jr., MD, FACEP, Mary M. Newman, BS, and Kristin R. Hanson, BA, EMT CONTENTS INTRODUCTION THE CHALLENGE OF PROVIDING EARLY DEFIBRILLATION AUTOMATED EXTERNAL DEFIBRILLATORS STRATEGIES FOR EARLY DEFIBRILLATION EARLY DEFIBRILLATION PROGRAMS AND MODELS ESTABLISHING A COMMUNITY-BASED AED PROGRAM ESTABLISHING AN ON-SITE AED PROGRAM SUMMARY REFERENCES INTRODUCTION The value of early intervention in critically ill patients has long been recognized. As early as the 1700s, scientists recognized the value of mouth-to-mouth respiration and the medical benefits of electricity (1). In the modern era, advances in resuscitation began to proliferate. In 1947, Claude Beck successfully resuscitated a 14-year-old boy through the use of open chest massage and an alternating current (AC) defibrillator, the kind that is used in wall outlets. In 1956, Paul Zoll demonstrated the effectiveness of closed chest massage with the use of an AC defibrillator. In the late 1950s, Peter Safar, William Kouwenhoven, James Jude and others began to study sudden cardiac arrest (CA) and in 1960, they demonstrated the efficacy of mouth-to-mouth ventilation and closed chest cardiac massage (2). In 1961, Bernard Lown demonstrated the superiority of direct current (DC) defibrillators, the kind provided by batteries. In 1966, J. Frank Pantridge and John Geddes developed the world’s first mobile intensive care unit (MICU) in Belfast, Northern Ireland, as a way to bring early advanced medical care to patients with cardiac emergencies (3). In 1969, William Grace established the first MICU in the United States in New York City (4). Subsequently, there were efforts in the United States and throughout the world to emulate and build on this concept. In the late 1960s and early 1970s, paramedic programs were developed by Eugene Nagel in Miami, Leonard Cobb in Seattle, Leonard Rose in Portland, Michael Criley in Los Angeles, and James Warren and Richard Lewis in Columbus. In the 1980s, Mickey Eisenberg, Richard Cummins, From: Contemporary Cardiology: Cardiopulmonary Resuscitation Edited by: J. P. Ornato and M. A. Peberdy © Humana Press Inc., Totowa, NJ 229 230 Cardiopulmonary Resuscitation and colleagues demonstrated the effectiveness of rapid defibrillation in Seattle, Wash- ington (5), while Kenneth Stults demonstrated the same in rural Iowa (6). This growing body of research demonstrated the importance of rapid care for victims of sudden CA by showing that survival improved when basic life support (mouth-to-mouth ventilation and closed chest compressions) was provided within 4 minutes and advanced life sup- port (defibrillation, intravenous medications and fluids, and advanced airway manage- ment) within 8 minutes. Subsequent studies found that the benefits of advanced life support were primarily the result of electrical countershock for patients in ventricular fibrillation (VF). From these findings, a model of care called the “Chain of Survival,” was first described by Mary Newman (7), and then by Cummins et al. (8), and eventually adopted by the Citizen CPR Foundation, the American Heart Association (AHA) and others. The Chain of Survival consists of four action steps that must occur in rapid succession to provide the patient the greatest likelihood for resuscitation: early access (call 911 or the local emergency number to notify the emergency medical services [EMS] system and summon on-site help); early cardiopulmonary resuscitation (CPR; begin immediately); early defibrillation; and early advanced care (transfer care to EMS professionals upon their arrival at the scene). THE CHALLENGE OF PROVIDING EARLY DEFIBRILLATION Growing appreciation of the value of early defibrillation prior to hospital arrival and of the need for improved care of trauma victims led to the development of EMS systems in most nonrural communities throughout the United States. Through the efforts of dedi- cated individuals who underwent training as emergency medical technicians and para- medics, along with government funding of well-equipped ambulances designed specifically for providing emergency medical care outside the hospital, great strides were made in improving the initial care provided to persons with out-of-hospital emergencies. Despite these advances, decades later, the death toll from sudden CA remains as high as 98 to 99% (9,10), with a national average of 93% (11). The reason for the dismal survival rate from sudden CA became profoundly evident— time to intervention. Although the development of EMS systems is perhaps one of the greatest improvements in US health care this century, expecting such systems to effec- tively treat victims of sudden CA within our current medical understanding and the limitations of EMS response intervals clearly is fallacious. Spaite et al. developed a useful description of the time intervals between patient collapse and provision of care (Fig. 1; [12]). There have been many efforts made to shorten each of these time intervals. Addi- tionally, significant advances in each phase of out-of-hospital emergency response have lead to significant improvements over the years. There is clearly a limit, however, to minimizing response-time intervals. Even small improvements in survival come at a high price. Nichol et al. demonstrated that an improvement in response time of 48 seconds would cost an estimated $40,000 to $368,000 per quality adjusted life year gained depen- dent on system configuration (13). Thus, traditional EMS systems should not be expected to provide the first few minutes of emergency cardiovascular care, because it often is not deliverable at a reasonable cost. AUTOMATED EXTERNAL DEFIBRILLATORS Fortunately, medical technology has now provided a solution to this dilemma. The advent of automated external defibrillators (AEDs) now allows persons with very little Chapter 13 / Public Access Defibrillation 231 Fig. 1. Emergency medical services time-interval model. training and no formal medical background to provide the lifesaving intervention of early defibrillation. AEDs are essential weapons in the current battle against sudden CA, and so a brief review of their characteristics is in order. The key components of an AED are as follow: • computer to perform ECG analysis, • battery, • capacitor, • defibrillation pads and connector cable, and • external shell with control buttons. Although each manufacturer’s device varies slightly, they are relatively consistent in their operation. Turning the device on typically initiates a series of verbal instructions. The device prompts the user to attach the defibrillation pads to the patient’s chest. By detecting a change in impedance, the AED knows when the pads have been attached. (In devices in which the pads are not pre-attached, the device will prompt the user to attach the connector cable to the AED.) Once the pads are placed on the chest, the device initiates an electrocardiogram (ECG) analysis, typically evaluating two short segments of ECG strip for morphology, rate, and nonphysiologic signals (artifact and interference). If analysis of both of these segments agrees that a shock is indicated, the device charges the capacitor and advises the user of the finding. When the capacitor is charged, the device prompts the user to push the “shock” button. Some devices currently on the market will warn the user to “clear” the patient, that is, make sure no one is touching the patient, and then automatically deliver the shock, without requiring the user to push any buttons. The AED automatically initiates reanalysis after a shock to determine if another shock is needed; it will repeat this process for up to three consecutive shocks. After a third con- secutive shock, the device will withhold analysis for 1 minute and prompt the user to do CPR during that interval. In all cases, users are guided by voice prompts that transfer decision making from the user to the computerized device. 232 Cardiopulmonary Resuscitation The algorithms used to define shockable rhythms in AEDs have been continually refined over the last 20 years and are now quite sophisticated and accurate. Several evaluations have found their specificity to be close to 100%, which means that the device will not shock ECG rhythms that would not be shocked by an advanced care provider performing manual defibrillation. The sensitivity typically is 90 to 95% with most “misses” being very fine VF (14,15). Multiple models of AEDs are now available and new ones are entering the market on a regular basis (Fig. 2). They include both new brands and upgraded models of existing brands. To see the current models on the market, visit the National Center for Early Defibrillation website (www.early-defib.org) (16). A variety of AED improvements have been proposed recently. One concern is the need to shorten the “hands-off interval,” during which chest compressions are withheld (17).This interval consists of listening to prompts, applying defibrillation pads, AED rhythm analysis, capacitor charging, and shock delivery and typically takes 60 to 90 seconds, even for proficient users. Another consideration is whether or not AEDs should incorporate communication capabilities to automatically alert the local 911 center when and where a device is activated and/or allow the telecommunication officer to speak with the user directly. Both options add additional cost, size, and weight to the device. Thus, the dilemma is whether it is better to have the smallest, most portable, lowest