Part 4: The Automated External Defibrillator
2000; Lippincott Williams & Wilkins; Volume: 102; Issue: suppl_1 Linguagem: Inglês
10.1161/circ.102.suppl_1.i-60
ISSN1524-4539
Tópico(s)Mechanical Circulatory Support Devices
ResumoHomeCirculationVol. 102, No. suppl_1Part 4: The Automated External Defibrillator Free AccessOtherDownload EPUBAboutView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessOtherDownload EPUBPart 4: The Automated External Defibrillator Key Link in the Chain of Survival Originally published22 Aug 2000https://doi.org/10.1161/circ.102.suppl_1.I-60Circulation. 2000;102:I-60–I-76Other version(s) of this articleYou are viewing the most recent version of this article. Previous versions: August 22, 2000: Previous Version of Record Major Guidelines ChangesFollowing are the major guidelines changes related to use of automated external defibrillators (AEDs) in basic life support: Early defibrillation (shock delivery within 5 minutes of EMS call receipt) is a high-priority goal.Healthcare providers with a duty to perform CPR should be trained, equipped, and authorized to perform defibrillation (Class IIa).For in-hospital defibrillation: a. Early defibrillation capability, which is defined as having appropriate equipment and trained first responders, should be available throughout hospitals and affiliated outpatient facilities (Class IIa).b. The goal of early defibrillation by first responders is a collapse-to-shock interval, when appropriate, of <3 minutes in all areas of the hospital and ambulatory care facilities (Class I).c. Response time intervals for in-hospital resuscitation events are often inaccurate and must be corrected before documented times to defibrillation can be considered reliable (Class IIa).Evidence supports establishment of public access defibrillation (PAD) programs in the following cases: a. The frequency of cardiac arrest events is such that there is a reasonable probability of one AED use in 5 years (estimated event rate of 1 sudden cardiac arrest per 1000 person-years).b. An EMS call–to-shock time interval of 25 kg body weight) is a Class IIb recommendation.Use of AEDs in infants and children <8 years of age is not recommended (Class Indeterminate).Biphasic waveform defibrillation with shocks ≤200 J is safe and has equivalent or higher efficacy for termination of ventricular fibrillation (VF) compared with higher-energy escalating monophasic-waveform shocks (Class IIa).IntroductionPublic access defibrillation, which places AEDs in the hands of trained laypersons, has the potential to be the single greatest advance in the treatment of VF cardiac arrest since the development of CPR.1234567891011 Time to defibrillation is the most important determinant of survival from cardiac arrest.12345678910111213141516 PAD provides the opportunity to defibrillate victims of cardiac arrest within a few minutes, even at sites remote from traditional EMS responders. Extraordinary survival rates—as high as 49%—have been reported in PAD programs.1718192021222324 These rates are twice those previously reported for the most effective EMS systems.25AEDs are sophisticated, computerized devices that are reliable and simple to operate, enabling lay rescuers with minimal training to administer this lifesaving interven-tion.12345678910111213141516171819202122232426 Flight attendants, security personnel, sports marshals, police officers, firefighters, lifeguards, family members, and many other trained laypersons have used AEDs successfully.15161718192021222324 AEDs are located in airports, airplanes, casinos, high-rise office buildings, housing complexes, recreational facilities, shopping malls, golf courses, and numerous other public locations.15162324272829 AEDs are also used by healthcare professionals in ambulances, hospitals, dental clinics, and physicians' offices.293031323334With the inclusion of AED use as a BLS skill, BLS now encompasses the first 3 links in the Chain of Survival (early access, early CPR, and early defibrillation).35 AEDs widely used by the public and distributed throughout the community significantly advance the concept proposed more than 2 decades ago: the community should become the "ultimate coronary care unit."36Principle of Early DefibrillationEarly defibrillation is critical to survival from cardiac arrest for several reasons: (1) the most frequent initial rhythm in witnessed sudden cardiac arrest is VF; (2) the most effective treatment for VF is electrical defibrillation; (3) the probability of successful defibrillation diminishes rapidly over time; and (4) VF tends to convert to asystole within a few minutes.2537383940414243444546 Many adults in VF can survive neurologically intact even if defibrillation is performed as late as 6 to 10 minutes after sudden cardiac arrest, particularly if CPR is provided.2537383940414243444546 The performance of CPR while awaiting the arrival of the AED appears to prolong VF, contributing to preservation of heart and brain function.3940 Basic CPR, however, is unlikely to convert VF to a normal rhythm.The speed with which defibrillation is performed is the major determinant of the success of resuscitative attempts for treatment of VF cardiac arrest.38394041424344454647484950515253545556 Survival rates after VF cardiac arrest decrease approximately 7% to 10% with every minute that defibrillation is delayed.2537383940414243444546474849505152 (See Figure 1.41 ) A survival rate as high as 90% has been reported when defibrillation is achieved within the first minute of collapse.43444546 When defibrillation is delayed, survival rates decrease to approximately 50% at 5 minutes, approximately 30% at 7 minutes, approximately 10% at 9 to 11 minutes, and approximately 2% to 5% beyond 12 minutes.2537383940414243444546474849505152 One historical observational study suggests that survival may be improved if CPR is performed by first responders for 1 minute before defibrillation when defibrillation is delayed ≥4 minutes57 and no bystander CPR is performed.Survival rates from cardiac arrest can be remarkably high if the event is witnessed. For example, when people in supervised cardiac rehabilitation programs experience a witnessed cardiac arrest, defibrillation is usually performed within minutes; in 4 studies of cardiac arrest in this setting, 90 of 101 victims (89%) were resuscitated.43444546 This is the highest survival rate reported for a defined out-of-hospital population.Communities with no out-of-hospital ACLS services but with early defibrillation programs have reported improved survival rates among patients with cardiac arrest when survival rates for EMT care with and without AEDs were compared.4748495051 The most impressive results were reported by King County, Washington, where the survival rate of patients with VF improved from 7% to 26%,47 and rural Iowa, where the survival rate rose from 3% to 19%.48 More modest results have been observed in rural communities in southeastern Minnesota,49 northeastern Minnesota,50 and Wisconsin.51 After implementation of early defibrillation programs by EMS personnel in 5 European regions, survival to discharge from VF cardiac arrest was as high as 27% to 55%.58Clearly the earlier defibrillation occurs, the better the prognosis.38394041424344454647484950515253545556 Emergency personnel have only a few minutes after a victim's collapse to reestablish a perfusing rhythm. CPR can sustain a patient for a short time but cannot directly restore an organized rhythm. Restoration of an adequate perfusing rhythm requires defibrillation and advanced cardiovascular care, which must be administered within a few minutes of the initial arrest.37 The use of AEDs increases the range of personnel who can use a defibrillator, shortening the time between collapse and defibrilla-tion.474849505153545556 This exciting prospect accounts for the addition of this intervention as an integral component of BLS.Early defibrillation (shock within 5 minutes of EMS call receipt) is a high-priority goal of EMS care. Every community should assess its capability to provide this intervention and institute whatever measures are necessary to make this recommendation a reality.History of AEDsIn a prophetic report of what was to follow in the next 2 decades, Diack and colleagues59 described experimental and clinical experience with the first AED. Subsequently, other studies provided supportive evidence for the potential role of such a device for widespread provision of rapid defibrillation.606162In the ensuing years, clinical studies have documented various aspects of AED performance, confirming the high sensitivity and specificity of the AED algorithms as well as the safety and efficacy of the devices.626364656667686970717273747576Another major advance in the use of AEDs was the development of a small (6.25-lb) AED specifically designed for home use. This AED delivered up to 3 nonescalating 180-J monophasic damped sinusoidal shocks and instructed the operator with easy-to-follow audible prompts. New AED models and manufacturers soon entered the field. Clinical evaluation confirmed the safety and efficacy of this AED in termination of out-of-hospital VF arrest.727677 Home trials were conducted and reported, but the concept of home defibrillation for patients at high risk was not yet ready for acceptance.151678798081In the last few years there has been a significant increase in the use of AEDs in early defibrillation programs in a variety of settings, including EMS systems, police departments, casinos, airport terminals, and commercial aircraft, among others.121317182021222324828384 In most of these settings, use of AEDs by BLS ambulance providers or first responders (PAD level 1 responders) in early defibrillation programs has been associated with a significant increase in survival rates. In some cases no benefit from such early defibrillation has been observed, usually in rural areas or systems in which EMS response is rapid enough to preclude benefit.148586 Also, improved survival will not be likely when infrequent bystander CPR and delays in dispatch impose weaknesses in other aspects of the Chain of Survival.87 Long arrest-to-shock times (mean 23.8 minutes) and a low occurrence of bystander CPR (9%) were accompanied by a low survival rate (6%) from VF after introduction of AEDs in a large Asian city.88 These and similar studies suggest that the introduction of AEDs into ambulance services may not significantly improve outcome unless other links in the Chain of Survival are optimized.87 Guidelines for implementation of early defibrillation programs have been published that emphasize the components that are likely to result in improved patient outcomes, especially the critical links in the Chain of Survival.899091Advances in defibrillation waveform technology have been incorporated into AEDs, following the transition from monophasic to biphasic waveforms with implantable cardioverter-defibrillators (ICDs).91A Experimental and clinical evidence supporting the transition to biphasic waveforms in ICDs was abundant and consistent.9293949596979899100101 The use of biphasic defibrillation waveforms permits a reduction in the size and weight of AEDs, a major consideration in many settings, such as aircraft. Recommendations for specifying algorithm performance and demonstrating the equivalence of alternative waveforms were published by the American Heart Association Subcommittee on AED Safety and Efficacy in 1997.102Contemporary AEDsThe term "AED" refers to an automated external defibrillator that incorporates a rhythm analysis system and a shock-advisory system.103104 The AED "advises" a shock and the operator must take the final action (press the SHOCK button) to deliver the shock. Fully automated external defibrillators do not require pressing the SHOCK button, and they are available only for special situations.Automated Analysis of Cardiac RhythmsCurrent AEDs are highly sophisticated, microprocessor-based devices that analyze multiple features of the surface ECG signal, including frequency, amplitude, and some integration of frequency and amplitude, such as slope or wave morphology (Figure 2). Various filters check for QRS-like signals, radio transmission, or 50- or 60-cycle interference as well as loose electrodes and poor electrode contact. Some intermittent radio transmissions can produce an ECG artifact if a transmitter or receiver is used within 6 feet of a patient during rhythm analysis. Some devices are programmed to detect spontaneous movement by the patient or movement of the patient by others.103104AEDs have been extensively tested, both in vitro against libraries of recorded cardiac rhythms105 and clinically in numerous field trials.5960626364676872 Their accuracy in rhythm analysis is high.626364 The rare errors noted in field trials have been almost solely errors of omission (sensitivity) in which the device failed to recognize certain varieties of VF or tachycardia or when operators failed to follow recommended operating procedures, such as avoidance of patient movement.66Inappropriate Shocks or Failure to ShockExtensive clinical experience has revealed that AEDs are infrequently affected by movement of the patient (eg, seizures and agonal respirations), repositioning of the patient, or artifactual signals, although some rare difficulties have been reported.596062636466676872 Failure to follow the manufacturer's instructions for use of a fully automated external defibrillator has in rare instances (<0.1%) resulted in delivery of inappropriate electrical countershocks.12 AEDs should be placed in the analysis mode only when full cardiac arrest has been confirmed and only when all movement, particularly patient transport, has ceased. Agonal respiration poses a problem because some devices may not be able to complete analysis cycles if the patient continues to have gasping respirations. Use of radio receivers and transmitters should be avoided during rhythm analysis. The major errors reported in clinical trials have been occasional failures to deliver shocks to rhythms that may benefit from electrical therapy, such as extremely fine or coarse VF.626466 Occasionally the analysis and treatment cycles of implanted and automated defibrillators can conflict.6466106Ventricular TachycardiaAlthough AEDs are not designed to deliver synchronized shocks, all AEDs will shock monomorphic and polymorphic ventricular tachycardia (VT) if the rate exceeds preset values. AEDs should be operated only on patients who are unresponsive, not breathing, and have no signs of circulation.With this approach, the operator serves as a second verification system to confirm that the patient has suffered a cardiac arrest. In an apneic patient without signs of life, electrical shocks are indicated whether the rhythm is supraventricular tachycardia (SVT), VT, or VF. There have been rare reports of shocks delivered to responsive patients with perfusing ventricular or supraventricular arrhythmias.1262 These are operator errors, not device errors, and are preventable when rescuers are well trained and possess good patient assessment skills.67Throughout this chapter, for laypersons the term "signs of circulation" means quickly evaluating the victim for normal breathing, coughing, or movement. For healthcare professionals the term "signs of circulation" means quickly performing a pulse check while simultaneously evaluating the victim for breathing, coughing, or movement.Waveforms and Energy LevelsThe energy settings for defibrillators are designed to provide the lowest effective energy needed to terminate VF. If energy and current are too low, the shock will not terminate the arrhythmia; if energy and current are too high, myocardial damage may result.107108109110111 There is no clear relation between body size and energy requirements for defibrillation in adults. Modern AEDs fall into 2 broad categories of waveforms: monophasic and biphasic. Energy levels vary by type of device. Monophasic waveforms deliver current that is primarily of 1 polarity (ie, direction of current flow). They are further subdivided by the rate at which the current pulse decreases to zero; namely, either gradually (damped sinusoidal or instantaneously (truncated exponential). The waveforms of biphasic defibrillators indicate a sequence of 2 current pulses; the polarity of the second is opposite that of the first.In a prospective out-of-hospital study of monophasic manual defibrillators, defibrillation rates and the proportion of patients resuscitated and later discharged from the hospital were virtually identical in patients who received initial monophasic damped sine (MDS) waveform shocks of 175 J and 320 J.112 The recommended first-shock energy for monophasic waveform defibrillation is 200 J.112 For monophasic devices the recommended second shock is 200 to 300 J; the recommended third shock is 360 J.112 The intent of this escalating energy dosage protocol is to maximize shock success (termination of VF) while minimizing shock toxicity.107108109110111The first biphasic waveform for use in an AED was approved in the United States in 1996. This impedance-compensating biphasic truncated exponential (BTE) waveform was incorporated into an AED that discharged nonescalating 150-J shocks. Impedance compensation was achieved by adjusting first-phase tilt, relative duration of the 2 phases, and total duration to a maximum of 20 ms. Experimental work in animals suggested the superiority of this waveform over monophasic truncated exponential (MTE) waveforms.113 In-hospital studies during ICD testing compared 115-J and 130-J shocks using the BTE waveform with MDS waveform shocks of 200 J and 360 J.114115 This in-hospital data indicated that for short-duration VF, BTE shocks at low energy (115 J and 130 J) were as effective as the 200-J MDS shocks traditionally used for the first shock.114115 Fewer ST-segment changes were observed after transthoracic defibrillation of short-duration VF with the 115- and 130-J BTE shocks compared with those after 200-J MDS shocks.116Another in-hospital study comparing an MDS waveform with a damped sinusoidal version of a biphasic waveform ("Gurvich") concluded that this biphasic waveform was likewise superior to the MDS waveform in terminating short-duration VT and VF.117Early clinical experience with the 150-J, impedance-compensated BTE waveform for treatment of out-of-hospital long-duration VF was also positive.118119 This experience, along with in-hospital clinical data, formed the basis for the AHA evidence-based review of this low-energy biphasic waveform defibrillation, which led to an initial Class IIb recommendation.120 Since then, cumulative experience with this waveform in 100 patients with VF was reported, confirming its efficacy in terminating VF arrest outside the hospital.121 The aggregate data with this waveform in VF arrest from one EMS system (Rochester, Minn) also affirmed the efficacy of this waveform for terminating VF.82 This experience was compared retrospectively with that of the MDS waveform in the same EMS system.82 The growing body of evidence is now considered sufficient to support a Class IIa recommendation for this low-energy, BTE waveform.Other versions of biphasic waveforms have been introduced and have undergone initial evaluation during electrophysiology study and ICD implantation and testing. Experience with short-duration VF, in which a low-energy (120- to 170-J), constant-current, rectilinear biphasic waveform was used has recently been reported.122 This waveform has also been very effective in terminating atrial fibrillation during elective cardioversion with energies as low as 70 J.123 At this time no studies have reported experience with other biphasic waveforms in long-duration VF in out-of-hospital arrest. When such data becomes available, it will need to be assessed by the same evidence-evaluation process as used for the biphasic AED and this guidelines process.The data indicates that biphasic waveform shocks of relatively low energy (≤200 J) are safe and have equivalent or higher efficacy for termination of VF compared with higher-energy escalating monophasic waveform shocks (Class IIa). The safety and efficacy data related to specific biphasic waveforms must be evaluated on an individual basis in both in-hospital (electrophysiology studies, ICD testing) and out-of-hospital settings.Evaluation of Defibrillation Waveform PerformanceThe evaluation of defibrillation shock waveform efficacy requires the adoption of standard descriptors of defibrillation and postshock rhythms.124 Clinical investigators should uniformly apply such descriptors in the assessment of defibrillation waveforms. The term "defibrillation" means reversal of the action of fibrillation. Defibrillation is not a synonym for "shock." Thus, defibrillation should be understood to mean termination of fibrillation and should not be confused with other resuscitation outcomes, such as restoration of a perfusing rhythm, admission to hospital, or discharge survival.125 These additional end points may occur during resuscitation as a consequence of many variables, including time from collapse to shock and other interventions, such as CPR and drug therapy.In several recent studies,82119126 a successful defibrillatory shock was defined as the absence of VF 5 seconds after shock delivery. This definition of shock outcome was one of several considered by the 1999 Evidence Evaluation experts as acceptable to define "success" in evaluation of defibrillator waveforms. Thus, asystole or non-VF electrical activity at the postshock end point constitutes "success" because VF has been terminated. This is consistent with data from electrophysiological mapping studies confirming the time course of termination of VF after shock delivery, and clinically it is an easily measurable point in time after a shock.127128 At this point the direct effect of the shock on VF is not influenced by many other interventions that may ensue after shock delivery, such as chest compressions, ventilation, and administration of drugs, which themselves have an impact on cardiac rhythm after shocks. Examining the rhythm 5 seconds after each of the first series of shocks, before any drugs or other advanced life support interventions are initiated, will yield the most useful specific information about shock efficacy. In addition, tracking the postshock rhythm during the first minute after shock delivery will provide additional data, such as whether an organized rhythm is supraventricular or idioventricular and whether or not a perfusing rhythm accompanies restoration of organized electrical activity.As new defibrillation waveforms evolve and are evaluated in out-of-hospital arrest, it is essential that standardized definitions of shock efficacy be accepted and uniformly applied by clinical investigators engaged in waveform research. The definitions proposed here help meet that need.Operation of the AEDBefore attaching the AED, the operator should first determine whether special situations exist that contraindicate the use of the AED or require additional actions before its use.Special Situations That May Require Additional ActionsWhile preparing to use the AED, the operator must identify 4 possible circumstances (special situations) that may require rescuers to modify their actions before or during AED use. These situations include victims in water, those <8 years of age or <25 kg, those with transdermal medication patches, and those with implanted pacemakers or ICDs. Metal surfaces are not included as a special circumstance because they pose no shock hazard to either victim or rescuer.WaterWater is a good conductor of electricity and may provide a pathway for energy from the AED to rescuers and bystanders treating the victim. There is a small possibility that rescuers or bystanders may receive shocks or minor burns if they are within such a pathway. Water on the skin of the chest can also provide a direct path of energy from one electrode pad to the other (arcing) and can decrease the effectiveness of the shock delivered to the heart. It is critical to quickly remove the victim from freestanding water and dry the victim's chest before using the AED. If the victim has a diving injury or other possible spinal injury, care should be taken to maintain cervical spine immobilization while moving the victim and performing resuscitation.ChildrenCardiac arrest is less common in children than adults, and its causes are more diverse.129130131132 Approximately 50% of pediatric cardiac arrests occur in children <1 year old.129 Most of these are caused by sudden infant death syndrome and respiratory disease.129130131132 Beyond the first 6 months of life, injuries and drowning are the major causes of cardiac arrest.129130131132 The most common terminal rhythm observed in patients ≤17 years of age is asystole or pulseless electrical activity.129131132133134135136137 When pediatric cardiac arrest rhythms are reported, estimates of VF range from 7% to 15%.129131133134135138 In some studies, pediatric patients with VF who receive defibrillation at the scene have a higher initial resuscitation rate and are more likely to be discharged from the hospital with good neurological outcomes than pediatric patients who present with non-VF rhythms.131133Experience with AEDs in children is very limited. The sensitivity and specificity for children of the AED algorithm need further study. The data suggests that AEDs can accurately detect VF in children of all ages (sensitivity),139140141 but there is inadequate data on the ability of AEDs to correctly identify nonshockable tachycardic rhythms in infants (specificity).141 Although the available data is encouraging, more data in larger pediatric populations is needed to define AED algorithm sensitivity and specificity.More studies are also needed to determine AED energy doses that are safe and effective for children. In adults, clinical reports of biphasic waveform AED use have described energy doses as low as 120 J, with success rates equal to 200-J monophasic shocks for termination of VF; less postresuscitation myocardial dysfunction was observed after lower-energy shocks.122142143 Currently available AEDs deliver energy doses that exceed the recommended monophasic dose of 2 to 4 J/kg in most children 25 kg; therefore, the delivered initial dose from a monophasic or biphasic AED (150 to 200 J) will be 25 kg body weight), particularly in the out-of-hospital setting. A weight of 25 kg corresponds to a body length of approximately 50 in (128 cm) using a Broselow color-coded tape.144AIn summary, although VF is not a common arrhythmia in children, it is observed in as many as 15% of pediatric and adolescent arrests.129131133134135137 In these patients rapid defibrillation may improve outcomes.131133138 Multicenter or controlled studies of AED algorithm sensitivity and specificity are needed, as well as a clearer definition of appropriate energy doses for children of all ages and sizes.For these reasons, use of AEDs in children ≥8 years old (approximately >25 kg body weight) is a Class IIb recommendation. Use of AEDs in infants and children <8 years old is not recommended, primarily because of the lack of data concerning sensitivity, specificity, safety, and efficacy (Class Indeterminate). Healthcare providers who routinely care for children at risk for arrhythmias and cardiac arrest (eg, in-hospital settings) should continue to use defibrillators capable of appropriate energy adjustment. For infants and children <8 years old who are in cardiac arrest, the initial priorities continue to be support of the airway, oxygenation, and ventilation.Transdermal MedicationsAED electrodes should not be placed directly on top of a transdermal medication patch (eg, nitroglycerin, nicotine, analgesics, hormone replacements, antihypertensives), because the patch may block delivery of energy from the electrode pad to the heart and may cause small burns to the skin.145 The only problems reported with shocks over a transdermal patch have involved patches with a metal backing. Metal backing for patches is no longer being used, so this potential problem has been eliminated. Medication patches should be removed and the area wiped clean before the AED electrode pad is attached.Implanted Pacemakers/ICDsDefibrillators that deliver a limited number of low-energy shocks directly to the myocardium have been implanted in selected patients with a history of malignant arrhythmias. These devices create a hard lump beneath the skin of t
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