Automated external defibrillator | |
---|---|
Acronym | AED |
Synonyms | defibrillator, defib |
Specialty | Cardiology |
Inventor(s) | Frank Pantridge |
Related items | Manual defibrillator |
An automated external defibrillator or automatic electronic defibrillator (AED) is a portable electronic device that automatically diagnoses the life-threatening cardiac arrhythmias of ventricular fibrillation (VF) and pulseless ventricular tachycardia, [1] and is able to treat them through defibrillation, the application of electricity which stops the arrhythmia, allowing the heart to re-establish an effective rhythm.
With simple audio and visual commands, AEDs are designed to be simple to use for the layperson, and the use of AEDs is taught in many first aid, certified first responder, and basic life support (BLS) level cardiopulmonary resuscitation (CPR) classes. [2]
The portable version of the defibrillator was invented in the mid-1960s by Frank Pantridge in Belfast, Northern Ireland and the first automatic, public-use defibrillator was produced by the Cardiac Resuscitation Company in the late 1970s. The unit was launched under the name Heart-Aid. [3]
An automated external defibrillator is used in cases of life-threatening cardiac arrhythmias which lead to sudden cardiac arrest, which is not the same as a heart attack. The rhythms that the device will treat are usually limited to:
In each of these two types of shockable cardiac arrhythmia, the heart is electrically active, but in a dysfunctional pattern that does not allow it to pump and circulate blood. In ventricular tachycardia, the heart beats too fast to effectively pump blood. Ultimately, ventricular tachycardia leads to ventricular fibrillation. In ventricular fibrillation, the electrical activity of the heart becomes chaotic, preventing the ventricle from effectively pumping blood. The fibrillation in the heart decreases over time, and will eventually reach asystole.
AEDs, like all defibrillators, are not designed to shock asystole ('flat line' patterns) as this will not have a positive clinical outcome. The asystolic patient only has a chance of survival if, through a combination of CPR and cardiac stimulant drugs, one of the shockable rhythms can be established, which makes it imperative for CPR to be carried out prior to the arrival of a defibrillator.
Uncorrected, these cardiac conditions (ventricular tachycardia, ventricular fibrillation, asystole) rapidly lead to irreversible brain damage and death, once cardiac arrest takes place. After approximately three to five minutes in cardiac arrest, [4] irreversible brain/tissue damage may begin to occur. For every minute that a person in cardiac arrest goes without being successfully treated (by defibrillation), the chance of survival decreases by 7 percent per minute in the first three minutes, and decreases by 10 percent per minute as time advances beyond ~three minutes. [5]
AEDs are designed to be used by laypersons who ideally should have received AED training. However, sixth-grade students have been reported to begin defibrillation within 90 seconds, as opposed to a trained operator beginning within 67 seconds. [6] This is in contrast to more sophisticated manual and semi-automatic defibrillators used by health professionals, which can act as a pacemaker if the heart rate is too slow (bradycardia) and perform other functions which require a skilled operator able to read electrocardiograms.
Bras with a metal underwire and piercings on the torso must be removed before using the AED on someone to avoid interference. [7] [8] The American television show MythBusters found evidence that use of a defibrillator on a woman wearing an underwire bra can lead to arcing or fire but only in unusual and unlikely circumstances. [9]
In a study analyzing the effects of having AEDs immediately present during Chicago's Heart Start program over a two-year period, of 22 individuals, 18 were in a cardiac arrhythmia which AEDs can treat. Of these 18, 11 survived. Of these 11 patients, 6 were treated by bystanders with absolutely no previous training in AED use. [10] [11]
Automated external defibrillators are generally either kept where health professionals and first responders can use them (health facilities and ambulances) as well as public access units which can be found in public places including corporate and government offices, shopping centres, restaurants, public transport, and any other location where people may congregate.
In order to make them highly visible, public access AEDs are often brightly coloured and are mounted in protective cases near the entrance of a building. When these protective cases are opened or the defibrillator is removed, some will sound a buzzer to alert nearby staff to their removal, though this does not necessarily summon emergency services; trained AED operators should know to phone for an ambulance when sending for or using an AED. In September 2008, the International Liaison Committee on Resuscitation issued a 'universal AED sign' to be adopted throughout the world to indicate the presence of an AED, and this is shown on the right. [12]
A trend that is developing is the purchase of AEDs to be used in the home, particularly by those with known existing heart conditions. [13] The number of devices in the community has grown as prices have fallen to affordable levels. There has been some concern among medical professionals that these home users do not necessarily have appropriate training, [14] and many advocate the more widespread use of community responders, who can be appropriately trained and managed.
Typically, an AED kit will contain a face shield for providing a barrier between patient and first aider during rescue breathing; a pair of nitrile rubber gloves; a pair of trauma shears for cutting through a patient's clothing to expose the chest; a small towel for wiping away any moisture on the chest, and a razor for shaving those with very hairy chests. [15]
Most manufacturers recommend checking the AED before every period of duty or on a regular basis for fixed units. Some units need to be switched on in order to perform a self check; other models have a self check system built in with a visible indicator.
All manufacturers mark their electrode pads with an expiration date, and it is important to ensure that the pads are in date. The typical life expectancy of AED pads are between 18 and 30 months. [16] This is usually marked on the outside of the pads. Some models are designed to make this date visible through a 'window', although others will require the opening of the case to find the date stamp.[ citation needed ]
It is also important to ensure that the AED unit's batteries have not expired. The AED manufacturer will specify how often the batteries should be replaced. Each AED has a different recommended maintenance schedule outlined in the user manual. Common checkpoints on every checklist, however, also include a monthly check of the battery power by checking the green indicator light when powered on, condition and cleanliness of all cables and the unit, and check for the adequate supplies. [17]
An AED is "automatic" because of the unit's ability to autonomously analyse the patient's condition. To assist this, the vast majority of units have spoken prompts, and some may also have visual displays to instruct the user.
"External" refers to the fact that the operator applies the electrode pads to the bare chest of the victim (as opposed to internal defibrillators, which have electrodes surgically implanted inside the body of a patient).
When turned on or opened, the AED will instruct the user to connect the electrodes (pads) to the patient. Once the pads are attached, everyone should avoid touching the patient so as to avoid false readings by the unit. The pads allow the AED to examine the electrical output from the heart and determine if the patient is in a shockable rhythm (either ventricular fibrillation or ventricular tachycardia). If the device determines that a shock is warranted, it will use the battery to charge its internal capacitor in preparation to deliver the shock. The device system is not only safer - charging only when required, but also allows for a faster delivery of the electric current.
When charged, the device instructs the user to ensure no one is touching the patient and then to press a button to deliver the shock; human intervention is usually required to deliver the shock to the patient in order to avoid the possibility of accidental injury to another person (which can result from a responder or bystander touching the patient at the time of the shock). Depending on the manufacturer and particular model, after the shock is delivered most devices will analyze the patient and either instruct CPR to be performed, or prepare to administer another shock.
Many AED units have an 'event memory' which store the ECG of the patient along with details of the time the unit was activated and the number and strength of any shocks delivered. Some units also have voice recording abilities [18] to monitor the actions taken by the personnel in order to ascertain if these had any impact on the survival outcome. All this recorded data can be either downloaded to a computer or printed out so that the providing organisation or responsible body is able to see the effectiveness of both CPR and defibrillation. Some AED units even provide feedback on the quality of the compressions provided by the rescuer. [19] [20]
The first commercially available AEDs were all of a monophasic type, which gave a high-energy shock, up to 360 to 400 joules depending on the model. This caused increased cardiac injury and in some cases second and third-degree burns around the shock pad sites. Newer AEDs (manufactured after late 2003) have tended to utilise biphasic algorithms which give two sequential lower-energy shocks of 120–200 joules, with each shock moving in an opposite polarity between the pads. Others may give a stepped approach to energy delivery, usually in a 200J, a second 200J, then 300J, and finally 360J shock, with any further shocks also being 360 Joules. This lower-energy waveform has proven more effective in clinical tests, as well as offering a reduced rate of complications and reduced recovery time. [21]
Unlike regular defibrillators, an automated external defibrillator (AED) requires minimal training to be used (or even no training). That is possible because all AEDs approved for use in the United States and many other countries use an electronic voice to prompt users through each step. Many AEDs now include visual prompts in case of a hearing impaired user. Most units are designed for use by non-medical operators. Their ease of use has given rise to the notion of public access defibrillation (PAD).
An AED automatically diagnoses the heart rhythm and determines if a shock is needed. Automatic models will administer the shock without the user's command. Semi-automatic models will tell the user that a shock is needed, but the user must tell the machine to do so, usually by pressing a button. In most circumstances, the user cannot override a "no shock" advisory by an AED. Some AEDs may be used on children – those under 55 lbs (25 kg) in weight or under age 8. If a particular model of AED is approved for pediatric use, all that is required is the use of more appropriate pads[ failed verification ]. [22]
Observational studies have shown that in out of hospital cardiac arrest, public access defibrillators when used were associated with 40% median survival. When operated by non-dispatched lay first responders they have the highest likelihood of leading to survival. [23]
Automated external defibrillators are now easy enough to use that most states in the United States include the "good faith" use of an AED by any person under Good Samaritan laws. [24] "Good faith" protection under a Good Samaritan law means that a volunteer responder (not acting as a part of one's occupation) cannot be held civilly liable for the harm or death of a victim by providing improper or inadequate care, given that the harm or death was not intentional and the responder was acting within the limits of their training and in good faith. In the United States, Good Samaritan laws provide some protection for the use of AEDs by trained and untrained responders. [25] AEDs create little liability if used correctly; [26] NREMT-B and many state Emergency Medical Technician (EMT) training and many CPR classes incorporate or offer AED education as a part of their program.
In addition to Good Samaritan laws, Ontario, Canada also has the "Chase McEachern Act (Heart Defibrillator Civil Liability), 2007 (Bill 171 – Subsection N)", passed in June, 2007, [27] which protects individuals from liability for damages that may occur from their use of an AED to save someone's life at the immediate scene of an emergency unless damages are caused by gross negligence.
Legislation in Australia varies by state, with separate liability issues relating to providing and using AED equipment. Each state and territory has enacted "Good Samaritan" laws that offer legal protection to a person who gives assistance in a medical emergency - the standard of care expected corresponds to their training (or lack of training). [28] In New South Wales, the Work Health and Safety Regulation (2011) requires an employer to use a risk assessment to ensure that there is adequate provision for first aid; when there is a sufficient risk it warrants providing a defibrillator. [29]
In 2012, AED's (automated external defibrillators) were under scrutiny by the U.S. Food and Drug Administration (FDA) which considered reclassifying AEDs as class III premarket approval devices. Technical malfunctions likely contributed to more than 750 deaths in the 5-year period between 2004 and 2009, in most cases by component failures or design errors. During the same period, up to 70 types of AEDs were recalled, including recalls from every AED manufacturer in the world. [30]
In January and February 2015, the FDA issued this news release: "The FDA issued a final order that will require AED manufacturers to submit premarket approval applications (PMAs), which undergo a more rigorous review than what was required to market these devices in the past. The agency's strengthened review will focus on the critical requirements needed to ensure the safety and reliability of AEDs and their necessary accessories, including batteries, pad electrodes, adapters and hardware keys for pediatric use." [31] [32]
In the United Kingdom there is concern that poor maintenance may make public defibrillators unreliable. The Henley Standard reported on 21 July 2017 that more than half the defibrillators in Henley-on-Thames and the surrounding area were at risk of failing, either because of low battery power or because adhesive pads had deteriorated. [33]
The first use of an external defibrillator on a human was in 1947 by Claude Beck. [34] The portable version of the external defibrillator was invented in 1957 by Frank Pantridge in Belfast, Northern Ireland, a pioneer in emergency medical treatment. [35] [36] Pantridge's defibrillator required a trained operator to perform the shock procedure and charted a course for many new innovations in external defibrillation. [37]
In the late 1970s the Heart-Aid was developed as the first truly automated external defibrillator that was designed for the public. The principles of ABC assessment and a human voice relaying instructions helped bystanders respond to a sudden cardiac event while waiting for the first responders to get to scene. [3] Many of the early innovations in the Heart-Aid model are still part of the current generation of AEDs, although some innovations, like the airway electrode have fallen from use.
In a study published in 2017, researchers in Poland selected the main entrances of buildings which had AEDs, although the researchers themselves did not know the exact locations of the devices. In drills of pretend heart attack, the average time to bring the AED to the patient was 96 seconds, with a time that ranged from 52 to 144 seconds. This met the three minute goal. In some cases, the use of the AED required the continuous presence of building personnel. Future improvements include more obvious signage and public-access AEDs which do not require a staff member of the building to either retrieve or use the device. [38] [39]
Cardiac arrest, also known as sudden cardiac arrest, is when the heart suddenly and unexpectedly stops beating. As a result, blood cannot properly circulate around the body and there is diminished blood flow to the brain and other organs. When the brain does not receive enough blood, this can cause a person to lose consciousness. Coma and persistent vegetative state may result from cardiac arrest. Cardiac arrest is also identified by a lack of central pulses and abnormal or absent breathing.
Cardiopulmonary resuscitation (CPR) is an emergency procedure consisting of chest compressions often combined with artificial ventilation, or mouth to mouth in an effort to manually preserve intact brain function until further measures are taken to restore spontaneous blood circulation and breathing in a person who is in cardiac arrest. It is recommended for those who are unresponsive with no breathing or abnormal breathing, for example, agonal respirations.
Cardioversion is a medical procedure by which an abnormally fast heart rate (tachycardia) or other cardiac arrhythmia is converted to a normal rhythm using electricity or drugs. Synchronized electrical cardioversion uses a therapeutic dose of electric current to the heart at a specific moment in the cardiac cycle, restoring the activity of the electrical conduction system of the heart. Pharmacologic cardioversion, also called chemical cardioversion, uses antiarrhythmia medication instead of an electrical shock.
Defibrillation is a treatment for life-threatening cardiac arrhythmias, specifically ventricular fibrillation (V-Fib) and non-perfusing ventricular tachycardia (V-Tach). A defibrillator delivers a dose of electric current to the heart. Although not fully understood, this process depolarizes a large amount of the heart muscle, ending the arrhythmia. Subsequently, the body's natural pacemaker in the sinoatrial node of the heart is able to re-establish normal sinus rhythm. A heart which is in asystole (flatline) cannot be restarted by a defibrillator; it would be treated only by cardiopulmonary resuscitation (CPR) and medication, and then by cardioversion or defibrillation if it converts into a shockable rhythm.
Ventricular fibrillation is an abnormal heart rhythm in which the ventricles of the heart quiver. It is due to disorganized electrical activity. Ventricular fibrillation results in cardiac arrest with loss of consciousness and no pulse. This is followed by sudden cardiac death in the absence of treatment. Ventricular fibrillation is initially found in about 10% of people with cardiac arrest.
Asystole is the absence of ventricular contractions in the context of a lethal heart arrhythmia. Asystole is the most serious form of cardiac arrest and is usually irreversible. Also referred to as cardiac flatline, asystole is the state of total cessation of electrical activity from the heart, which means no tissue contraction from the heart muscle and therefore no blood flow to the rest of the body.
An implantable cardioverter-defibrillator (ICD) or automated implantable cardioverter defibrillator (AICD) is a device implantable inside the body, able to perform defibrillation, and depending on the type, cardioversion and pacing of the heart. The ICD is the first-line treatment and prophylactic therapy for patients at risk for sudden cardiac death due to ventricular fibrillation and ventricular tachycardia.
Basic life support (BLS) is a level of medical care which is used for patients with life-threatening condition of cardiac arrest until they can be given full medical care by advanced life support providers. It can be provided by trained medical personnel, such as emergency medical technicians, qualified bystanders and anybody who is trained for providing BLS and/or ACLS.
Ventricular tachycardia is a cardiovascular disorder in which fast heart rate occurs in the ventricles of the heart. Although a few seconds of VT may not result in permanent problems, longer periods are dangerous; and multiple episodes over a short period of time are referred to as an electrical storm. Short periods may occur without symptoms, or present with lightheadedness, palpitations, shortness of breath, chest pain, and decreased level of consciousness. Ventricular tachycardia may lead to coma and persistent vegetative state due to lack of blood and oxygen to the brain. Ventricular tachycardia may result in ventricular fibrillation (VF) and turn into cardiac arrest. This conversion of the VT into VF is called the degeneration of the VT. It is found initially in about 7% of people in cardiac arrest.
The Seattle & King County Emergency Medical Services System is a fire-based two-tier response system providing prehospital basic and advanced life support services.
Precordial thump is a medical procedure used in the treatment of ventricular fibrillation or pulseless ventricular tachycardia under certain conditions. The procedure has a very low success rate, but may be used in those with witnessed, monitored onset of one of the "shockable" cardiac rhythms if a defibrillator is not immediately available. It should not delay cardiopulmonary resuscitation (CPR) and defibrillation, nor should it be used in those with unwitnessed out-of-hospital cardiac arrest.
Commotio cordis is a rare disruption of heart rhythm that occurs as a result of a blow to the area directly over the heart at a critical instant during the cycle of a heartbeat. The condition is 97% fatal if not treated within three minutes. This sudden rise in intracavitary pressure leads to disruption of normal heart electrical activity, followed instantly by ventricular fibrillation, complete disorganization of the heart's pumping function, and cardiac arrest. It is not caused by mechanical damage to the heart muscle or surrounding organs and is not the result of heart disease.
The chain of survival refers to a series of actions that, properly executed, reduce the mortality associated with sudden cardiac arrest. Like any chain, the chain of survival is only as strong as its weakest link. The six interdependent links in the chain of survival are early recognition of sudden cardiac arrest and access to emergency medical care, early CPR, early defibrillation, early advanced cardiac life support, and physical and emotional recovery. The first three links in the chain can be performed by lay bystanders, while the second three links are designated to medical professionals. Currently, between 70 and 90% of cardiac arrest patients die before they reach the hospital. However, a cardiac arrest does not have to be lethal if bystanders can take the right steps immediately.
The history of cardiopulmonary resuscitation (CPR) can be traced as far back as the literary works of ancient Egypt. However, it was not until the 18th century that credible reports of cardiopulmonary resuscitation began to appear in the medical literature.
William Bennet Kouwenhoven, also known as the "Father of Cardiopulmonary Resuscitation," is famous for his contributions to the development of the closed-chest cardiac massage and his invention of the cardiac defibrillator. After obtaining his doctorate degree in engineering from the Karlsruhe Technische Hochschule in Germany, Kouwenhoven began his career as the dean at the Johns Hopkins University in Baltimore. Kouwenhoven focused his research mainly on improving and saving lives of patients through the application of electricity. With the help and cooperation of the Johns Hopkins School of Medicine's Department of Surgery and an Edison Electric Institute grant, Kouwenhoven was able to develop a closed-chest defibrillator. For his contributions to the field of medical science, he became the first ever recipient of an honorary degree conferred by the Johns Hopkins School of Medicine. Two years before his death, Kouwenhoven was also awarded the Albert Lasker Award for Clinical Medical Research.
Pediatric advanced life support (PALS) is a course offered by the American Heart Association (AHA) for health care providers who take care of children and infants in the emergency room, critical care and intensive care units in the hospital, and out of hospital. The course teaches healthcare providers how to assess injured and sick children and recognize and treat respiratory distress/failure, shock, cardiac arrest, and arrhythmias.
A wearable cardioverter defibrillator (WCD) is a non-invasive, external device for patients at risk of sudden cardiac arrest (SCA). It allows physicians time to assess their patient's arrhythmic risk and see if their ejection fraction improves before determining the next steps in patient care. It is a leased device. A summary of the device, its technology and indications was published in 2017 and reviewed by the EHRA Scientific Documents Committee.
Arrhythmias, also known as cardiac arrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults – is called tachycardia, and a resting heart rate that is too slow – below 60 beats per minute – is called bradycardia. Some types of arrhythmias have no symptoms. Symptoms, when present, may include palpitations or feeling a pause between heartbeats. In more serious cases, there may be lightheadedness, passing out, shortness of breath, chest pain, or decreased level of consciousness. While most cases of arrhythmia are not serious, some predispose a person to complications such as stroke or heart failure. Others may result in sudden death.
Rearrest is a phenomenon that involves the resumption of a lethal cardiac dysrhythmia after successful return of spontaneous circulation (ROSC) has been achieved during the course of resuscitation. Survival to hospital discharge rates are as low as 7% for cardiac arrest in general and although treatable, rearrest may worsen these survival chances. Rearrest commonly occurs in the out-of-hospital setting under the treatment of health care providers.
Every year sudden cardiac arrest (SCA) kills between 35,000 and 45,000 people in Canada and approximately 350,000 people in the United States; 85% of SCAs are caused by ventricular fibrillation (VF). Receiving defibrillation from an automated external defibrillator (AED) is a key component of the 'chain of survival' for victims of SCA. Chances of survival from a SCA decrease by 7–10% every minute that a victim does not receive defibrillation. Attempts at reducing time until defibrillation have largely focused on improving traditional emergency medical service (EMS) responders and implementing publicly available defibrillator (PAD) programs. In the United States approximately 60% of SCAs are treated by EMS. Equipping police vehicles with AEDs and incorporating them in the emergency dispatching process when a SCA is suspected, can reduce the time until defibrillation for a victim suffering an out-of-hospital sudden cardiac arrest. There are numerous studies which confirm a strong coloration between equipping police vehicles with AEDs and reduced time until defibrillation which ultimately translates into improved survival rates from SCA. As a result of these demonstrable statistics, police departments across North America have begun equipping some or all of their police vehicles with AEDs.
We got a short lesson in using an AED, which is an Automated External Defibrillator. We had the thrill of yelling, "Clear!" Unfortunately this also brought on a little anxiety when Sean mentioned if the patient were a woman with a metal underwire in her bra or with metal piercings on her torso, we'd have to remove them.
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