An automated external defibrillator (AED) is a portable electronic

device that automatically diagnoses the life-threatening cardiac arrhythmias

of ventricular fibrillation and pulseless ventricular tachycardia, 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.

Conditions That The Device Treats

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

• Ventricular tachycardia (V-Tach)
• Ventricular fibrillation (V-Fib)

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.

Effect of Delayed Treatment

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, 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 3 minutes and decreases 

by 10 percent per minute as time advances beyond about 3 minutes.

Requirements for Use

AEDs are designed to be used by laypersons who ideally should have received AED training.

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.

Placement and Availability

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.

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.

Simplicity of Use

Unlike regular defibrillators, an automated external defibrillator requires minimal training to use. 

It 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 pounds in weight or under the age of 8 years old.

If a particular model of AED is approved for pediatric use, all that is required is the use of more appropriate pads.

All AEDs approved for use in the United States use an electronic voice to prompt users through each step. 

Because the user of an AED may be hearing impaired, many AEDs now include visual prompts as well. 

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), which experts agree 

has the potential to be the single greatest advance in the treatment of out-of-hospital cardiac arrest 

since the invention of CPR.

Benefit

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.

Liability

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.

"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. 

AEDs create little liability if used correctly.

Many CPR classes incorporate or offer AED education as a part of their program.

Note: this was taken from https://en.wikipedia.org/wiki/Automated_external_defibrillator