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The What, When, Where, Why & How of AEDs

Many questions arise when it comes to Automated External Defibrillators (AEDs). In this guide, we seek to answer the most common questions about this important, lifesaving technology!

We’ll begin with some definitions of what an AED is and what it is not.

AED Medical Abbreviation: Automated External Defibrillator

Some people mistakenly define AEDs as “automatic external defibrillators” rather than “automated external defibrillators.”  Even some AED laws have made this mistakeThere are also many typos, misspellings, and references to AEDs. Here are a few of our favorites: 

  • defibUlator
  • defiBRAlater or defiBRAlator
  • Defibillator or defibilator
  • And, of course, the famously redundant “AED defibrillator” (aka the automated external defibrillator defibrillator)

Cutting to the chase…

What is an AED machine? 

An Automated External Defibrillator (AED) is a machine that is used to treat cardiac arrest, a life-threatening condition where the heart suddenly stops beating properly. By sending an electric shock to the heart of a person in cardiac arrest, the AED restores a normal heart rhythm. AEDs are designed for use by laypersons with very little training; check out your device’s user manual for instructions on how to use your specific AED.

How does an AED work?

While AED machines use advanced algorithms and offer lifesaving therapy, they are actually built with only a few key components. The main AED parts are: 

  • Electrode pads: Electrode pads are the sticky pads that are applied to the patient’s chest. The electrode pads are what reads the patient’s heart rhythm. If a shock is determined to be necessary by the AED’s processor, then the shock travels between the pads and through the patient’s heart.
  • Battery: The battery is used to charge the AED’s capacitor so that it has enough energy to deliver a life-saving shock. The battery also plays an important role in running self-tests and AED diagnostics to make sure that the AED is functioning properly.
  • Capacitor: The capacitor stores and releases energy. Capacitors are very common electrical components and they come in different sizes or capacities. For AEDs, the capacitor has to be large enough to store enough energy, and then release it all at once, to save a patient’s life.
  • Processor: The processor is the brains behind the AED. The processor is used to analyze the patient’s rhythm to determine whether or not the patient is in a shockable rhythm

AEDs are capable of automatically detecting two forms of cardiac arrhythmias or irregular heart rhythms: ventricular fibrillation and pulseless ventricular tachycardia. If either of these rhythms are detected by the AED, the device delivers a controlled electric shock to the victim. Most people are familiar with in-hospital defibrillators or those used by emergency medical services that are part of advanced life support (ALS) units. AEDs are different because they are “automated” and completely take the guesswork out of determining whether or not someone needs a shock. AED operators do not need to read and interpret a patient’s ECG which depicts the heart rhythm. The AED performs the heart rhythm analysis for them. 

Since AED machines are becoming increasingly present in public settings, especially where there is a lot of human traffic, AEDs can often be used immediately when a person goes into cardiac arrest instead of having to wait for the paramedics or police to administer the life-saving treatment.  

So, if you are wondering why AEDs are used or what an AED is used for…  The purpose of AEDs is to allow laypeople to save lives!

How to use an AED?

There are several models of FDA-approved AED units. Each unit has voice instructions to help coach responders through the rescue process and AEDs are designed to be used by anyone with limited training. In fact, one of the FDA’s quality-assurance requirements is to review human factors testing to make sure that the defibrillator is easy to use. 

While every AED unit operates a little differently, and you should consult your unit’s owners manual for device-specific instructions, AEDs do have common characteristics. 

First, let’s brush up on cardiac arrest response best practices. For more detailed information, check out our guide: CALL-PUSH-SHOCK

STEP 1 – CALL: Recognize cardiac arrest and call 911

  1. Scene Safety: perform a quick survey of the scene to make sure that it’s safe for you to help
  2. Check for responsiveness: if the victim is not responsive and not breathing normally, they might be in cardiac arrest
  3. Call 911

STEP 2 – PUSH: Perform CPR

  1. Start CPR: push hard and fast on the center of the chest while calling 911 and asking another person to get the AED

STEP 3 – SHOCK: When the AED arrives, here are the steps to using an AED:

  1. Turn it on: Listen to the voice prompts 
  2. Expose the patient’s chest: You need to expose their chest so that you can apply the AED electrode pads. Make sure that their chest is dry so that the electrodes are able to adhere to the skin completely
  3. Apply the AED electrodes on the patient’s bare chest: Follow the AED’s instructions and look at the graphics on the electrode pads for proper pad placement. With most electrodes, one pad should be placed on the patient’s right side, just below the collarbone, and the second pad goes on the left side, below the armpit.
  4. Analyzing: Once the AED notices that the pads have been properly applied, the defibrillator will give a quick prompt and analyze the patient’s heart rhythm 
  5. Delivering a shock (if needed): If the AED determines that the patient is in cardiac arrest and that a shock is needed, the way it delivers the shock depends on whether the AED is a semi-automatic model or a fully-automatic model.
    Fully-automatic AED: if a shock is required it will charge and tell you to stand clear from the patient. Then, it will count down and automatically deliver the shock without requiring you to press a button.
    Semi-automatic AED: if a shock is required, it will charge and, once ready to deliver a shock, it will prompt you to push a button. The button is usually flashing and easy to locate in the middle of an emergency, but make sure you don’t accidentally press the power button!
  6. Perform CPR & Re-analyze. AEDs are programmed with the American Heart Association’s guidelines. The current AHA’s protocols call for two-minutes of CPR in between AED heart rhythm analysis periods. Follow the AED instructions. 
  7. Continue listening to the AED until EMS arrives and takes over the rescue.


How to use an AED on a woman?

Using an AED on a man and woman is exactly the same. If the victim is not responsive, apply the electrode pads and listen to the AED voice prompts. Did you know that women receive help from bystanders 27% less often than men?! 

When to use an AED?

Always check your AED’s user manual for specific instructions on how and when to use your AED. In general, most AEDs are meant to be used on people who are unresponsive and not breathing properly

Sometimes it can be tough for laypeople to determine if someone is breathing properly or not. Learn more about how to determine if someone isn’t breathing properly.

AED units use smart technology and can evaluate a patient’s heart rhythm once the electrode pads have been properly applied. Since AEDs only deliver a shock to patients in cardiac arrest, they are safe to use by non-medical people with limited training. 

When NOT to use an AED?

Just because AED units can be used by almost anyone (there’s even research showing that untrained children can successfully use AEDs), this doesn’t mean that AEDs are toys. Do not use AEDs on people who are conscious or responsive. Consciousness is a contraindication for the use of an AED. 

Can an AED be used on an infant?

Yes, children and infants can go into cardiac arrest. In fact, 7,000 to 10,000 children die of sudden cardiac arrest every year in the United States. 

To use an AED on a child, you need to determine whether or not the AED requires a separate set of child electrode pads or if the AED has a built-in attenuator. The attenuator is what decreases the energy of the electric shock to the appropriate level for a child under 8 or less than 50 pounds.

  • If your AED requires a separate set of electrodes, you need to buy them and make sure that they are available with the AED. Then, during the emergency,  install the child pads, power on the AED, and listen to the voice prompts just like you would for an adult patient.
  • If your AED allows you to use the same pads for adult and pediatric patients, you only need to press the button to change the device to child or pediatric mode on your AED!

Learn more about pediatric electrode pads here.

What are the types of AEDs?

There are a few different types of AEDs (not to be mistaken with brands of AEDs), or, more accurately, types of defibrillators.

Manual defibrillators

Manual defibrillators are the machines you are accustomed to seeing on TV. They are usually in hospitals or in the back of ambulances. Manual defibs allow the operator to view the patient’s ECG and make adjustments to the clinical therapy delivered. For instance, they might decide to MANUALLY deliver electricity to the patient instead of using an AUTOMATED algorithmic decision.

Manual defibs can also come with different attachments, like blood pressure cuffs, SPO2 attachments, and 12-lead monitoring. They can also help with pacing and cardioversion, unlike AEDs. Since they offer more sophisticated capabilities, they are typically used by medical professionals for monitoring patients. Manual defibrillators are sometimes also referred to as “monitors.”

These devices are much larger and heavier than AEDs, making them less portable. 

Since they are more complex, these devices are always used by professionals and not laypeople.

You might be familiar with the following manual defibrillator manufacturers and brands:

  • Philips MRx
  • Philips RDT Tempus
  • Philips XL & XL+
  • Physio Control LIFEPAK 15
  • Physio Control LIFEPAK 20
  • ZOLL E Series Defibrillator
  • ZOLL M Series Defibrillator
  • ZOLL R Series Monitor/Defibrillator
  • ZOLL X Series Monitor/Defibrillator for EMS
  • ZOLL X Series Monitor/Defibrillator for Hospital Transport

Professional AED units

Professional AED models are a hybrid between full-fledged manual defibrillators and automated defibrillators. Professional models have a screen that displays the patient’s ECG and they can be configured with 3-lead attachments. Thus, they are used by professional first responders like firefighters and paramedics.

Some agencies give police officers the professional model, which we don’t recommend since it’s typically more expensive for no added value. Why? Because most police officers don’t need the ability to analyze the heart rhythm. They just need the AED to automatically analyze the heart rhythm and deliver a shock when necessary.

You might be familiar with the following professional AED manufacturers and brands:

  • Cardiac Science Powerheart AED G3 Pro
  • Defibtech Lifeline VIEW/ECG
  • Phillips FR2 AED
  • Physio Control LIFEPAK 1000
  • ZOLL AED Pro

Automated External Defibrillators (AED)

AEDs differ from their professional counterparts because they are specifically built for lay people. Bystanders don’t need all the bells and whistles; they just need to grab a publicly available AED unit to save someone’s life. AEDs use smart technology to analyze and determine shockable rhythms.

There are two types of AEDs: semi-automatic AEDs and fully-automatic AEDs

AEDs are also more affordable than professional models and manual defibs.

Aside from Avive, you might be familiar with the following AED manufacturers and brands: 

  • Cardiac Science
  • Defibtech
  • HeartSine
  • Philips
  • Physio Control (formerly Medtronic, and now owned by Stryker)
  • ZOLL

Other Questions

How do you inspect/test an AED machine? 

Having an AED can save the life of someone in cardiac arrest, but the machine needs to be in working order. The AED maintenance requirements vary from model to model, so you should check the instructions for your specific AED. 

All devices perform “self-checks” routinely. They also have audible and visual alert indicators that represent their readiness status, similar to a fire extinguisher that may “blink” red and “chirp” when it needs a new battery.

If you don’t have a connected AED that can tell you the readiness status and expiration dates of your electrode pads wirelessly and remotely, then you need to manually:

  • Check the readiness indicator (at least monthly, although some AEDs, like the Cardiac Science PowerHeart G3 require daily checks)
  • Check the expiration dates of various components such as the battery and electrode pads. Typically, the battery will need to be replaced every two to four years. The electrode pads will need to be replaced periodically. Even if your pads haven’t been used, they have an expiration date which is stated by the manufacturer

Other items you should check include:

  • Looking for any physical damage due to falls, mishandling, theft, or wear-and-tear 
  • After use or training, wipe off dirt and any unwanted debris that may compromise future use
  • Use the AED manufacturer’s service checklist to ensure thorough maintenance 
  • Make sure that the AED is accessible and easy to locate. Check to ensure that nothing is accidentally blocking your AED or AED signage


How much does an AED machine cost?

The cost of most common AED models typically ranges between $1,250 and $3,000. Refurbished or recertified units may retail at significantly lower prices, however, they come with risks like limited product warranties. 

In addition to the initial purchase price, AEDs periodically have electrode pads and batteries that expire. These expired parts require replacement (approximately every 2-4 years depending on the brand of AED). Electrodes and batteries can be expensive – one model has a battery that is over $400 for a four-year battery, and another has an electrode pad that is over $150! 

Prior to purchase, consumers should check out the total cost of ownership (purchase price + cost of replacement supplies) over a designated period of time so that they understand their total “all-in” investment.


How many joules are in an AED machine?

The power delivered by an AED varies by model. The most conventional power ratings are 150, 200, or 360 joules. There is also another important classification when it comes to the electric shock delivered by an AED. AEDs can either be monophasic, meaning that the electric charge travels in one direction, or biphasic, in which case the charge travels in both directions. Both of these waveforms have been shown to be effective, but modern AEDs almost exclusively use biphasic waveforms. 


What is Public Access to Defibrillation (PAD)?

Public access defibrillation (PAD) is an initiative in many communities to locate portable defibrillators in areas that have high human traffic such as offices, schools, and public parks. As the name implies, the goal is to give the public access to life-saving defibrillation. 

The AHA categorizes responders into three groups: targeted responders who work in placement locations such as employees; nontraditional responders such as police, firefighters, and flight attendants; and lay responders who are conveniently close to people at high risk of cardiac arrest such as family members and friends. 

Many studies indicate that widespread PAD programs save lives. To increase the effectiveness of PAD programs, communities often pair widespread AED deployment with broad CPR training and AED awareness activities.


Why is electrode pad placement for AED important? 

The correct placement of AED electrode pads is critical for successful defibrillation. The pads are responsible for analyzing a patient’s heart rhythm to determine if they need an electric shock and, if yes, then delivering the shock into the victim’s heart. 

The ideal pad placement enables efficient delivery of a shock to the heart muscle. Each AED manufacturer has their own icon with the correct pad placement for their AED unit, so make sure to check where the pads should be placed for the device that you own. 

If your AED has a child setting, make sure to also check where the child pads should be placed.


What is the depth of chest compressions in CPR? 

CPR compressions help circulate oxygen-rich blood to the brain and other vital organs, sustaining life until an AED can provide a shock that will restart a patient’s heart. CPR “buys time.”

Compressions should be performed at a rate of 100-120 compressions per minute. The depth of each compression varies slightly depending on whether the patient is an adult or a child. 

Depth of CPR Compressions for Adults – The 2015 CPR guidelines by the AHA recommend a depth of between 2 and 2.4 inches (5 to 6 cm) applied in the center of the chest, pushing down on the sternum and allowing the chest to recoil all the way up between compressions. One study cited by Vadeboncoeur at al. found that the outcomes of out-of-hospital cardiac arrest improved with increased depth of compressions, with a compression depth of at least 5.1 cm yielding the best outcomes. The mean depth of compressions among survivors (10.6% of the 593 sampled patients) was 53.6mm compared to 48.8 mm among non-survivors. This suggests a positive correlation between compression depth and cardiac arrest survival. 

Depth of CPR Compressions for Children – The thoracic area of children is much more fragile than that of an adult. In addition to shallower compressions, the responder may need to use one hand. When administering CPR on an child, it is reasonable that responders provide compressions that depress at least one third on the chest diameter. This is about approxiamtely 1.5 inches (4 cm) for infants and 2 inches (5 cm) for prepubescent children according to the 2015 AHA CPR guidelines.

Many studies have indicated that the accuracy of chest compression depth, particularly in cases when CPR is performed by lay rescuers, falls outside the recommended depth. Feedback devices that measure the quality of the compressions attempt to remedy this problem. However, one study showed that a feedback device, while showing some benefit for paramedics, had a negative impact or “deleterious effect” for non-paramedic responders.

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