Using an automated external defibrillator on a child under eight requires adjustments that most bystanders are never taught. The core issue is energy dose: a standard AED delivers a shock calibrated for an adult-sized heart, and a small child’s myocardium is more vulnerable to damage from that full charge. Pediatric-specific pads, different pad placement, and an understanding of why childhood cardiac arrest behaves differently from the adult version all factor into doing this safely and effectively.
Why Children Under Eight Are a Special Case
AEDs were originally designed for adults, and the energy they deliver reflects that. A typical adult shock is 150 to 360 joules, depending on the device. For a child who weighs 25 kilograms or less, that amount of energy is disproportionately large relative to the size of the heart muscle. The goal of defibrillation in any patient is to deliver enough energy to interrupt a chaotic heart rhythm and allow a normal one to resume, while keeping the dose low enough to avoid damaging the heart itself. An ideal pediatric dose maximizes the chance of restoring a normal perfusing rhythm while minimizing the risk of myocardial injury from an excessive shock.1PubMed Central. Energy doses for paediatric defibrillation in cardiac arrest: systematic review and meta-analysis
Children’s hearts are not simply smaller versions of adult hearts. They have thinner ventricular walls and less total muscle mass, which means the same electrical energy spreads through a proportionally larger fraction of the tissue. In animal research comparing pediatric-level and adult-level shock doses in young piglets, adult dosing caused significantly more cardiac troponin elevation and greater depression of heart function four hours after resuscitation. Troponin is a marker of heart muscle injury, and the difference was stark: none of the piglets that received pediatric-level shocks showed troponin elevations, compared to more than half of those that received adult-level shocks.2Journal of the American College of Cardiology. Better outcome after pediatric defibrillation dosage than adult dosage in a swine model of pediatric ventricular fibrillation
Pediatric Pads and How They Reduce Energy
Most major AED manufacturers sell pediatric electrode pads (sometimes called pediatric key-child pads or pediatric attenuators) that are designed for children roughly under eight years old or under 25 kilograms. These pads do not change the AED’s internal programming in a complicated way. Instead, they contain a built-in resistor or energy-attenuating circuit that absorbs a portion of the shock before it reaches the child’s chest. The AED fires its normal output, but only a reduced fraction of that energy is actually delivered to the patient.3PubMed. Energy attenuator for pediatric application of an automated external defibrillator The result is a shock in the range of roughly 50 to 75 joules, which is closer to the recommended weight-based dose for a young child.
This design was intentional. Redesigning every AED to detect a child’s size and automatically reduce output would be expensive and slow to deploy. By putting the attenuation circuit inside the pads themselves, manufacturers let existing AEDs serve children without any hardware changes to the device. You open the pediatric pad package, attach the pads, and the AED does the rest. Some newer AEDs have a pediatric mode switch instead of separate pads, but the principle is the same: reduce the delivered energy.
Pad Placement on a Small Chest
In adults, the standard pad positions are one on the upper right chest below the collarbone and one on the lower left side of the ribcage. For a child under eight, the chest may be too small for both pads to sit in those positions without overlapping or touching each other. If the pads touch, the electrical current can arc between them across the skin surface instead of traveling through the heart, which renders the shock useless and can burn the skin.
The solution is anterior-posterior placement: one pad goes on the center of the chest over the breastbone, and the other goes on the center of the back between the shoulder blades. This positions the heart directly between the two electrodes and works well even on very small torsos. Most pediatric pad packaging includes diagrams showing this placement. If you are using adult pads on a child because pediatric pads are not available, anterior-posterior placement becomes even more important, since adult pads are physically larger and more likely to overlap on a small chest.
What If Only Adult Pads Are Available
This is the scenario that causes the most hesitation, and it should not. Every major resuscitation guideline is clear: if a child is in cardiac arrest and you have an AED but only adult pads, use the adult pads. A shock at adult energy levels is far better than no shock at all. The same guidance extends all the way down to infants. The American Red Cross Scientific Advisory Council has stated that AEDs should be used in infants with suspected cardiac arrest if a manual defibrillator with a trained rescuer is not immediately available, and that if pediatric pads are not available, adult pads should be used.4PubMed. The Use of Automated External Defibrillators in Infants: A Report From the American Red Cross Scientific Advisory Council
Published case evidence supports this position. A review of AED use across all age groups confirmed that standard adult AEDs are now indicated for every age group, with a preference for pediatric pad application for small children and babies, but with adult pads recommended when pediatric pads are unavailable.5PubMed. Inappropriate Shocks and Power Delivery Using Adult Automatic External Defibrillator Pads in a Pediatric Patient The risk of myocardial injury from an adult-level shock exists, but it is a recoverable problem. A child who remains in a lethal heart rhythm without any shock has no chance of recovery at all.
The practical takeaway is simple: check the AED for pediatric pads first, use them if they are there, and if they are not, do not waste time looking for them elsewhere. Apply the adult pads, turn on the AED, and follow the voice prompts.
Why Childhood Cardiac Arrest Is Different From the Adult Version
In adults, cardiac arrest is usually a primary cardiac event. The heart develops a lethal arrhythmia, often ventricular fibrillation, due to coronary artery disease or an electrical abnormality. The AED was built for exactly this scenario, and shockable rhythms are common in adult out-of-hospital arrests.
In children, the picture is inverted. Most pediatric cardiac arrests begin as respiratory events. A child stops breathing due to drowning, choking, an asthma attack, or a severe infection, and the resulting oxygen deprivation eventually causes the heart to stop. By the time the heart gives out, the rhythm is typically asystole or pulseless electrical activity, neither of which responds to defibrillation. Research on outcomes of out-of-hospital cardiac arrest in children found that survivors who were neurologically normal had experienced a respiratory arrest only and were resuscitated quickly, while among 80 patients who had a true cardiac arrest, only 6 survived to hospital discharge, and all had neurological damage.6N Engl J Med. Outcome of out-of-hospital cardiac or respiratory arrest in children
This means that for most pediatric emergencies, high-quality CPR with effective rescue breathing is the intervention that matters most. The AED still belongs in the response, because it will analyze the rhythm and tell you whether a shock is advised. But the odds that it will advise a shock are lower than in an adult scenario. In the minority of pediatric cases where a shockable rhythm is present, prompt defibrillation can be lifesaving.7The American Journal of Emergency Medicine. Pediatric out-of-hospital cardiac arrest caused by left coronary-artery agenesis with primary shockable rhythm
When Shockable Rhythms Do Occur in Children
Although shockable rhythms are uncommon in pediatric arrests overall, they are not rare enough to ignore. Certain conditions push the probability upward. Children with congenital heart disease, inherited arrhythmia syndromes like long QT, or a history of cardiac surgery are more likely to develop ventricular fibrillation. Sudden cardiac arrest during organized sports, while rare, also tends to be a primary electrical event where the heart is otherwise healthy but receives a precisely timed blow to the chest or develops an arrhythmia under exertion. In those situations, the AED is the most important device on the scene.
This is why AEDs are increasingly placed in schools, recreational facilities, and youth sports venues. A bystander does not need to diagnose the rhythm. The AED does that work. The bystander’s job is to turn it on, attach the pads, and follow the prompts. If the rhythm is shockable, the device delivers the shock. If it is not, the device tells you to continue CPR. There is no scenario in which attaching an AED to a child causes harm through the analysis alone. The device will not shock a rhythm that does not warrant it.
Survival Outcomes When Bystanders Use AEDs on Children
The evidence on what happens when lay rescuers actually apply AEDs to children is encouraging. A systematic review of lay rescuer AED use found that bystander AED application was associated with roughly three to four times higher survival to hospital discharge in children aged 1 to 12 and in adolescents aged 13 to 18. The improvement was similar when looking at survival with favorable neurological outcomes.8Resuscitation Plus. Lay rescuer use of automated external defibrillators in infants, children and adolescents: A systematic review Those numbers reflect real-world bystander use, not just what happens in controlled hospital settings, which makes them directly relevant to anyone wondering whether grabbing an AED for a child is worthwhile.
The caveat is that these numbers capture the subset of cases where the AED found a shockable rhythm and delivered a shock. The overall survival rate from pediatric out-of-hospital cardiac arrest remains low because most cases involve non-shockable rhythms. But for the children who do have a shockable rhythm, immediate AED use dramatically changes the odds. The effect is large enough that hesitating because the patient is a child rather than an adult is one of the worst decisions a bystander can make.
Infants Under One Year
Infants are the age group where rescuers feel the most uncertainty, and the guidance is the least intuitive. The chest is tiny, the ribs are soft, and everything about the situation screams fragility. But the recommendation is the same in principle: use an AED if cardiac arrest is suspected and a manual defibrillator with a trained provider is not immediately available. Pediatric-attenuating pads are preferred, and if those are not available, adult pads should be used.4PubMed. The Use of Automated External Defibrillators in Infants: A Report From the American Red Cross Scientific Advisory Council
Anterior-posterior pad placement is essential for infants. Even pediatric pads may be large relative to a newborn’s torso, and placing one on the front and one on the back prevents overlap. Some rescuers worry about the pads covering too much of the chest. As long as the pads do not touch each other, covering a large portion of a small chest is acceptable and actually helps ensure the current passes through the heart.
Infant cardiac arrest outside of the hospital is extraordinarily rare in the absence of a pre-existing condition or a catastrophic event like drowning or trauma. When it does happen, the minutes before an ambulance arrives are the only window for intervention. Having an AED available and being willing to use it is the factor most within a bystander’s control.
Common Mistakes and Misconceptions
The biggest misconception is that using an AED on a child is dangerous. It is not. The AED analyzes the rhythm before deciding whether to shock, and it will not deliver energy to a heart that does not need it. The second biggest misconception is that you need special training to use an AED on a child. While training is always helpful, AEDs are designed to be used by untrained bystanders. The voice prompts walk you through every step, including pad placement.
Another common error in practice is delaying the AED to focus exclusively on CPR. CPR is critical and should start immediately, but someone else should be retrieving the AED at the same time. If you are alone, current guidelines for children generally recommend performing about two minutes of CPR before leaving to get an AED, because the underlying cause is more likely respiratory and those initial breaths and compressions address the oxygen deficit. For witnessed sudden collapse in a child, especially during sports or exertion, the AED should be retrieved as quickly as possible because the likelihood of a shockable rhythm is higher.
A subtler mistake is removing the pads after the AED says “no shock advised.” That message means the rhythm is not shockable at that moment, not that the AED is no longer needed. Leave the pads in place and continue CPR. The AED will re-analyze the rhythm at intervals and may advise a shock later if the rhythm changes.
What Happens at the Hospital After a Pediatric AED Shock
If a child receives one or more AED shocks before paramedics arrive, the hospital team will want to know how many shocks were delivered and, if possible, the energy level. Most AEDs log this data internally, and the device should go with the patient or be made available to the receiving hospital. Clinicians use this information to assess whether the child’s heart sustained any injury from the defibrillation itself.
Cardiac troponin levels are typically monitored in the hours after resuscitation. As the animal research demonstrated, higher energy doses are associated with greater troponin release and more depression of heart function.2Journal of the American College of Cardiology. Better outcome after pediatric defibrillation dosage than adult dosage in a swine model of pediatric ventricular fibrillation If adult pads were used, the clinical team anticipates a higher energy delivery and monitors accordingly. This does not mean the bystander made the wrong call by using adult pads. It means the team adjusts its post-resuscitation care to account for what happened in the field. The bystander’s job was to restore a pulse, and using whatever pads were available was the right decision.
Echocardiography and continuous cardiac monitoring typically follow for at least 24 to 48 hours to watch for arrhythmias, impaired pumping function, or signs of ongoing injury. Most children who are successfully resuscitated from a shockable rhythm with appropriate energy doses recover cardiac function well, particularly when the time from collapse to first shock was short. The brain, not the heart, is usually the organ most at risk for lasting damage after a prolonged arrest, and that damage is determined far more by how quickly CPR and defibrillation began than by whether the shock dose was perfectly calibrated.