An Automated External Defibrillator (AED) treats sudden cardiac arrest by delivering an electrical shock to reset the heart’s rhythm. These devices use specific electrode pads engineered to safely accommodate patients of varying sizes, adapting the electrical energy for the patient’s body mass. A common question arises in an emergency: what happens when the only available pads are not the right size? The answer lies in understanding the technical and physiological differences built into the pads.
Understanding the Electrical Differences in AED Pads
The fundamental distinction between adult and pediatric AED pads centers on the amount of electrical energy delivered. Adult pads are intended for individuals typically over eight years old or weighing more than 55 pounds (25 kg), delivering a full energy shock, often ranging from 120 to 360 Joules.
Pediatric pads are designed for children under eight years old or those weighing less than 55 pounds. These pads include a built-in resistor or attenuation circuit that significantly reduces the energy output. This mechanism typically lowers the delivered energy to a safer dose, often around 50 Joules, appropriate for a smaller body mass.
Beyond electrical output, the physical size and recommended placement of the pads differ. Adult pads are larger, designed for anterior-lateral placement (upper right chest and lower left side) to ensure the current effectively passes through the adult heart.
Pediatric pads are smaller to prevent them from touching on a small child’s chest, which would cause an electrical short-circuit. For children, the recommended placement is often anterior-posterior (one pad on the chest, the other on the back) to ensure the shock travels through the smaller heart.
The Safety and Efficacy of Using Pediatric Pads on Adults
Using pediatric AED pads on an adult risks treatment failure because the delivered energy is significantly attenuated. An adult heart experiencing ventricular fibrillation requires a high-energy shock (150 Joules or more) to stop the chaotic electrical activity and allow a normal rhythm to resume. The attenuated dose of approximately 50 Joules is often insufficient to successfully defibrillate a larger adult heart due to its greater mass and higher electrical impedance.
The American Heart Association advises against using pediatric pads on an adult due to the likelihood of an ineffective shock. However, if adult pads are completely unavailable, some experts suggest a low-energy shock is preferable to no shock at all in a witnessed cardiac arrest. This follows the principle that any attempt to interrupt the lethal rhythm provides a chance for survival.
Time spent attempting to use suboptimal equipment is time lost performing high-quality cardiopulmonary resuscitation (CPR), the most reliably helpful intervention until effective defibrillation occurs. If a rescuer must use pediatric pads on an adult, they should immediately inform emergency medical services (EMS). The operator must continue CPR and follow the AED’s prompts, recognizing that success chances are reduced due to the insufficient electrical dose.
The Extreme Danger of Using Adult Pads on Children
Using adult AED pads on a child presents a far greater risk of harm due to a major energy overdose. Adult pads deliver a full-strength shock (150 to 360 Joules), which is several times the safe limit for a child’s smaller, developing heart. Delivering this high voltage can cause severe myocardial damage, tissue injury, and external burns.
A primary danger involves the physical size of the pads and the patient’s small torso. Adult pads are large and may overlap or touch when applied to a small child’s chest. If the conductive pads touch, the electrical current will short-circuit along the skin, completely bypassing the heart and rendering the treatment ineffective.
If pediatric pads are unavailable, using adult pads is considered an absolute last resort, requiring specific modifications to minimize harm. The adult pads must be placed in an anterior-posterior position (one pad on the chest, the other on the back) to maximize the distance between them and prevent contact. This placement helps ensure the current flows through the heart, though the risk of an energy overdose remains significant.