An Automated External Defibrillator (AED) is a portable medical device designed to treat sudden cardiac arrest by delivering an electrical shock to restore a regular heart rhythm. These devices are designed for use by untrained or minimally trained bystanders, making them a crucial link in the chain of survival outside of a hospital setting. Although the AED unit itself has a long lifespan, it functions only through the readiness of its consumable parts. Regular oversight is required because these components are subject to strict expiration dates.
The Critical Expiration of AED Components
The readiness of an AED depends entirely on two primary components that carry expiration dates: the electrode pads and the lithium-based battery pack. Pads are single-use consumables that must be replaced immediately after a cardiac event, regardless of whether a shock was delivered. These pads typically have a shelf life of between 18 and 30 months, a date determined by the manufacturer to guarantee their efficacy.
The battery has two distinct time limits. The first is its specified shelf life while stored outside the device. The second, and more practical, limit is the installed standby life, which is the expected duration the battery will power the AED while it is in the “rescue-ready” state. This standby life usually ranges from two to five years, depending on the manufacturer and the specific AED model.
Manufacturers print the expiration dates clearly on the pad packaging and the battery itself, providing a simple metric for maintenance. Ignoring these dates means the device may not function when needed. The expiration reflects the physical and chemical limitations of these components.
Understanding Component Shelf Life and Functionality
The expiration date on electrode pads is related to the integrity of the conductive gel layered onto the pad’s surface. This gel is necessary to ensure strong adhesion to the patient’s skin and efficient electrical conductivity for shock delivery. Over time, the water-based electrolyte gel naturally begins to dry out, even while the pads remain sealed in their foil packaging.
As the gel degrades, two failures occur: the pad’s adhesive property weakens, and its ability to conduct electricity is reduced. A pad that does not adhere firmly may peel away from the skin during chest compressions, breaking the circuit necessary to analyze the heart rhythm or deliver a shock. Reduced conductivity means the electrical energy may not transmit effectively across the chest wall, diminishing defibrillation success.
Battery expiration is driven by the chemistry of self-discharge and the device’s operational requirements. All batteries, including the lithium variants used in AEDs, lose capacity over time, even when they are not actively powering the device. Furthermore, every modern AED performs routine internal self-tests, often daily or weekly, to check component connections.
These self-tests, while necessary for confirming readiness, draw a small amount of power, cumulatively reducing the total available capacity over the standby period. Once the battery pack falls below the manufacturer’s specified capacity threshold, it cannot be guaranteed to deliver the high-energy electrical shock required. This capacity loss, not a sudden failure, is the primary reason for the battery’s expiration date.
Ensuring AED Readiness and Regulatory Compliance
Ensuring an AED is ready for use requires a maintenance schedule that extends beyond checking expiration dates. Most AEDs feature a visual status indicator, typically a green checkmark or light, which confirms the device has successfully passed its most recent internal self-test. If this indicator shows a red ‘X’ or a flashing light accompanied by an audible chirping sound, it signals a component failure or low battery, requiring immediate attention.
Beyond the automated checks, AED owners should conduct a physical inspection at least monthly. This inspection verifies the presence of the device, checks the status indicator, and confirms the expiration dates on the pads and battery are in the future. Maintaining detailed records of these inspections and all component replacements is necessary for responsible ownership.
AEDs are regulated medical devices, and maintenance must adhere to the manufacturer’s specifications, which supports local regulatory and legal compliance. Proper maintenance is a requirement for Good Samaritan laws in many jurisdictions. Failure to keep the device in rescue-ready condition could potentially negate legal protections for the owner. Consistent log-keeping and timely replacement ensure the device is prepared to function as intended.