The Automated External Defibrillator (AED) is a portable device designed to treat sudden cardiac arrest by delivering an electrical shock to the heart. This shock interrupts life-threatening heart rhythms, such as ventricular fibrillation, allowing the heart to potentially restart with a normal beat. Rapid application of the AED is directly linked to improved survival rates, as the chance of survival decreases by up to 10% with every minute of delay.
Activating the Device and Preparing the Patient
The first step when an AED arrives is to power the device on. Most models start automatically when the cover is opened or require pressing a clearly marked power button. Activating the AED initiates voice prompts, which guide the rescuer step-by-step and minimize the chance of error under stress.
While the AED is starting up, the patient’s chest must be quickly and completely exposed by removing all clothing. The chest needs to be bare, dry, and free of excessive hair so the electrode pads adhere properly and allow the electrical current to pass efficiently. If the patient is wet or has significant chest hair, a rapid towel-dry or quick shave is necessary before applying the pads.
Cardiopulmonary resuscitation (CPR) should continue with minimal interruption until the AED pads are ready to be placed on the patient’s chest. Continuous chest compression maintains blood flow to the brain and other organs, buying time until the heart rhythm can be analyzed. The AED will provide instructions to pause compressions when it is time to attach the pads.
Applying the Pads and Initiating Analysis
Once the chest is prepared, apply the electrode pads directly to the skin following the diagrams printed on the pads and the AED unit. For an adult, the standard placement is anterolateral: one pad is placed on the upper right side of the chest, just below the collarbone, and the other pad is placed on the lower left side of the rib cage, slightly below the armpit. This positioning ensures the heart lies directly in the path of the electrical current.
If the patient is a child under eight years old or weighs less than 55 pounds, pediatric pads should be used if available, as these deliver an attenuated, or reduced, shock. If only adult pads are available, they should be placed in an anteroposterior configuration, with one pad on the center of the chest and the other on the patient’s back between the shoulder blades, ensuring they do not touch. After the pads are firmly affixed, the connector cable must be plugged into the AED unit, signaling the device to begin its analysis phase.
The AED will announce that it is “Analyzing Rhythm.” During analysis, no one must touch the patient, as any movement or contact can create electrical interference that may distort the heart rhythm reading. The rescuer must announce, “Stand clear,” to ensure everyone is safely away from the patient.
Delivering the Shock and Resuming CPR
If the AED determines the heart is in a shockable rhythm, such as ventricular fibrillation, it will charge its capacitor and advise, “Shock Advised.” The rescuer must again ensure all bystanders are clear of the patient by shouting a phrase like, “I’m clear, you’re clear, everybody’s clear,” before pushing the shock button. The shock causes a sudden contraction of the patient’s muscles, which is a normal response to the electrical discharge.
If the AED determines that no shock is needed, either because the heart has no electrical activity or the rhythm is non-shockable, it will advise, “No Shock Advised.” In either scenario—whether a shock was delivered or not—the AED will instruct the rescuer to resume CPR. This two-minute cycle of chest compressions and rescue breaths must begin without delay, as the priority shifts back to maintaining blood flow.
The AED pads must remain attached, and the device should be left turned on throughout the entire resuscitation effort. The AED is programmed to re-analyze the heart rhythm automatically after two minutes of CPR. It will then advise another shock, if necessary, or continue prompting the rescuer to perform CPR until emergency medical services arrive to take over care.