An Automated External Defibrillator (AED) is a portable medical device designed to treat sudden cardiac arrest, a condition where the heart’s electrical activity becomes chaotic. The sole purpose of the AED is to deliver a controlled electrical shock, known as defibrillation, to stop this chaotic rhythm and allow the heart’s natural pacemaker to reset. This intervention is time-sensitive, and correct application is paramount. Precise placement of the electrode pads ensures the electrical current travels effectively through the heart muscle, maximizing the chance of restoring a normal, life-sustaining rhythm.
The Standard Anterior-Lateral Position
For adult patients, the standard and most commonly instructed method for pad placement is the anterior-lateral position. This placement is designed to create an optimal pathway for the current to pass directly across the heart’s ventricles. The two pads must be applied to the patient’s bare chest, following the diagrams typically printed on the pads themselves.
The first pad, the anterior electrode, is positioned on the upper right side of the chest, just below the collarbone and to the right of the breastbone. The second pad, the lateral electrode, is placed on the lower left side of the chest, several inches below the armpit along the mid-axillary line. This positioning avoids placing the pads directly over the breastbone, which could reduce the effectiveness of the shock.
This strategic diagonal alignment ensures the electrical energy travels through the mass of the heart muscle. Following this standard placement is crucial, as any significant deviation can increase the resistance to the electrical current.
Adjustments for Specific Patient Conditions
While the anterior-lateral position is the default, certain patient circumstances require modification to ensure both safety and effectiveness.
Implanted Devices and Metal
If a patient has an implanted medical device, such as a pacemaker or an implantable cardioverter-defibrillator (ICD), the pad must be placed at least one inch away from the device. These devices are usually visible as a small bulge under the skin, often near the collarbone. Placing a pad directly over one could damage the implant or block the current from reaching the heart.
Similarly, any significant metal jewelry, such as necklaces or piercings, should be removed or moved to the side. If metal is in the path of the current, it can cause burns to the skin or create an electrical arc that bypasses the heart. For female patients with large or prominent breasts, the pad should be placed underneath the breast tissue, rather than on top of it, to ensure full contact with the chest wall.
Alternative Placement
In situations where the standard anterior-lateral placement is impossible due to severe chest trauma, surgical scars, or the presence of an implanted device, an alternative anterior-posterior position can be used. This involves placing one pad on the center of the chest and the other on the back, between the shoulder blades. This alternative path still allows the electrical current to traverse the heart.
Essential Steps Before Applying Pads
Before the electrode pads are affixed to the skin, several preparatory steps must be completed to ensure the shock is delivered effectively.
The most immediate concern is ensuring the patient’s chest is completely bare, dry, and free of any moisture. Water and sweat conduct electricity, which can reduce the current delivered to the heart and potentially cause burns to the skin.
If excessive chest hair prevents the pads from fully adhering to the skin, it must be removed rapidly, typically by shaving the area where the pads will be applied. Poor pad contact drastically increases the electrical resistance, which lessens the impact of the shock. The AED kit often contains a razor or scissors for this purpose.
The rescuer must also confirm the patient is unresponsive and not breathing normally before attempting to use the device. Once the pads are correctly placed and plugged into the AED, the device will analyze the heart’s rhythm. It is imperative to follow the AED’s verbal commands and ensure no one touches the patient during the analysis or the subsequent shock delivery.