AED Operation Review
The automated external defibrillator (AED) is one of the most important tools in EMS. Early defibrillation is the single most effective intervention for ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT), the most common initial rhythms in witnessed sudden cardiac arrest. For every minute defibrillation is delayed, the chance of survival decreases by 7 to 10%. AED operation is a critical NREMT testing topic, and questions often go beyond basic operation to test your knowledge of special situations and troubleshooting.
The standard AED sequence is: power on the device, attach pads to the patient's bare dry chest, allow the AED to analyze the rhythm, deliver a shock if advised (ensure all personnel are clear of the patient), and immediately resume CPR for 2 minutes after the shock before allowing the next analysis. This sequence integrates with the BLS cardiac arrest algorithm.
Pad Placement Considerations
Standard pad placement is anterolateral: one pad on the upper right chest below the clavicle and to the right of the sternum, and the other on the left lateral chest below the armpit. The current flows through the heart between the two pads. Alternative placements include anteroposterior (one pad on the anterior chest over the heart, one on the back between the shoulder blades), which may be preferred for very large patients or when standard placement is not possible.
Special placement situations include:
- Implanted pacemaker or defibrillator: Place the pad at least 1 inch (2.5 cm) away from the implanted device (visible as a lump under the skin, usually below the left clavicle).
- Medication patches: Remove any transdermal medication patches from the chest before applying pads. Patches can block current delivery and may burn the skin.
- Excessive chest hair: Hair prevents pad adhesion and creates air pockets that reduce current delivery. If pads do not adhere, use a razor (included in most AED kits) to shave the pad areas.
- Wet chest: Dry the chest before applying pads. Water conducts electricity and can cause surface arcing between pads, reducing current delivery to the heart.
Pediatric AED Considerations
For children ages 1 to 8 (or weighing less than 25 kg), use pediatric pads or a dose attenuator if available. Pediatric pads deliver a reduced energy dose appropriate for the smaller heart. If pediatric pads are not available, use adult pads. For infants under 1 year, a manual defibrillator is preferred, but an AED with pediatric pads is acceptable, and an AED with adult pads can be used if no other option exists. When using adult pads on a small child, place one pad on the chest and one on the back to prevent overlap.
Troubleshooting AED Issues
The AED may advise "no shock" for several reasons: the rhythm is not shockable (asystole or PEA), pads are not adhering properly, the device is malfunctioning, or there is excessive artifact from movement. If you receive a "no shock" message, continue CPR and allow the AED to reanalyze after 2 minutes. If you suspect a pad adhesion issue, press firmly on the pads to improve contact or replace them. If the AED prompts "check pads" or "check electrode," ensure the pads are firmly attached and the cable is fully connected to the device. Movement artifact can trigger false "no shock" messages; ensure everyone has stopped touching the patient during analysis. Never delay CPR to troubleshoot an AED issue; continue compressions while your partner addresses the device.