The full AED rescue sequence runs roughly 90 seconds from power-on to first shock — and every second matters because survival drops 7–10% per minute of delay (AHA). Understanding the six-step logic in advance lets a rescuer execute under stress without being slowed down by uncertainty about what the device is doing.
Quick answer
An AED operates in 6 sequential steps: power on → pad placement → rhythm analysis → shock decision → shock delivery (or “no shock advised”) → CPR cycle. The device handles rhythm interpretation. The rescuer handles pad placement, clearing the patient before shock, and CPR between cycles.
The 6 steps in real-time
1
2
3
4
5
6
What happens inside the device
The AED’s internal circuitry charges a capacitor to deliver the shock energy. Most modern AEDs use biphasic waveform technology — the shock pulse reverses polarity midway, which improves defibrillation effectiveness at lower energy levels vs older monophasic devices. Philips uses SMART Biphasic; ZOLL uses Rectilinear Biphasic; LIFEPAK uses ADAPTIV Biphasic. The clinical outcomes across these proprietary waveforms are broadly equivalent.
What the rescuer does vs what the device does
| Rescuer responsibility | Device responsibility |
|---|---|
| Power on the device | Voice prompts in plain English |
| Expose chest, apply adhesive pads | Detect electrical activity via pads |
| Stay clear during analysis | Interpret the heart rhythm |
| Stay clear during shock | Decide whether to shock |
| Begin CPR when prompted | Deliver shock or announce “no shock advised” |
| Continue CPR for 2 minutes | Re-analyze rhythm every 2 minutes |
Frequently asked questions
How long does the full AED rescue sequence take?
From power-on to first shock: roughly 90 seconds. From first shock through EMS arrival: typically 6–8 minutes of continuous AED + CPR cycles.
What if the AED says “no shock advised”?
Continue CPR. The patient’s rhythm may not be shockable (asystole, pulseless electrical activity). The device will re-analyze every 2 minutes and shock if/when defibrillation becomes indicated.
Can the rescuer be shocked by the AED?
No, as long as the rescuer is not touching the patient during the shock. The audible “Stand clear” prompt is the trigger to step back.
What energy does the AED deliver?
Adult shock: ~150–200 joules first shock, escalating on subsequent shocks. Pediatric shock: ~50 joules (energy is reduced via key, button, or auto-detect depending on model).
What if the patient is wet?
Quickly dry the chest before applying pads. Move the patient out of standing water if safely possible. AEDs work on damp surfaces, but pad adhesion requires a dry chest.
Do I need to keep using the AED until EMS arrives?
Yes. Continue AED + CPR cycles until EMS takes over or the patient shows signs of life (breathing, movement). Do not remove pads.
Run the math for your specific facility
Get the 60-second AED recommendation matched to your environment, training level, and budget. Free, no email required.
Sources
Educational content. Not a substitute for hands-on CPR + AED training. In a medical emergency, call 911.
