2.3 AED Use and Safe Defibrillation

2.3 AED Use and Safe Defibrillation

An automated external defibrillator (AED) is a portable device that analyzes the cardiac rhythm and, if it detects a shockable rhythm (ventricular fibrillation, VF; or pulseless ventricular tachycardia, pVT), advises a shock. Early defibrillation is the most powerful intervention for adult sudden cardiac arrest, so exam items test two things relentlessly: speed (minimize the pause around the shock) and safety (clear the patient).

The AED sequence, step by step

Pad placement

The standard adult placement is anterolateral: the right pad goes on the upper-right chest, just below the clavicle and to the right of the sternum; the left pad goes on the lower-left chest, below the axilla along the mid-axillary line. This routes the defibrillation vector through the bulk of the ventricular muscle. An anteroposterior (front-and-back) placement is an acceptable alternative, and is used when anterolateral pads would overlap (small adults, children). Pads must make full skin contact and must not touch each other.

Minimizing the pre-shock and post-shock pauses

The biggest survival lever in AED use is shortening the pauses around the shock. Keep compressions going while the pads are applied and while the device boots. When the AED announces it is analyzing, stop compressions and ensure no one is touching the patient, because motion artifact can corrupt the rhythm analysis. If a shock is advised, the rescuer clears the patient verbally and visually ("I'm clear, you're clear, oxygen clear, everyone clear"), then presses the shock button to deliver one shock.

The instant the shock is delivered, the team resumes CPR immediately, beginning with chest compressions — there is no pulse check after the shock. The AED will prompt the next analysis after about 2 minutes of CPR.

'No Shock Advised' means non-shockable

If the AED announces "No Shock Advised," the rhythm is non-shockable (pulseless electrical activity, PEA; or asystole). The correct response is the same in spirit: resume CPR immediately, starting with compressions, without checking a pulse. The AED has already assessed the rhythm; an immediate post-message pulse check only wastes hands-on-chest time. Reassessment happens at the planned 2-minute rhythm check, not by habit after every analysis.

Special situations and safety

• Wet chest / water: drag the patient out of standing water and dry the chest so the shock is not shunted across the skin.
• Excessive chest hair: shave or briskly rip off a pre-applied pad to remove hair if the pads will not adhere; poor contact wastes the shock and can cause burns.
• Medication patches: remove a transdermal patch (e.g., nitroglycerin) and wipe the skin before placing a pad over that spot.
• Implanted device (pacemaker/ICD): you will see or feel a hard bulge under the skin, usually upper-left chest. Place the pad at least 1 inch (2.5 cm) away from the bulge so the device does not block the shock.
• Pediatric use: use pediatric pads / a pediatric attenuator for children under 8 years or under 25 kg if available; if not, use adult pads rather than withholding defibrillation, ensuring the pads do not touch (use anteroposterior placement).

Common traps

• Stopping compressions while someone slowly opens the AED case.
• Checking a pulse immediately after every shock (delays CPR).
• Touching the patient during analysis or shock.
• Placing a pad directly over a medication patch or an ICD bulge.

AED vs. manual defibrillation, and why early shocks matter

An AED is fully automated: it interprets the rhythm and tells the rescuer whether to shock, which is why minimally trained lay rescuers can use one safely. In ACLS, the team often uses the manual defibrillator in the same device, where a trained provider reads the monitor and decides to shock, choosing the energy (a biphasic device typically uses the manufacturer's recommended setting, often 120-200 J, or a default of 200 J if unknown; older monophasic devices used 360 J).

** Survival from witnessed VF arrest falls roughly 7-10 percent for every minute defibrillation is delayed without CPR; good bystander CPR slows that decline and buys time until the shock. This is the core reason the adult lone-rescuer rule is phone-first and why public-access AEDs are placed in airports, gyms, and schools.

Single shocks, not stacked shocks

Current guidance directs a single shock followed immediately by CPR, not the obsolete practice of stacking three shocks in a row. Modern biphasic waveforms terminate VF with high first-shock success, and resuming compressions immediately is more valuable than re-checking the rhythm, because even a successful shock often leaves a brief non-perfusing rhythm that compressions support. The team re-analyzes after the 2-minute CPR cycle.

Memorize the loop: analyze, clear, shock once, immediately resume CPR for 2 minutes, repeat — adding rhythm-specific drugs (epinephrine, amiodarone) on the ACLS side without ever sacrificing compression time to do so.