Operation:

1. Power On: Turn on the AED. Some models automatically power on when the lid is opened. The device will then provide clear voice prompts and visual cues.
2. Attach Pads: Expose the patient's bare chest. Apply two electrode pads to specific locations on the patient's chest as indicated by diagrams on the pads themselves or the AED unit. Standard adult pad placement involves one pad below the right collarbone and the other near the left armpit on the lower ribcage. For pediatric patients (usually less than 9 years of age), an anterior-posterior placement may be preferred. Ensure good skin contact; if excessive chest hair is present, it may need to be quickly trimmed or shaved to ensure adhesion. Dry the chest thoroughly if wet.
3. Analyze Rhythm: Once the pads are correctly attached, the AED will instruct all rescuers to "stand clear" and will analyze the patient's heart rhythm. During this analysis, CPR must stop, and no one should touch the patient to avoid interfering with the ECG signal and to ensure rescuer safety if a shock is delivered.
4. Deliver Shock (if indicated):
   • If a shockable rhythm (V-fib or pVT) is detected, the AED will announce "shock advised" and begin charging.
   • The AED will then instruct the user to "clear" the patient again and press the "shock" button. It's imperative to visually confirm that no one is touching the patient before delivering the shock.
   • If a non-shockable rhythm (e.g., asystole or normal sinus rhythm) is detected, the AED will advise "no shock advised" and prompt the rescuer to continue CPR.
5. Resume CPR: Immediately after the shock (or if no shock was advised), resume chest compressions. Most AEDs provide a metronome or voice prompts to guide the rate and depth of compressions for two minutes.
6. Re-analyze: After two minutes of CPR, the AED will prompt another rhythm analysis, and the cycle repeats until emergency medical services (EMS) arrive and take over, or the patient regains consciousness and normal breathing.

Special Considerations and Contraindications:

• Do Not Resuscitate (DNR) Orders: If a patient has a valid DNR order, an AED should not be used. However, sudden cardiac arrest often occurs in a community setting without a family member present to clarify advanced directives or code status. When in doubt, it is imperative to intervene.  
• Traumatic Arrest: Generally, AEDs are not indicated for cardiac arrest secondary to severe trauma, unless there's a strong suspicion of a medical cause for the arrest in a trauma patient. Massive internal or external hemorrhage leads to pulseless electrical activity (PEA) or asystole, which are not shockable rhythms.
• Wet Environment: The patient should be moved to a dry area and their chest dried before applying pads and delivering a shock to prevent arcing and ensure effective energy delivery.
• Implanted Devices: Avoid placing AED pads directly over implanted pacemakers or implantable cardioverter-defibrillators (ICDs). Position the pad at least 1 inch (2.5 cm) away from the device.
• Medication Patches: Remove any transdermal medication patches (e.g., nitroglycerin, nicotine) from the chest area and wipe the skin clean before applying AED pads, as they can block energy delivery or cause burns.
• Movement: Do not use an AED in a moving vehicle.
• Children under 1 year: Manual defibrillators are preferred for infants under 1 year of age. If a manual defibrillator is not available, attenuated pediatric pads or even adult pads (if no pediatric pads are available) may be considered, but with caution and understanding of the energy delivered.
• Flammable Vapors: Avoid using an AED in the presence of flammable gases or liquids, as a spark could ignite them.