An Automated External Defibrillator (AED) is a device designed to treat Sudden Cardiac Arrest (SCA), a condition where the heart’s electrical activity is chaotic, preventing it from effectively pumping blood. This chaotic rhythm, often ventricular fibrillation, requires an electrical shock to reset the heart’s electrical system. While the shock is a necessary intervention, it is only one step in maximizing the chance of survival. The moment the AED delivers its energy is immediately followed by crucial hands-on action that must continue until professional help arrives.
Immediately Resume Chest Compressions
The most important action after the AED delivers an electrical shock is to immediately resume chest compressions. The instruction from the device to “Start CPR” or “Continue CPR” must be followed without delay, even before checking for a pulse or signs of movement. This immediate action is necessary because even if the shock successfully corrects the heart’s electrical rhythm, the heart muscle itself is often stunned and may not begin pumping blood effectively right away.
High-quality chest compressions are required to circulate oxygenated blood to the heart and the brain, which are deprived of oxygen during cardiac arrest. Resumption of compressions should be swift to minimize the “perishock pause,” the time between the shock delivery and the restart of chest compressions. Shorter pauses are associated with better outcomes. Minimizing this interruption ensures a higher chest compression fraction.
To provide effective circulation, compressions should be delivered at a rate of 100 to 120 compressions per minute. The correct depth for an adult is at least 2 inches, but no more than 2.4 inches. It is also important to allow the chest to fully recoil after each compression, which allows the heart to refill with blood before the next pump. The rescuer should immediately restart the 30 compressions followed by 2 breaths cycle, or continuous compressions if trained only in hands-only CPR, unless the patient is clearly moving or breathing normally.
Maintaining the AED and CPR Cycle
The compressions must continue for approximately two minutes after the shock, which constitutes one full cycle of Cardiopulmonary Resuscitation (CPR) before the AED re-analyzes the heart rhythm. During this period, the AED will often provide voice prompts or a metronome feature to help the rescuer maintain the correct compression rate. The goal of this two-minute period is to circulate the blood and give the heart muscle time to recover its ability to pump effectively following defibrillation.
At the end of this cycle, the AED will prompt the rescuer to stand clear so it can perform a re-analysis. If the heart is still in a shockable rhythm, the AED will advise another shock. The rescuer must clear the patient before delivering the energy.
If the AED determines the rhythm is no longer shockable, or if the patient has regained a pulse, the device will advise “No Shock Advised.” If the patient remains unresponsive and is not breathing normally, the rescuer must continue the cycle of CPR until Emergency Medical Services (EMS) personnel arrive to take over care. The AED pads must remain attached, and the machine should not be turned off until EMS takes control of the situation.