An Automated External Defibrillator (AED) analyzes the heart rhythm and delivers a shock only when it detects a specific, chaotic pattern like ventricular fibrillation (VF) or pulseless ventricular tachycardia (pVT). When the AED says, “No Shock Advised,” it means the heart is in a non-shockable rhythm, such as asystole (no electrical activity) or Pulseless Electrical Activity (PEA). Since these rhythms will not respond to an electric shock, the immediate action is to manually circulate blood and oxygen.
The rescuer must immediately resume high-quality cardiopulmonary resuscitation (CPR) without delay after the “No Shock Advised” prompt. Chest compressions are the only way to deliver oxygenated blood to the brain and heart when the heart is not pumping effectively. The standard of care requires a compression-to-breath ratio of 30 compressions followed by 2 rescue breaths.
Compressions should be delivered at a rate of 100 to 120 per minute, pushing down at least two inches, but no more than 2.4 inches, on the center of the chest. Allowing the chest to fully recoil between compressions is important, as this ensures the heart can refill with blood. This two-minute cycle of CPR is performed continuously, and interruptions must be minimized to less than ten seconds, since stopping compressions halts all blood flow.
The Reassessment and Re-analysis Phase
CPR must be maintained for approximately two minutes before the AED automatically prompts the rescuer to pause for a new analysis. This two-minute window, which equates to about five cycles of 30 compressions and 2 breaths, is intended to circulate blood and oxygen. Circulation may potentially make a non-shockable rhythm transition into a shockable one. The AED uses voice prompts to guide the rescuer to stand clear so it can analyze the heart rhythm without interference.
During this pause, the rescuer should quickly check the victim for signs of life, such as movement, coughing, or normal breathing. If the victim shows definitive signs of life, CPR should be stopped. Otherwise, the rescuer must allow the AED to complete its analysis, which will state one of two outcomes: “Shock Advised” or “No Shock Advised, continue CPR.”
If the AED detects a shockable rhythm, it will instruct the rescuer to deliver a shock, or it may deliver it automatically depending on the device model. If the message is still “No Shock Advised,” the rescuer must immediately resume the cycle of high-quality CPR for another two-minute period. The AED continues this cyclical process of two minutes of CPR followed by re-analysis until professional help arrives or the victim shows signs of recovery.
Transitioning Care and Monitoring the Victim
Throughout the entire process, the AED pads must remain firmly attached to the victim’s chest, and the device should be left running. Leaving the pads on ensures that if the heart rhythm changes to a shockable one, the AED can quickly detect it and advise a shock without delay. Never turn the AED off, as the professional medical team will need the data it has recorded.
If the victim regains consciousness, begins to breathe normally, or starts moving, CPR should be discontinued immediately. If the person is breathing normally but remains unresponsive, they should be carefully rolled onto their side into the recovery position. This position helps keep the airway open and reduces the risk of aspiration if the person vomits.
When Emergency Medical Services (EMS) personnel arrive, the rescuer should provide a concise report of the events. This information should include the approximate time the person collapsed, the number of CPR cycles performed, and the number of times the AED advised or delivered a shock. This handover of information is important for the patient’s continuing medical treatment.