A person has collapsed, is unresponsive, and is not breathing, and you have quickly deployed an Automated External Defibrillator (AED). After attaching the pads and initiating the analysis, the AED delivers the message: “No Shock Advised.” This situation is common and demands an immediate, focused response. The device is not malfunctioning; it is indicating that the heart’s electrical rhythm cannot be corrected by an electrical shock. Understanding this feedback is the first step in a precise protocol designed to maximize the patient’s chance of survival.
Why the AED Indicates No Shock
The purpose of an AED is to deliver a controlled electrical shock to the heart, but only when the heart’s electrical activity is chaotically disorganized. This chaotic state is known as ventricular fibrillation (VF), or sometimes pulseless ventricular tachycardia (pVT) in adults, where the heart muscle merely quivers instead of pumping blood effectively. Defibrillation works by momentarily stunning the heart, allowing its natural pacemaker to potentially restart a normal, organized rhythm.
The “No Shock Advised” message means the AED has detected a non-shockable rhythm. The two main non-shockable rhythms in cardiac arrest are Pulseless Electrical Activity (PEA) and Asystole. In Asystole, often called a flatline, there is no detectable electrical activity. PEA is characterized by organized electrical activity, but the heart fails to contract forcefully enough to circulate blood. Since there is no chaotic electrical pattern to “reset,” a shock is ineffective for both Asystole and PEA, confirming that intervention must shift entirely to mechanical support.
Immediate Action: Continuing High-Quality CPR
The moment the AED delivers the “No Shock Advised” message, the rescuer must immediately resume Cardiopulmonary Resuscitation (CPR). Minimizing the hands-off time between the AED analysis and the start of compressions is paramount to maintaining blood flow to the brain and heart. Effective CPR becomes the only viable intervention to artificially circulate oxygenated blood until advanced medical personnel arrive.
High-quality chest compressions must be maintained without interruption. The compression rate must range between 100 and 120 compressions per minute. The depth is equally important, requiring the chest of an adult to be compressed at least 2 inches (5 to 6 centimeters).
For the lay rescuer or a team without an advanced airway in place, compressions must be alternated with rescue breaths in a ratio of 30 compressions followed by 2 ventilations. Between each compression, the rescuer must ensure full chest wall recoil, avoiding leaning on the chest. Full recoil allows the heart to refill with blood before the next compression, ensuring maximum blood flow.
Reassessment and Transition to Advanced Care
The CPR cycle must continue uninterrupted for approximately two minutes before the AED re-analyzes the patient’s heart rhythm. This two-minute period of high-quality compressions provides the best chance of building up blood pressure and converting a non-shockable rhythm into a shockable one. The AED will prompt the rescuer to stand clear for the re-analysis to prevent interference with the device’s reading.
If multiple rescuers are present, they should switch roles as the AED prepares to re-analyze, or after five cycles of the 30:2 ratio. Switching compressors every two minutes prevents physical fatigue, which can lead to a drop in the quality and depth of compressions. Maintaining high-quality compressions is paramount.
Following the re-analysis, the AED will again advise either “No Shock Advised” or recommend a shock. If the “No Shock” message is repeated, the rescuer must immediately resume CPR for another two-minute cycle. If a shock is now advised, the rescuer follows the standard protocol, ensuring minimal pause in compressions before and after the shock delivery. This procedural loop continues until Emergency Medical Services (EMS) or Advanced Life Support (ALS) personnel arrive to take over patient care.