The question of using an Automated External Defibrillator (AED) before Cardiopulmonary Resuscitation (CPR) is common in sudden cardiac arrest. Both are life-saving interventions serving distinct purposes. CPR involves manual chest compressions and rescue breathing to circulate blood and oxygen. An AED analyzes the heart’s electrical rhythm and delivers a shock to reset it. The accepted protocol prioritizes immediate action to maximize survival.
The Standard Emergency Protocol
Upon finding an unresponsive person who is not breathing normally, first ensure the scene is safe. Immediately call the local emergency number, such as 911, to activate emergency medical services. If an AED is not immediately accessible, request one be brought to the scene. The priority is to begin high-quality chest compressions without delay, rather than waiting for the device.
CPR starts immediately following the emergency call, initiating a cycle of chest compressions and rescue breaths. Compressions must be delivered hard and fast (100 to 120 per minute) to manually pump blood to the brain and vital organs. This mechanical action is the most immediate form of life support available until specialized equipment arrives. If two or more people are present, one should begin CPR while the other retrieves the AED.
The AED should be applied to the victim’s bare chest as soon as it is available, even if CPR is underway. The device provides voice prompts guiding the rescuer through attaching the pads and analyzing the heart’s rhythm. If the AED determines a shockable rhythm, it prompts the user to deliver an electrical shock. If no shock is advised, the rescuer must immediately resume chest compressions.
How CPR and AED Address Different Problems
The rationale for this sequence lies in understanding the distinct physiological problems each intervention addresses during cardiac arrest. In most adult cases, the heart’s electrical system malfunctions, resulting in chaotic, ineffective quivering (ventricular fibrillation). An AED is the only intervention that can correct this electrical problem by delivering a controlled shock to reset the heart’s rhythm.
CPR addresses the immediate consequence of the heart stopping: the cessation of blood flow and oxygen delivery. Chest compressions mechanically force blood to circulate, maintaining a minimal supply of oxygen and nutrients to the heart and brain. This manual circulation is a temporary bridge, keeping cells alive until the heart’s electrical rhythm can be restored.
High-quality CPR is important preparation for the defibrillation shock. By manually circulating blood, compressions deliver oxygen to the heart muscle, making the heart more susceptible to a successful rhythm reset. Without this preparatory CPR, a shock delivered to an oxygen-starved heart may be less effective at restoring a sustainable beat. CPR buys time and primes the heart, while the AED provides the definitive treatment for the electrical failure.
The Critical Role of Time
The immediate start of CPR is required due to the rapid decline in survival rates every minute the heart is stopped. For every minute that passes without intervention, a person’s chance of survival decreases by approximately 7% to 10%. This narrow window emphasizes the need for immediate action, which CPR provides.
The brain and vital organs suffer irreversible damage quickly due to the lack of oxygenated blood flow. While the AED fixes the electrical problem, the delay in locating and retrieving the device is too long to leave the victim without circulation. Immediate bystander CPR can effectively double or triple a person’s chance of survival by slowing tissue death.
The goal is not to choose between CPR or the AED, but to minimize the time the victim is without support. The moment cardiac arrest is recognized, CPR must be initiated to provide artificial circulation. This is followed by applying the AED the instant it arrives. This rapid response ensures the brain receives immediate support while preparing the heart for electrical therapy.