The use of an Automated External Defibrillator (AED) during cardiac arrest is a time-sensitive intervention designed to deliver an electrical shock to restore a normal heart rhythm. High-quality cardiopulmonary resuscitation (CPR) focuses on effective chest compressions, which are the most important action for maintaining blood flow to the brain and heart. When using an AED, the primary goal is to minimize any interruption in these life-sustaining compressions. Every phase of the rescue must be coordinated to ensure compressions continue for the maximum possible duration.
The Critical Role of Minimizing Pauses
Minimizing the time compressions are stopped is critical because blood circulation to the heart muscle and brain rapidly drops with every interruption. The quality of blood flow is measured by the Coronary Perfusion Pressure (CPP), the pressure gradient that drives blood into the heart muscle itself. Effective chest compressions generate this pressure, but stopping compressions causes the CPP to fall to zero almost instantly. It then takes multiple compressions to rebuild this pressure to an effective level.
This physiological reality emphasizes maximizing the Chest Compression Fraction (CCF), which is the proportion of total resuscitation time that chest compressions are actively being performed. Current recommendations aim for a CCF of at least 60%, with an ideal target of 80% or higher, to maximize perfusion. A low CCF significantly reduces the chances of achieving a successful return of spontaneous circulation (ROSC) and successful defibrillation. Therefore, any necessary pause, such as for the AED to analyze the rhythm, must be kept to an absolute minimum, ideally under 10 seconds.
Seamless AED Setup and Pad Placement
The process of preparing the AED must be performed concurrently with ongoing chest compressions to prevent a hands-off period. The AED must be immediately powered on upon arrival, as the device provides critical audio instructions. If multiple rescuers are present, one should continue compressions while the second manages the AED setup. The patient’s chest must be fully exposed, requiring clothing to be cut away, and the skin must be clean and dry to ensure proper pad adhesion.
Correct placement of the electrode pads is essential for the AED to accurately analyze the rhythm and deliver an effective shock. In adults, one pad is placed on the upper right chest below the collarbone, and the other is placed on the lower left chest below the ribcage. If the patient is a child, pediatric pads should be used, or adult pads can be placed without touching or overlapping. The pads should be applied to the bare skin while compressions are underway, pausing only briefly to firmly press the pads onto the chest for full contact. Once attached, the pad connector cable is plugged into the AED, readying the device for the next phase.
Guidelines for the Shock Delivery Phase
Once the pads are connected, the AED prompts all rescuers to stand clear as it begins to analyze the patient’s heart rhythm. This analysis pause is the first unavoidable interruption in compressions and must be kept as short as possible. The rescuer must ensure no one is touching the patient during the analysis, as movement can interfere with the device’s reading. If the AED determines a shockable rhythm is present, it will charge and advise a shock, requiring the rescuer to loudly announce “clear” before pressing the shock button.
The moment the shock is delivered, chest compressions must be resumed immediately, without any delay for a pulse or rhythm check. This zero-delay resumption is based on evidence that a successful shock often converts the rhythm into a non-perfusing state. The patient still requires immediate support because they often remain pulseless for a significant period after defibrillation. Compressions are necessary to circulate blood and oxygen until a stable rhythm can be established. If the AED advises “No Shock Advised,” compressions must also be restarted immediately, and the AED will re-analyze the rhythm after approximately two minutes of ongoing CPR.