Out-of-Hospital Cardiac Arrest (OHCA) occurs when the heart’s electrical system malfunctions, causing an abrupt loss of heart function, breathing, and consciousness. Without immediate intervention, this condition is rapidly fatal. The OHCA Chain of Survival represents a sequence of coordinated, time-sensitive actions taken to maximize the victim’s chance of survival and neurological recovery. Each step is interdependent, meaning the outcome relies on the successful execution of all preceding links, starting with the bystander and extending through specialized hospital care.
The Critical First Steps
The initial two links of the Chain of Survival depend entirely on the immediate action of a bystander. The first action is the prompt recognition of cardiac arrest and the activation of the emergency response system. A person experiencing cardiac arrest will suddenly collapse, be unresponsive, and will either not be breathing or will be taking abnormal, gasping breaths, often referred to as agonal respirations.
Upon recognizing these signs, the bystander must immediately call for emergency medical services (EMS). Trained dispatchers use a protocol called Dispatcher-Assisted CPR (DA-CPR), instructing the caller on how to begin compressions immediately. The goal of this first link is to achieve the start of chest compressions within 60 seconds of the emergency call.
The second link is the provision of early Cardiopulmonary Resuscitation (CPR), which circulates oxygenated blood to the brain and heart until professional help arrives. For an adult victim, high-quality chest compressions involve pressing down hard and fast in the center of the chest. The compression rate should be between 100 and 120 compressions per minute, with a depth of at least 2 inches, but no more than 2.4 inches.
For lay rescuers, the use of “Hands-Only CPR” is strongly recommended, focusing solely on continuous, high-quality chest compressions without the need for rescue breaths. Minimizing interruptions during compressions is paramount, as maintaining the flow of blood to the brain is the primary objective during these early minutes. Effective bystander CPR can significantly increase the victim’s chance of survival until defibrillation can be performed.
Restoring the Heart’s Rhythm
The third link is rapid defibrillation, necessary because many sudden cardiac arrests are caused by a chaotic electrical disturbance. The two primary shockable rhythms are Ventricular Fibrillation (VF) and Pulseless Ventricular Tachycardia (pVT), where the heart chambers quiver uselessly. Defibrillation delivers a controlled electrical shock to momentarily stun the heart, resetting the electrical activity and allowing the heart’s natural pacemaker to potentially regain a normal rhythm.
The accessibility and ease of use of an Automated External Defibrillator (AED) in public places is a major component of this link. AEDs are sophisticated devices designed for use by untrained individuals and operate using simple voice and visual prompts. The rescuer’s main actions are to turn the device on, apply the electrode pads to the victim’s bare chest, and follow the instructions.
The AED will automatically analyze the heart’s rhythm and will only advise and deliver a shock if a shockable rhythm like VF or pVT is detected. If the device advises a shock, the rescuer ensures no one is touching the victim and presses the shock button, or the shock is delivered automatically. Immediately following the shock, or if no shock is advised, the rescuer must promptly resume high-quality chest compressions.
Professional and Post-Resuscitation Care
The fourth link is the provision of effective advanced resuscitation by Emergency Medical Services (EMS) personnel. These trained providers bring a higher level of care, including Advanced Cardiac Life Support (ACLS) protocols. Their interventions include establishing intravenous (IV) or intraosseous (IO) access to administer medications and inserting advanced airway devices, such as endotracheal tubes, to ensure adequate oxygenation.
A primary medication administered by EMS is epinephrine, a vasopressor given every three to five minutes, which helps increase blood flow to the heart and brain. EMS providers use rhythm analysis and advanced interventions while minimizing interruptions to chest compressions. The fifth link begins once the victim achieves Return of Spontaneous Circulation (ROSC) and is transported to a hospital.
Post-cardiac arrest care, delivered in a specialized unit, focuses on preserving brain function and treating the underlying cause of the arrest. Targeted Temperature Management (TTM) is a common intervention where the patient’s body temperature is precisely controlled, often maintained between 32°C and 36°C for at least 24 hours. TTM reduces the risk of secondary brain injury that can occur after blood flow is restored.
The most recent extension of the Chain of Survival includes a sixth, long-term link focused on recovery. This phase encompasses rehabilitation, observation, and psychological support, recognizing that survival involves maximizing the patient’s physical, cognitive, and emotional well-being. Specialized diagnostics, such as cardiac catheterization, are also performed to identify and treat reversible causes of the cardiac arrest, such as a blocked coronary artery.