Basic Life Support (BLS) is a standardized set of procedures designed to maintain a casualty’s oxygenation and circulation until advanced medical help arrives. This sequence focuses on immediate, non-invasive interventions to counter the effects of cardiac arrest. Executing these steps maximizes the chance of a successful outcome. BLS hinges on the rescuer’s ability to execute these steps in the correct order, ensuring that help is activated and life-sustaining compressions are started quickly.
Scene Safety and Emergency Activation
The first action upon encountering a potentially unresponsive person is to ensure the environment poses no danger to the rescuer or the patient. A safe scene allows the rescuer to focus entirely on the patient. After confirming the scene is safe, the rescuer must determine if the person is responsive by tapping their shoulder and shouting loudly, asking if they are okay.
If the person does not respond, the next step is to activate the emergency response system. A lone rescuer should immediately call 911 (or the local emergency number) on a mobile phone and put the call on speaker, or call for help from bystanders. The rescuer should also instruct a specific bystander to retrieve an Automated External Defibrillator (AED) and return immediately. This activation of help must happen before starting physical interventions.
If the person is unresponsive and is not breathing or is only gasping, the rescuer should assume the patient is in cardiac arrest. Agonal gasps, which can sound like snores, are not considered normal breathing and indicate a medical emergency. Lay rescuers should not spend more than about 10 seconds checking for a pulse before starting compressions.
Performing Chest Compressions and Rescue Breaths
Once cardiac arrest is recognized, the sequence of intervention follows the C-A-B logic: Compressions, Airway, Breathing. This order prioritizes chest compressions, which circulate oxygenated blood to the brain and heart. The patient must be positioned on a firm, flat surface for effective compressions.
To perform compressions, the rescuer places the heel of one hand in the center of the patient’s chest, with the other hand placed on top. The rescuer must push straight down to achieve the correct depth. Compressions should be delivered at a rate of 100 to 120 beats per minute, described as “hard and fast.”
For an average adult, the compression depth should be at least 2 inches (5 centimeters), but should not exceed 2.4 inches (6 centimeters). Allowing the chest to fully recoil between each compression is important, as this allows the heart to refill with blood. The goal is to minimize interruptions in compressions, keeping the hands-off time to less than 10 seconds.
After 30 compressions, the rescuer should open the airway and deliver two rescue breaths. The airway is opened using the head-tilt/chin-lift maneuver, which moves the tongue away from the back of the throat. Each breath should be given over about one second, and the rescuer should observe a visible chest rise to confirm the breath was effective. The rescuer then immediately returns to chest compressions, maintaining the 30 compressions to 2 breaths ratio.
Operating the Automated External Defibrillator
The Automated External Defibrillator (AED) is integrated into the BLS sequence as soon as it arrives. Defibrillation delivers an electrical shock to stop an abnormal heart rhythm, potentially allowing a normal rhythm to resume. The rescuer must turn the AED on and follow the device’s voice and visual prompts.
The rescuer must quickly expose the patient’s chest and apply the electrode pads directly to the skin. One pad is typically placed on the upper right side of the chest, and the other is placed on the lower left side below the armpit. Ensure the chest is dry and any medication patches are removed before attaching the pads.
Once the pads are attached, the device will prompt the rescuer to clear the patient for rhythm analysis. If the AED detects a shockable rhythm, it will advise a shock and charge itself. The rescuer must ensure no one is touching the patient before pressing the shock button.
If a shock is delivered, or if the AED advises no shock is needed, the rescuer must immediately resume chest compressions. The AED will typically prompt the rescuer to continue Cardiopulmonary Resuscitation (CPR) for two minutes before it re-analyzes the rhythm. The resuscitation effort continues by alternating between two minutes of CPR and rhythm analysis until advanced medical personnel take over.