Basic Life Support (BLS) is the foundational emergency care provided to individuals experiencing life-threatening cardiac or respiratory emergencies. The International Liaison Committee on Resuscitation (ILCOR) evaluates and publishes scientific consensus on resuscitation, ensuring global standards are informed by the latest evidence. The 2020 ILCOR guidelines re-emphasize high-quality cardiopulmonary resuscitation (CPR) and rapid defibrillation. Understanding this specific sequence is paramount because swift, coordinated action significantly improves the likelihood of survival for a victim of sudden cardiac arrest.
Initial Steps: Safety and Activation
The immediate first step is to confirm scene safety, ensuring the environment poses no threat to the rescuer or the victim. Once safe, the rescuer should approach the victim, check for responsiveness by tapping and shouting, and quickly assess for normal breathing. If the victim is unresponsive and not breathing normally, the emergency response system must be activated immediately.
For a single rescuer, activation includes dispatching someone to retrieve an Automated External Defibrillator (AED) while the rescuer remains with the victim. Healthcare providers check for a pulse for no more than ten seconds. If no pulse is felt or if there is any doubt, the rescuer must assume cardiac arrest and begin chest compressions without delay. The risk of harm from performing CPR on a victim who is not in cardiac arrest is low, supporting the recommendation for lay rescuers to start compressions if they are unsure.
The Adult BLS Sequence: Compressions and Rescues
The adult BLS sequence follows the compressions-airway-breathing (C-A-B) approach, prioritizing immediate blood circulation to the brain and heart. High-quality chest compressions are delivered at a rate of 100 to 120 per minute to maximize blood flow.
The compression depth for an adult should be at least 2 inches (5 cm) but not exceed 2.4 inches (6 cm). Proper technique involves placing the heel of one hand in the center of the victim’s chest, on the lower half of the sternum, with the second hand laced over the first. This depth ensures adequate pressure while minimizing the risk of injury.
The rescuer must ensure full chest wall recoil between compressions, allowing the heart to refill with blood. After 30 compressions, the rescuer delivers two rescue breaths, establishing the standard 30:2 compression-to-ventilation ratio for adult BLS.
To deliver the rescue breaths, the rescuer uses the head-tilt, chin-lift maneuver to open the airway. The rescuer pinches the victim’s nose shut, creates a seal over the mouth, and delivers a breath lasting about one second, watching for visible chest rise. This 30:2 cycle is repeated continuously until the AED arrives, the victim shows signs of life, or advanced medical help takes over.
Integrating the Automated External Defibrillator (AED)
Rapid defibrillation is a critical link in the Chain of Survival. Once the AED arrives, the rescuer should power it on immediately and follow the device’s voice prompts. Chest compressions must continue while the AED pads are attached to the victim’s bare chest.
The pads are typically placed high on the right side of the chest and low on the left side, following the diagrams printed on the pads. Once connected, the device analyzes the heart’s rhythm, prompting all rescuers to stand clear. The AED will advise whether a shockable rhythm is detected.
If a shock is advised, the rescuer must loudly confirm that everyone is clear before pushing the shock button. After the shock is delivered, or if the AED advises no shock is needed, the rescuer must immediately resume chest compressions. CPR is interrupted only briefly for rhythm analysis and shock delivery, and compressions must be restarted within ten seconds.
Sequence Modifications for Infants and Children
Specific modifications are required for pediatric victims, defined as infants (less than one year old) and children (one year old to the onset of puberty). Since cardiac arrest in children is most often caused by respiratory failure, the delivery of rescue breaths is a higher priority for this population.
Compression-to-Ventilation Ratios
For a single rescuer, the compression-to-ventilation ratio remains 30 compressions to two breaths, consistent with the adult sequence. When two or more rescuers are present, the ratio changes to 15 compressions to two breaths to increase the frequency of ventilation.
Compression Depth and Technique
The recommended compression depth is approximately 4 centimeters (about 1.5 inches) for infants and 5 centimeters (about 2 inches) for children.
The technique varies based on the patient’s size. For infants, rescuers use the two-fingers technique or the two-thumb-encircling hands technique for two-rescuer CPR. For a child, compressions are performed with the heel of one or two hands, depending on the child’s size, to achieve the appropriate depth.