What is Basic Life Support (BLS)?
Basic life support is the foundation for saving lives after cardiac arrest, consisting of immediate recognition of cardiac arrest, early high-quality CPR with chest compressions prioritized before rescue breaths, and rapid defibrillation with an automated external defibrillator (AED). 1
Core Definition and Purpose
BLS refers to maintaining airway patency and supporting breathing and circulation without the use of equipment other than a protective shield. 1 The primary objective is to provide oxygen to the heart and brain until advanced treatment can restore spontaneous circulation—essentially a "holding operation" that maintains adequate ventilation and circulation until the underlying cause of arrest can be reversed. 1, 2
Critical time sensitivity: Failure of circulation for 3-4 minutes (less if initially hypoxemic) leads to irreversible cerebral damage, making rapid institution of BLS essential. 1
Essential Components of BLS
BLS comprises four fundamental elements that follow a specific sequence: 1
- Initial assessment - Immediate recognition of sudden cardiac arrest based on unresponsiveness and absence of normal breathing (patient not breathing or only gasping) 1
- Airway maintenance - Opening and maintaining airway patency 1
- Rescue breathing - Expired air ventilation to provide oxygenation 1
- Chest compressions - External cardiac compression to maintain circulation 1
When all elements are combined, the term cardiopulmonary resuscitation (CPR) is used. 1
The CAB Sequence: A Critical Change
The American Heart Association changed the sequence from ABC to CAB to prioritize immediate chest compressions over airway positioning and rescue breaths, minimizing time to first compression. 3, 4 This represents one of the most important modern updates to BLS practice. 1
The "Look, Listen, and Feel" step was removed from the BLS algorithm to reduce time delays. 1, 4
High-Quality CPR Requirements
High-quality chest compressions are the most critical component of BLS because they maintain perfusion during cardiac arrest. 1 Specific parameters include: 1, 3
- Compression depth: At least 2 inches (5 cm) for adults 3, 4
- Compression rate: 100-120 compressions per minute 3, 4
- Complete chest recoil between compressions 3, 4
- Minimal interruptions in chest compressions 3, 4
- Avoid excessive ventilation 4
Compression-to-Ventilation Ratios
The ratio varies based on rescuer training and patient age: 3
- Single rescuers (all ages except newborns): 30 compressions to 2 breaths 3
- Two healthcare provider rescuers (pediatric): 15 compressions to 2 breaths 3
Hands-Only CPR for Lay Rescuers
The American Heart Association encourages hands-only (compression-only) CPR for untrained lay rescuers, which is easier to perform and can be guided by dispatchers over the telephone. 1, 3, 4 This approach removes barriers to bystander intervention and has been shown to be effective. 5
Who Can Perform BLS
BLS can be performed by both lay rescuers (bystanders) and healthcare providers. 3 The distinction is important:
- Lay rescuers: Should NOT check for a pulse; should focus on recognizing unresponsiveness and abnormal breathing 4
- Healthcare providers: Should check for a pulse, but limit the time to no more than 10 seconds to avoid delay in initiating chest compressions 4
Early Defibrillation Component
Rapid defibrillation is a powerful predictor of successful resuscitation and should be considered part of BLS. 4 The development of automated external defibrillators has allowed minimally trained people to extend their BLS skills. 1
Rescuers should retrieve an AED if nearby and easily accessible. 4 When implemented effectively with witnessed out-of-hospital ventricular fibrillation arrest, survival rates can approach 50%. 1, 3
Impact on Survival
Early CPR can improve the likelihood of survival, yet CPR is often not provided until professional emergency responders arrive. 1 The evidence demonstrates:
- Bystander CPR is associated with successful return of spontaneous circulation and neurologically intact survival 1
- Survival rates >70% with good neurologic outcome have been reported for out-of-hospital respiratory arrest when bystander resuscitation is provided 1
- Early resuscitation and prompt defibrillation (within 1-2 minutes) can result in >60% survival 6
- Each missed minute in applying defibrillation decreases survival rate by 7%-10% 6
BLS as Part of the Chain of Survival
BLS represents the first three links in the American Heart Association's Chain of Survival: prevention, early CPR, and prompt access to the emergency response system. 1, 3 Both BLS and advanced cardiovascular life support (ACLS) are sequential stages of care, with BLS being the foundation. 1, 3
Team-Based Approach for Healthcare Providers
For highly trained rescuers in appropriate settings, a simultaneous, choreographed approach is recommended for chest compressions, airway management, rescue breathing, rhythm detection, and shocks by an integrated team. 1, 3, 4
Common Pitfall to Avoid
The most critical pitfall is delay in starting chest compressions. Any confusion or hesitation results in lost time and decreased survival. 1 Healthcare providers must immediately begin CPR once they recognize unresponsiveness with no breathing or only gasping, after activating the emergency response system. 1