Why do we give 2 breaths in cardiopulmonary resuscitation (CPR)?

Why We Give 2 Breaths in CPR

The 2-breath technique during CPR exists to maintain adequate oxygenation during cardiac arrest while minimizing interruptions to chest compressions, with current guidelines recommending a 30:2 compression-to-ventilation ratio for trained rescuers performing CPR without an advanced airway. 1

The Physiological Rationale

Oxygen Delivery During Cardiac Arrest

• During the first several minutes of sudden cardiac arrest (particularly VF), the oxygen content in arterial blood remains adequate, making chest compressions initially more critical than ventilations 1
• However, over time oxygen in the blood is consumed and oxygen in the lungs becomes depleted, making ventilations increasingly important for prolonged arrests 1
• During CPR, cardiac output is only 25-33% of normal, so oxygen uptake from the lungs and CO2 delivery to the lungs are reduced, meaning lower-than-normal tidal volumes (500-600 mL) can maintain effective oxygenation 1, 2

The Compression-Ventilation Balance

• The 30:2 ratio represents a compromise between maintaining circulation (compressions) and oxygenation (breaths) 1
• Interruptions to chest compressions cause coronary perfusion pressure to drop rapidly, and several compressions are needed after each pause to rebuild perfusion pressure 1, 3
• The goal is to pause compressions for less than 10 seconds to deliver the 2 breaths 1

Current Guideline Recommendations

For Trained Rescuers (Without Advanced Airway)

• Deliver cycles of 30 compressions followed by 2 breaths 1
• Each breath should be delivered over approximately 1 second 1, 2
• Target tidal volume of 500-600 mL (6-7 mL/kg) to produce visible chest rise 1, 2, 4
• The pause for both breaths should ideally be brief (3-4 seconds total) 2

For Untrained Lay Rescuers

• Compression-only CPR is recommended, with no breaths required 1
• Dispatchers should instruct untrained rescuers to provide compression-only CPR 1

After Advanced Airway Placement

• Once an endotracheal tube or supraglottic airway is placed, switch to continuous compressions with asynchronous ventilation 1
• Deliver 1 breath every 6 seconds (10 breaths per minute) without pausing compressions 1, 2

Why Specifically 2 Breaths?

Evidence Supporting the 2-Breath Approach

• The 30:2 ratio allows delivery of at least 60-70 compressions per minute while maintaining some ventilation 5
• Studies show that 83% of trained rescuers can deliver 2 breaths in less than 10 seconds, and 21% can do it in less than 5 seconds 5
• A median chest compression fraction of 65% can be maintained with the 30:2 ratio 5
• Research found no survival disadvantage when ventilation pauses were slightly longer than recommended, as long as adequate compressions were maintained 5

The Problem with More Frequent Ventilations

• The previously recommended 15:2 ratio (used before 2005) resulted in too many interruptions and insufficient chest compressions 1
• Manikin studies demonstrated that rescuers could not deliver adequate compressions per minute with 15:2 ratios 1
• The 30:2 ratio yields more chest compressions with minimal or no increase in rescuer fatigue 1

Critical Pitfalls to Avoid

Excessive Ventilation is Harmful

• Avoid hyperventilation (too many breaths or too large a volume) - this is a Class III recommendation (harm) 1, 2, 4
• Excessive ventilation increases intrathoracic pressure, decreases venous return to the heart, and diminishes cardiac output and survival 1, 2
• Excessive ventilation also causes gastric inflation leading to regurgitation and aspiration 1

Prolonged Pauses for Ventilation

• While trained rescuers often take 7-10 seconds for 2 breaths (longer than the ideal <5 seconds), this has not been associated with worse outcomes if adequate total compressions are maintained 5
• However, the goal remains to minimize interruptions and maintain a chest compression fraction of at least 60% 1

Common Technical Errors

• Taking deep breaths before rescue breathing (causes rescuer dizziness) - instead take regular breaths 1
• Delivering breaths too quickly or forcefully (increases gastric inflation risk) 1
• The most common cause of ventilation difficulty is an improperly opened airway, not inadequate breath volume 1

Special Populations

Asphyxial Arrest (Drowning, Children)

• Ventilations are particularly important for victims of asphyxial arrest because they are hypoxemic at the time of cardiac arrest 1
• For pediatric cardiac arrest, the same 30:2 ratio applies for single rescuers 1

EMS Provider Considerations

• A large trial of 23,711 adults found no significant difference in survival between continuous compressions with asynchronous ventilation (9.0%) versus 30:2 CPR (9.7%) before advanced airway placement 1
• This supports that either approach is reasonable for EMS providers, though 30:2 remains the standard recommendation 1

The Bottom Line Algorithm

Without advanced airway:

• Start with 30 chest compressions at 100-120/minute 1
• Pause briefly and deliver 2 breaths over 1 second each 1
• Ensure visible chest rise with each breath 1, 2
• Resume compressions immediately 1
• Continue 30:2 cycles 1

With advanced airway:

• Continuous compressions at 100-120/minute without pauses 1, 4
• Asynchronous ventilation at 1 breath every 6 seconds (10/minute) 1, 2