What defines one cycle of cardiopulmonary resuscitation (CPR)?

What is One Cycle of CPR

One cycle of CPR consists of 30 chest compressions followed by 2 rescue breaths, and you should perform approximately 5 such cycles continuously for 2 minutes before pausing to reassess rhythm. 1, 2

Defining the CPR Cycle

The American Heart Association defines the CPR cycle structure based on two key parameters:

Compression-to-Ventilation Ratio

• For single rescuers and two or more rescuers in adults: Deliver 30 chest compressions followed by 2 breaths (30:2 ratio) 1, 2
• For pediatric patients with two or more rescuers: Use 15 compressions followed by 2 breaths (15:2 ratio) 1
• With an advanced airway in place: Provide continuous compressions at 100-120/minute with asynchronous ventilations (1 breath every 6 seconds in adults, or every 2-3 seconds in children), eliminating the traditional "cycle" structure 1, 2

Duration of Continuous CPR

• Each CPR period lasts 2 minutes before any interruption for rhythm assessment or pulse check 1, 3, 2
• During these 2 minutes, you will complete approximately 5 cycles of 30:2 (or about 10 cycles of 15:2 in pediatric two-rescuer scenarios) 2, 4
• Research confirms that newly trained providers complete five cycles of 30:2 CPR in approximately 115 seconds (just under 2 minutes), making "5 cycles" and "2 minutes" functionally equivalent 4

Critical Quality Metrics Within Each Cycle

Compression Technique

• Depth: At least 2 inches (5 cm) in adults; at least one-third anteroposterior diameter in children 1, 2
• Rate: 100-120 compressions per minute 1, 2
• Recoil: Allow complete chest recoil between compressions without leaning on the chest 1, 2

Minimizing Interruptions

• Keep all pauses under 10 seconds, as longer interruptions significantly reduce coronary perfusion pressure 1, 3, 2
• The median time to deliver 2 rescue breaths is 7 seconds (with 83% of rescuers completing ventilations in under 10 seconds), which is acceptable despite the guideline target of 5 seconds 5
• Do not interrupt compressions to check pulse or rhythm during the 2-minute cycle unless the patient shows obvious signs of recovery 2

When to Pause and Reassess

After completing 2 minutes (approximately 5 cycles) of continuous CPR:

• Pause briefly (< 10 seconds) for rhythm analysis using an AED or manual defibrillator 1, 3, 2
• If a shockable rhythm is detected, deliver one shock and immediately resume compressions for another 2-minute cycle 1, 3
• If a non-shockable rhythm is present, immediately resume compressions for another 2-minute cycle 1, 3
• Change compressors every 2 minutes (or sooner if fatigued) at the time of rhythm checks to maintain compression quality 1, 2

Common Pitfalls to Avoid

• Do not count time instead of cycles: While 2 minutes is the target duration, counting "5 cycles of 30:2" is easier for most rescuers to follow and ensures adequate compression delivery 4
• Do not check pulse immediately after defibrillation: This wastes critical perfusion time—resume compressions immediately and wait until the next 2-minute rhythm check 3, 2
• Avoid excessive ventilation: Over-ventilating increases intrathoracic pressure and reduces cardiac output; stick to 2 breaths per cycle 1, 2
• Do not delay compressions for airway setup: Compressions take priority (C-A-B sequence) 2

Evidence Regarding Cycle Structure and Outcomes

Research demonstrates that the 30:2 ratio is more challenging to adhere to than continuous compressions (48.3% adherence vs 58.6%), but when performed correctly, 30:2 CPR is associated with better survival to hospital discharge compared to continuous chest compressions 6. For bystander-administered CPR under telephone guidance, compression-only CPR (eliminating the ventilation component entirely) improves survival to discharge by 2.4% compared to interrupted 30:2 CPR, though this applies specifically to untrained bystanders, not healthcare providers 7.

The 30:2 ratio delivers more total compressions per minute (457 vs 379) and reduces no-flow time (22 seconds vs 33 seconds per 5-minute period) compared to the older 15:2 ratio, without increasing provider fatigue or perceived exertion 8.