We often hear that effective CPR requires a chest compression fraction of more than 80%, as recommended by ILCOR. On paper, this seems straightforward. But in real-life resuscitation, is it really achievable? Let’s break it down with some math.

The Limits of Conventional CPR (30:2)

A cycle of 30 compressions and 2 breaths takes about 21 seconds:

• 18 seconds for compressions, with only 12 seconds truly effective (since cerebral perfusion begins after about 10 compressions).
• 3 seconds for the 2 ventilations.

Result: out of 21 seconds, only 57% generates effective perfusion.
Extended over 2 minutes, that equals 68.6 seconds of perfusion out of 120 seconds… and that’s assuming no errors and flawless transitions.

Adding the AED

With an AED (e.g., Zoll 3):

• 2 minutes of compressions
• 8 seconds of rhythm analysis
• 4 seconds for the shock

A complete cycle takes 132 seconds. Out of this, only 51.5% is effective perfusion—far from the recommended 80%.

The Impact of Compression-Only CPR

Now, let’s imagine the same sequence but with compressions only, no ventilations:

• 8 seconds for rhythm analysis
• 4 seconds for shock delivery
• ~6 seconds at the start of the cycle to build perfusion pressure

That’s 18 seconds without perfusion out of 132 seconds, leaving 114 effective seconds (86%). Finally, we hit the target!

The Optimal Sequence: What Recent Data Suggest

For a witnessed cardiac arrest of cardiac origin, evidence supports a simplified approach during the first minutes:

0–6 minutes (up to 3 shocks)

• Chest compressions only
• If available: high-flow oxygen via non-rebreather mask + oropharyngeal airway for passive oxygenation
• Strategies to maximize chest compression fraction:
  • Switch compressors during AED analyses
  • Do not perform pulse checks unless there are clear signs of life
  • Do not stop compressions for airway insertion
  • Do not initiate transport during these first 6 minutes (unless absolutely necessary)

After 6 minutes, if no ROSC

• Insert a supraglottic airway and provide controlled ventilation (~500 mL per breath) with capnography
• Monitor capnography to confirm airway position and detect early signs of ROSC
• Consider double sequential defibrillation (to be explored in a future publication)
• Prepare for rapid transport to an ECMO-capable center — in patients <70 years old, with refractory, shockable arrest, and continuous CPR without interruptions
• Use an automated chest compression device (LUCAS, Autopulse) to ensure quality

During transport

• Optimized ventilation (500 mL per breath) with a device that tracks tidal volume (e.g., Zoll Real-BVM)
• Continuous capnography for airway monitoring and early ROSC detection
• Head-up positioning: promising in recent studies, though data remain limited

Advanced Cardiac Life Support (ACLS)

• Search for and address reversible causes (Hs & Ts)
• Tailor interventions to the presentation, but do not delay transport in patients who are strong ECMO candidates.

Conclusion

The math is clear: with conventional CPR, we fall well short of the 80% compression fraction goal. To truly give patients the best chance of neurologically intact survival, we must maximize chest compressions, simplify the first minutes, and above all prioritize rapid defibrillation.

The faster we defibrillate, the greater the chance of acting on a heart that still has enough energy (ATP) to convert and sustain a rhythm compatible with life.