When giving CPR cycles, the goal is to minimize interruptions to chest compressions. Every second you pause compressions, blood flow to the brain and heart drops rapidly, and it takes several compressions to build that pressure back up. The American Heart Association recommends that compressions make up more than 80% of total CPR time, a metric called chest compression fraction.
Why Pauses in Compressions Are So Harmful
Chest compressions work by mechanically squeezing the heart to push blood forward through the body. This creates a buildup of pressure in the aorta (the body’s main artery) that drives blood into the coronary arteries, which feed the heart muscle itself. That pressure is what gives the heart a chance to restart.
When you stop compressing, even briefly, blood “runs off” from the aorta and that driving pressure collapses. Research published in Circulation measured this effect precisely: the pressure dropped by about 7 mmHg during just two rescue breaths. After each pause, it took 3 to 7 compressions to rebuild the pressure to its previous level. This means the first several compressions after any interruption are significantly less effective than the ones that came before the pause. In that study, the average pressure during the first two compressions of each cycle was only 14 mmHg, compared to 21 mmHg for the final two compressions before the pause.
This pattern repeats every single cycle. The more often you interrupt, the more time the heart spends receiving inadequate blood flow.
How Pauses Affect Survival
The connection between shorter pauses and better outcomes is consistent across studies. A 2024 study of pediatric cardiac arrests found that every additional 5 seconds added to the longest compression pause was associated with a 3% lower chance of survival with good neurological outcome. The same pattern held for hospital discharge and for achieving return of spontaneous circulation (when the heart starts beating on its own again).
Pauses around defibrillation are especially critical. A study of out-of-hospital cardiac arrests found that keeping the pause before a shock under 3 seconds and the pause after a shock under 6 seconds dramatically improved outcomes. When both targets were met, the odds of the heart restarting were roughly 13 times higher than when pauses were longer. Even optimizing just one of those windows made a significant difference.
Common Reasons for Interruptions
During CPR, compressions get interrupted for several reasons:
- Rescue breaths. In standard 30:2 CPR, you deliver 30 compressions followed by 2 breaths. Guidelines recommend keeping that ventilation pause under 5 seconds.
- Rhythm checks. Rescuers periodically stop to assess whether the heart has returned to a normal rhythm. These should be as brief as possible.
- Defibrillation. An AED or manual defibrillator requires a brief pause to analyze the rhythm and deliver a shock.
- Provider switches. Fatigue degrades compression quality quickly, so rescuers rotate. The swap should happen during a planned pause, like a rhythm check, rather than creating an additional one.
Each of these is necessary at some point, but the goal is to keep every pause as short as possible and avoid any unnecessary ones.
The 80% Compression Fraction Target
Chest compression fraction is the percentage of total CPR time spent actively compressing. The AHA sets the target at greater than 80%. That means in any given minute of CPR, you should be compressing for at least 48 seconds. The remaining time accounts for brief, unavoidable pauses like ventilations and rhythm checks.
Hitting this target requires discipline. It means having your rescue breaths ready to deliver the instant you reach 30 compressions, keeping rhythm checks to a few seconds, and resuming compressions immediately after a defibrillator shock rather than waiting to see if the shock worked. One study found that a “minimally interrupted” approach to CPR tripled the odds of survival to hospital discharge compared to conventional techniques that involved longer post-shock pauses and rhythm checks.
Incomplete Chest Recoil Is the Other Thing to Minimize
Interruptions aren’t the only problem. Between compressions, you also need to minimize leaning on the chest. After each compression, the chest wall needs to fully spring back to its resting position. This recoil creates a brief drop in pressure inside the chest cavity that acts like a suction force, pulling blood back into the heart from the veins. Without that refill, the next compression has less blood to push forward.
Leaning on the chest, even slightly, prevents full recoil. This raises the baseline pressure inside the chest, reduces the amount of blood returning to the heart, and lowers coronary perfusion pressure. The AHA guidelines specifically flag incomplete recoil as a factor that can compromise resuscitation outcomes. Your hands should stay in contact with the chest, but you need to release all your weight between compressions so the chest returns fully to its natural position.
Putting It Together in Practice
High-quality CPR comes down to a handful of targets working together. Compress at a rate of 100 to 120 per minute, push to a depth of at least 2 inches (5 cm) but no more than 2.4 inches (6 cm) in adults, allow full chest recoil between compressions, and keep your compression fraction above 80%. Of all these factors, minimizing interruptions is arguably the easiest to control and one of the most impactful on survival.
If you’re performing CPR with a partner, assign roles clearly before starting. One person compresses while the other prepares the bag-mask or positions the AED. Plan your switches to coincide with rhythm checks every 2 minutes so you don’t create extra pauses. If you’re alone and untrained in rescue breathing, continuous chest compressions without ventilations (hands-only CPR) eliminates ventilation pauses entirely and is the recommended approach for bystanders.