Television dramas paint a pretty rosy picture of survival rates after cardiac arrest. Studies show that laypeople in the US expect as high as 75% of people to survive after their hearts stop if they receive CPR. Unfortunately, survival rates range between 2 and 11% when cardiac arrest occurs outside the hospital. They improve to an average of around 18% when arrest occurs at the hospital.

What the popular opinion gets right: Survival rates for people who receive CPR are much higher than for those who don’t, and the quality of CPR also significantly impacts survival chances.

The body breaks down quickly after cardiac arrest. Even when CPR is performed well, it still only provides about 10-20% of normal blood flow to the heart and between 30 and 40% to the brain. But, if CPR is performed well and early, survival chances can as much as triple.

So, what qualifies as “quality CPR”? The common denominator is training, of course. But even among people who are trained in CPR, different behaviors impact the relative benefits of intervention and the chances that a victim will survive. 

Ratio of compressions to breaths:

• There is little to no benefit to providing more than 12 breaths per minute during CPR when the rescuer uses the recommended ratio of 30 compressions to two breaths. There is evidence, however, that when compressions are too slow survival rates drop quickly (as much as 30% in-hospital). So, time spent providing extra breaths reduces the number of compressions and the chance of survival.

Depth of compressions and releases:

When rescuer compressions are shallower than about 2 inches (for adults; you can read more on the pediatric chain of survival here), survival is reduced by around 30%. Similarly, if the rescuer leans on the victim after compressions, restricting full chest expansion, blood flow is not optimally increased, arterial pressure may be increased, and survival chances are reduced. 

Dos and Don’ts:

The American Heart Association provides other guidance for layperson rescuers intended to improve the speed at which the correct care is provided, all meant to reduce or eliminate interruptions (and improve the rate of survival after arrest):

• When available, prep and use the AED ASAP
  • The shorter the time to the first shock, the better. The AHA recommends “applying the pads and charging the defibrillator during ongoing chest compressions” in order to eliminate delay. 
• Immediately re-introduce compressions after a shock or breath. Don’t wait. 
• Do not lean on the victim after as the chest expands after compressions.
• If medical personnel are not present, make sure that someone calls 911 while the rescuer is performing CPR. If nobody else is present, turn on the phone speaker and commence CPR.
• When possible, switch rescuers often to prevent fatigue and ensure the optimal rate and depth of compressions (if possible, rescuers should rotate every two minutes or after 5 sets of 30 compressions and 2 breaths). 

As ever, the upshot is that every minute– every second– counts. The shorter the time between links in the chain of survival (link) the better the outcomes, in the hospital and out.

Unless otherwise linked, the data above comes from the  AHA journal article here.