The Science Behind Compressions

Many people are aware of the importance of compressions in the BLS sequence, but few probably give much thought to how compressions work and why they are of such high importance.

Consider the following facts regarding the heart, a truly miraculous organ!

People may incorrectly assume that the purpose of chest compressions is to restart the heart. In order to understand exactly what compressions do, it helps to have some background regarding how the heart functions.

The heart is essentially a pump. Each time the heart beats it sends oxygen-rich blood from the heart throughout the body, delivering oxygen to every organ, tissue and cell of the body. Blood that is depleted of oxygen is returned to the heart, where it is again enriched with oxygen. This cycle is repeated with every heartbeat.

When the heart stops, so does the flow of oxygen-enriched blood to the organs that depend on it to survive. Organs and tissues that are deprived of oxygen begin to die within minutes. The brain is especially sensitive to oxygen deprivation — this is where CPR comes in.

Cardiac compressions take over the function of the heart. When a CPR provider presses down on a victim’s chest, the heart is compressed, forcing blood out of the heart to the brain. When the CPR provider releases the chest (chest recoil), the heart is allowed to fill up with blood again. Compressions are obviously not as effective as the heart itself, but they do provide just enough oxygen to the heart and brain to keep them alive until advanced medical care (including life-saving drugs and defibrillation) can be provided. In addition, when the chest is released, oxygen rich blood flows into the arteries that feed the heart itself. Keeping the heart fed with oxygen is essential in saving the patient because a heart that has not been fed with blood and oxygen will not respond to defibrillation.

High quality compressions make the difference between life and death. Although drugs and defibrillation are important, without quality compressions these efforts will likely fail. Defibrillation has been shown to be more successful when quality compressions are delivered beforehand while the defibrillator is being set up. In addition, drugs are of no use unless they are circulated throughout the body by compressions. Compressions are the foundation of quality BLS.

Now that you know how compressions work and why they are crucial to a successful resuscitation, you can learn how to provide quality compressions. Push hard and push fast!


Last reviewed by on Mar 30, 2017