What Actually Happens in the Body When You Perform CPR?

Your heart normally works as a remarkably efficient pump. With every beat, it keeps blood circulating around your body, delivering oxygen to your brain and other vital organs.

During cardiac arrest, the heart suddenly stops pumping blood effectively. The person becomes unresponsive and is not breathing normally. Because normal circulation has stopped, the brain and other organs are no longer receiving the steady supply of oxygenated blood they need. This is why cardiac arrest is so time critical. The body has not suddenly stopped needing oxygen; it has lost the mechanism that normally transports it.

When you begin CPR and press firmly on the centre of the chest, each compression increases pressure inside the chest and compresses the heart and surrounding structures. This helps propel blood forward through the circulatory system.

Equally important is what happens when you release the pressure. Allowing the chest to recoil fully helps the heart refill with blood before the next compression. Repeating this cycle creates a small but important amount of artificial circulation when the heart is no longer able to maintain adequate circulation by itself.

This is why good CPR is physically demanding and why the depth, rate and quality of chest compressions matter. You are not simply pressing on someone's chest. You are temporarily helping the body perform one of the heart's most important functions: moving blood.

The brain has a constant need for oxygen, but it cannot receive that oxygen without blood flow. When the heart stops pumping effectively, the normal delivery of oxygen to the brain is interrupted. Chest compressions help move some oxygenated blood towards the brain and other vital organs. CPR cannot reproduce the circulation created by a healthy beating heart, but it can help maintain some blood flow during those critical minutes.

In practical terms, CPR is helping to buy time: time for someone to contact emergency medical services, time for an automated external defibrillator (AED) to become available, and time for professional medical care to arrive.

Blood circulation is only part of the picture. The body also needs oxygen. Rescue breaths introduce additional oxygen into the lungs, while chest compressions help move oxygenated blood around the body. This is why conventional CPR combines chest compressions with rescue breaths when the rescuer is trained and able to provide them.

The appropriate CPR response can also differ depending on who needs help. Babies and children, for example, may experience cardiac arrest for different reasons from adults. This is one of the reasons practical CPR training is so valuable: it teaches you how to adapt what you have learnt to the person and situation in front of you.

This is one of the most common misunderstandings about CPR, helped along by years of dramatic television scenes. CPR does not usually make a stopped heart suddenly begin beating normally again. Its immediate purpose is to maintain some circulation until more advanced treatment becomes available.

An AED plays a different role. It analyses the electrical activity of the heart and, when an appropriate shockable rhythm is detected, can deliver a controlled electrical shock. Not every cardiac arrest requires or responds to a shock, which is why an AED analyses the heart rhythm before advising whether one should be delivered. CPR and an AED therefore do different jobs, but both can form part of the response to cardiac arrest.

This is an understandable concern, particularly when the person needing CPR is an elderly parent or someone physically frail. Effective chest compressions require considerable force, and injuries such as fractured ribs can occur.

However, a person in cardiac arrest is already experiencing an immediate, life-threatening medical emergency. The priority is to recognise what is happening, contact emergency medical services, and begin appropriate CPR.

This is also where training can make an enormous difference. Practising CPR in a controlled environment allows you to experience what effective chest compressions actually feel like before the person beneath your hands is someone you love.

For parents and grandparents, few thoughts are more frightening than having to perform CPR on a child. Fortunately, learning what to do can replace at least some of that fear with practical knowledge.

Children are not simply smaller adults. The circumstances that lead to cardiac arrest can differ, and CPR techniques are adapted according to the child's age and size. The same applies to infants.

This is why parents, grandparents, teachers, babysitters and anyone who regularly cares for children can benefit from learning CPR specifically for babies and children. In an emergency, knowing those differences matters.

Perhaps the simplest way to understand CPR is to think of it as a bridge. On one side is the moment a person's heart stops pumping effectively. On the other is the advanced medical care that may give that person their best chance of survival.

The person performing CPR helps bridge those critical minutes by maintaining some circulation until professional help can take over. And, for most of us, the person lying there will never simply be “the casualty”. It may be your husband or wife, your mother or father, your child, a grandparent, a colleague or someone you have cared for every day for years.

Learn more about CPR and first aid training through the South African First Aid League: First Aid League training and courses