Howstuffworks "How CPR Works"

You're playing your usual weekend pick-up basketball game with friends. Without warning, one of your teammates suddenly crumples to the ground. You scream out his name, but there's no response. His face turns pale and bluish, and you can't see his chest rise and fall to breathe. You listen for a heartbeat, but you can't find a pulse at all. You quickly grab your cell phone and dial 911.

Every year, this type of scenario is played out more than 600 times a day in the United States alone. Without rapid medical intervention, the prognosis is grim. Sudden cardiopulmonary arrest is the leading cause of death for all adults, male or female.

Fortunately, modern medicine has come up with a number of tools to combat cardiopulmonary arrest. Many of these emergency procedures require medical training and/or complex equipment, but one, cardiopulmonary resuscitation (CPR), can be used in the field by lay people with only a little bit of training. In this article, we'll explore how this simple first aid technique can help save lives.

PLEASE NOTE: This article is not intended to be used as a method for teaching CPR. For proper CPR training, consult your local hospital or American Red Cross location for available classes.

Cardiopulmonary Arrest

Cardiopulmonary arrest simply means that your heart (cardio) and lungs (pulmonary) aren't working -- your heart isn't beating, and you aren't breathing. Many different things can lead to cardiopulmonary arrest, including:

Stroke
Drug overdose
Heart attack
Near drowning
Choking
Blood loss
Electric shocks
Carbon monoxide poisoning

A heart attack, for example, can damage the heart muscle and impede its ability to vigorously contract, resulting in cardiopulmonary arrest. If you've read How Your Heart Works, you know that the heart is a muscle that expands and contracts under the electrical control of a special group of pacemaking cells. The pumping action of the heart pushes blood teeming with oxygen and other nutrients out to the rest of your body. If your heart isn't beating properly or at all, blood isn't supplied to your body, and oxygen and other vital nutrients don't get delivered to your tissues and organs (including your heart). With no energy to power your body, vital organs like your heart and lungs stop working, and you are in a state of cardiopulmonary arrest.

In a heart attack, something like a blood clot obstructs one of your coronary arteries and cuts off blood flow to your heart.

Cardiopulmonary arrest is an extremely dangerous situation. Within 4 to 6 minutes without oxygen, your brain cells begin to die off rapidly. With each additional minute, the damage builds up. Most people cannot survive long in such a state.

CPR Basics

Cardiopulmonary resuscitation (CPR) is a first-aid technique used to keep victims of cardiopulmonary arrest alive and to prevent brain damage while more advanced medical help is on the way. CPR has two goals:

keep blood flowing throughout the body
keep air flowing in and out of the lungs

While the modern emergency room has high-tech equipment and an arsenal of drugs to help treat victims of cardiopulmonary arrest, CPR is a simple technique that requires little or no equipment. What you do is pretty basic:

Blow into the victim's mouth to push oxygenated air into the lungs. This allows oxygen to diffuse through the lining of the lungs into the bloodstream.
Compress the victim's chest to artificially re-create blood circulation.

Here are the steps that make up CPR:

Photo courtesy of University of Washington

It sounds pretty simple, but as you can see above, CPR must be performed in a specific, timed sequence to accurately mimic your body's natural breathing pattern and the way your heart pumps. When someone collapses right in front of you, your first reaction is often sheer terror. But while you're panicked and unable to act, valuable minutes are slipping away. To counter this, many organizations such as the American Heart Association and the American Red Cross offer classes that train you in CPR and basic first aid and give you hands-on practice to hone your CPR skills. Then, if you are confronted with an emergency situation, you are prepared to jump into action.

CPR Step-by-Step

Checking For A Pulse Cardiopulmonary arrest means that both heart and lungs have stopped working properly, so it would make sense to check and see whether a victim is breathing and whether or not their heart is beating. However, current CPR guidelines don't require a layperson to check the victim's pulse before starting CPR. Why is this?

The answer is that the average person has a lot of trouble finding and determining pulse accurately. Think about how difficult it can be to find your own pulse, and then imagine trying to repeat the process on an unresponsive person. If someone is not breathing, their heart is already in danger of quitting (if it hasn't already) due to lack of oxygen. Since the first steps in CPR address the victim's respiratory state, you can try and get them breathing again right away. Then, you can check for a pulse. Skipping an initial pulse check simplifies CPR and saves valuable time; every minute that you delay starting CPR reduces the odds that the victim will survive by 7-10 percent.

What should you do to help a seemingly unconscious victim? The first thing you'll want to do is to figure out whether or not the victim is really unconscious. Just like you were trying to get them out of bed, you should call out to them, tap them, and gently shake them to try and provoke a response. You also should check to see if they are breathing. If you try and perform CPR on someone who is not in cardiopulmonary arrest, you can actually hurt them!

If you can't rouse them, the very next thing to do is have someone call 911 so that professional paramedics will be on their way to the scene while you are performing CPR. This is very important, because, with the exception of choking, CPR doesn't address the underlying causes of cardiopulmonary arrest. It is only meant to buy time until the victim can get intensive medical care.

After you've called for medical assistance, you need to begin CPR. In order for CPR to work, the victim must be lying on his or her back on a flat surface. If the victim is face-down, gently roll the person toward you while making sure that you support their neck. Once the person is on their back, you can then use the American Heart Association's "ABCs of CPR" to guide you through the rest of process:

Airway: clear obstructed airways
Breathing: perform mouth-to-mouth breathing
Circulation: start chest compressions

We'll talk about each of these steps in detail in the following section.

The ABCs

Here's a summary of how you might perform CPR on a non-responsive adult (There is actually a different procedure used to save infants and young children). To learn all about CPR in detail, so that you could actually practice and perform this life-saving act, you should sign up for training from an organization like the American Red Cross.

A is for Airway
When you pass out, your tongue relaxes, and it can roll back in your mouth and block your windpipe. Before you can start CPR on an unconscious person, you'll probably need move their tongue out of the way. Here's how to clear a blocked airway:

Place the palm of your hand across the victim's forehead and push down gently.
With the other hand, slowly lift the chin forward and slightly up.
Move the chin up until the teeth are almost together, but the mouth is still slightly open.

Tilting the head back and lifting the chin move the tongue out of the airway. At this point, you should check again for breathing. If the victim is choking on something, you may see their chest heave as they try to breathe, but you won't be able to feel or hear air being exhaled. You'll have to take additional measures to clear out what's blocking their windpipe, including:

Compressing the abdomen with forceful thrusts. This creates pressure that forces the object up and out of the windpipe.
Trying to manually dislodge the object with your fingers.

Once this is done, you have to check for signs of breathing again. Just clearing out the windpipe may sometimes be enough to allow the victim to start breathing on their own! If the victim starts breathing and moving around on their own, you can stop CPR. If this doesn't happen, you'll have to help them breath, by providing mouth-to-mouth resuscitation.

B is for Breathing
Your lungs have one main function: remove carbon dioxide and take up oxygen. Normally, the muscles in your chest contract and expand your chest cavity, allowing your lungs to fill up with air. Oxygen and carbon dioxide diffuse across the immense surface area of your lungs. Finally, your chest muscles relax, and you exhale. (To learn more about lungs, see How Your Lungs Work).

Rescue breathing uses your lungs to force air into the victim's lungs at regular intervals. The timing of each breath (about 1.5 to 2 seconds per breath) mimics normal breathing. However, the process is much more like blowing up a balloon than real breathing. You inhale deeply, form a tight seal with your mouth over their mouth, and exhale strongly to push air out of your mouth into theirs. Because you also pinch the victim's nostrils closed, the air has nowhere to go except down into the lungs, which expand as they fill with air.

Mouth-to-mouth breathing is hard work. Normally, when you inhale, the chest muscles drive the process. In artificial respiration, you're working against the victim's relaxed chest muscles. When the chest muscles are relaxed, the chest cavity is small, keeping the lungs in a deflated state. As a rescuer, you have to exhale forcefully into the victim's mouth for 1 to 2 seconds to overcome this resistance. As the lungs fill with air, the victim's chest is pushed up at the same time; you can actually see it rise. When you remove your mouth from the victim's and break the air seal, their chest falls and once again deflates the lungs. As in normal breathing, this results in air being exhaled from the victim's mouth.

Does air exhaled from someone else's mouth really provide enough oxygen to save an unconscious person? Normally, the air you inhale contains about 20 percent oxygen by volume, and your lungs remove about 5 percent of the oxygen in each breath. The air you blow into a victim's mouth thus contains about 15 to 16 percent oxygen, which is more than enough to supply their needs.

After you've given the victim two breaths, you then check to see whether or not they have a pulse and whether they are able to breathe on their own. This will determine what you do next.

If the victim . . .	you should
Is breathing and has a pulse	stop CPR, and stay with them until help arrives.
Is not breathing and has a pulse	continue rescue breathing.
Has no pulse	begin chest compressions, alternating with rescue breathing.

C is for Circulation
If the victim's heart is not beating, all your breathing efforts are for naught; the oxygen that you're getting into their circulation isn't going anywhere! Once again, you have to take over for a failing organ. This time you essentially become a surrogate heart to pump oxygenated blood out to the rest of the victim's body. How can you have any effect on blood flow from outside of the body? All it takes is your hands and some strength. The steps are simple:

Kneeling by the victim, place the heel of your hands one atop the other about .4 to .8 inches (1 to 2 cm) from tip of the breastbone.
Using the weight of your body, push the victim's chest down. You should compress their chest 1 to 2 inches (2.54 to 5.08 cm).
Hold in this position for half a second, then relax for half a second
Repeat steps two and three 29 more times.
Give the victim two rescue breaths as you did before to deliver more oxygen to the blood.
Repeat steps 1 through 5 three more times, then check for a pulse.

In reality, all you are doing is squeezing the heart between the breastbone and the backbone to force blood out. Compressing the chest creates positive pressure inside the chest that pushes oxygenated blood out of the heart through the aorta. From here, it travels to the brain and then on to other parts of the body, delivering oxygen for cellular respiration. When you relax, the pressure inside the victim's chest subsides. Deoxygenated blood moves back into the heart from the veins.

As the chest is compressed, positive pressure is created inside the chest, and oxygenated blood is pushed through the arteries to the brain and other organs. When you release, the pressure drops, and blood flows back into the heart from the veins.

CPR's Role in Rescue

CPR extends the window of opportunity to perform more elaborate first aid procedures. By itself, CPR cannot save the majority of victims of cardiopulmonary arrest. CPR only temporarily restores circulation to only 10 to 30 percent of what it would be with a healthy heart. Further, in about two-thirds of people in cardiopulmonary arrest, the heart goes into what's known as ventricular fibrillation. In this state, the heart muscle quivers rapidly, like a bowl of Jell-O™, and is unable to beat properly. CPR cannot stop ventricular fibrillation, and only about 4 percent of patients who receive CPR alone will survive an attack.

An implantable defibrillator developed by scientists at NASA

In order to restore a normal heartbeat, an electrical shock must be delivered to the heart. This is called defibrillation. The shock itself doesn't switch the heart back on - it's not like flipping a tripped circuit breaker. Instead, defibrillation actually stops the heart briefly! This gives the pacemaking cells a chance to re-establish a normal heartbeat.

So why do CPR at all if it can't address the root causes of cardiopulmonary arrest? The bottom line is that CPR is an important part of a comprehensive response to a cardiac emergency. Defibrillation requires special equipment that has to be brought to the patient, and CPR can keep a patient alive until a defibrillator arrives. When CPR is started within 4 minutes and defibrillation within 10 minutes of an attack, the survival rate skyrockets to 43 percent. Other factors that contribute to survival are:

Rapid access to emergency care from paramedics and other medical professionals.
Quick provision of other supportive medical care, such as epinephrine, a drug that stimulates the heart.

CPR and Infectious Disease

It's clear that CPR is an effective part of the emergency response to cardiopulmonary arrest, one that could potentially save thousands of lives a year. Yet, in most cases, victims aren't getting this lifesaving treatment, even when bystanders are familiar with CPR.

Why won't people perform CPR on strangers? It turns out that a large number of people are afraid of contracting some nasty disease during mouth-to-mouth resuscitation. This fear was heightened by the emergence of deadly infectious diseases, such as HIV, that are spread by bodily fluids. Even though there have been no documented cases of anyone ever catching AIDS during CPR, there is still a chance, however tiny, of this happening.

To assuage the public's fear, CPR training now incorporates personal protective gear during the various steps. Some of the safety devices used include:

Gloves - Gloves prevent contact with saliva (if you have to reach in their mouth) and blood (if the victim has cuts or abrasions).
Personal resuscitation masks - A personal resuscitation mask allows you to provide artificial respiration through a barrier that prevents contact with saliva and mucus membranes.

A personal resuscitation mask from Rondex

The one drawback is that you have to carry your CPR kit with you everywhere. Most people don't plan when they go into cardiopulmonary arrest, so you never know where you might need your gear.

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