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

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:

• When the victim isn’t breathing, blow into the their mouth to push oxygenated air into the lungs. This allows oxygen to diffuse through the lining of the lungs into the bloodstream.
• If the victim doesn’t have a pulse, compress the victim's chest to artificially re-create blood circulation. If you are unsure if there is a pulse, perform chest compressions anyway, since it is usually difficult to find a pulse, especially in a stressful situation.

Here are the steps that make up CPR:

First ensure that the scene is safe, and that you aren’t in danger by helping the victim.

Wake the person by tapping their shoulders and shouting, “Are you o.k.?”

If there is no response, call 911 immediately.

Next Open their airway by carefully tilting the head back and lifting the chin.  This removes the tongue from the back of the throat.

Check for breathing for five seconds, if no breathing, give two slow breaths.

Check for pulse for 10 seconds, if no pulse, begin chest compressions.

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.

Pretty soon, you will see video demonstrations which will show you the speed and flow of this procedure, and you will have an opportunity to test yourself to see if you remember the steps.

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.  That will be covered in a little bit)

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:

1. Place the palm of your hand across the victim's forehead and push down gently.
2. With the other hand, slowly lift the chin forward and slightly up.
3. 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:

1. Compressing the abdomen with forceful thrusts. This creates pressure that forces the object up and out of the windpipe.
2. 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.

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.

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:

1. 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.
2. 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).
3. Hold in this position for half a second, then relax for half a second
4. Repeat steps two and three 29 more times.
5. Give the victim two rescue breaths as you did before to deliver more oxygen to the blood.
6. 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.