What to do for CPR.
The Heart and Stroke Foundation actually suggests that you do CAB instead of ABC. Check for Circulation first, if a person is bleeding and has a main artery cut, they will die a lot sooner then they would if they are without oxygen for a few minutes. They have a good point here, if a person bleeds out, that is irreversible, there is nothing you can do to fix that, but if a person dies because of a heart attack, they can be brought back. I have personally witnessed this, from the time this person had a heart attack till the paramedics got their first heart beat was 45 minutes. Goes to show that you shouldn't give up CPR too soon. This person, six years later, has only some short term memory loss.
Before you would do any type of checking, you would first check around where the person is lying to see if there are any other dangers that could harm you. If you put yourself in danger trying to help someone, you may both die and accomplish nothing, so always make sure it's safe to approach a person before you do anything to help. The normal also is to delegate and have someone call 911, but if your by yourself, you would try to assess the situation first and see if the person has a pulse before you would make the call, depending on the situation, there might not be anyone to call.
Using the diagram below you would first do figure D and check circulation, especially for bleeding, then you would go to figure A and check the airway. You want to make sure there are no obstructions in the persons mouth before doing CPR, let say the person happens to have a piece of gum or food in their mouth, you could end up blowing the gum or food down their throat and causing a bigger problem, so do a sweep of their mouth with your finger to make sure there is nothing there to complicate things. When you tilt the head back to open the passageway up better as in figure B, if you have a shirt or towel rolled up to put under the persons neck, this will help keep the persons head in this position much easier.
If the person does not have a pulse and are not breathing you would start by doing chest compressions. You want to place the heel of your hand in the middle of the chest, on the breastbone and in between the nipples as shown in figure E. Now place your other hand on top of this hand and interlace your fingers. Keeping your arms stretched out straight in front of you, on an adult, you want to compress the chest about 2 inches and then release so that the chest recoils before compressing again, your aiming for about 100 compressions per minute, but only do 30 and then check for breathing, this should take you about 18 seconds to do 30 compressions. If the person isn't breathing after the compressions, start giving them mouth to mouth resuscitation.
When giving mouth to mouth you want to squeeze the person's nose closed so as not to lose any air when you're blowing into their mouth. Watch to see if their chest rises as your gently blowing in their mouth, if it does not, recheck the airway and try again. Only do this twice and then go back to giving 30 compressions even if their chest does not rise after the second try. If air is going into their chest, then allow the air to release, (the chest will return to normal), before blowing in again. You have to keep trying to do these rotations until the person either starts breathing on their own, or until help comes. If no one comes to help and you get too tired to continue on, then you'll have to let them go, but at least you will have made an effort to keep this person alive.
When doing CPR, they claim that the compressions are more important than doing mouth to mouth resuscitation. When your doing compressions, you're pumping blood to the brain which is more important than oxygen at this point.