When a person is found unconscious the first step is to try to arouse him. The person might simply have fainted or be sleeping. Shake the person and call out to him loudly. If there is no response it is possibly that he is suffering from a respiratory or cardiac arrest.
Check for breathing. Lean in so that your ear is close to the person's mouth and nose. Listen for breath sounds. You should be close enough that the warmth or stirring of breath can be felt on your skin. If breathing is detected, do not start CPR. If breathing is not felt, then you will need to do rescue breathing.
Before beginning CPR send for help. Have someone call for an ambulance. It is vital to get medical assistance as quickly as possible. CPR is tiring for the person administering it and cannot be done for very long. The paramedics can be on their way while CPR is being given, improving the victim's chance of survival. Even if the person is breathing, if he cannot be awaken the paramedics should be called. The person could have other medical problems that need immediate attention.
Position the head for rescue breathing. Tilt the head back by lifting the chin. Pinch the nose closed and give the person two quick breaths. For each breath make sure the chest is seen rising and falling. If it does then the airway is clear and air is reaching the lungs. If not, reposition the head and try again. If the air still does not cause the chest to inflate then clear the airway before continuing. This can be done with the Heimlich maneuver. Once the airway is clear administer the two rescue breaths and continue with CPR.
Check for pulse and breathing. After the two breaths check for breathing as you did before. Also place two fingers on the pulse point on the side of the neck below the ear and just above the collarbone. If the patient is breathing then it means the heart is beating. Monitor the patient until the paramedics arrive. If there is a pulse but no breathing then continue the rescue breathing until the victim begins to breath or until paramedics arrive to take over. If there is no pulse and no breathing continue CPR until help arrives.
Measure the width of two fingers above the bottom of the breastbone. Place the palm of your hand against the breastbone so the side of the hand is above the fingers. Cover the first hand with your other hand and interlace your fingers. With your elbows locked give 15 chest compressions. The downward force should be enough to depress the breastbone approximately 2 inches.
Give two more breaths as described before. The process of two breaths and 15 chest compressions should be repeated until help arrives or until the victim begins to breath on their own.