Although breathing definitely is a “vital” sign of life, during the first steps of CPR the emphasis is on good compressions FIRST. Providing the recommended depth and rate of speed for compressions will produce pressure in the chest cavity and on the heart directly creating blood pressure which in turn will the create circulation.
Once someone has stopped breathing and their heart has stopped pumping there is still a viable amount of oxygen for about 10 minutes remaining in the lungs, organs and cells. Externally the rescuer can begin to immediately create the needed pressure to circulate that oxygenated blood throughout the body.
For untrained or unprepared rescuers this is perhaps the only care they may be able to provide the victim until EMS arrives on scene. This is referred to as “hands only CPR”. However if the rescuer is aware of the victim’s health history or has a pocket mask (recognized ventilation equipment) the best CPR will follow the latest algorithm of CAB. Providing the victim oxygen will continue to keep the brain viable and other vital organs alive.