At all levels of care, the<unk> protocol exists to remind the person delivering treatment of the importance of airway, breathing, and circulation to the maintenance of a patient's life. These three issues are paramount in any treatment, in that the loss (or loss of control of) any one of these items will rapidly lead to the patient's death. The three objectives are so important to successful patient care that they form the foundation of training for not only first aid providers but also participants in many advanced medical training programs. Hypoxia, the result of insufficient oxygen in the blood, is a potentially deadly condition and one of the leading causes of cardiac arrest. Cardiac arrest is the ultimate cause of clinical death for all animals (although with advanced intervention, such as cardiopulmonary bypass a cardiac arrest may not necessarily lead to death), and it is linked to an absence of circulation in the body, for any one of a number of reasons. For this reason, maintaining circulation is vital to moving oxygen to the tissues and carbon dioxide out of the body. Airway, breathing, and circulation, therefore work in a cascade; if the patient's airway is blocked, breathing will not be possible, and oxygen cannot reach the lungs and be transported around the body in the blood, which will result in hypoxia and cardiac arrest. Ensuring a clear airway is therefore the first step in treating any patient; once it is established that a patient's airway is clear, rescuers must evaluate a patient's breathing, as many other things besides a blockage of the airway could lead to an absence of breathing. CPR The basic application of the<unk> principle is in first aid, and is used in cases of unconscious patients to start treatment and assess the need for, and then potentially deliver, cardiopulmonary resuscitation. In this simple usage, the rescuer is required to open the airway (using a technique such as "head tilt - chin lift"), then check for normal breathing. These two steps should provide the initial assessment of whether the patient will require CPR or not. In the event that the patient is not breathing normally, the current international guidelines (set by the International Liaison Committee on Resuscitation or ILCOR) indicate that chest compressions should be started. Previously, the guidelines indicated that a pulse check should be performed after the breathing was assessed, and this made up the 'circulation' part of the initialism, but this pulse check is no longer recommended for lay rescuers. Some trainers continue to use circulation as the label for the third step in the process, since performing chest compressions is effectively artificial circulation, and when assessing patients who are breathing, assessing 'circulation' is still important. However, some trainers now use the C to mean Compressions in their basic first aid training.
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