Before 2010, the resuscitation steps of CPR were ABC, A is airway, airway; B is breathing; C is circulation, circulation, that is, open the airway, artificial respiration, and then chest compressions. Why did the 2010 CPR guidelines change to CAB? This is because a large number of evidence-based medical facts confirm that the cause of most cardiac arrests is sudden death due to cardiovascular disease, rather than respiratory asphyxia or obstruction. Therefore, after cardiac arrest, the most important thing is to scramble to re-establish the artificial circulation, prompting blood flow to meet the demand for oxygen supply to all important organs such as brain, heart and lungs. Undoubtedly, at this time, cardiac compression (C) is the most important step, between milliseconds, determining life and death. Therefore, ABC was changed to CAB.