In external chest compressions, the depth of compressions for adults should be at least 5 cm, but should avoid exceeding 6 cm. 2015 latest version of CPR guidelines for adult CPR quality highlights several key points: 1, compression techniques: place the palms of both hands flat and cross overlapping, minimize the contact area between the palms and the thorax, and try to keep the arms in a straight position during compressions, using arm force and their own gravity to provide Compression orientation: the junction of the midline of the two nipples and the lower 1/3 of the sternum; 3, compression frequency: 100-120 compressions/min; 4, compression depth: adjust the compression depth to 5≤h<6 cm; 2, compression ventilation: reduce compression interruptions, make compressions account for at least 60% of the overall resuscitation goal, continuous resuscitation and advanced airway, the recommended ventilation rate of 10 times/min. Relevant studies have shown that if timely and effective cardiopulmonary resuscitation is performed immediately after cardiac arrest, the survival rate will be 70% to 80%. If performed within 4 min of cardiac arrest, the success rate is 32%; if delayed more than 4 min, the success rate is only 17%.