In the face of cardiac arrest patients, if the on-site witnesses perform  chest compressions in a timely manner, the chances of successful resuscitation  of patients will be greatly increased. CPR can save lives at critical moment and  it is necessary for us to learn it.

　　1. Confirm the situation on site. It is necessary to make sure the  environment is safe and quickly come to the patient to check consciousness and  breathing. You could pat the patient's shoulder with both hands, call the  patient, and observe the patient's chest and abdomen for 5-10 seconds for  undulations. You may count in four-digit figures, which uses exactly one second  by counting, and count for 10 seconds to confirm the patient's consciousness and  breathing.

　　2. Dial 120 emergency number. If the patient is alone, he or she should  dial 120 to explain the situation and location. If anyone else is present, he or  she need to call the emergency number immediately.

　　3. Lift the patient's jaw, tilt the head back, and open the airway. You  need to kneel on the patient's side, with hands overlapping, with the palm root  centered at the midpoint of the nipple line in the middle of the chest, leaning  forward and watching the patient's face change, and conduct vertical press  continuously and quickly. The frequency is 100-120 times per minute, and the  pressing range should be more than 5 cm. 2 mouth-to-mouth artificial  respirations should be performed after every 30 presses.