A mouth-to-mouth breath is recommended to be completed within 4-5 seconds, but the blowing time is usually 1-2 seconds. When blowing, it is necessary to see the full rise and fall of the chest before releasing the mouth, to make the chest rebound, and to remove the carbon dioxide formed after the exchange of the lungs from the mouth before blowing for the second time. It is generally recommended not to do artificial respiration for more than 5 seconds, because the ratio of chest compressions to artificial respiration in CPR is 30:2. It is generally recommended that the duration of two artificial respirations should not be more than 10 seconds, so it is recommended that the duration of artificial respiration should not be more than 5 seconds each time. This is because too long a time may affect the chest compressions, thus affecting the recovery of circulation.