Asphyxia refers to the respiratory process due to some reasons of obstruction or abnormality, produced by the whole body organs and tissues hypoxia, carbon dioxide retention caused by tissue cell metabolic disorders, dysfunction and morphological and structural damage to the pathological state, is one of the most important causes of death in critical illness. The development of asphyxia is a continuous process generally can be divided into 6 periods: 1, pre-asphyxia: lasts about half a minute, but also due to individual training and tolerance of different and different, such as good swimmers can last more than 1 minute; 2, inspiratory dyspnea: lasts about 1-1.5 minutes; 3, expiratory dyspnea (also known as the period of convulsions): lasts about a few seconds or even dozens of seconds, not exceeding 1 minute; 4, apnea: lasts about 1 minute; 4, apnea period: lasts about 1-2 minutes; 4, apnea: lasts about 1 minute; 4, apnea period: lasts about 1-2 minutes. Minutes; 4, apnea: lasts about 1-2 minutes; 5, terminal respiration: duration is variable, about 1 to several minutes; 6, respiratory arrest: duration varies from person to person, can be from a few minutes to tens of minutes, and finally the heart stops and death. It is generally believed that artificial respiration within 3 minutes of the asphyxiation period, can be fully resuscitated; after 4-5 minutes, there is still a possibility of survival; if after 8-9 minutes, it is difficult to resuscitate.