In the past, hyperbaric oxygen was mainly used to treat critical illnesses such as poisoning, decompression sickness and gas gangrene. In recent years, hyperbaric oxygen has produced varying degrees of efficacy for an increasing number of critical illnesses. Although the medical community has so far conducted a large number of animal tests and clinical practice studies on its therapeutic mechanism, the therapeutic mechanism of many critical illnesses is still under exploration, and even a unified understanding has not yet been formed. In the nearly two decades of medical practice of hyperbaric oxygen at home and abroad, the efficacy of hyperbaric oxygen on the treatment of more and more critical illnesses, even very obvious efficacy, has attracted the great attention of the medical community. According to domestic and international data, hyperbaric oxygen has expanded from treating only critical illnesses such as poisoning, decompression sickness and gas gangrene to treating a variety of critical illnesses including blood loss, shock, cardiac and respiratory arrest, severe trauma, cranio-cerebral injury, drowning, radiation injury, and special infections. These critical illnesses have a common feature, that is, they often have ischemia and hypoxia as one of their main pathological mechanisms. The ischemia and hypoxia, acidosis, edema and degenerative necrosis of the body’s cells and tissues and organs all depend on effective oxygen to reverse. Only oxygen supply under hyperbaric conditions can produce more obvious therapeutic effects on the above critical illnesses. Compared with normobaric oxygen, hyperbaric oxygen can produce qualitative changes in therapeutic efficacy, forming a series of new mechanisms of action. It has a role that cannot be replaced by pharmacotherapy and other treatments. Especially for some of the above critical illnesses that have not been treated with other treatments, after hyperbaric oxygen treatment, sometimes can achieve unexpected results. Typical cases: Case 1, male, 16 months old child, drowned for 5 minutes, heart and respiratory arrest when rescued, sent to local hospital half an hour later, deep coma, transferred to our hospital two days later. He was transferred to our hospital two days later. There was no significant progress in pediatric resuscitation, and hyperbaric oxygen therapy was started on the fifth day. Case 2, male, 17 years old, construction patient, February 8, 1985 work by 380V electric shock, cardiac arrest, the site did not give timely CPR, 15 minutes after the site unit of the doctor arrived at the scene, emergency rescue to a hospital, ECG shows ventricular fibrillation, electroshock defibrillation resuscitation, respiratory recovery, still in a deep coma, continue conventional resuscitation no progress. the afternoon of February 12, that is, has been the fourth day. He was sent from the county hospital to the higher hospital for emergency treatment, and was treated with hyperbaric oxygen that night and sent to the ICU after being discharged from the chamber. starting, he was treated twice a day with a pressure of 2.5 ATA, and three days later once a day with 2-2.5 ATA, and was still in a comatose state until March 13, i.e., about 25 times, but began to respond to painful stimuli, and was still in a comatose state due to a hip abscess (incision and drainage up to On March 23, his body temperature was normalized, and on March 24 (about 36 hyperbaric treatments), he became clearer, but had psychiatric symptoms of restlessness and moaning. Hyperbaric oxygen therapy was continued up to 60 times. The patient was able to answer questions accurately, his muscle strength was normal, and he was basically cured, except for a slight delay in response and a slightly poor calculation ability. the ECG was initially widely and highly abnormal, and was reported normal at the end of the course of treatment. About 1 month later, another 3 courses (30 times) of hyperbaric oxygen therapy were performed, and intelligence, thinking and calculation power were normal. Follow-up: work and life were normal, and he got married six years later. Case 3: Female, 48 years old, severe barbiturate poisoning (194 tablets of luminal, 30mg/tablet), cardiac arrest three times, two times clearly recorded, 15 minutes and 20 minutes respectively, the latter time longer, the emergency physician had mistakenly written a death diagnosis report (a “fake death” phenomenon). The patient was resuscitated by the emergency department, but was still in a deep coma, and started hyperbaric oxygen therapy on the third day. Case 4: Female, 41 years old, with late onset radiation injury and radioactive proctitis. After total hysterectomy for uterine body cancer and radiation treatment 1.5 months later, she started to have blood in the stool about 4 months later, with total blood stool, severe anemia, and hemoglobin 59g/L, which was ineffective after multiple treatments. He could only receive blood transfusion once every half month. By July 1984, a total of more than 10,000 ml of blood was transfused in two years. In July 1984, hyperbaric oxygen therapy was administered, and the condition improved after 20 treatments, and the number of stools was significantly reduced from 17-18 times per day to 2 times per day. After 40 days of treatment, the stool routine examination was normal. After 60 treatments, the hemoglobin increased to 93g/L and no longer required blood transfusion. Six months later, the anal finger diagnosis: (-) resumed normal work. With the rapid development of modern society, craniocerebral injury has been one of the common traumas, which is increasing year by year. The First Affiliated Hospital of Zhongshan Medical University statistics from 1984 to 1990 related data, 337 cases of cerebral contusion were treated with hyperbaric oxygen, 164 cases (48.7%) were cured or basically cured, 106 cases (31.5%) were apparently effective, 60 cases ( 17.8%). The total effective rate reached 98%, and in 1995, the First Affiliated Hospital of Nanjing University reported 240 cases with a total effective rate of 97% (233/240). Beijing Chaoyang Hospital statistics of 51 reports about hyperbaric oxygen treatment of craniocerebral injury before 1997 in China, a total of 5216 cases, 13 of the 51 set control, a total of 594 cases, the cure rate of 53.9% and the total effective rate of 94.8% of the hyperbaric group after analysis, significantly higher than the control group (28.9% and 85.8%, respectively). The authors counted 42 papers on hyperbaric oxygen therapy for craniocerebral injury published in the 10th National Conference on Hyperbaric Medicine of the Chinese Medical Association in 2001, and the total number of reported cases reached more than 9260, with the cure rate ranging from 52.7% to 87% and the total effective rate ranging from 94.5% to 100%. The authors also compiled reports from 10 medical units on hyperbaric oxygen therapy for persistent vegetative state (PVS) with heavy craniocerebral injury as the main cause, with a cumulative total of 406 cases, with basic cure rates ranging from 31.6% to 46.7% and effective rates ranging from 76.4% to 91%. The above cases suggest that hyperbaric oxygen is an important treatment for craniocerebral injury, and it is extremely valuable to improve the prognosis, and it can become a conventional therapy after surgical treatment or non-surgical treatment of craniocerebral injury. In the practice of hyperbaric oxygen administration, there are the following points are worth noting. First, the earlier the use of hyperbaric oxygen therapy, the better. According to our experience and clinical practice reports, we should consider whether hyperbaric oxygen therapy should be used in the first ten minutes of resuscitation, the “golden hour” of trauma treatment, and consider the possibility and the best time to use hyperbaric oxygen therapy according to the changes of the condition during the whole process of rescuing patients with critical illness. The possibility of using hyperbaric oxygen therapy and the best time to apply it should be considered in the whole process of rescuing critically ill patients. Most of the critical illnesses with ischemia and hypoxia as the main pathological mechanism have different degrees of efficacy after the use of hyperbaric oxygen therapy. Secondly, even when clinical treatment is no longer effective, it is not excluded that hyperbaric oxygen can be considered to be used again. According to the data, there are many cases that the patient’s life was saved by using hyperbaric oxygen therapy when the clinical treatment was ineffective. Thirdly, for critical illnesses where ischemia and hypoxia are the main pathological mechanisms, it is very important that hyperbaric oxygen and related departments work in close cooperation with each other. In hospitals with conditions, we can even consider clinical rescue and comprehensive treatment under the condition of hyperbaric oxygen directly in the oxygen chamber. At present, many clinical departments in our hospitals do not know much about the indications for hyperbaric oxygen treatment and its therapeutic effects and treatment characteristics. Even for patients with hyperbaric indications, they often neglect to use hyperbaric medical treatment in clinical care and sometimes miss the best time for hyperbaric treatment. This is related to the general lack of understanding of hyperbaric medicine in the medical community, and also directly related to the lack of active propaganda in the hyperbaric community itself. Therefore, it is necessary to strengthen the extensive publicity and popularization of hyperbaric medicine. The patients treated with hyperbaric oxygen come from various clinical departments, so the doctors of various clinical departments, especially the medical staff of ICU and emergency department, should also have a certain degree of understanding and mastery of hyperbaric oxygen medicine, so that they can do a good job of cooperation and collaboration with related disciplines when implementing hyperbaric oxygen rescue treatment for critical and serious diseases.