In recent years, the development of hyperbaric medicine is relatively fast, and the advantages of hyperbaric oxygen therapy are increasingly understood by the majority of medical personnel, but there are some doctors who are still skeptical about it. Beijing Tiantan Hospital is famous for its expertise in treating central nervous system diseases, and the hyperbaric oxygen department of the hospital has been established for more than 10 years, giving full play to the advantages of hyperbaric oxygen in treating such critical diseases. Now we ask the relevant experts to explain the technical points of it. 1.What is the basic principle of hyperbaric oxygen treatment for craniocerebral injury? The main cause of craniocerebral injury is hypoxia, and the special mechanism of brain tissue hypoxia after brain injury leads to other clinical treatment methods are difficult to improve. Hyperbaric oxygen therapy can improve brain tissue hypoxia in a timely and effective manner. Hyperbaric oxygen therapy is a kind of physical therapy in which the patient is placed in a closed chamber with high air pressure (usually it is considered that the pressure should be above 1.4 atmospheres) to inhale pure oxygen intermittently. The main mechanism of hyperbaric oxygen therapy for brain injury is as follows: Under high air pressure, oxygen can be dissolved into the blood rapidly due to the physics, and the amount of dissolution is proportional to the ambient pressure. As the ambient pressure rises, the amount of dissolved oxygen dissolved into the blood increases. Studies have shown that the amount of physical dissolved oxygen that can be dissolved in blood is 17-21 times higher than that at atmospheric pressure under the high pressure state of 2~3 atmospheres that is commonly used in clinical practice only. 3 atmospheres of high pressure oxygen state, the amount of physical dissolved oxygen per 100 ml of arterial blood is about 6.80 ml, which is sufficient to meet the basic need of 6.08 ml of oxygen per 100 ml of arterial blood for the human body to maintain life. In other words, under the hyperbaric state of 3 atmospheres, the physical dissolved oxygen dissolved into the blood alone, without relying on hemoglobin-bound oxygen at all, is sufficient to maintain the basic needs of the patient’s vital organs. This basic principle of hyperbaric oxygen therapy has the following therapeutic effects on brain injury: (1) Reduce the energy consumption of injured brain tissue. (2) It can overcome the microcirculatory disorder caused by cerebral edema well and rapidly relieve the brain tissue hypoxia. (3) Compensate for the oxygen supply to the brain tissues that have lost blood supply due to microvascular injury. (4) In hyperbaric state, because normal tissues are not hypoxic, their blood vessels are properly constricted through feedback mechanism, because less blood supply can meet their demand for oxygen. In contrast, hypoxic tissues, because of hypoxia and edema, do not have vasoconstriction, which allows them to have a significant increase in oxygen supply without reducing the amount of blood supply. This effect is clinically known as the “anti-stealing effect”, which not only facilitates the timely supply of relatively more oxygen to the hypoxic brain tissue, but also facilitates the reduction of water content in the whole brain. This mechanism has a direct role in reducing intracranial pressure and treating cerebral edema. 2.When can hyperbaric oxygen therapy be started after craniocerebral injury? Craniocerebral injury itself is a pathological diagnosis, and many diseases can lead to it. The common ones are: traumatic brain injury, cerebral hemorrhage, cerebral infarction, intracranial infection, carbon monoxide poisoning, cardiac arrest, postoperative brain tumor, asphyxia, etc. Among them, there are both direct damage to the brain caused by external force or infection, and indirect damage caused by many internal diseases such as destruction of cerebrovascular circulation or lack of oxygen in body circulation. Because of the diverse and complex etiology, the early and late stages of the disease, and the wide variation in the criticality of the disease, hyperbaric oxygen therapy needs to be performed by doctors who understand both neurology and hyperbaric medical expertise. In many cases, it is necessary to cooperate with doctors from various clinical disciplines to develop a comprehensive treatment plan, of which hyperbaric oxygen can only be used as one of the treatment tools. In principle, as long as the patient has the conditions for hyperbaric oxygen therapy, the earlier the treatment is started, the better. 3.What is the dosage and duration of hyperbaric oxygen therapy? The dose of hyperbaric oxygen therapy is determined by a combination of factors such as pressure, single dwell time, daily treatment frequency and the number of consecutive treatment days, which is also the focus of attention and research of medical professionals in hyperbaric medicine at home and abroad. At present, the commonly used conventional hyperbaric oxygen therapy program is: 1.75~2.25 atmospheres, 20 minutes of elevated pressure – 60 minutes of oxygen inhalation at steady pressure, with 5~10 minutes of air breathing break at 30 minutes – 20~30 minutes of decompression, once a day for about two hours, 20~60 times of continuous treatment, which can be completed by intermittent rest according to the patient’s specific conditions. It has been reported in the literature that patients with brain injury can complete hyperbaric oxygen therapy more than 60 times according to the situation, which is more conducive to the recovery of neurological functions of patients. Currently, the indications for hyperbaric oxygen in the United States and European Union countries included in health insurance are 14 categories of diseases, and the average number of hyperbaric oxygen treatments is 20-40 times. There is no limit to the maximum number of hyperbaric oxygen treatments. Our clinical practice confirms that the dosage of hyperbaric oxygen therapy is completely different for clinical diseases of different nature and course. For example, for some craniocerebral injuries, if hyperbaric oxygen therapy can intervene in the acute stage, the patient will achieve significant results after several hyperbaric oxygen therapy sessions, and then decide to continue the time and duration of hyperbaric oxygen therapy according to the patient’s specific condition assessment, usually need to complete 30~60 hyperbaric oxygen therapy sessions. 4.Why do some patients not wake up after hyperbaric oxygen therapy and have brain atrophy and ventricular enlargement changes? Brain injury is a disease with complex pathology and critical condition. Hyperbaric oxygen therapy is only one of the methods, and it needs to be combined with other treatment methods according to the specific situation and used at the right time and in the right amount. The final prognosis of the patient depends to a large extent on the degree of primary injury and the degree of control of secondary injury during the acute phase. Primary injury refers to the destruction of certain brain tissues in a short period of time due to various causes in the early stage of the disease. This part of the injury is not helped by any treatment at a later stage and is irreversible. Clinically, only various feasible means can be used to control and treat in a timely manner the inflammatory reaction, the pathological process of hemorrhage and edema produced by the tissues surrounding the subsequent injury, in order to minimize the scope and extent of secondary injury. For a variety of reasons, such as the criticality and complexity of the condition of these patients in the acute phase, coupled with the fact that hyperbaric oxygen therapy is not yet widespread, many hospitals do not have the conditions and facilities for hyperbaric oxygen therapy, and even if they do, they do not have the ability to resuscitate critically ill patients in hyperbaric chambers, most patients who really start to seek hyperbaric oxygen therapy have already entered the stable phase of their condition or have moved on. In other words, the irreversible damage to the brain has basically formed before hyperbaric oxygen therapy is started. This makes the patient miss the best period of hyperbaric oxygen therapy, and even if a long course of hyperbaric oxygen therapy is given later, the efficacy is limited. In addition, most of such patients are in long-term coma, mostly with tracheotomy and repeated infections, resulting in a weak nutritional status and physical condition. Clinical emphasis should be placed on improving microcirculation on the basis of nutritional support, intensive nursing care, and strengthening physical fitness, as well as applying hyperbaric oxygen and rehabilitation therapy at the right time and in the right amount. Even so, the prognosis of such patients is very poor. The brain atrophy and ventricular enlargement on imaging should be the inevitable result of the late pathological evolution of irreversible injury in the acute phase, and not caused by hyperbaric oxygen therapy.