Cardiopulmonary resuscitation (CPR) is an emergency measure for patients in cardiac and respiratory arrest. In the past 30 years, the epidemiology of cardiac arrest, hemodynamic and in vivo pathophysiological changes in CPR have been extensively explored and great progress has been made. Many of the research results have been applied to clinical practice, which has improved the success rate of resuscitation, but there are still many issues that remain inconclusive. Now some of the current problems in CPR for colleagues to discuss. 1, the understanding of CPR sequence The purpose of CPR is to protect the brain and restore the pumping function of the heart. Domestic books and journals have been emphasizing the ABC sequence in CPR. The authors believe that the ABC sequence lacks strong theoretical and experimental support; on the contrary, the CAB sequence does have good reasons: ① Under normal physiological condition, the consciousness is still clear when the respiration is stopped artificially for several minutes; while once the heart stops for more than 5 seconds, the As syndrome, cyanosis and respiratory arrest can occur. This fully illustrates that the brain’s tolerance potential for hypoxia is much greater than the damage caused by ischemia. This is because once hypoxia or lack of oxygen occurs, brain cells can maintain their function through anaerobic metabolism and intracellular energy reserves. Once blood flow is interrupted (cardiac arrest), hypoxia increases and metabolic toxins cannot be excreted from the kidneys, increasing the damage to the organism. Meurs ing concluded that when CPR was started after 5 minutes of cardiac arrest and only cardiac compressions without ventilation were performed within the first 2 minutes, the decrease in PaO2 and the increase in PaCO2 within 30 seconds were not clinically significant, and the PaO2 was still as high as 6.97 kPa (1 kPa = 7 kPa) after 45 seconds. (1 kPa = 7.5 mmHg), and Chandra et al. concluded that early after cardiac arrest, even if cardiac compressions alone were performed without ventilation, the ventilation requirements of the body could still be basically maintained. (3) Recent clinical studies have found that patients in cardiac arrest are prone to spontaneous shortness of breath, which can lead to large changes in intratracheal pressure and rapid opening of the acoustic valves, and the change in their tension is sufficient to maintain airway patency and gas exchange, which is a spontaneous resuscitation response. The incidence of shortness of breath has been shown to be 40% to 60%, and according to the “chest pump” theory, the rebound of the chest after chest compressions will also help to ventilate the lungs. Within the first 8 minutes of CPR, the tidal volume from precordial compressions and voluntary shortness of breath is sufficient to maintain arterial blood gases at a high level. ④ The literature reports that the first precordial tap or extracardiac compressions can lead to resuscitation with the termination of an As syndrome episode or ventricular fibrillation (ventricular fibrillation) , and adherence to the ABC sequence will inevitably delay resuscitation. Recent data show that cardiac arrest accounts for 70% of sudden deaths, mostly caused by ventricular fibrillation, so Li Zonghao, an expert in prehospital emergency care in China, has pointed out that traditional CPR should be challenged. ⑤ If artificial respiration is administered first, even if local (pulmonary) blood oxygenation is increased, it still cannot play its proper role because there is no hemodynamic force, and at the same time, metabolic toxins accumulate without excretion and pH decreases, so that oxygenation capacity decreases, so C and A are the best choice to be performed simultaneously. However, in practice, artificial respiration requires skilled technique, and there are also psychological and hygienic hesitations, so even experienced personnel are often unable to perform it immediately, thus wasting much valuable time. In contrast, manual chest compressions are simple, easy to perform, and effective, which can greatly gain time and provide the opportunity to prepare for other measures that are difficult to perform in a hurry. Based on the above reasons, the authors believe that the order of ABC should not be emphasized in the resuscitation of cardiac and respiratory arrest, but rather CAB; if it is caused by asphyxia, the order of ACB or even CAB should be used. Foreign scholars also have similar views on this. The most important factor in the success of resuscitation is the time of cardiac arrest and the severity and reversibility of the patient’s original disease. The chance of successful resuscitation decreases linearly with the prolonged duration of cardiac arrest because of the deteriorating circulatory hemodynamics associated with prolonged CPR. Progressive ischemic damage (permanent organ damage and vasodilation) occurs throughout the body as the duration of cardiac arrest increases. Therefore, the main goal of resuscitation is to restore the patient’s cardiac function as soon as possible. In the past, the time limit for resuscitation was considered to be 4-5 minutes, beyond which the higher neurological functions could not be restored to normal even if the heart was resuscitated. But in the past 20 years, with the development of clinical medicine and resuscitation, this time limit has been extended several times. However, the views are very different. The 1995 edition of Emergency Medicine defines it this way: “After about 30 minutes of basic life support (BL S) and advanced life support (ALS), the myocardium is unresponsive and resuscitation can be considered terminated.” Many experts disagree on this time, with requirements of 8-10 minutes, 20 minutes, 25 minutes, 1 hour, 2 hours, and no specific time. Such differences create difficulties for clinical practice and teaching, and also provide an opportunity to explore its scientific truth. The definition itself does not stand up to scrutiny and is prone to disagreement. There are two issues that should be clarified here: one does not include the time of non-medical response after out-of-hospital cardiac arrest. Should a zombie brought to emergency care also adhere to BLS? The second is that if there is a momentary or transient voluntary heartbeat in BLS, where does the time start to be calculated? According to the limit of cardioembolic ischemia, the authors propose the “3 15-minute” criterion based on years of clinical practice: (1) If it can be determined that the heart has stopped for more than 15 minutes before the start of CPR, CPR should be considered to be abandoned. E (USA), and less than the 30 minutes stipulated by Liang Guanghuan. According to some data, none of the CPR cases survived after 12 minutes of cardiac arrest; Stephenson et al. analyzed 1,200 successful CPR cases in which only 6% survived after more than 4 minutes of cardiac arrest, and all of them had serious neurological sequelae; Zhang Tianzhong reported that brain death occurs after more than 5 minutes of circulatory interruption. It can be seen that CPR is almost meaningless for those with cardiac arrest for more than 15 minutes. (2) In standard BLS and ALS, if the heart continues to be unresponsive for more than 15 minutes or if effective artificial circulation cannot be achieved despite BLS resuscitation (and no open-heart condition) for more than 8-15 minutes, termination of resuscitation should be considered. In patients with advanced primary disease or severe irreversible disease, resuscitation may be terminated without hesitation. This time concept is greater than the criteria described in the literature. It has been suggested, both nationally and internationally, that ineffective resuscitation beyond 4 to 5 minutes, even if survived, may result in permanent and severe brain damage or possible brain death. Hemodynamic studies of chest compressions have demonstrated that compressions provide limited blood supply to tissues and organs, and even with technically accurate chest compressions, when cerebral blood flow is less than 20% to 30% of normal and myocardial blood flow is less than 10%, survival is not guaranteed; and it has been demonstrated that when myocardial perfusion is too low for more than 15 minutes, the myocardium is completely necrotic, and even restoration of high perfusion cannot save the necrotic myocardium. Brain cells are more sensitive to ischemia and hypoxia, so 15-minute BLS should be abandoned if it is not successful. Although there are reports in the literature of patients surviving BLS for long periods of time (up to 145 minutes), this is an exceptional phenomenon. It is uncertain whether any of the few survivors have permanent severe brain damage or a very low quality of life. Even though some patients are resuscitated effectively and their voluntary heartbeat or even respiration is restored, brain death has already occurred, so its true medical significance remains to be explored and the relationship between the individual and the general should not be discussed in the same way as the general rule. (3) The decision to terminate resuscitation should also take into account some special patients, such as drowning. At the same time, emotional, ethical, legal and family views should be taken into account to avoid unnecessary disputes. In case of disagreement, medical staff should do active missionary and explanatory work to terminate resuscitation in 15 to 30 minutes. Because meaninglessly prolonging the resuscitation time will only cause a waste of human and material resources, which is actually detrimental to both doctors and patients and does not meet the requirements of the times, and is also contrary to modern ethical guidelines and medical purposes.