Chronic postoperative pain is a clinically important problem that can have serious physical, psychological, and socioeconomic consequences, and in the last decade or so there has been a significant increase in the awareness of postoperative chronic pain. Postoperative chronic pain has been recognized as an important complication after surgery. The 1999 IAsP newsletter states that the following should be included in the diagnosis of postoperative chronic pain: pain triggered by surgical operation; persistence for at least 2 months; and exclusion of other causative factors of pain such as chronic infection or persistent malignant disease. I. Epidemiology and risk factors of persistent postoperative pain Clinical procedures that are prone to postoperative chronic pain include post-amputation, open-heart surgery, mastectomy, hysterectomy, and inguinal hernia repair. The incidence of postoperative chronic pain and associated risk factors vary from one surgery to another because of the wide disparity in the site of trauma, the population receiving the surgery, and the impact of the consequences of the surgery on the patient. (The incidence of chronic pain after open thoracotomy has been reported in the literature to be 26%. 80%, which is the most common chronic pain after various surgeries. In one of our studies, the chronic pain after transseptal open heart surgery was 65.3% at 3 months, 62.6% at 6 months, and still reached 49.3% at 12 months. And the incidence of chronic pain after bypass surgery via median sternotomy was 32.6%. Intercostal nerve injury, unrelieved postoperative pain, postoperative radiotherapy, and painful chest wall resection were the main risk factors. It is worth noting that intercostal nerve cryopreservation as an analgesic method, although it has a good analgesic effect on acute pain after open-heart surgery, can increase chronic postoperative pain, especially neuropathic-like pain, compared with epidural analgesia. (B) Chronic pain after bone and joint surgery The incidence of CGRP after orthopedic surgery is about 2.3%. 37%, and the incidence of chronic pain after osteoarthroplasty is 12%. (iii) Chronic pain after mastectomy The incidence of chronic pain after mastectomy is up to 50%. Intercostal brachial plexus injury, postoperative chemotherapy or radiotherapy, preoperative depression and anxiety, and preoperative pain intensity are the main risk factors affecting the incidence of postoperative pain. (iv) Phantom limb pain The incidence is as high as 50%. 80%. It is mainly related to the degree of preoperative pain, the degree of intraoperative trauma, postoperative pain intensity, psychological factors and other factors. (v) Others The hernia repair is not a major operation, but its postoperative incidence of chronic pain reaches 12%, which can significantly affect the quality of life of patients. The main risk factors include injury to the inferior iliac abdominal nerve, iliac inguinal nerve, and genitofemoral nerve; preoperative pain, young patients, women, recurrent hernia surgery, and preoperative pain with other sites. The incidence of chronic pain after hysterectomy in patients with combined preoperative pelvic pain, history of cesarean delivery, pain as the main indication for surgery, and pain at other sites is 5% to 32%, and 5% after cesarean delivery. lO%. Second, the clinical manifestations of postoperative chronic pain are diverse, such as chronic pain after open-heart surgery is mostly pathological pain manifestations, such as spontaneous pain, nociceptive allergy and nociceptive hypersensitivity, in which 1/3 of the patients’ pain can affect the emotions; pain after mastectomy town manifests phantom pain, scar pain and neuropathic pain; for chronic pain after amputation is mainly stump pain and phantom limb pain, sometimes it is difficult for patients to distinguish Sometimes it is difficult for patients to distinguish phantom limb pain, residual limb pain and other abnormal sensations. The possible mechanisms of postoperative chronic pain The main causative mechanisms of postoperative pain include three aspects: preoperative high-risk factors, intraoperative nerve injury, and postoperative inflammation or disease recurrence. The mechanism of postoperative chronic pain is very complex, and the exhaustive mechanism is not fully understood so far, but one thing is certain, that is, central sensitization triggered by continuous excitation of injurious receptors is one of the main causes of postoperative chronic pain. Studies on various animal models of neuropathic pain have shown that the process of nerve injury re-repair causes neuropathic pain due to abnormal discharge, ectopic proliferation of nerve fibers, inflammatory factors and nerve growth factors that mediate sympathetic outgrowth phenomenon and increase in pain transmitters. The mechanism of chronic pain after open-heart surgery can be caused by the trauma caused by intraoperative stretching, compression or even severing of intercostal nerves, muscles and ribs and postoperative inflammation of these tissues, as well as mechanical injuries such as chest tubes repeatedly rubbing the chest wall and pleura, which produce a series of inflammatory transmitters and pain transmitters that constantly stimulate the center to produce central sensitization, which is then transmitted downward from the center to make patients feel pain. On the other hand, the process of peripheral sensitization of damaged nerves, muscles, ribs, etc. in the process of damage as well as re-repair, resulting in abnormal discharge, ectopic proliferation of nerve fibers, locally produced inflammatory factors and nerve growth factors, etc. aggravates the formation of nociception and its degree. Prolonged central sensitization can also lead to permanent changes in the central nervous system, such as necrosis of inhibitory neurons, which are subsequently replaced by new bovine excitatory afferent neurons and the formation of abnormal synapses. Many drugs do not respond to the persistent central sensitization and intractable pain caused by the above-mentioned changes, thus making clinical treatment extremely difficult. IV. Prevention and treatment Chronic pain after surgery has been one of the major complications after various types of surgery, and despite the prevalence of this problem, the awareness of postoperative chronic pain and effective measures to reduce the risk are not as good as they should be. Postoperative chronic pain is usually neuropathic and more difficult to treat, so prevention is key. Based on the recognition of central sensitization, scholars proposed the concept of preemptive analgesia more than a decade ago, which means that analgesics are given before the onset of pain to effectively block the transmission of injurious stimuli to the center. However, subsequent studies have found that as long as small peripheral sensory afferent nerves are activated by repeated stimulation, they are susceptible to central sensitization, which could explain the great inconsistency in the results of studies on preemptive analgesia. The consensus now is to advocate more preventive analgesia (preventive analgesia), that is, to truly block the occurrence of central sensitization, pain treatment must be provided throughout the perioperative period before, during, and after surgery in order to effectively prevent chronic postoperative pain. Good postoperative analgesia should not only stop the process of central sensitization in the short term, but also continue to stop the process of peripheral sensitization for a longer period of time after surgery. This suggests that after a good postoperative analgesia, the anesthesiologist should continue to focus on the pain management of the patient one week later or even after discharge. (i) Multimodal treatment of acute postoperative pain Preventive analgesic techniques can reduce certain chronic postoperative pain syndromes. Effective treatment of acute postoperative pain, especially treatment of pain with neuropathic features such as burning and paresthesias, can prevent the development of chronic pain. Aggressive and comprehensive postoperative pain management should not be neglected, and to effectively prevent the occurrence of central remodeling, analgesics should be used throughout the preoperative, intraoperative, and postoperative phases until wound healing is complete. For pain that cannot be completely relieved by nerve block, such as pain after open-heart surgery, a multimodal analgesic approach is advocated in order to effectively block the transmission of peripheral injurious stimuli to the center and prevent central sensitization. Due to the diversity of surgical modalities and the numerous risk factors associated with pain after different procedures, it is not possible to have one approach to prevent and treat all surgically induced central sensitization. Studies have shown that 400 mg of gabapentin orally every 6 h starting late preoperatively until 8 days postoperatively and EMLA209 applied daily for several days and 3 days postoperatively, combined with 0.75% bupivacaine axillary brachial plexus and 3, 4, and 5 intercostal nerve blocks are effective in reducing chronic pain after radical breast cancer surgery. In addition, administration of the antidepressant griseofulvin 75 mg from late preoperative to 2 weeks postoperatively significantly reduced the incidence of chronic pain at 6 months after breast surgery. A clinical history of surgery was found in 20% of patients with cGRP. Studies have shown that oral vc 500m2/day after 50 days of treatment in patients undergoing fracture surgery significantly reduced the incidence of cGRP in patients one year after fracture surgery compared to placebo (7%: 22%). Preoperative oral celecoxib 400 mg compounded with intra-articular injections of local anesthetics, colistin and morphine compounded with cold compresses reduced pain in the acute phase and chronic pain after orthopedic surgery. However, once neuropathic inflammation develops, cox. 2 inhibitors will have no therapeutic effect in bright silicon, indicating that the preventive effect of cOx. 2 on postoperative chronic pain is more important than the therapeutic effect. (B) Reduce intraoperative nerve injury Minimizing intraoperative nerve injury is an important means to reduce or prevent postoperative pain. Complete nerve amputation is less painful than that caused by ligation or compression. A survey of Danish orthopaedic surgeons published in 2007 showed that 30% of them still ligated nerves during amputation. Nerve ligation is known to be a common method for establishing neuropathic pain models in animal experiments. (iii) Reducing unnecessary surgery or using minimally invasive procedures Before considering surgery, chronic postoperative pain should be weighed as a patchouli complication after surgery, and unnecessary and potentially more invasive procedures should be avoided. On the other hand, minimally invasive procedures can be used as much as possible, such as laparoscopic surgery can significantly reduce the incidence of chronic pain after open surgery. V. Future research goals Based on the existing understanding of the mechanisms of chronic pain occurrence, researchers have tried various modulations or alterations in the links that may be involved in the central sensitization process in order to achieve a reduction in the incidence of postoperative chronic pain, but the consistency of the results is not very satisfactory. There is still a lack of large-sample prospective studies, and the available studies have not yet included all risk factors, so the available evidence does not yet provide a robust preventive and therapeutic measure. Future large-sample, randomized controlled studies are needed to further support the role of prophylactic multimodal analgesic techniques in reducing chronic postoperative pain syndromes.