Patients with obstructive sleep apnea hypopnea syndrome (OSAHS) suffer from apnea and hypoventilation due to repeated collapsed obstruction of the upper airway during sleep, resulting in nocturnal hypoxia, microarousals and disrupted sleep architecture, leading to daytime drowsiness and inattention, which seriously affects patients’ quality of life and may be combined with hypertension, coronary artery disease, diabetes mellitus and other multi-organ functional impairments [1]. In recent decades, this disease has been one of the hotspots of research in clinical medicine and has received extensive attention from many disciplines, including otorhinolaryngology-head and neck surgery, respiratory medicine, stomatology, cardiovascular medicine, and neurology. Common treatments include long-term behavioral interventions, continuous positive airway pressure (CPAP), orthodontic appliances and surgical treatment. However, for patients with structural abnormalities of the upper airway and those who do not tolerate CPAP, surgical treatment of OSAHS, represented by upper airway reconstruction surgery, has been highly regarded and gradually developed as an important method of OSAHS treatment. This article introduces the preoperative evaluation of OSAHS surgical treatment, the improvement and development of surgical methods, the factors affecting surgical efficacy and the current controversies on OSAHS surgical treatment. I. Preoperative evaluation In order to clarify the indications for surgery and ensure the safety of surgery, preoperative inquiries should be made about the presence of comorbidities such as hypertension, diabetes and coronary heart disease, in addition to symptoms such as snoring and breath-holding during sleep and daytime drowsiness. Epidemiological studies have shown that OSAHS is an independent risk factor for hypertension, with 30% of patients with hypertension having OSAHS and 50% to 80% of patients with OSAHS having hypertension. OSAHS is closely related to glucose tolerance and insulin resistance. 30.1% of patients with OSAHS and 13.9% of patients with simple snoring also have diabetes, and 20% of patients with OSAHS and 13.9% of patients with simple snoring have abnormal glucose tolerance; insulin sensitivity decreases as the degree of OSAHS increases, As the degree of OSAHS increases, insulin sensitivity decreases and fasting and postprandial glucose increases significantly in patients with severe OSAHS. Therefore, blood glucose should be checked, blood pressure should be measured, and electrocardiogram should be done upon admission, and any abnormalities should be adjusted and controlled in time to exclude contraindications to surgery. Physical examination mainly includes body mass index (BMI), neck circumference, waist circumference measurement, nasal examination, Friedman typing, staging and assessment of jaw development, which is beneficial to the selection of surgical plan, risk assessment and efficacy prediction. Polysomnography (PSG) is the gold standard for the diagnosis of OSAHS, and the test results are helpful for the determination of disease severity and differential diagnosis. Although there is no reliable method to accurately determine the site of obstruction in OSAHS patients, X-ray cephalometry, upper airway CT and electronic (fiberoptic) rhinolaryngoscopy are valuable for determining the site of obstruction, which is beneficial for determining the surgical plan and improving the efficacy. Because OSAHS patients are mostly combined with obesity, hypertension, diabetes and other multi-system diseases, and are in long-term hypoxia, they have greater surgical and anesthetic risks. Preoperative continuous positive pressure ventilation is beneficial to control systemic diseases and reduce the risk of surgery and anesthesia. For patients with severe obesity, preoperative prophylactic tracheotomy is necessary to ensure airway patency. Improvement and development of surgical methods 1. Nasal surgery 44% of OSAHS patients have nasal stenosis, and nasal resistance is significantly higher than normal. Nasal obstruction can lead to increased upper airway resistance, increased negative pressure in the pharyngeal cavity during inspiration, loss or weakening of the nasal-pharyngeal nerve reflex and open-mouth breathing, which in turn aggravates upper airway obstruction. The main factors of nasal obstruction include inferior turbinate hypertrophy, nasal septum deviation and nasal valve area stenosis. The purpose of nasal ventilation reconstruction surgery is to relieve nasal obstruction and restore its normal ventilation function. Depending on the cause of nasal obstruction, the surgical methods include inferior turbinate removal or radiofrequency ablation, septum correction, nasal flap reconstruction, etc. Nasal surgery can improve the snoring symptoms in patients with simple snoring and mild OSAHS, while it has no significant efficacy for patients with moderate to severe OSAHS and no significant decrease in AHI after surgery, but it is still an important part of OSAHS treatment, especially for improving the compliance of CPAP treatment. 2. palatopharyngeal area surgery In 1964, Ikematsu applied palatopharyngoplasty and partial uvulopalatopharyngoplasty to treat habitual snoring, which was modified and named uvulopalatopharyngoplasty (UPPP) by Fujita in 1981 and firstly applied to the treatment of OSAHS patients [7]. Traditional uvulopalatopharyngoplasty is prone to complications such as open nasal voice, nasopharyngeal reflux from feeding, nasopharyngeal stenosis, and pharyngeal foreign body sensation because the uvula is not preserved and the palatopharynx loses its normal physiological state. For unselected patients their surgical success rate (AHI drop greater than 50% and less than 20 beats/hour) is about 40% [8]. The UPPP procedure was modified by Fairbanks in 1993 to maximize the shortening of both sides of the soft palate while preserving the central musculature, which is important for preventing nasopharyngeal stenosis and maintaining the function of the soft palate. Han Demin et al [10] concluded in 2000 that the uvula has the functions of assisting swallowing, articulation, respiration and protection, so the traditional UPPP procedure was improved by preserving the uvula intact, dissecting and removing the fatty tissue in the palatal sail gap, and expanding the soft palate forming area. The incidence of complications such as hemorrhage, open nasal voice, incoming juice nasal reflux, and pharyngeal foreign body sensation is significantly lower than that of traditional UPPP surgery. If a reduction of AHI by more than 50% is defined as effective, the effectiveness rates are 53,3% (routine otorhinolaryngological examination), 68,7% (fiberoptic laryngoscopy + Muller test) and 82,4% (continuous upper airway manometry), depending on the obstruction localization method. Friedman et al [11] designed the Z-palatoplasty (ZPP) in 2004 and combined it with lingual root plasma radiofrequency ablation for the treatment of OSAHS patients with resected tonsils, with a significantly higher success rate at 6 months postoperatively (68%) than in the UPPP group (28%). The main improvement of this procedure is that the mucosa and submucosa of the oral surface of the soft palate are removed and the soft palate is dissected in the midline, and the soft palate is pulled and sutured anterolaterally. Since the soft palate muscle tissue was preserved during surgery, the occurrence of permanent palatopharyngeal closure insufficiency could be reduced. Yi Hongliang and Yin Shankai et al [12] combined ZPP with tonsillectomy and pharyngoplasty and named it Z-palatopharyngoplasty (Z-Palatopharyngoplasty, ZPPP), which was applied to treat tonsils of 1 to 3 degrees in size and posterior airway space (PAS) ≥ 11 mm Friedman type II and III OSAHS patients with a success rate of 64,7%. The hard palate truncation and soft palate advancement was proposed by Woodson in 1997 and applied clinically [13]. The procedure is performed by truncating a portion (approximately 1 cm) of the posterior edge of the hard palate, lifting the palatal tendon membrane forward together with the soft palate and fixing it to the truncated hard palate to widen the posterior airway of the hard palate. It is characterized by increasing the tissue tension on both sides of the nasopharynx without affecting the shape and appearance of the face, and can reduce the collapse of the pharyngeal cavity to a greater extent than the UPPP surgery. It is suitable for patients with posterior soft palate stenosis, overgrown hard palate, bony stenosis of the nasopharyngeal airway and obstruction of the palatine pharynx after UPPP or laser assisted uvulopalatoplasty (LAUP), with a success rate of 67% to 68,8% [13-14]. Radiofrequency ablation (RFA), uses the energy generated by bipolar radiofrequency to convert the electrolyte between the radiofrequency tip and the tissue into a plasma. The charged ions in the plasma are accelerated by the electric field and then, at a relatively low temperature (40-70°C), cause the cells in the target tissue to gradually disintegrate on a molecular basis, creating a cutting and tissue decongestion effect. This technique can be applied to several parts of the upper airway, such as the inferior turbinate, soft palate, tonsils and tongue root, etc. In 1997, Powell et al. reported the clinical results of this technique in patients with OSAHS. Because of its low temperature and minimal side injuries, pain and postoperative complications are relatively few. This technique is mainly applied to patients with habitual snoring, upper airway resistance syndrome (UARS) and mild OSAHS to reduce snoring symptoms [16]. Radiofrequency-assisted UPPP and radiofrequency ablation or partial excision of the tongue root can be applied to the treatment of patients with moderate to severe OSAHS, but strong evidence of their clinical effectiveness is lacking. 3.Surgery in the linguopharyngeal region chin-lingual muscle anterior displacement hyoid suspension: Riley equal to 1986 proposed chin-lingual muscle anterior displacement hyoid suspension, that is, the chin spine together with the chin-lingual muscle is moved forward, so that the tension of the chin-lingual muscle is increased and the tongue root is pulled forward, thus enlarging the posterior airway gap at the linguopharyngeal level. The success rate of this procedure in combination with UPPP in treating OSAHS patients with obstruction in both the palatopharyngeal and linguopharyngeal planes is approximately 65% to 67%. The traditional chin-lingual muscle anterior transfer is more invasive, more difficult to perform, and takes longer to operate. Wang Lin’e and Yin Shankai improved this procedure, which simplified the operation and reduced the treatment cost and complications. Later, the Genial Bone Advancement Trephine system (GBAT system) was developed and improved based on the chin spine anatomy, which further simplified the operation, reduced trauma and operative time, and achieved similar efficacy as the traditional chin-lingual advancement [26-28]. . 4. Maxillary and mandibular advancement: The etiology of OSAHS is complex, among which jaw dysplasia is one of the main causes. For patients with OSAHS with jaw dysplasia, maxillomandibular advancement (MMA) is preferred to enlarge the upper airway and correct the maxillofacial deformity. Maxillomandibular advancement is also an option for patients with failed stage I surgery or severe OSAHS. Its surgical success rate is 95%-100%, and it is currently the most effective treatment for OSAHS other than tracheotomy. Yi Hongliang and Yin Shankai recently applied MMA to treat 10 patients with OSAHS, and 6 patients were followed up for more than 6 months with a significant rate (success rate) of 83% and an efficiency rate of 100%. However, the technique is more invasive and difficult to perform, and the facial shape is altered and the occlusal relationship may be disturbed. For patients with OSAHS who strongly hope to achieve cure through surgery, with jaw dysplasia or failed first-stage surgery, bimaxillary advancement is not the best choice. 5.Distraction osteogenesis: Distraction osteogenesis (DO) technique produces stress on the bone tissue through progressive external pulling, and stimulates the active growth of bone tissue through the stress, thus achieving the purpose of new bone growth. This technique has the advantages of minimal trauma, low recurrence rate, and simultaneous expansion of soft and hard tissues. As this technique continues to mature, its application in patients with craniomaxillofacial deformity with OSAHS is gradually increasing. The maxillary rapid traction arch expansion technique is performed by means of an orthodontic appliance attached to the maxillary molars on both sides, which gradually applies expansion forces to both sides to expand the dental arch, elevate the soft palate, widen the effective nasal ventilation area, and expand the mandibular arch by compensatory action. This technique must be applied before cartilage osteogenesis in the hard palate area at the age of 5 to 16 years, and combined with tonsil adenoidectomy can successfully treat children with OSAHS who have narrow maxillary dental arches. In children with OSAHS with craniomaxillofacial deformities who require tracheotomy due to airway obstruction or who have undergone tracheotomy but cannot be extubated, traction osteogenesis can be applied to both resolve the craniomaxillofacial deformity and relieve the airway obstruction, thus avoiding tracheotomy or permanent banding [33]. Adult patients with OSAHS with craniomaxillofacial deformities who require anterior displacement of the jaw by more than 15 mm should undergo traction osteogenesis. In patients with severe micromaxilla with OSAHS, multiple traction osteogenesis can be performed at multiple sites and at the same site at the same time. In patients with both maxillary and mandibular hypoplasia, traction osteogenesis can be performed on both the upper and lower jaws. Traction osteogenesis is an effective treatment for patients with jaw deformity with OSAHS, saving neonatal and pediatric patients from tracheotomy or early extubation, and significantly improving the symptoms of adult patients with OSAHS. In the 1960s, Kuhlo et al [46] first applied tracheotomy to treat obstructive sleep apnea syndrome, which led to remission and prolonged life in some critically ill patients. Although tracheotomy can effectively relieve airway obstruction in patients with OSAHS, however, it is mostly unacceptable because it requires the wearing of an anterior cervical tracheotomy cannula for life, which seriously affects the quality of life. In 1981, Fujita proposed uvulopalatopharyngoplasty and used it for the treatment of OSAHS, which shifted the principle of OSAHS surgery from bypass ventilation to upper airway reconstruction. With the widespread development of UPPP surgery, the problems of unsatisfactory long-term outcome in some patients and surgical complications such as asphyxia, nasopharyngeal reflux, and open nasal voice gradually emerged, and the surgical treatment of OSAHS was once controversial. CPAP is undeniably the current treatment of choice for OSAHS; however, 8-15% of patients refuse CPAP treatment despite education and persuasion [48], and the long-term compliance of patients treated with CPAP ranges from 46% to 83%, for which surgical treatment is an important alternative option. In patients who cannot tolerate CPAP treatment due to nasal obstruction, surgical removal of nasal obstruction can significantly improve compliance [50]. In patients with OSAHS with significant anatomical abnormalities of the upper airway (e.g., tonsillar and adenoid hypertrophy, jaw hypoplasia, etc.), surgery can be the first-line treatment. For patients without significant anatomical abnormalities of the upper airway who refuse or do not comply with CPAP treatment, a reasonable surgical plan is also expected to achieve better results if the patient has a desire for surgery and the site of obstruction is determined by obstruction localization methods. With the progressive understanding of the role of upper airway obstruction in the cause of OSAHS and the anatomical structure and function of the soft palate area, various surgical treatment techniques are paying more attention to preserving the normal structure and physiological function, reducing surgical complications, and improving the therapeutic effect while focusing on the expansion of the upper airway ventilation cross-sectional area, therefore, surgical treatment still has an important role in the field of OSAHS treatment.