Introduction: Obesity, defined as a body mass index (BMI) between 30 and 39.9 kg/m2, and extreme obesity, with BMI more than 40 kg m2 is a multisystem, chronic, proinflammatory disorder with a worldwide increasing prevalence called "globesity". There is a known significant increase in perioperative complications among obese patients. Standards of care for bariatric and non-bariatric surgery and for the intensive care units (ICU) exist but are not well defined nor clearly followed. Recent studies suggest intraoperative protective mechanical ventilation for the obese, but the gold standard has not yet been found and the best intraoperative ventilation strategy remains to be defined. Surgical procedures in the oral cavity increase the risk of perioperative complications of obese population. Oral surgeries of obese patients under general endotracheal anesthesia are a special challenge. Any form of regional anesthesia is inadequate, duration of surgery is short but requires deep level of anesthesia after which a fast awakening and mostly rapid release from hospital are expected. Surgical procedures in the oral cavity due to possible postoperative upper airway oedema increase the risk of postoperative hypoxia in obese patients. Therefore, intraoperative mechanical ventilation with good ventilation-perfusion ratio, without creating new atelectasis and postoperative respiratory decompensation is important for the rapid recovery of obese patients after oral surgical precedures. Aims: The aim of this prospective randomised study was to evaluate preoperative and early postoperative change in respiratory function parameters within and between three groups of patients who were ventilated with higher PEEP levels (PEEP 7, PEEP 10) and with alveolar recruitment maneuvers (ARM) or with lower PEEP level without ARM. To estimate change in preoperative and postoperative degree of dyspnoea measured on Modified Borg Scale, connection between the various risks of difficult intubation and obesity, intraoperative effect of different PEEP values and ARM on systemic circulatory stability. Patients and methods: Following the permission of the Ethics Committee, 75 obese patients (30-65 year old and ASA status II-III) scheduled for oral surgical procedures under general endotracheal anesthesia with expected duration exceeding 2,5 hrs, who gave written informed consent were randomized into three groups according to strategy of intraoperative mechanical ventilation. 1) control group: positive end-expiratory pressure (PEEP) of 4 cmH2O was continously applied without ARM; 2) experimental group (ARM and PEEP 7): PEEP level of 7 cmH2O was continously applied and ARM was provided every 30 min; 3) experimental (ARM and PEEP 10): PEEP level of 10 cmH2O was continously applied and ARM was provided every 30 min. Anaesthesia technique and fluid volume administration were standardized. Patients were ventilated with a tidal volume of 7 ml/kg ideal body weight and an inspired oxygen fraction to 0,4. Measurements were performed before and after induction of anesthesia, every 30 min during anesthesia and postoperatively after 15 min, in 1st, 3rd and 24 th hour. NCT03144609. Results: Among the control (PEEP 4) and tested (PEEP 7 and PEEP 10) groups, neither between the two examined (PEEP 7 and PEEP 10) groups there were not statistically significant differences in the anthropometric characteristics of the subjects. The mean age of patients was 49.5 years (SD 10.6), the average BMI was 35.6 (SD 5.6), with no gender difference. The mean value of the neck circumferences of the obese patients was 54.2 (SD 6.9) cm, significantly higher in males (p = 0.03). Patients had an abdominal obesity type with a average ratio of waist to hip (W/H) ratio greater than 1.1 (women 0.99 +/- 0.19, males 1.11 +/- 0.18). There was a significant positive correlation of the neck circumferences, the Mallampati and the Cormarck-Lehane classification with the W/H ratio. There was positive correlation of the Ariscat scor for postoperative lung complications and preoperative degree of dysponea with the BMI. Significant negative correlation of preoperative paO2/FiO2 ratio and SaO2 with a percentage of deviation from ideal body weight was found. There was no correlation of the number of teeth with parameters of impaired ventilation and/or difficult intubation and with BMI. Obese patients with mandibular or maximal prognatism showed good correlation with smaller interdental space, less neck flexibility, and shorter tireomental or sternomental distances. By ROC analysis it was found that the values of neck circumferences greater than 57 cm had 86.7% sensitivity and 81.7% specificity in prediction of difficult intubation. The use of higher values of PEEP and ARM in obese patients resulted in a significant decrease of a dypnoea scor in the first hours of postoperative period compared to the control group. PEEP 10 group showed higher Carrico index, higher oxygen saturation and lower dyspnoea scor in the postoperative period compared to PEEP 7. groop. Slight to moderate respiratory failure after surgery was only present in the control group in 5 patients (20%). The progressive gradual increase in pulmonary complience was in the groups where higher PEEP values and ARM were applied, with a statistically significant difference with the control group where the pulmonary complience showed a gradual decrease trend. PEEP of 10 cmH2O showed statistically significant improvement in oxygen saturation during surgery with a more pronounced reduction in MAP, but statistically insignificant compared to other patient groups. The circulating stability was not impaired neither by using higher values of PEEP nor by the ARM. Conclusion: Significant improvements in laboratory and clinical respiratory parameters in the early postoperative period, without intraoperative circulatory instability, were obtained using higher PEEP values with periodic ARM compared to mechanical ventilation with lower PEEP and without ARM, in obese patients undergoing oral surgery under general anesthesia. More favorable impact on the respiratory function was found in PEEP 10 group compared to PEEP 7 group. This method could be the best strategy for mechanical ventilation of obese patients in the prevention of postoperative hypoxia after oralsurgical procedures in which rapid release from hospital without respiratory complication are expected. Further multicentric randomized research are required to validate and standardize this management approach.