The World Health Organization (WHO) has proposed the use of 80% high-dose inhalation oxygen (FiO2) during surgery to reduce postoperative infection in adult patients undergoing general anesthesia. However, high-dose inhaled oxygen increases the risk of oxygen toxicity by increasing reactive oxygen species, and according to a recent research, hyperoxia in the ICU is one of the causes of mortality. In patients with general anesthesia requiring intubation, high-dose inhaled oxygen was associated with postoperative pulmonary complications in a dose-proportional manner and was significantly associated with mortality within 30 days after surgery. Therefore, it is necessary to study the optimum oxygen concentration during surgery to reduce postoperative pulmonary complications in general anesthesia patients who require intubation. Esophagectomy for esophageal cancer still has higher morbidity and mortality rates than other common procedures. There are several factors such as aneurysmal leakage, esophageal substitute necrosis, cardiac complications, and pulmonary complications. Pulmonary complications have been reported to be a very important factor. Therefore, various methods have been proposed to reduce pulmonary complications after esophageal cancer surgery. One of them is minimally invasive surgery. However, even in the case of a thoracoscopic operation using a robot, one lung ventilation is inevitable for securing the visual field during surgery, and hypoxia and hyperoxia are known to be associated with postoperative acute lung injury. Therefore, in order to reduce postoperative pulmonary complications in the esophagectomy using robots, it is necessary to study the optimum oxygen concentration during surgery. The recently developed oxygen reserve index (ORI) uses a non-invasive sensor attached to the finger, similar to pulse oximetry, to detect persistent hyperoxia of more than 100 mmHg and less than 200 mmHg. Therefore, if the oxygen reserve index is used for robotic esophagectomy, which requires one lung ventilation, the degree of oxygenation of the patient can be monitored continuously and accurately. The authors will measure the oxygen reserve index in robotic esophagectomy, and analyze the correlation between oxygen reserve index and postoperative pulmonary complications. Furthermore, the cut-off value of the oxygen reserve index, which can reduce pulmonary complications, will be calculated.