Effects of Different Inhaled Oxygen Concentrations on Lung Function in Older Patients After Laparoscopic Gastrointestinal Surgery Under General Anesthesia

Inclusion Criteria: * Age not less than 65 years * American Society of Anesthesiologists grades I-III * No history of drug allergies or abnormal anesthesia. * The duration of mechanical ventilation was expected to be more than 2 hours. * Laparoscopic Gastrointestinal Surgery * The preoperative oxygen saturation was not less than 94%. * The patients will be planned to extubate in the operating room. Exclusion Criteria: * History of acute lung injury or acute respiratory distress syndrome (ARDS) within 3 months. * Cardiac function Class IV (New York Heart Association classification) * Chronic renal failure (renal cell filtration rate \<30 ml min-11.73/m2), severe liver disease * Patients with blurred consciousness and cognitive dysfunction * Severe coagulation dysfunction. * Without preoperative oxygen inhalation, blood oxygen level \<94%, and severe pulmonary dysfunction * Patients with endotracheal tubes were admitted to the intensive care unit (ICU) after surgery. * Body mass index (BMI) \>30kg/m2 * Inability to complete the study