This study intends to evaluate the effect of different inhaled oxygen concentrations on the effect of lung recruitment in patients undergoing abdominal surgery. During perioperative mechanical ventilation, higher FiO2 is usually given to prevent the occurrence of hypoxemia, but there are no conclusions about the setting of optimal FiO2 during surgery. Dynamic pulmonary compliance enables real-time monitoring of alveolar changes and is used to assess pulmonary function in intraoperative patients. The value of compliance represents the number of air-containing alveoli; the more alveoli are trapped, the less air-containing tissue there is and the lower the compliance. Lung recruitment, as part of a lung-protective ventilation strategy, is effective in opening alveoli and improving oxygenation. This single-center, randomized controlled trial will explore the optimal inspired oxygen concentration that allows patients to benefit from lung recruitment and the duration of improvement in lung compliance after lung recruitment.