Compared with adults, children have higher metabolic needs, and the airway is more likely to collapse. Before tracheal intubation after anesthesia induction, the patient 's spontaneous breathing completely disappears. At this critical stage, the residual oxygen of the lung is consumed, resulting in hypoxemia and atelectasis. Therefore, it is necessary to explore the best oxygenation strategy during intubation. In addition, ultrasound has become a common equipment in the operating room. It has the advantages of portability, repeatability, and no radiation, and can provide strong support for the diagnosis of gastric distension.