Atelectasis occurs in patients of all ages who receive mechanical ventilation under general anesthesia, and although fatal cases are rare, it is known as a cause of postoperative hypoxia or fever. In pediatric patients, it has a particularly high incidence of 68-100%, and the incidence is inversely proportional to age. Pediatric patients,compared to adults, have a small capacity for functional residual capacity while a high metabolic demand, making them fundamentally vulnerable to hypoxia. Increased atelectasis during anesthesia causes hypoxia not only during anesthesia but also during recovery after anesthesia. Therefore, it is important to establish and apply a strategy to minimize the occurrence of atelectasis during mechanical ventilation under general anesthesia in pediatric patients. The aim of this study is to investigate whether pressure support ventilation at emergence period could reduce the incidence of postoperative atelectasis in infants undergoing surgery under general anesthesia.

Inclusion Criteria:

1. infant patients aged 0 day to 13 month
2. American Society of Anesthesiologists (ASA) classification 1~2 who are scheduled for elective surgery under general anesthesia

Exclusion Criteria:

1. patients with symptomatic bronchopulmonary dysplasia
2. patients with uncorrected congenital heart or pulmonary disease
3. Hemodynamically unstable requiring preoperative vasopressor administration
4. fever (>37.5°) or URI symptoms on the day of surgery