Inclusion Criteria:  children aged 6 months to 10 years old under general anesthesia ASA I-III  Exclusion Criteria:  If the parents of the patient cannot communicate in Korean If mechanical ventilation is not planned (for example, A1 pulley) emergency operation a child whose ultrasound image quality is expected to deteriorate due to diseases such as thoracic deformity, scoliosis, or rib fractures If lateral position was not available