A Titration of Fractional Inspired Oxygen Using Oxygen Reserve Index in Child

Inclusion Criteria: * Children under 7 years of age undergoing surgery under unilateral pulmonary ventilation * Children with American Society of Anesthesiology physical status I, II, III Exclusion Criteria: * Patient who have chronic respiratory failure * Patient who have a history of bronchopulmonary dysplasia, respiratory distress syndrome of neonate, laryngomalacia, tracheomalacia or tracheal stenosis * Patient whose initial Oxygen Reserve Index value is zero * Patient who need supplementary oxygen before surgery