Procedural sedation is an established and safe intervention and is widely used in diagnostic and therapeutic procedures for pediatric patients. Nonetheless, problems of the respiratory system such as upper airway obstruction, hypoventilation and apnea are frequent adverse events. We postulate that respiratory instability is less frequent in patients high flow nasal cannula vs. standard care on respiratory stability, i.e. low flow nasal cannula, in pediatric procedural sedation. The purpose of this pilot study is to estimate the effect of HFNC (high flow nasal cannula) on the respiratory instability in children undergoing upper gastrointestinal endoscopy under pediatric procedural sedation (PPS).