 Background: Respiratory failure is one of the most common reasons for admission to the Pediatric Critical Care Unit PCCU. 17 of children admitted to a PCCU require some form of invasive or non-invasive mechanical respiratory support. HHFNC therapy was first introduced in early 2000 and hence is a relatively new mode of respiratory support. One of the proposed mechanisms of action of HHFNC is by providing airway positive pressure hence considered as non-invasive mode of ventilation in pediatrics. However, the actual amount of positive airway pressure that HHFNC provides at increasing flow rates has not been well studied in children. 