Humidified high flow nasal oxygen therapy decreases dilution of the inhaled oxygen and, by matching patient's peak flow, allows accurate delivery of the set FiO2 throughout the whole inspiratory phase.The purpose of this study is to determine the impact of hign-flow nasal therapy on pediatric hypercapnic respiratory failure by comparing with nasal continuous positive airway pressure.

Humidified high flow nasal oxygen therapy decreases dilution of the inhaled oxygen and, by matching patient's peak flow, allows accurate delivery of the set FiO2 throughout the whole inspiratory phase.The purpose of this study is to determine the impact of hign-flow nasal therapy on pediatric hypercapnic respiratory failure by comparing with nasal continuous positive airway pressure

Inclusion Criteria:

1. Age ranges from 1 to 18 years

2. Hypercapnic respiratory failure:

   PaO2<60mmHg and PaCO2 >50 mmHg

3. Candidate for non-invasive respiratory support as a result of:

   1. an intention to manage the patient with non-invasive (no endotracheal tube) respiratory support
   2. an intention to extubate the patient being managed with intubated respiratory support to non-invasive support

Exclusion Criteria:

1. Participation in a concurrent study that prohibits the use of HHFNC
2. Active air leak syndrome
3. Patients with abnormalities of the upper and lower airways; such as Pierre- Robin, Treacher-Collins, Goldenhar, choanal atresia or stenosis,
4. Patients with significant abdominal or respiratory malformations including tracheo-esophageal fistula, intestinal atresia, omphalocele, gastroschisis, and congenital diaphragmatic hernia
5. PaCO2<50mmHg