The infant that is randomized to the HFNC therapy arm 1 will be placed on high flow at 1 L/kg/min (up to a maximum of 20 L/min) on fraction of inspired oxygen (FiO2) of 21 %. They will remain on FiO2 of 21% for a minimum of 10 minutes while monitoring SpO2. If oxygen saturation (SpO2) is <90%, FiO2 will be slowly increased to maintain SpO2 ≥ 90 %.

The infant that is randomized to the HFNC therapy arm 2 will be placed on high flow at 1.5 L/kg/min (up to a maximum of 20 L/min) on fraction of inspired oxygen (FiO2) of 21 %. They will remain on FiO2 of 21% for a minimum of 10 minutes while monitoring SpO2. If SpO2 is <90%, FiO2 will be slowly increased to maintain SpO2 ≥ 90 %.

The infant that is randomized to the HFNC therapy arm 3 will be placed on high flow at 2 L/kg/min (up to a maximum of 20 L/min) on fraction of inspired oxygen (FiO2) of 21 %. They will remain on FiO2 of 21% for a minimum of 10 minutes while monitoring SpO2. If SpO2 is <90%, FiO2 will be slowly increased to maintain SpO2 ≥ 90 %.

Patients placed on High Flow Nasal Cannula by treating physician will be randomized to initial flow rates of 1 L/kg/min, 1.5 L/kg/min, or 2 L/kg/min

Determined by Respiratory Distress Assessment Instrument (RDAI) score and Respiratory Assessment Change Score (RACS) and heart rate improvement by 10%.

The RDAI score assigns a score base on respiratory rate (RR), extent of wheezing, and retractions. It ranges from 0-17, higher score indicates severe bronchiolitis.

To determine RACS:

• A decrease in RR by 10% is +1 change unit. Increase of 10% was defined as -1 change unit.
• Subsequent RDAI score is subtracted from the previous RDAI score to obtain the change. (ie. if initial score is 7 and the reassessment score is 3, the patient has a score of +4) Positive score is indicative of improvement, and negative score demonstrates deterioration.

The overall RACS is calculated as the sum of change scores. Improvement is defined as RACS ≥ 4 positive units. No improvement was defined as RACS < 4 positive units.

• Need for an increase in initial flow setting as determined by treating physician during the first 24 hours of hospitalization
• Escalation to other forms of non-invasive ventilatory support (i.e. NCPAP or BIPAP)
• Need for invasive ventilation