Bronchiolitis is a common illness of the respiratory tract caused by infection of the tiny airways within the lungs called bronchioles. At present the standard care of hospitalized children with bronchiolitis is oxygen via nasal prongs. In this study the investigators would like to compare standard ward management with a new method of delivering oxygen called high flow nasal cannula oxygen therapy (HFNOT). HFNOT involves breathing warmed, moistened oxygen through nasal cannulae at a flow rate of 8 liters/minute. Accumulated experience suggests that HFNOT eases the child's work of breathing and reduces need for ICU admission and invasive respiratory support.

We propose a prospective open randomised controlled trial to compare high flow nasal cannula oxygen therapy (HFNOT) with standard oxygen therapy for infants hospitalised with bronchiolitis. This study will be the first of its kind, as currently there is no evidence in the published literature.

All children will be cared for by the same medical team on two wards. All aspects of care other than oxygen delivery will not be specified, and be at the discretion of the physicians. HFNOT will not be used as an escalation of care on the wards.

Randomisation will be performed by REDcap, in blocks of 6 patients. Patients will be identified in Emergency, informed consent obtained, and treatment started prior to transfer to the ward.

For patients randomised to HFNOT, the flow rate will be fixed at 8 liters/minute, and the inspired oxygen concentration titrated to maintain saturations above 92%.

Interim statistical analysis will be conducted to determine any positive or negative effect of HFNOT therapy. The first interval analysis will be performed after 50 subjects, the second after 100 subjects. If an effect is found, the study will be terminated following discussion with the hospital statistician and ethics board. Whichever treatment arm is found to be beneficial will be instituted as standard care for children with bronchiolitis.

Inclusion Criteria:

• All children under 18 months of age with a clinical diagnosis of bronchiolitis requiring admission to hospital for observation and oxygen.

Exclusion Criteria:

• Infants admitted directly to ICU from Emergency.
• Prior positive pressure home ventilation.
• Tracheostomy.
• Nasogastric tubes in situ on admission.
• Upper airway abnormality.
• Congenital heart disease.