We randomly assigned children younger than 5 years with severe pneumonia and hypoxaemia to receive oxygen therapy by either bubble CPAP ( 5 L/min starting at a CPAP level of 5 cm H2O ) , standard low-flow nasal cannula ( 2 L/min ) , or high-flow nasal cannula ( 2 L/kg per min up to the maximum of 12 L/min ) .