Nasal cannulas are designed so that each nostril accepts a port that has continuous flow passing through it. Although the gas can be humidified as it leaves the source, it cannot be easily heated. The gas entering the nostril is cool; once it is heated in the nose, it has a lower humidity. Cannulas come in sizes suitable for infants of various sizes cared for in cribs, radiant warmers, and incubators. Because the cannula flow is mixed with the infant’s minute ventilation and entrainment from oral gas, as well as with the flow from the cannula and the oxygen content of the gas source.