Final answer:
Humidified oxygen is administered to children with spasmodic croup to help minimize tissue edema by loosening mucus and making it easier for them to breathe.
Step-by-step explanation:
The child with spasmodic croup is receiving humidified oxygen because it helps in minimizing tissue edema in the respiratory tract. This treatment eases breathing by reducing inflammation and loosening mucus, making it easier for the child to breathe. Contrary to increasing surface tension, this approach actually helps to decrease the viscosity of secretions in the airways, thus facilitating better air passage and promoting healing.
It does not necessarily provide an environment free of pathogens or act as a mode for delivering inhalant drugs, although humidified environments can be less conducive to some pathogens. Additionally, warm, humidified air helps to prevent damage to lung tissues which can occur when dry, cold air is inhaled.