In what situation is Heliox most beneficial?

Heliox, a combination of helium and oxygen, is most beneficial during severe asthma attacks due to its unique physical properties. The lower density of helium compared to regular air can significantly reduce airway resistance during breathing. This is particularly advantageous in a clinical situation where a patient is experiencing severe bronchospasm, which causes constriction and narrowing of the airways. By using heliox, the airflow is improved because the lighter gas mixture can more easily pass through obstructed airways, helping to alleviate the respiratory distress associated with such attacks. This results in enhanced gas exchange and can lead to a quicker resolution of symptoms.

In this context, while the other options involve situations where oxygen is crucial for treatment, they do not highlight the specific advantages that heliox brings, particularly under the conditions of severe airway obstruction and difficulty breathing that are characteristic of a severe asthma attack.