The Therapist Is Evaluating a Small Tachypneic Infant Receiving Heliox

The therapist is evaluating a small tachypneic infant receiving heliox mixture 70:30 through an infant hood. Although the SpO₂ has improved, the child shows signs of worsening work of breathing. What is the most probable mechanism to explain this situation?

A) The FiHe is too low in a 70:30 mixture to change work of breathing in this infant.
B) The flow going through the infant hood is inadequate.
C) A greater concentration of helium is present at the top of the hood and away from the infant's nose and mouth.
D) The infant is breathing too fast; thus heliox is not reaching the airways.