The therapist is about to administer a bronchodilator to a patient who is experiencing an asthma flare. Which of the following gases or gas mixtures offers the opportunity to deliver more of the bronchodilator through this patient's obstructed airways?

A. 100% oxygen
B. heliox
C. compressed air
D. nitric oxide

?ANS: B
A. Incorrect response: See explanation B.
B. Correct response: A helium-oxygen mixture (heliox) is less dense than air. Theoretically, heliox has the capability to flow through partial obstructions with less of a velocity increase than air or 100% O2. Any time any gas flows through a partial obstruction, the velocity of the flow increases as the gas traverses the narrowing. However, with heliox, the velocity increase is less because helium is a less dense gas. Consequently, more of the heliox will flow through the partial obstruction to the area distal to that obstruction. The heliox is expected to deliver more of the bronchodilator throughout the lungs of the asthmatic patient.
C. Incorrect response: See explanation B.
D. Incorrect response: See explanation B.