The therapist is using an O2 flowmeter set at 15 L/minute to deliver an 80-20 helium-oxygen gas mixture. Calculate the actual flow that the patient is receiving

A. 8 L/minute
B. 12 L/minute
C. 18 L/minute
D. 27 L/minute

ANS: D
A. Incorrect response: See explanation D.
B. Incorrect response: See explanation D.
C. Incorrect response: See explanation D.
D. Correct response: When an 80-20 heliox mixture flows through an O2 flowmeter, the therapist must multiply the flow indicated on the flowmeter by 1.8 to determine the actual flow of heliox the patient is receiving. An O2 flowmeter is calibrated for O2 mixtures only, and not for heliox. Therefore an O2 flowmeter set at 15 L/minute will deliver about 27 L/minute of heliox to the patient, that is,
15 L/minute × 1.8 = 27 L/minute
The factor for a 70-30 heliox mixture is 1.6, and for 60-40 is 1.4.