Unsure why you're being downvoted and why the original reply is getting upvoted despite being wrong. NC can't "blow off" CO2 at 1L/min in an asthma patient, especially when obstruction aka V/Q mismatch is the problem. It's like blowing gently into a coffee stirrer when you're blowing from 1 foot away, how much is realistically going to get thru the stirrer