High-Flow Nasal Cannula (HFNC) in the ED

One problem with nasal cannula; those % numbers mean nothing.

one of the reasons the pulmonologists hate nasal cannula is that there is no way to quantitate what percentage of oxygen the patient is actually inspiring; multiple factors influence this in particular respiratory rate when you mouth breath you generate a venturi effect at the mouth that draws nasal air in as well. How fast you are breathing and how deeply influence and whether your mouth is open effects how much of this air is inhaled and thus the concentration of oxygen

https://onlinelibrary.wiley.com/doi/pdf/10.1111/resp.12268
” Results: The FiO2 increased by 0.038/L/min of oxygen.
Respiratory rate had a significant effect on the FiO2.
A normal respiratory rate of 15 breaths/min and
oxygen supplementation via nasal cannula at 2 L/min
resulted in an FiO2 of 0.296; however, FiO2 decreased by
0.012 at 20 breaths/min and 0.004 at 10 breaths/min.
The mean FiO2 decreased by 0.024 with the mouth
open.The FiO2 and PAO2 were observed to decrease with
increasing VE.
Conclusions: Continuous measurement of the FiO2
using a transtracheal catheter provides detailed insight
into inspiratory changes of the FiO2 delivered by nasal
cannulae. Our study confirms that respiratory rate, VE
and mouth position significantly influence the inspired
oxygen concentration. These parameters should be
accounted for when prescribing oxygen. “