Background:We have observed that clinicians believe there is a difference in oxygen delivery between a standard low-flow nasal cannula (LFNC) and one labeled for high-flow use (HFNC), independent of the oxygen flow setting. In particular, for cannulas made by Westmed, the LFNC is recommended (depending on distributor) for flows of 1–5 L/min, while the HFNC is recommended for flows of 6–15 L/min. Hence, clinicians have come to believe that you need to use different cannulas depending on the desired oxygen flow. The purpose of this study was to test this assumption by comparing FIO2 delivery for LFNC and HFNC over the range of 1–15 L/min. Methods:An adult mannequin head (Michigan Instruments) was attached to a breathing simulator (IngMar ASL 5000) which is capable of measuring lung FIO2. The simulator was set to closed-loop volume control mode with VT = 490 mL, C = 50 mL/cm H2O, R = 4 cm H2O/L/s, f = 15, increase = 25%, hold = 0%, release = 30%. LFNC (Westmed 0556) and HFNC (Westmed 0549) were attached to the nares of the mannequin (mouth opening blocked) and run at 5, 10, and 15 L/min (verified with a Citrix H4 flow meter). The experiment was repeated once. Conclusions:This study shows that the assumption of needing different types of cannulas depending on flow is false. FIO2 depends only on source oxygen flow, not cannula design for this manufacturer.
Sorg et al. (Fri,) studied this question.