Comparison of FIO 2 Delivery With Low Flow vs High Flow Cannulas: A Simulation Study

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 V_T = 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.

Results:

The difference in FIO₂ (%) between LFNC and HFNC was clinically unimportant (see Table).

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.

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