Humidity and Inspired Oxygen Concentration During High-Flow Nasal Cannula Therapy in Neonatal and Infant Lung Models.

BACKGROUND

High-flow nasal cannula therapy (HFNC) for neonate/infants can deliver up to 10 L/min of heated and humidified gas, and F can be adjusted to between 0.21 and 1.0. With adults, humidification and actual F are known to vary according to inspiratory and HFNC gas flow, tidal volume (V), and ambient temperature. There have been few studies focused on humidification and F in HFNC settings for neonates/infants, so we performed a bench study to investigate the influence of gas flow, ambient temperature, and respiratory parameters on humidification and actual F in a neonate/infant simulation.

METHODS

HFNC gas flow was set at 3, 5, and 7 L/min, and F was set at 0.3, 0.5, and 0.7. Spontaneous breathing was simulated using a 2-bellows-in-a-box model of a neonate lung. Tests were conducted with V settings of 20, 30, and 40 mL and breathing frequencies of 20 and 30 breaths/min. Inspiratory time was 0.8 s with decelerating flow waveform. The HFNC tube was placed in an incubator, which was either set at 37°C or turned off. Absolute humidity (AH) and actual F were measured for 1 min using a hygrometer and an oxygen analyzer, and data for the final 3 breaths were extracted.

RESULTS

At all settings, when the incubator was turned on, AH was greater than when it was turned off ( < .001). When the incubator was turned off, as gas flow increased, AH increased ( < .001); however, V did not affect AH ( = .16). As gas flow increased, actual F more closely corresponded to set F . When gas flow was 3 L/min, measured F decreased proportionally more at each F setting increment ( < .001).

CONCLUSIONS

AH was affected by ambient temperature and HFNC gas flow. Actual F depended on V when gas flow was 3 L/min.