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 FIO2can be adjusted to between 0.21 and 1.0. With adults, humidification and actual FIO2are known to vary according to inspiratory and HFNC gas flow, tidal volume (VT), and ambient temperature. There have been few studies focused on humidification and FIO2in 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 FIO2in a neonate/infant simulation.


METHODS
HFNC gas flow was set at 3, 5, and 7 L/min, and FIO2was 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 VTsettings 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 FIO2were 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 (P< .001). When the incubator was turned off, as gas flow increased, AH increased (P< .001); however, VTdid not affect AH (P= .16). As gas flow increased, actual FIO2more closely corresponded to set FIO2. When gas flow was 3 L/min, measured FIO2decreased proportionally more at each FIO2setting increment (P< .001).


CONCLUSIONS
AH was affected by ambient temperature and HFNC gas flow. Actual FIO2depended on VTwhen gas flow was 3 L/min.
Medical Equipment Center, Tokushima University Hospital, 2-50-1 Kuramoto, Tokushima 770-8503, Japan.
Yusuke
Y
Chikata
Faculty of Medicine, Tokushima University, 3-18-15 Kuramoto, Tokushima 770-8503, Japan.
Saki
S
Ohnishi
Critical Care and Emergency Medicine, Tokushima University Graduate School, 3-18-15 Kuramoto, Tokushima 770-8503, Japan. nmasaji@tokushima-u.ac.jp.
Masaji
M
Nishimura
D000072601:Cannula; D006801:Humans; D006813:Humidity; D007223:Infant; D007231:Infant, Newborn; D001239:Inhalation; D008953:Models, Anatomic; D010100:Oxygen / Q000032:analysis*; D010102:Oxygen Inhalation Therapy / Q000295:instrumentation / Q000379:methods*; D013696:Temperature; D013990:Tidal Volume
D010100:Oxygen
HFNC; gas flow; humidification; hygrometer; oxygen analyzer; oxygen therapy; spontaneous breathing