Differential impact of flow and mouth leak on oropharyngeal humidification during high-flow nasal cannula: a neonatal bench study.

Background: Heated humidification is paramount during neonatal high-flow nasal cannula (HFNC) therapy. However, there is little knowledge about the influence of flow rate and mouth leak on oropharyngeal humidification and temperature.

Methods: The effect of the Optiflow HFNC on oropharyngeal gas conditioning was investigated at flow rates of 4, 6 and 8 L min with and without mouth leak in a bench model simulating physiological oropharyngeal air conditions during spontaneous breathing. Temperature and absolute humidity (AH) were measured using a digital thermo-hygrosensor.

Results: Without mouth leak, oropharyngeal temperature and AH increased significantly with increasing flow (P < 0.001). Mouth leak did not affect this increase up to 6 L min, but at 8 L min, temperature and AH plateaued, and the effect of mouth leak became statistically significant (P < 0.001).

Conclusions: Mouth leak during HFNC had a negative impact on oropharyngeal gas conditioning when high flows were applied. However, temperature and AH always remained clinically acceptable.