BACKGROUND: Heated, humidified, high-flow nasal cannula oxygen therapy (HHHFNC) 
has been used to improve ventilation in preterm infants. There are no data on 
airway pressures generated and efficacy in bronchiolitis.
OBJECTIVE: The objective of this study was to determine nasopharyngeal (NP) 
pressures generated with HHHFNC therapy in bronchiolitis.
METHODS: We conducted a prospective, observational study to measure NP pressures 
at varying flow rates of HHHFNC therapy in moderate to severe bronchiolitis. 
Vital signs, bronchiolitis severity scores, and oxygen saturation were also 
noted.
RESULTS: Twenty-five patients were enrolled (mean, 78.1 [SD, 30.9] days; weight, 
5.3 [SD, 1.1] kg). Nasopharyngeal pressures increased linearly with flow rates 
up to 6 L/min. Beyond 6 L/min, pressure increase was linear but less 
accelerated. On average, NP pressure increased by 0.45 cm H2O for each 1-L/min 
increase in flow rate. There were significant differences between pressures in 
open- and closed-mouth states for flow rates up to 6 L/min. At 6 L/min, the 
pressure in open-mouth state was 2.47 cm H2O and that in closed-mouth state was 
2.74 cm H2O (P < 0.001). Linear regression analysis revealed that only flow (not 
weight or gender) had an effect on generated pressure. Bronchiolitis severity 
scores improved significantly with HHHFNC therapy (pre: 14.5 [SD, 1.4], post: 
10.4 [SD, 1.2]; P < 0.001).
CONCLUSIONS: Increasing flow rates of HHHFNC therapy are associated with linear 
increases in NP pressures in bronchiolitis patients. Larger studies are needed 
to assess the clinical efficacy of HHHFNC therapy in bronchiolitis.