Effort of Breathing in Children Receiving High-Flow Nasal Cannula

Objective: High-flow humidified nasal cannula is often used to provide noninvasive respiratory support in children. The effect of high-flow humidified nasal cannula on effort of breathing in children has not been objectively studied, and the mechanism by which respiratory support is provided remains unclear. This study uses an objective measure of effort of breathing (Pressure. Rate Product) to evaluate high-flow humidified nasal cannula in critically ill children. Design: Prospective cohort study. Setting: Quaternary care free-standing academic children's hospital. Patients: ICU patients younger than 18 years receiving high-flow humidified nasal cannula or whom the medical team planned to extubate to high-flow humidified nasal cannula within 72 hours of enrollment. Interventions: An esophageal pressure monitoring catheter was placed to measure pleural pressures via a Bicore CP-100 pulmonary mechanics monitor. Change in pleural pressure (Delta Pes) and respiratory rate were measured on high-flow humidified nasal cannula at 2, 5, and 8L/min. Delta Pes and respiratory rate were multiplied to generate the Pressure.Rate Product, a well-established objective measure of effort of breathing. Baseline Pes, defined as pleural pressure at end exhalation during tidal breathing, reflected the positive pressure generated on each level of respiratory support. Measurements and Main Results: Twenty-five patients had measurements on high-flow humidified nasal cannula. Median age was 6.5 months (interquartile range, 1.3-15.5 mo). Median Pressure,Rate Product was lower on high-flow humidified nasal cannula 8L/min (median, 329 cm H2O.min; interquartile range, 195-402) compared with high-flow humidified nasal cannula 5L/min (median, 341; interquartile range, 232-475; p = 0.007) or high-flow humidified nasal cannula 2L/min (median, 421; interquartile range, 233-621; p < 0.0001) and was lower on high-flow humidified nasal cannula 5L/min compared with high-flow humidified nasal cannula 2L/min (p = 0.01). Baseline Pes was higher on high-flow humidified nasal cannula 8L/min than on high-flow humidified nasal cannula 2L/min (p = 0.03). Conclusions: Increasing flow rates of high-flow humidified nasal cannula decreased effort of breathing in children, with the most significant impact seen from high-flow humidified nasal cannula 2 to 8L/min. There are likely multiple mechanisms for this clinical effect, including generation of positive pressure and washout of airway dead space.