Background

Optimal HFNC flow rates in children < 3 yrs HFNC (high flow nasal canula) has become an essential method of respiratory support in patients with hypoxemic respiratory therapy. It has shown significant benefit in children with bronchiolitis and decreasing the need for invasive mechanical ventilation. When deciding to place a young pediatric patient on HFNC, what flow rates should we be starting at and at what point should we begin to think about escalating the method of respiratory support?

Study: Weiler, T et al. The Relationship Between HFNC Flow Rate and Effort of Breathing in Children. Journal of Pediatrics. 2017; 189:66-71.

Methods: Single-center prospective observation study that enrolled 21 patients (3 years and younger) who were receiving HFNC. Esophageal pressure probes and respiratory inductance plethysmography bands were placed in order to calculate respiratory rate and peak to trough change in esophageal pressure. The measurements allowed them to calculate the pressure rate product (PRP) which is a previously validated metric of patient effort of breathing. Measurements were recorded at 0.5, 1.0, 1.5 and 2.0 L/kg/min with max flow rate of 30 L/min. Measurements were taken twice daily while on HFNC.

Results/Conclusions: The study achieved their goal sample size of 20 patients. A dose dependent relationship was observed between increasing flow rate and greater percentage change in PRP from baseline. The greatest reduction was seen at 2 L/kg/minutes. Patients < 8 kg had the largest improvement in breathing effort. The smallest difference was seen between 1.5 and 2 L/kg/min suggesting a plateauing effect and patients that have little improvement on 2 L/kg/min may require escalation of respiratory support.

Take Home Point: In young pediatric patients with hypoxemic respiratory failure, HFNC can decrease the need for invasive mechanical ventilation. Starting at or titrating to a flow rate of 2 L/kg/minute (max of 30 L/min) may provide the maximum benefit and patients requiring rates higher than this, may benefit more from CPAP, Bilevel or invasive mechanical ventilation.