Effects of Flow, Cannula and Circuit Size on Aerosol Delivery Via High-Flow Nasal Cannula in a Pediatric Model

Abstract

Background: Use of high-flow nasal cannula (HFNC) as an interface to deliver aerosol has gained significant interest over the past few years. Recent studies have investigated factors influencing aerosol delivery in infant, toddler and adult models, however, data in older pediatric models is lacking. In older children, extra-large pediatric or small adult size HFNC cannulas may be appropriate, but cannula and circuit size may impact aerosol delivery. The aim of this study was to compare aerosol delivery using two different cannula and circuit sizes at varying flows in a simulated pediatric model. Methods: A pediatric training manikin (TruCorp) with an anatomically correct airway of a 6-year-old, was connected to a breathing simulator (ASL 5000, Ingmar Medical) via a collecting filter at the level of the carina to simulate a spontaneously breathing child weighing approximately 20-25 kg (V_T 150 mL, RR 28, I:E 1:2.5, peak insp flow 23.8 L/min). Two HFNC configurations were tested; 1) Junior - Optiflow junior breathing circuit (RT330) + XL junior 2 nasal cannula (OJR418), and 2) Adult – adult breathing circuit (RT280) + Optiflow small adult nasal cannula (OPT942) all by Fisher & Paykel Healthcare. A vibrating mesh nebulizer (Aerogen Solo, Aerogen) was placed at the inlet of the humidifier (F&P 850) set at 37 C. 5 mg albuterol (2 mg/mL) was nebulized for each condition at nasal cannula flows of 3, 6, and 12 L/min (n = 3). Drug was eluted from filters and assayed via UV spectrophotometry (276 nm). Dependent T-test and One-way ANOVA used for statistical analysis. Results: Aerosol deposition was greatest at 3 L/min regardless of HFNC configuration, P < .05. At 3 L/min there was no significant difference in the inhaled dose between configurations (adult 12.6 ± 0.5% vs junior 10.1 ± 1.8%, P = .08). But, at 6 and 12 L/min, inhaled dose was greater in the adult versus junior configuration (10.5 ± 1.1% vs 6.5 ± 1.0%, P = .009) and (5.7 ± 0.3% vs 2.3 ± 0.6%, P = .001) respectively. Conclusions: In this simulated pediatric model, aerosol delivery through HFNC was greatest at lower flows regardless of HFNC configuration. At higher flows, aerosol deposition was significantly increased with the larger cannula and circuit.