Abstract
Trans-nasal aerosol deposition during distressed breathing is higher than quiet breathing, and decreases as administered gas flow increases. We hypothesize that inhaled dose is related to the ratio of gas flow to patient inspiratory flow (GF:IF). An adult manikin (Laerdal) with a collecting filter placed at trachea was connected to a dual-chamber model lung, which was driven by a ventilator to simulate quiet and distressed breathing with different inspiratory flows. Gas flow was set at 5, 10, 20, 40 and 60 L/min. Albuterol (2.5mg in 1 mL) was nebulized by vibrating mesh nebulizer at the inlet of humidifier at 37 °C for each condition (n = 3). Drug was eluted from the filter and assayed with UV spectrophotometry (276 nm). GF:IF was the primary predictor of inhaled dose (p < 0.001). When the ratio was < 1.0, the inhaled dose was higher than ratio > 1.0 (21.8 ± 3.8% vs. 9.0 ± 3.7%, p < 0.001), and the inhaled dose was similar between quiet and distressed breathing (22.3 ± 5.0% vs. 21.3 ± 2.7%, p = 0.379). During trans-nasal aerosol delivery, GF:IF primarily affected the inhaled dose. Compared to the ratio above 1.0, the ratio below 1.0 produced a higher and more-consistent inhaled dose.
Highlights
High-flow nasal cannula (HFNC) is primarily a method of oxygen administration, in which gas flow exceeds patient inspiratory flow [1]
During quiet breathing (RR = 15 bpm, I:E = 1:2, Ti = 1.33s), inhaled dose increased as nasal cannula gas flow decreased (p < 0.001), with greatest deposition at the lowest flow of 5 L/min
With inspiratory flows of 13.5, 22.5 and 31.5 L/min, the inhaled dose increased as the inspiratory flow increased at all nasal cannula gas flow settings (p = 0.027) (Figure 2a)
Summary
High-flow nasal cannula (HFNC) is primarily a method of oxygen administration, in which gas flow exceeds patient inspiratory flow [1]. Aerosol with HFNC has been described with bronchodilators for asthmatic [2], bronchiolitis [3,4], or chronic obstructive pulmonary disease (COPD) patients [5,6,7], and inhaled epoprostenol for patients with pulmonary hypertension or hypoxemia [8]. For patients who need long durations of aerosol administration, such as inhaled epoprostenol for pulmonary hypertension [8] or bronchodilator for refractory asthmatics [2], the use of traditional interfaces such as mask or mouth piece is complicated by lack of patient comfort and tolerance. HFNC has been described as a feasible route to deliver continuous aerosolized medication; clinical observations report that pediatric patients appear more comfortable and less anxious during bronchodilator nebulization via HFNC than mask or mouthpiece [3,4]
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