Abstract
(1) Background: Aerosol delivery via high-flow nasal cannula (HFNC) has attracted increasing clinical interest. In vitro studies report that the ratio of HFNC gas flow to patient inspiratory flow (GF:IF) is a key factor in the efficiency of trans-nasal aerosol delivery. (2) Methods: In a randomized controlled trial, patients with a history of COPD or asthma and documented positive responses to inhaled bronchodilators in an outpatient pulmonary function laboratory were recruited. Subjects were randomized to receive inhalation at gas flow ratio settings of: GF:IF = 0.5, GF:IF = 1.0, or GF = 50 L/min. Subjects were assigned to inhale saline (control) followed by salbutamol via HFNC with cumulative doses of 0.5 mg, 1.5 mg, 3.5 mg, and 7.5 mg. Spirometry was performed at baseline and 10-12 min after each inhalation. (3) Results: 75 subjects (49 asthma and 26 COPD) demonstrating bronchodilator response were enrolled. Per the robust ATS/ERS criteria no difference was observed between flows, however using the criteria of post-bronchodilator forced expiratory volume in the first second (FEV(1)) reaching the screening post-bronchodilator FEV(1) with salbutamol, a higher percentage of subjects receiving GF:IF = 0.5 met the criteria at a cumulative dose of 1.5 mg than those receiving GF:IF = 1.0, and GF = 50 L/min (64% vs. 29% vs. 27%, respectively, p = 0.011). Similarly at 3.5 mg (88% vs. 54% vs. 46%, respectively, p = 0.005). The effective dose at GF:IF = 0.5 was 1.5 mg while for GF = 50 L/min it was 3.5 mg. (4) Conclusions: During salbutamol delivery via HFNC, cumulative doses of 1.5 mg to 3.5 mg resulted in effective bronchodilation. Applying the robust ATS/ERS criteria no difference was observed between the flows, however using the more sensitive criteria of subjects reaching post screening FEV(1) to salbutamol via HFNC, a higher number of subjects responded to the doses of 0.5 mg and 1.5 mg when HFNC gas flow was set at 50% of patient peak inspiratory flow.