Pressurized Metered Dose Inhaler Aerosol Delivery Within Nasal High-Flow Circuits: A Bench Study

Obstructive patients may benefit from nasal high-flow (NHF) therapy, but the use of pressurized metered-dose inhalers (pMDIs) has not been evaluated in this situation. Using an adult circuit and medium-sized cannula, we have tested different NHF rates, pMDI positions, breathing patterns, spacers, and spacer orientation. First, we evaluated albuterol delivery at the nasal cannula outlet. The second set of experiments made use of a nasopharyngeal cast to estimate the mass of albuterol potentially reaching the lungs. Albuterol was caught on filters placed at the cannula outlet and downstream of the nasal cast, and albuterol was quantified by spectrophotometry. The highest amounts of albuterol delivered at the cannula outlet were observed with a 30 L/min flow rate (vs. 45 and 60 L/min) and placing the device close to the nasal cannula (in comparison with a position on the dry side of the humidification chamber). The use of a spacer was associated with higher delivery. The highest albuterol delivery was observed placing the spacer close to the nasal cannula, oriented for aerosol delivery following the gas flow and a 30 L/min NHF rate. Using this optimal setting, activating the pMDI at the beginning of inspiration (compared to expiration) increased albuterol delivery downstream of the nasopharyngeal cast. Whether in a quiet- or distress-breathing pattern, our measurements showed an amount of albuterol potentially delivered to the lungs exceeding 10% of the actuated dose in optimal conditions. Albuterol delivery with pMDIs is feasible within NHF circuits. Drug delivery sufficient to induce bronchodilation can be achieved using a spacer placed just upstream of the nasal cannula, a low NHF rate, and activation of the pMDI at the beginning of inspiration. Further testing in a clinical setting is required, however.