Question addressed by studyAdministration of aerosol to patients receiving high flow nasal oxygen (HFNO) ranges from concurrent aerosol delivery by mouthpiece to aerosol via cannula alone. This study examines the conditions to provide optimal aerosol delivery with low or high flow nasal oxygen with concurrent mouthpiece or through nasal cannula alone, and the impact on fugitive aerosols.Materials and MethodsA vibrating mesh nebulizer delivered salbutamol via mouthpiece, aerosol holding chamber and nasal cannula to an adult head model simulating relaxed breathing. The inhaled dose (%) (mean±sd) was assayed from a filter distal to the trachea. Optical particle sizers were used to measure fugitive aerosol concentrations during aerosol delivery.ResultsConcurrent low flow nasal oxygen (LFNO) and aerosol delivery with a mouthpiece and aerosol holding chamber increased the inhaled dose (%) available, 31.44±1.33% when supplemented with 2 LPM of nasal oxygen. Concurrent HFNO above 30 LPM resulted in a lower inhaled dose (%) compared to aerosol delivered through HFNO alone. The addition of concurrent low or high flow nasal oxygen resulted in no increase in aerosol levels in the test room.Answer to question posedConcurrent low flow nasal oxygen with a mouthpiece and aerosol holding chamber is an effective and safe means of aerosol delivery.

There are variations in the values reported for aerosol drug delivery across in vitro experiments throughout the published literature, and often with the same devices or similar experimental setups. Factors contributing to this variability include, but are not limited to device type, equipment settings, drug type and quantification methods. This study assessed the impact of head model choice on aerosol drug delivery using six different adults and three different paediatric head models in combination with a facemask, mouthpiece, and high-flow nasal cannula. Under controlled test conditions, the quantity of drug collected varied depending on the choice of head model. Head models vary depending on a combination of structural design differences, facial features (size and structure), internal volume measurements and airway geometries and these variations result in the differences in aerosol delivery. Of the widely available head models used in this study, only three were seen to closely predict in vivo aerosol delivery performance in adults compared with published scintigraphy data. Further, this testing identified the limited utility of some head models under certain test conditions, for example, the range reported across head models was aerosol drug delivery of 2.62 ± 2.86% to 37.79 ± 1.55% when used with a facemask. For the first time, this study highlights the impact of head model choice on reported aerosol drug delivery within a laboratory setting and contributes to explaining the differences in values reported within the literature.

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