• Yosuf W Subat, Todd J Meyer, Keith D Torgerud, Kaiser G Lim, Paul D Scanlon, and Alexander S Niven.
• Division of Pulmonary, Critical Care, and Sleep Medicine, Department of Medicine, Mayo Clinic, Rochester, Minnesota.
• Respir Care. 2022 Aug 1; 67 (8): 899905899-905.

BackgroundMethacholine challenge testing (MCT) is a common bronchoprovocation technique used to assess airway hyper-responsiveness. We previously demonstrated that the addition of a viral filter to the nebulizer exhalation limb substantially reduced expelled particles during MCT. Our aim was to evaluate whether this modification affects the delivered dose of methacholine.MethodsA mechanical ventilator was connected to a lung simulator with breathing frequency 15 breaths/min, tidal volume 500 mL, inspiratory-expiratory ratio 1:1, with a sinusoidal waveform. We compared methacholine dose delivery using the Hudson Micro Mist or AeroEclipse II BAN nebulizers powered by either a dry gas source or a compressor system. A filter placed in line between the nebulizer and test lung was weighed before and after 1 min of nebulized methacholine delivery. Mean inhaled mass was measured with and without a viral filter on the exhalation limb. Dose delivery was calculated by multiplying the mean inhaled mass by the respirable fraction (particles < 5 μm) and inhalation time. Unpaired t test was used to compare methacholine dose delivery with and without viral filter placement.ResultsThe addition of a viral filter did not significantly affect methacholine dose delivery across all devices tested. Using a 50-psi dry gas source, dose delivered with or without a viral filter did not differ with the Hudson (422.3 μg vs 282.0 μg, P = .11) or the AeroEclipse nebulizer (563.0 μg vs 657.6 μg, P = .59). Using the compressor, dose delivered with and without a viral filter did not differ with the Hudson (974.0 μg vs 868.0 μg, P = .03) or the AeroEclipse nebulizer (818.0 μg vs 628.5 μg, P = .42).ConclusionsThe addition of a viral filter to the nebulizer exhalation limb did not affect methacholine dose during bronchoprovocation testing. Routine use of a viral filter should be considered to improve pulmonary function technician safety and infection control measures during the ongoing COVID-19 pandemic.Copyright © 2022 by Daedalus Enterprises.

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