• Dominic Dellweg, Jens Kerl, Amayu Wakoya Gena, Hayder Alsaad, and Conrad Voelker.
• Department for Pulmonary and Intensive Care Medicine, Kloster Grafschaft, Schmallenberg, Germany.
• Crit. Care Med. 2021 Jul 1; 49 (7): e693e700e693-e700.

ObjectivesSevere acute respiratory syndrome coronavirus 2 is transmitted through aerosols and droplets. Nasal high-flow therapy could possibly increase the spreading of exhalates from patients. The aim of this study is to investigate whether nasal high-flow therapy affects the range of the expiratory plume compared with spontaneous breathing.DesignInterventional experiment on single breaths of a healthy volunteer.SettingResearch laboratory at the Bauhaus-University Weimar.SubjectsA male subject.InterventionsVideos and images from a schlieren optical system were analyzed during spontaneous breathing and different nasal high-flow rates.Measurements And Main ResultsThe maximal exhalation spread was 0.99, 2.18, 2.92, and 4.1 m during spontaneous breathing, nasal high-flow of 20 L/min, nasal high-flow of 40 L/min, and nasal high-flow of 60 L/min, respectively. Spreading of the expiratory plume in the sagittal plane can completely be blocked with a surgical mask.ConclusionsNasal high-flow therapy increases the range of the expiratory air up to more than 4 meters. The risk to pick up infectious particles could be increased within this range. Attachment of a surgical mask over the nasal high-flow cannula blocks the expiratory airstream.Copyright © 2021 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the Society of Critical Care Medicine and Wolters Kluwer Health, Inc.

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