Objectives: Severe 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. Design: Interventional experiment on single breaths of a healthy volunteer. Setting: Research laboratory at the Bauhaus-University Weimar. Subjects: A male subject. Interventions: Videos and images from a schlieren optical system were analyzed during spontaneous breathing and different nasal high-flow rates. Measurements and Main Results: The 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. Conclusions: Nasal 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. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's website (http://journals.lww.com/ccmjournal). Drs. Dellweg and Voelker designed the study. Dr. Kerl, Mr. Gena, and Dr. Alsaad conducted the experiments. Gena and Dr. Voelker analyzed the data acquired from the optical system. Dr. Kerl analyzed the data from the polygraphic system. Dr. Dellweg drafted the article. Drs. Alsaad and Voelker reviewed and edited the article. All authors have read the article and agree with the content. The authors have disclosed that they do not have any potential conflicts of interest. For information regarding this article, E-mail: d.dellweg@fkkg.de This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal. Copyright © by 2021 by the Society of Critical Care Medicine and Wolters Kluwer Health, Inc. All Rights Reserved.
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