Exhalation Spreading During Nasal High-Flow Therapy at
Different Flow Rates
by Dellweg, Dominic; Kerl, Jens; Gena, Amayu Wakoya; Alsaad,
Hayder; Voelker, Conrad
Critical Care Medicine: July 2021 -
Volume 49 - Issue 7 - p e693-e700
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.
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