Exhalation Spreading During Nasal High-Flow Therapy at Different Flow Rates

Crit Care Med. 2021 Jul 1;49(7):e693-e700. doi: 10.1097/CCM.0000000000005009.


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.

MeSH terms

  • Adult
  • Cannula*
  • Disease Transmission, Infectious / prevention & control
  • Exhalation*
  • Healthy Volunteers
  • Humans
  • Male
  • Microscopy, Video
  • Oxygen Inhalation Therapy / methods*
  • Pulmonary Ventilation*
  • Respiratory Rate
  • Tidal Volume