key: cord-0973098-55wshnna authors: Kobayashi, Hisato; Takimoto, Takayuki; Kitaoka, Hiroko; Kijima, Takashi title: Aerosol Spread with Use of High-Flow Nasal Cannula: A Computational Fluid Dynamics Analysis date: 2020-06-13 journal: J Hosp Infect DOI: 10.1016/j.jhin.2020.06.010 sha: e849c05b8c9da881eb09db407e07598cf0043ced doc_id: 973098 cord_uid: 55wshnna nan Regarding the use of high-flow nasal cannula (HFNC) in COVID-19 patients, although some researchers claim that HFNC is unlikely to contaminate the surroundings, others are strongly concerned about the risk of aerosol spread with HFNC [1], [2] . Hui et al. conducted a study with mannequins and claimed that aerosol spread does not increase if HFNC is properly fitted to the face [3] . On the other hand, Cheung et al. pointed out that the HFNC modes and models in that study differed from widely-used ones, and advised against the use of HFNC for COVID-19 patients [4] . Leonard et al. showed by computational simulation that wearing a surgical mask over the HFNC might reduce the aerosol spread [5] . However, keeping the mask properly fitted is challenging; if the mask comes off, or shifts aside, the aerosol may spread to the surroundings. Aerosols enter the upper airway by the closing-opening movements of the vocal cord during coughing and speaking [6] . A previous study showed that nasal secretory cells are potential targets of SARS-CoV-2 [7] . Therefore, HFNC, which has a CO 2 wash-out effect, may wash out the viruses from the upper airway into the surroundings. No previous study has numerically analysed the distribution of particles diffused in a room during multiple spontaneous breathing (SB) with HFNC. We investigated the aerosol dispersion during SB with and without HFNC using computational fluid dynamics (AcuSolve, Altair Engineering, USA). The analysis was performed in two steps: 1. Preliminary simulation: particle density of the exhaled air from the nostrils was constantly sent from the cannula, and the excess airflow was discharged from the gap. Assuming a particle density in the upper airway wall of 100%, the particle density distribution in the airway was calculated by coupled analysis of Navier-Stokes and diffusion equations (diffusion coefficient: 10 -10 m 2 /s) during breathing. In order to clarify the difference with and without high flow, breathing condition with the mouth closed was analysed. The result was that the average concentration of particles in the nostrils was approximately 58% without HFNC and 80% with HFNC. Furthermore, the total amount of particles discharged during one respiratory cycle was about ten times higher with high flow because the exhaled air volume through the nostrils was extremely increased with high flow. 2. Indoor air simulation: distribution of particles exhaled from the nostrils A 3D model of a room (3.0 m*2.0 m*2.0 m) with ceiling ventilation, a bed, and a human body on the floor was created. The human body was equipped with outlets imitating the nostrils. The same flow rate as in the preliminary simulation was used (SB ± HFNC). In the first analysis, the particle concentration in the nasal cavity increased about 1.5 times with high flow. Although not supported experimentally, this result suggests that reduction of particle concentration due to dilution with high flow does not occur. Considering that the overwhelming air flow rate of HFNC is added to the air flow from the nostril, the effect of change in the particle concentration in the exhaled air on the number of discharged particles can be ignored. Therefore, the second step analysis was performed assuming that the particle concentration in the nostrils was 100% in simulations with/without HFNC. The results are shown in the video. Aerosol spread was more extensive during SB with HFNC than during SB without HFNC, suggesting that medical staff may inhale aerosol strongly recommend avoidance of HFNC as much as possible, and when it is used, that strict precautions against aerosol spreading are employed. TK was responsible for the coordination of the study. HKi was the chief investigator. HKo, TT, HKi and TK developed and check the study design. All authors contributed to the writing of the final manuscript. None. bio-aerosol dispersion COVID-19: Respiratory support outside the intensive care unit Exhaled air dispersion during high-flow nasal cannula therapy versus CPAP via different masks Staff safety during emergency airway management for COVID-19 in Hong Kong Preliminary Findings on Control of Dispersion of Aerosols and Droplets During High-Velocity Nasal Insufflation Therapy Using a Simple Surgical Mask: Implications for the High-Flow Nasal Cannula Aerosol emission and superemission during human speech increase with voice loudness SARS-CoV-2 receptor ACE2 is an interferon-stimulated gene in human airway epithelial cells and is detected in specific cell subsets across tissues This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. [1] Li J, Fink JB, Ehrmann S. High-flow nasal cannula for COVID-19 patients: low risk