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      Exhaled air dispersion and use of oronasal masks with continuous positive airway pressure during COVID-19

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      1 , 2 , 3
      European Respiratory Review
      European Respiratory Society

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          Abstract

          We applaud F erioli et al. [1] for their review of practical measures that can be taken to help protect healthcare workers from severe acute respiratory syndrome-coronavirus-2 infection. We urge caution in interpreting data from table 1, which lists maximum air dispersion distance with a variety of oxygen administration and ventilatory support strategies. Reporting that continuous positive airway pressure (CPAP) via oronasal mask at 20 cmH 2O has negligible air dispersion is potentially misleading. Much of the data from this table is derived from a series of studies by H ui and co-workers [2–5], in which a human patient simulator was used to model exhaled air dispersion with a variety of supportive devices. With this model, the group measured exhaled air dispersion using a laser to detect particles in distinct zones; the median and paramedian sagittal planes, i.e. directly in front of the simulator. To measure dispersion while wearing CPAP, they measured a specific oronasal mask (Quattro Air, ResMed Inc.), which contains exhaust vent holes that are evenly distributed circularly around the elbow connection point of the air tubing. Thus, exhaled air exits the mask in a continuous, circumferential flow. It is unsurprising that no distinct air jet could be measured in the median sagittal plane ( i.e. in the midline, in front of the patient) since airflow is: 1) diverted diffusely (rather than a directed jet); and 2) circumferential (more laterally) with this mask design. The authors noted that the circumferential nature of the exhaust holes was the likely reason that they could not measure an exhaled jet.

          Abstract

          Caution is advised regarding the recently published conclusion that use of oronasal masks with CPAP has negligible room contamination via exhaled air dispersion of SARS-CoV-2 viral particles https://bit.ly/39cC4m8

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          Most cited references5

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          Protecting healthcare workers from SARS-CoV-2 infection: practical indications

          The World Health Organization has recently defined the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection a pandemic. The infection, that may cause a potentially very severe respiratory disease, now called coronavirus disease 2019 (COVID-19), has airborne transmission via droplets. The rate of transmission is quite high, higher than common influenza. Healthcare workers are at high risk of contracting the infection particularly when applying respiratory devices such as oxygen cannulas or noninvasive ventilation. The aim of this article is to provide evidence-based recommendations for the correct use of “respiratory devices” in the COVID-19 emergency and protect healthcare workers from contracting the SARS-CoV-2 infection.
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            Exhaled air dispersion during high-flow nasal cannula therapy versus CPAP via different masks

            High-flow nasal cannula (HFNC) is an emerging therapy for respiratory failure but the extent of exhaled air dispersion during treatment is unknown. We examined exhaled air dispersion during HFNC therapy versus continuous positive airway pressure (CPAP) on a human patient simulator (HPS) in an isolation room with 16 air changes·h −1 . The HPS was programmed to represent different severity of lung injury. CPAP was delivered at 5–20 cmH 2 O via nasal pillows (Respironics Nuance Pro Gel or ResMed Swift FX) or an oronasal mask (ResMed Quattro Air). HFNC, humidified to 37°C, was delivered at 10–60 L·min −1 to the HPS. Exhaled airflow was marked with intrapulmonary smoke for visualisation and revealed by laser light-sheet. Normalised exhaled air concentration was estimated from the light scattered by the smoke particles. Significant exposure was defined when there was ≥20% normalised smoke concentration. In the normal lung condition, mean± sd exhaled air dispersion, along the sagittal plane, increased from 186±34 to 264±27 mm and from 207±11 to 332±34 mm when CPAP was increased from 5 to 20 cmH 2 O via Respironics and ResMed nasal pillows, respectively. Leakage from the oronasal mask was negligible. Mean± sd exhaled air distances increased from 65±15 to 172±33 mm when HFNC was increased from 10 to 60 L·min −1 . Air leakage to 620 mm occurred laterally when HFNC and the interface tube became loose. Exhaled air dispersion during HFNC and CPAP via different interfaces is limited provided there is good mask interface fitting.
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              Exhaled Air Dispersion During Noninvasive Ventilation via Helmets and a Total Facemask

              BACKGROUND Noninvasive ventilation (NIV) via helmet or total facemask is an option for managing patients with respiratory infections in respiratory failure. However, the risk of nosocomial infection is unknown. METHODS We examined exhaled air dispersion during NIV using a human patient simulator reclined at 45° in a negative pressure room with 12 air changes/h by two different helmets via a ventilator and a total facemask via a bilevel positive airway pressure device. Exhaled air was marked by intrapulmonary smoke particles, illuminated by laser light sheet, and captured by a video camera for data analysis. Significant exposure was defined as where there was ≥ 20% of normalized smoke concentration. RESULTS During NIV via a helmet with the simulator programmed in mild lung injury, exhaled air leaked through the neck-helmet interface with a radial distance of 150 to 230 mm when inspiratory positive airway pressure was increased from 12 to 20 cm H2O, respectively, while keeping the expiratory pressure at 10 cm H2O. During NIV via a helmet with air cushion around the neck, there was negligible air leakage. During NIV via a total facemask for mild lung injury, air leaked through the exhalation port to 618 and 812 mm when inspiratory pressure was increased from 10 to 18 cm H2O, respectively, with the expiratory pressure at 5 cm H2O. CONCLUSIONS A helmet with a good seal around the neck is needed to prevent nosocomial infection during NIV for patients with respiratory infections.
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                Author and article information

                Journal
                Eur Respir Rev
                Eur Respir Rev
                ERR
                errev
                European Respiratory Review
                European Respiratory Society
                0905-9180
                1600-0617
                30 September 2020
                19 August 2020
                19 August 2020
                : 29
                : 157
                : 200144
                Affiliations
                [1 ]EvalStat Research Institute (EVALRI), Palo Alto, CA, USA
                [2 ]Center for Sleep and Circadian Neurobiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
                [3 ]Division of Sleep Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
                Author notes
                Shannon S. Sullivan, EvalStat Research Institute, 3430 West Bayshore, Palo Alto, CA 94303, USA. E-mail: shannon.gaffey@ 123456gmail.com
                Article
                ERR-0144-2020
                10.1183/16000617.0144-2020
                8050613
                32817116
                ddf4c0ce-ec27-47bf-bead-1871c5446fef
                Copyright ©ERS 2020.

                This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial Licence 4.0.

                History
                : 20 May 2020
                : 16 July 2020
                Categories
                Correspondence
                4

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