Calculation of air change rates and post-aerosol pause times for a COVID-19 airway management enclosure
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CORRESPONDENCE
Calculation of air change rates and post-aerosol pause times for a COVID-19 airway management enclosure Andrew D. Milne, MD BEng MSc PEng MS PEng . J. Adam Law, MD
. Matthew I. d’Entremont, BEng
Received: 8 June 2020 / Revised: 12 June 2020 / Accepted: 13 June 2020 Ó Canadian Anesthesiologists’ Society 2020
To the Editor, Numerous enclosures have been developed to contain aerosols and reduce the risk of coronavirus disease (COVID-19) transmission to healthcare providers during airway management. These enclosures can function as a mechanical barrier to droplets and aerosols, but adding a filtered suction source may further reduce the exposure risk by evacuating the working space during airway management. Simulations with Glo-germ1 or smoke2 have qualitatively assessed the use of suction to evacuate these enclosures, and particle counters have been utilized to quantify aerosol removal.3 The United States Centers for Disease Control and Prevention (CDC) recommends a minimum of 15 air changes per hour (ACH) for operating rooms and 12 ACH for negative pressure rooms. It also specifies the times required to purge airborne contaminants from these rooms.4 At present, there are no standard ventilation requirements for COVID-19 containment enclosures and no studies have calculated the ACH or airborne contaminant removal times4 within such enclosures. We sought to quantify the flow rates induced A. D. Milne, MD BEng MSc PEng (&) Department of Anesthesia, Pain Management and Perioperative Medicine, Dalhousie University, Halifax, NS, Canada e-mail: [email protected] School of Biomedical Engineering, Dalhousie University, Halifax, NS, Canada M. I. d’Entremont, BEng MS PEng Nova Scotia Product Design and Development Centre, Dalhousie University, Halifax, NS, Canada J. Adam Law, MD Department of Anesthesia, Pain Management and Perioperative Medicine, Dalhousie University, Halifax, NS, Canada
by application of suction to a COVID-19 airway management enclosure and used these measurements to calculate the ACH and theoretical times for airborne contaminant removal.4 A prototype enclosure was developed for airway management in COVID-19 patients (Figure). The enclosure was evacuated using a suction line connected to a filter and a manifold pipe. Measurements were taken to determine the flow rates delivered by common suction sources available in the operating room. Flow rate testing was performed using a Puritan Bennett PTS 2000 ventilator tester (Mallinckrodt Inc, St Louis, MO, USA) placed in line with each suction source. Standard anesthesia machine and surgical canister suction sources with their associated pressure regulators were tested first. The anesthesia and surgical suction sources were connected with surgical suction tubing (7 mm diameter, 4.6 m long, Medline Industries Inc, Northfield, IL, USA) to the viral filter and manifold pipe. The second option tested was via direct attachment of the viral filter and manifold pipe to a 2.4 m long standard yellow medical vacuum hose and MEDVAC wall outlet suction (Amico
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