Protection of healthcare workers during aerosol-generating procedures with local exhaust ventilation

Abstract

Editor—During the Severe Acute Respiratory Syndrome Coronavirus-1 (SARS-CoV-1) epidemic, performing tracheal intubation and noninvasive ventilation is associated with viral transmission to healthcare workers.1Tran K. Cimon K. Severn M. Pessoa-Silva C.L. Conly J. Aerosol generating procedures and risk of transmission of acute respiratory infections to healthcare workers: a systematic review.PLoS One. 2012; 7e35797Crossref PubMed Scopus (1151) Google Scholar Medical interventions, in particular related to airway management, are classified as aerosol-generating procedures.2Harding H. Broom A. Broom J. Aerosol-generating procedures and infective risk to healthcare workers from SARS-CoV-2: the limits of the evidence.J Hosp Infect. 2020; 105: 717-725Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar To protect healthcare workers during aerosol-generating procedures, the emphasis has been on wearing personal protective equipment.3Public Health EnglandCOVID-19: guidance for the remobilisation of services within health and care settings – infection prevention and control recommendations.https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/954690/Infection_Prevention_and_Control_Guidance_January_2021.pdfDate: 2020Google Scholar Although this is an important measure, eliminating pathogens from room air is a superior intervention according to the US Centers for Disease Control and Prevention.4Kuhar D. Carrico R. Cox K. et al.Infection control in healthcare personnel: infrastructure and routine practices for occupational infection prevention and control services.2019: 1-8https://www.cdc.gov/infectioncontrol/pdf/guidelines/infection-control-HCP-H.pdfGoogle Scholar Air exchange rate is important to decrease aerosol concentrations, but adequate room ventilation is absent in many hospital environments.5Weiland N.H.S. Traversari R.A.A.L. Sinnige J.S. et al.Influence of room ventilation settings on aerosol clearance and distribution.Br J Anaesth. 2021; 126: E49-E52Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar We explored local exhaust ventilation (LEV), an engineering technique used to reduce airborne particle concentration by capturing contaminants or fumes directly at their source.6Flynn M.R. Susi P. Local exhaust ventilation for the control of welding fumes in the construction industry – a literature review.Ann Occup Hyg. 2012; 56: 764-776PubMed Google Scholar Because positioning of the extraction hood is an operator-dependent process, we included different hood positions to determine if this influences aerosol extraction. We hypothesised that LEV reduces aerosol concentration and distribution during a simulated aerosol-generating procedure. The experiments were performed in a resuscitation room in the emergency department of our academic teaching hospital (Supplementary Appendix 1). Room ventilation consisted of a neutral pressure hierarchy towards the hallway and an air exchange rate of 24 changes h−1. We simulated a tracheal intubation setting by positioning a manikin (ALS Simulator, Laerdal, Stavanger, Norway) supine on the patient bed. Two particle counters (model 2016; Lighthouse, Boven-Leeuwen, the Netherlands) were positioned 35 cm above the face: one at the head end of the bed to simulate an intubator and one at 1.5 m away to simulate an assistant. Both counters sampled air at 2.8 L min−1 (0.1 ft3 min−1) and counted particles sized 0.2–10.0 μm, storing data every minute. The LEV unit (UT200.2; ULT AG Umwelt-Lufttechnik, Löbau, Germany) was placed on the left side of the bed and generated a 635 m3 h−1 airflow with a 3200 Pa subatmospheric pressure at the tip of an extraction arm (Alsident 75–6555; Hammel, Denmark). The capturing hood (Square hood 1–754232; Alsident) was positioned near the face of the manikin (Fig. 1 online video). Air drawn in from the manikin facial area passed through a high-efficiency particulate air (HEPA-13) filter, certified to remove >99.95% of airborne particles, and was recirculated into the room. After recording baseline aerosol concentration, we nebulised normal saline into the manikin trachea for 10 min using a jet nebulizer (MaxiNeb® Duo; Medisize-Flexicare, Hoofddorp, the Netherlands). This was repeated three times for each of the following capturing hood positions: (i) vertically on the chest, (ii) at a 45° angle above the chest, and (iii) horizontally above the face (Supplementary Appendix 1). A sequence of three measurements was obtained during aerosol dispersal with the local exhaust ventilator switched off. Aerosol concentration was allowed to return to baseline after each measurement. All equipment was remotely operated and data were stored digitally for offline analysis. Room doors remained closed and no people were present in the room during the experiments. MATLAB (R2018b; MathWorks, Inc., Natick, MA, USA) and SigmaPlot (version 12.5; Systat Software, Inc., San Jose, CA, USA) were used for data analysis. Data for particles ≥0.2 μm were used because SARS-CoV-2 aerosols are of similar aerodynamic diameter (0.25–0.5 and >2.5 μm).7Liu Y. Ning Z. Chen Y. et al.Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals.Nature. 2020; 582: 557-560Crossref PubMed Scopus (1125) Google Scholar Data from three measurements were synchronised and averaged per minute. Descriptive statistics were mean (standard deviation [sd]). To detect a change in aerosol concentration during dispersal, we performed analysis of variance for repeated measurements with post hoc Tukey testing, if applicable. P-values <0.05 indicated statistical significance. If an increase in aerosol concentrations was observed, we rejected the hypothesis that LEV can effectively eliminate aerosols from the room with the hood in that position. Based on data from an earlier project,5Weiland N.H.S. Traversari R.A.A.L. Sinnige J.S. et al.Influence of room ventilation settings on aerosol clearance and distribution.Br J Anaesth. 2021; 126: E49-E52Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar assuming a baseline aerosol concentration of 0.5 (sd 0.2)×106 m−3 and accepting a power of 90%, a sample size of three measurements was sufficient to detect a two-fold increase in aerosol concentration with a significance level of 0.05 (Z-test). Aerosol concentration with the LEV enabled ranged between 0.6 (0.1) and 1.1 (0.1)×106 m−3 before and during aerosol emission, independent of various hood positions (Fig. 1). When the LEV was switched off, baseline aerosol concentrations were 3.3 (1.9) at bedside vs 3.4 (1.7)×106 m−3 at 1.5 m away. These increased to 11 (4.6) vs 12 (4.6)×106 m−3 during aerosol emission, respectively (P<0.001; Fig. 1). The results indicate that LEV effectively reduced exposure during a simulated aerosol-generating procedure independent of the position of the extraction hood. We conclude that LEV is a useful tool to protect healthcare workers from airborne pathogens. Other modalities to prevent aerosol dispersion during aerosol-generating procedures have been reported, in particular the ‘aerosol box’, a barrier that can be placed over the head of the patient during aerosol-generating procedure. However, contrary to what the name might suggest, this does not protect healthcare workers against infectious aerosols.8Sorbello M. Rosenblatt W. Hofmeyr R. Greif R. Urdaneta F. Aerosol boxes and barrier enclosures for airway management in COVID-19 patients: a scoping review and narrative synthesis.Br J Anaesth. 2020; 125: 880-894Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar Furthermore, adding an extra layer of complexity during aerosol-generating procedures might be time consuming and induce hypoxaemia in patients with COVID-19 and respiratory distress.9Begley J.L. Lavery K.E. Nickson C.P. Brewster D.J. The aerosol box for intubation in coronavirus disease 2019 patients: an in-situ simulation crossover study.Anaesthesia. 2020; 75: 1014-1021Crossref PubMed Scopus (152) Google Scholar,10Lim Z.J. Ponnapa Reddy M. Karalapillai D. Shekar K. Subramaniam A. Impact of an aerosol box on time to tracheal intubation: systematic review and meta-analysis.Br J Anaesth. 2021; 126: e122-e125Abstract Full Text Full Text PDF PubMed Scopus (16) Google Scholar Upgrading room ventilation to decrease the removal time of airborne pathogens5Weiland N.H.S. Traversari R.A.A.L. Sinnige J.S. et al.Influence of room ventilation settings on aerosol clearance and distribution.Br J Anaesth. 2021; 126: E49-E52Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar is probably more effective, but may require extensive engineering measures. Local exhaust ventilation offers several advantages. Firstly, it captures airborne particles directly at the source, and therefore reduces aerosol removal time in the room to zero. Secondly, because capturing hood positioning is not critical, it does not add much complexity to a potentially stressful procedure. Thirdly, a wide array of quality-controlled LEV equipment is already available, which limits the risk of designing a custom-made solution. Lastly, a mobile LEV device gives the opportunity to perform aerosol-generating procedures in rooms with low air exchange rates. This could prevent transporting patients to suitable environments, and hence delay of acutely necessary care. Two limitations need to be addressed. Firstly, people were absent in the room during the experiments, and their movements could create turbulence and thereby influence aerosol behaviour. This was necessary because people shed aerosols and particle counters are unable to distinguish these from nebulised saline. To approximate a real-world situation with turbulent airflow, we performed the experiment in a room equipped with a mixing-type ventilation system. Secondly, aerosols from normal saline were used, not from SARS-CoV-2. We do not expect that this influenced the results, because the aerodynamic diameter of SARS-CoV-2 aerosols is similar to the aerosols we used.7Liu Y. Ning Z. Chen Y. et al.Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals.Nature. 2020; 582: 557-560Crossref PubMed Scopus (1125) Google Scholar The authors thank Marco Scholten for technical assistance with the measurements. The authors declare that they have no conflicts of interest. 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