Brown, J

Cook, TM

Pickering, Anthony E

Shrimpton, Andrew J

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                          Shrimpton, A. J., Brown, J., Cook, TM., & Pickering, A. E. (2021).Airway procedures: the importance of distinguishing between high riskand aerosol generation. Anaesthesia, 76(S3), 28-29.https://doi.org/10.1111/anae.15383Peer reviewed versionLink to published version (if available):10.1111/anae.15383Link to publication record in Explore Bristol ResearchPDF-documentThis is the accepted author manuscript (AAM). The final published version (version of record) is available onlinevia Wiley at https://doi.org/10.1111/anae.15383. Please refer to any applicable terms of use of the publisher.University of Bristol - Explore Bristol ResearchGeneral rightsThis document is made available in accordance with publisher policies. Please cite only thepublished version using the reference above. Full terms of use are available:http://www.bristol.ac.uk/red/research-policy/pure/user-guides/ebr-terms/In response to:  JJ Pandit. Reconciling aerosol generation data with actual rates of infection data. Anaesthesia 2020  Authors: Andrew Shrimpton1, Jules Brown2, Tim Cook3, Anthony E. Pickering4  Affiliations:   1 - Anaesthetic Registrar, School of Physiology, Pharmacology & Neuroscience, University of Bristol, Bristol, BS8 1TD. Twitter @_andyshrimp 2 - Consultant, Department of Anaesthesia and Intensive Care Medicine, North Bristol NHS Trust, Bristol, BS10 5NB; Twitter @drjulesbrown 3 - Honorary Professor and Consultant, Department of Anaesthesia and Intensive Care Medicine, Royal United Hospital NHS Trust, Bath, UK. Twitter @doctimcook 4 - Professor of Neuroscience and Anaesthesia, School of Physiology, Pharmacology & Neuroscience, University of Bristol, Bristol, BS8 1TD. Twitter @TonyPi314  Correspondence to: Andrew Shrimpton, School of Physiology, Pharmacology & Neuroscience, University of Bristol, BS8 1TD. Email: Andy.Shrimpton@Bristol.ac.uk.      Airway procedures – the importance of distinguishing between high risk and aerosol generation. Dear Editor We are interested in Pandit’s assessment of the coronavirus-19 (COVID-19) infection risk from intubation [1]. First, we would like to correct a misinterpretation. We note Prof Pandit’s comment regarding our study: “contention of Brown et al. that aerosol‐generating procedures in COVID‐positive patients are safe”.  Our data do not support this statement and we did not make any such assertion. Our study examined the extent (or lack) of aerosol generation during intubation and extubation sequences [2]. We did not examine whether there is an increased risk of infection associated with being present during such procedures in patients infected with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2).  It is important in this discussion to distinguish between whether procedures are ‘aerosol generating’ or whether they increase the risk of disease transmission to healthcare staff (ie are ‘high risk’). Understanding risk associated with clinical practice has been somewhat hampered since the start of the COVID-19 pandemic in part because events and procedures being ‘high-risk’ and ‘aerosol-generating’ have been conflated. The designation of which procedures are deemed both high risk and aerosol generating appear largely based on limited data from the previous severe acute respiratory syndrome (SARS) epidemic [3]. Much of the evidence linking procedures to risk of healthcare infection is derived from retrospective, observational epidemiological studies of poor quality [3]. Importantly, these data also relate to a disease which (like middle eastern respiratory syndrome) has distinctly different viral dynamics from SARS-CoV-2 [4]. The limited data from the SARS epidemic showed an association between being present in the room during tracheal intubation of an infected patient, and a heightened risk of developing infection [3]. At no stage were any aerosols measured. The increased risk of infection associated with being present at the time of intubation during the SARS epidemic may have multiple explanations – only one of which is aerosol generation during the process of tracheal intubation. Healthcare workers whose job required them to enter the rooms of patients sick enough to require tracheal intubation may be exposed to infection risk through a number of other mechanisms including fomite contact before or after intubation, exposure to other procedures or other highly infectious patients, or simply prolonged presence in a high-risk environment.  Our results [2] demonstrated intubation and extubation generate less aerosol than a volitional cough - an event not defined as an aerosol generating procedure, but undoubtedly associated with high levels of aerosol generation [5]. Dhillon et al [6] reported findings some of which were consistent with ours and some of which were in conflict. We have since completed recruitment to a study, using a protocol developed by both groups, which we hope will provide clarity in those areas of previous conflicting results. This joint study focusses specifically on facemask ventilation (rather than tracheal intubation) as this was the main point of divergence in our findings. The intubateCOVID study explored the relationship between involvement in tracheal intubation and subsequent infection or symptoms of COVID-19, but despite its many strengths it showed only associations [7]. Importantly, there was no comparator group to examine whether those not involved with tracheal intubation had equally high rates of infection or symptoms, which is certainly plausible. In the current epidemic, epidemiological evidence suggests the risk of developing SARS-CoV-2 infection is notably higher in frontline healthcare worker groups who do not undertake AGPs compared to those who do [8]. Those involved in anaesthesia and critical care settings have lower rates of infection, hospital admission and deaths than other frontline healthcare staff. This makes it difficult to link risk of infections to tracheal intubation per se, and our study provides supportive evidence in showing low rates of aerosol generation.  The reason it is important to distinguish between infection risk related to medically generated aerosols and infection risk due to other mechanisms, such as close contact with an infected coughing patient, is because appropriate precautions may differ significantly. We believe there is a need to get the fundamentals right and examine whether those procedures currently designated to be ‘aerosol generating procedures’ do indeed create aerosols. This requires direct physical measurement which several studies including ours have now achieved. If procedures such as tracheal intubation do not increase aerosol generation but are associated with an increased risk of healthcare worker infection, then we need to explore other mechanisms to account for this heightened risk.  We can then better decide, in the current pandemic, which medical procedures are designated ‘aerosol generating’, ‘high risk’, both or neither.  References 1. Pandit JJ. Reconciling aerosol generation data with actual rates of infection data. Anaesthesia 2020. Epub 06 December. https://doi.org/10.1111/anae.15330 2. Brown J, Gregson FKA, Shrimpton A, et al. A quantitative evaluation of aerosol generation during tracheal intubation and extubation. Anaesthesia 2020. Epub 22 October. https://doi.org/10.1111/anae.15292. 3. Tran K, Cimon K, Severn M, Pessoa-Silva CL, Conly J. Aerosol generating procedures and risk of transmission of acute respiratory infections to healthcare workers: a systematic review. PLoS One 2012; 7: e35797. 4. Cevik M, Tate M, Lloyd O, Maraolo AE, Schafers J, Ho A. SARS-CoV-2, SARS-CoV, and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis. The Lancet Microbe 2020. https://doi.org/10.1016/S2666-5247(20)30172-5 5. Public Health England. Infection control precautions to minimise transmission of acute respiratory tract infections in healthcare settings 2016. https://www.gov.uk/government/publications/covid-19-personal-protective-equipment-use-for-aerosol-generating-procedures (accessed 14/12/2020). 6. Dhillon RS, Rowin WA, Humphries RS, et al. Aerosolisation during tracheal intubation and extubation in an operating theatre setting. Anaesthesia 2020. Epub 3 November. https://doi.org/10.1111/anae.15301 7. El‐Boghdadly K, Wong DJN, Owen R, et al. Risks to healthcare workers following tracheal intubation of patients with COVID‐19: a prospective international multicentre cohort study. Anaesthesia 2020; 75: 1437-47. 8. Cook TM, Lennane S. Occupational COVID‐19 risk for anaesthesia and intensive care staff – low‐risk specialties in a high‐risk setting. Anaesthesia 2020. Epub 11 December. https://doi.org/10.1111/anae.15358    

Airway procedures:the importance of distinguishing between high risk and aerosol generation

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