Aerosol-generating procedures are medical interventions considered high risk for transmission of airborne pathogens. Tracheal intubation of anaesthetised patients is not high risk for aerosol generation; however, patients often perform respiratory manoeuvres during awake tracheal intubation which may generate aerosol. To assess the risk, we undertook aerosol monitoring during a series of awake tracheal intubations and nasendoscopies in healthy participants. Sampling was undertaken within an ultraclean operating theatre. Procedures were performed and received by 12 anaesthetic trainees. The upper airway was topically anaesthetised with lidocaine and participants were not sedated. An optical particle sizer continuously sampled aerosol. Passage of the bronchoscope through the vocal cords generated similar peak median (IQR [range]) aerosol concentrations to coughing, 1020 (645-1245 [120-48,948]) vs. 1460 (390-2506 [40-12,280]) particles.l-1 respectively, p = 0.266. Coughs evoked when lidocaine was sprayed on the vocal cords generated 91,700 (41,907-166,774 [390-557,817]) particles.l-1 which was significantly greater than volitional coughs (p < 0.001). For 38 nasendoscopies in 12 participants, the aerosol concentrations were relatively low, 180 (120-525 [0-9552]) particles.l-1 , however, five nasendoscopies generated peak aerosol concentrations greater than a volitional cough. Awake tracheal intubation and nasendoscopy can generate high concentrations of respiratory aerosol. Specific risks are associated with lidocaine spray of the larynx, instrumentation of the vocal cords, procedural coughing and deep breaths. Given the proximity of practitioners to patient-generated aerosol, airborne infection control precautions are appropriate when undertaking awake upper airway endoscopy (including awake tracheal intubation, nasendoscopy and bronchoscopy) if respirable pathogens cannot be confidently excluded.

It is unclear if cardiopulmonary resuscitation is an aerosol-generating procedure and whether this poses a risk of airborne disease transmission to healthcare workers and bystanders. Use of airborne transmission precautions during cardiopulmonary resuscitation may confer rescuer protection but risks patient harm due to delays in commencing treatment. To quantify the risk of respiratory aerosol generation during cardiopulmonary resuscitation in humans, we conducted an aerosol monitoring study during out-of-hospital cardiac arrests. Exhaled aerosol was recorded using an optical particle sizer spectrometer connected to the breathing system. Aerosol produced during resuscitation was compared with that produced by control participants under general anaesthesia ventilated with an equivalent respiratory pattern to cardiopulmonary resuscitation. A porcine cardiac arrest model was used to determine the independent contributions of ventilatory breaths, chest compressions and external cardiac defibrillation to aerosol generation. Time-series analysis of participants with cardiac arrest (n = 18) demonstrated a repeating waveform of respiratory aerosol that mapped to specific components of resuscitation. Very high peak aerosol concentrations were generated during ventilation of participants with cardiac arrest with median (IQR [range]) 17,926 (5546-59,209 [1523-242,648]) particles.l-1 , which were 24-fold greater than in control participants under general anaesthesia (744 (309-2106 [23-9099]) particles.l-1 , p < 0.001, n = 16). A substantial rise in aerosol also occurred with cardiac defibrillation and chest compressions. In a complimentary porcine model of cardiac arrest, aerosol recordings showed a strikingly similar profile to the human data. Time-averaged aerosol concentrations during ventilation were approximately 270-fold higher than before cardiac arrest (19,410 (2307-41,017 [104-136,025]) vs. 72 (41-136 [23-268]) particles.l-1 , p = 0.008). The porcine model also confirmed that both defibrillation and chest compressions generate high concentrations of aerosol independent of, but synergistic with, ventilation. In conclusion, multiple components of cardiopulmonary resuscitation generate high concentrations of respiratory aerosol. We recommend that airborne transmission precautions are warranted in the setting of high-risk pathogens, until the airway is secured with an airway device and breathing system with a filter.

A lack of clinical aerosol evidence for oropharyngeal suctioning has caused uncertainty as to whether it should be designated an ‘aerosol-generating procedure’.1

The evidence base surrounding the transmission risk of 'aerosol-generating procedures' has evolved primarily through quantification of aerosol concentrations during clinical practice. Consequently, infection prevention and control guidelines are undergoing continual reassessment. This mixed-methods study aimed to explore the perceptions of practicing anaesthetists regarding aerosol-generating procedures. An online survey was distributed to the Membership Engagement Group of the Royal College of Anaesthetists during November 2021. The survey included five clinical scenarios to identify the personal approach of respondents to precautions, their hospital's policies and the associated impact on healthcare provision. A purposive sample was selected for interviews to explore the reasoning behind their perceptions and behaviours in greater depth. A total of 333 survey responses were analysed quantitatively. Transcripts from 18 interviews were coded and analysed thematically. The sample was broadly representative of the UK anaesthetic workforce. Most respondents and their hospitals were aware of, supported and adhered to UK guidance. However, there were examples of substantial divergence from these guidelines at both individual and hospital level. For example, 40 (12%) requested respiratory protective equipment and 63 (20%) worked in hospitals that required it to be worn whilst performing tracheal intubation in SARS-CoV-2 negative patients. Additionally, 173 (52%) wore respiratory protective equipment whilst inserting supraglottic airway devices. Regarding the use of respiratory protective equipment and fallow times in the operating theatre: 305 (92%) perceived reduced efficiency; 376 (83%) perceived a negative impact on teamworking; 201 (64%) were worried about environmental impact; and 255 (77%) reported significant problems with communication. However, 269 (63%) felt the negative impacts of respiratory protection equipment were appropriately balanced against the risks of SARS-CoV-2 transmission. Attitudes were polarised about the prospect of moving away from using respiratory protective equipment. Participants' perceived risk from COVID-19 correlated with concern regarding stepdown (Spearman's test, R = 0.36, p < 0.001). Attitudes towards aerosol-generating procedures and the need for respiratory protective equipment are evolving and this information can be used to inform strategies to facilitate successful adoption of revised guidelines.

AnaesthesiaEarly View Editorial Aerosols: time to clear the air? A. J. Shrimpton, Corresponding Author A. J. Shrimpton Doctoral Fellow andy.shrimpton@bristol.ac.uk @_andyshrimp orcid.org/0000-0001-6790-909X Anaesthesia, Pain and Critical Care Sciences, School of Physiology, Pharmacology and Neuroscience, University of Bristol, UK Correspondence to: A. J. Shrimpton Email: andy.shrimpton@bristol.ac.ukSearch for more papers by this authorA. E. Pickering, A. E. Pickering Professor @TonyPi314 orcid.org/0000-0003-0345-0456 Anaesthesia, Pain and Critical Care Sciences, School of Physiology, Pharmacology and Neuroscience, University of Bristol, UKSearch for more papers by this author A. J. Shrimpton, Corresponding Author A. J. Shrimpton Doctoral Fellow andy.shrimpton@bristol.ac.uk @_andyshrimp orcid.org/0000-0001-6790-909X Anaesthesia, Pain and Critical Care Sciences, School of Physiology, Pharmacology and Neuroscience, University of Bristol, UK Correspondence to: A. J. Shrimpton Email: andy.shrimpton@bristol.ac.ukSearch for more papers by this authorA. E. Pickering, A. E. Pickering Professor @TonyPi314 orcid.org/0000-0003-0345-0456 Anaesthesia, Pain and Critical Care Sciences, School of Physiology, Pharmacology and Neuroscience, University of Bristol, UKSearch for more papers by this author First published: 14 September 2022 https://doi.org/10.1111/anae.15864 This editorial accompanies an article by Hecker et al. Anaesthesia 2022; 77: 1097–1105. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Early ViewOnline Version of Record before inclusion in an issue RelatedInformation

Background: Open respiratory suctioning is defined as an aerosol generating procedure (AGP). Laryngopharyngeal suctioning, used to clear secretions during anaesthesia, is widely managed as an AGP. However, it is uncertain whether upper airway suctioning should be designated as an AGP due to the lack of both aerosol and epidemiological evidence. Aim: To assess the relative risk of aerosol generation by upper airway suctioning during tracheal intubation and extubation in anaesthetized patients. Methods: This prospective environmental monitoring study was undertaken in an ultraclean operating theatre setting to assay aerosol concentrations during intubation and extubation sequences, including upper airway suctioning, for patients undergoing surgery (N=19). An optical particle sizer (particle size 0.3-10 mm) sampled aerosol 20 cm above the patient's mouth. Baseline recordings (background, tidal breathing and volitional coughs) were followed by intravenous induction of anaesthesia with neuromuscular blockade. Four periods of laryngopharyngeal suctioning were performed with a Yankauer sucker: pre-laryngoscopy, post-intubation, pre-extubation and post-extubation. Findings: Aerosol was reliably detected {median 65 [interquartile range (IQR) 39-259] particles/L} above background [median 4.8 (IQR 1-7) particles/L, P<0.0001] when sampling in close proximity to the patient's mouth during tidal breathing. Upper airway suctioning was associated with a much lower average aerosol concentration than breathing [median 6.0 (IQR 0-12) particles/L, P=0.0007], and was indistinguishable from background (P>0.99). Peak aerosol concentrations recorded during suctioning [median 45 (IQR 30-75) particles/L] were much lower than during volitional coughs [median 1520 (IQR 600-4363) particles/L, P<0.0001] and tidal breathing [median 540 (IQR 300-1826) particles/L, P<0.0001]. Conclusion: Upper airway suctioning during airway management was not associated with a higher aerosol concentration compared with background, and was associated with a much lower aerosol concentration compared with breathing and coughing. Upper airway suctioning should not be designated as a high-risk AGP. 2022 The Author(s). Published by Elsevier Ltd on behalf of The Healthcare Infection Society. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

We were interested in Professor Pandit's assessment of the COVID-19 infection risk from intubation [1]. First, we would like to correct a misinterpretation. We note Professor 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 tracheal 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 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 (i.e. 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 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 tracheal intubation, exposure to other procedures or other highly infectious patients, or simply prolonged presence in a high-risk environment. Our results [2] demonstrated that tracheal 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 previously conflicting results. This joint study focuses specifically on facemask ventilation (rather than tracheal intubation) as this was the main point of divergence in our findings. The intubate COVID 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 aerosol-generating procedures compared with 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.

SummaryManual facemask ventilation, a core component of elective and emergency airway management, is classified as an aerosol generating procedure. This designation is based on a single epidemiological study suggesting an association between facemask ventilation and transmission from the SARS 2003 outbreak. There is no direct evidence to indicate whether facemask ventilation is a high-risk procedure for aerosol generation. We conducted aerosol monitoring during routine facemask ventilation, and facemask ventilation with an intentionally generated leak, in anaesthetised patients with neuromuscular blockade. Recordings were made in ultraclean theatres and compared against the aerosol generated by the patient’s own tidal breathing and coughs. Respiratory aerosol from tidal breathing was reliably detected above the very low background particle concentrations (191 (77-486 [3.8-1313]) versus 2.1 (0.7-4.6 [0-12.9] particles.l-1 median(IQR)[range], n=11, p=0.002). The average aerosol concentration detected during facemask ventilation both without a leak (3.0 particles.l-1 (0 – 9 [0-43])) and with an intentional leak (11 particles.l-1 (7.0 – 26 [1-62])) was 64-fold and 17-fold lower than that of tidal breathing (p=0.001 and p=0.002 respectively). The peak particle concentration during facemask ventilation both without a leak (60 particles.l-1 (0 – 60 [0-120])) and with a leak (120 particles.l-1 (60 – 180 [60-480]) were respectively 20-fold and 10-fold lower than a cough (1260 particles (800 – 3242 [100-3682]), p=0.002 and p=0.001 respectively). This study demonstrates that facemask ventilation, even performed with an intentional leak, does not generate high levels of bioaerosol. On the basis of this evidence, facemask ventilation should not be considered an aerosol generating procedure.

SummaryMany guidelines consider supraglottic airway use to be an aerosol‐generating procedure. This status requires increased levels of personal protective equipment, fallow time between cases and results in reduced operating theatre efficiency. Aerosol generation has never been quantitated during supraglottic airway use. To address this evidence gap, we conducted real‐time aerosol monitoring (0.3–10‐µm diameter) in ultraclean operating theatres during supraglottic airway insertion and removal. This showed very low background particle concentrations (median (IQR [range]) 1.6 (0–3.1 [0–4.0]) particles.l−1) against which the patient’s tidal breathing produced a higher concentration of aerosol (4.0 (1.3–11.0 [0–44]) particles.l−1, p = 0.048). The average aerosol concentration detected during supraglottic airway insertion (1.3 (1.0–4.2 [0–6.2]) particles.l−1, n = 11), and removal (2.1 (0–17.5 [0–26.2]) particles.l−1, n = 12) was no different to tidal breathing (p = 0.31 and p = 0.84, respectively). Comparison of supraglottic airway insertion and removal with a volitional cough (104 (66–169 [33–326]), n = 27), demonstrated that supraglottic airway insertion/removal sequences produced <4% of the aerosol compared with a single cough (p < 0.001). A transient aerosol increase was recorded during one complicated supraglottic airway insertion (which initially failed to provide a patent airway). Detailed analysis of this event showed an atypical particle size distribution and we subsequently identified multiple sources of non‐respiratory aerosols that may be produced during airway management and can be considered as artefacts. These findings demonstrate supraglottic airway insertion/removal generates no more bio‐aerosol than breathing and far less than a cough. This should inform the design of infection prevention strategies for anaesthetists and operating theatre staff caring for patients managed with supraglottic airways.

The potential aerosolised transmission of severe acute respiratory syndrome coronavirus-2 is of global concern. Airborne precaution personal protective equipment and preventative measures are universally mandated for medical procedures deemed to be aerosol generating. The implementation of these measures is having a huge impact on healthcare provision. There is currently a lack of quantitative evidence on the number and size of airborne particles produced during aerosol-generating procedures to inform risk assessments. To address this evidence gap, we conducted real-time, high-resolution environmental monitoring in ultraclean ventilation operating theatres during tracheal intubation and extubation sequences. Continuous sampling with an optical particle sizer allowed characterisation of aerosol generation within the zone between the patient and anaesthetist. Aerosol monitoring showed a very low background particle count (0.4 particles.l(-1)) allowing resolution of transient increases in airborne particles associated with airway management. As a positive reference control, we quantitated the aerosol produced in the same setting by a volitional cough (average concentration, 732 (418) particles.l(-1), n = 38). Tracheal intubation including facemask ventilation produced very low quantities of aerosolised particles (average concentration, 1.4 (1.4) particles.l(-1), n = 14, p < 0.0001 vs. cough). Tracheal extubation, particularly when the patient coughed, produced a detectable aerosol (21 (18) l(-1), n = 10) which was 15-fold greater than intubation (p = 0.0004) but 35-fold less than a volitional cough (p < 0.0001). The study does not support the designation of elective tracheal intubation as an aerosol-generating procedure. Extubation generates more detectable aerosol than intubation but falls below the current criterion for designation as a high-risk aerosol-generating procedure. These novel findings from real-time aerosol detection in a routine healthcare setting provide a quantitative methodology for risk assessment that can be extended to other airway management techniques and clinical settings. They also indicate the need for reappraisal of what constitutes an aerosol-generating procedure and the associated precautions for routine anaesthetic airway management.