A quantitative evaluation of aerosol generation during tracheal intubation and extubation

Abstract

We read with great interest the article by Brown et al. [1]. It posits that tracheal intubation and extubation should not be considered high‐risk aerosol‐producing procedures. We agree that with effective neuromuscular blockade during rapid sequence induction, tracheal intubation is unlikely to produce a large number of infectious aerosols. This study also included a small number of patients who required repeated attempts at intubation. These patients still produced a low number of aerosols suggesting that, even with prolonged airway instrumentation time, appropriate tracheal intubating conditions minimise the risk of aerosol production. The lack of aerosol generation during facemask ventilation is surprising and may be related to the patient population studied. In practice, the majority of critically ill COVID‐19 patients requiring tracheal intubation are likely to be obese and challenging to adequately mask ventilate. For these patients, if we presume there will be more leakage around the facemask seal, the degree of aerosol generation is likely to be increased as well. The authors note some of the study limitations, specifically that the reference cough used was one of the investigators, and that none of the subjects were COVID‐19 positive. A better control would be to take the average of volitional coughs from several individuals. It seems reasonable to assume that patients with respiratory symptoms of COVID‐19 would also have a higher propensity to cough forcefully. Based on the small reference sample (14 tracheal extubations), we cannot assume that coughs during tracheal extubation generate fewer aerosols than volitional coughs. As the authors point out, the use of a sampling funnel can be limiting and does not fully encapsulate the aerosol cloud nature of dispersion. The operating theatre utilised in their study has a very high air exchange rate with 500–650 air changes per hour. This far exceeds the Centers for Disease Control and Prevention recommendations of 15 air changes per hour and 12 for negative pressure rooms [2]. The authors state that they considered the effect of laminar flow on the observations by testing measurements with ventilation on and off, and did not notice any difference in particle measurement during coughing and tracheal intubation. However, they maintained high laminar flow rates during all tracheal extubations for pragmatic reasons. Aerosol particles generally follow airflow patterns imposed by ventilation, so it stands to reason that in settings without the same availability of ultraclean theatre ventilation air supply rates, particle measurements will be much higher [3]. Based on the above concerns, we believe that broad recommendations to relax personal protective equipment standards, continue elective surgery in the event of a second wave, and reduce our level of vigilance, would be premature at this juncture.