A quantitative evaluation of aerosol generation during tracheal intubation and extubation

Abstract

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.

Keywords: COVID-19; SARS-COV-2; aerosol-generating procedure; extubation; intubation.

Figure 1

Simulation of aerosol measurement approach within operating theatre environment. The sampling funnel was positioned 0.5 m above the source of aerosol in the airway management zone allowing a sampling stream of air (1 l.min⁻¹) to be routed to the optical particle sizer.

Figure 2

Aerosol measurements during intubation and extubation in operating theatre environment. (a) Temporal profile of aerosol generation from volitional coughs. Individual recordings (n = 38) represented on heat map showing the total number particle concentration over time. Average time course plotted (mean with 95%CI) showing a peak after 2 s and a rapid decay back to baseline. (b) Profile of the total number concentration of aerosol detected during the critical phase of intubation (arrow at 300 s marks completion of intubation with cuff up). When plotted on the same scale as the cough (b) then this looks essentially flat and when shown on a ten‐fold expanded scale below it can be seen that it is not significantly different to baseline as the confidence intervals always span zero (mean ± 95%CI). (c) Extubation recordings from each patient (n = 10) plotted as the average and individually as rows on heat map of number concentration of particles (lower, on same scale as b). This showed sporadic aerosol events (red, ringed) after cuff deflation set on a low baseline level of particles. The average concentration of aerosol shown above was low overall (mean ± 95%CI). (d) The extubation cough events (n = 5) had a similar aerosol particle size distribution to volitional coughs with a predominance of diameters < 1 µm (mean ± SD). (e) The extubation coughs were of a smaller magnitude than the volitional coughs (particle number concentration profile shown overlaid, mean ± 95%CI).