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letter
. 2020 Dec 1;22(4):391–393. doi: 10.51893/2020.4.rl2r

Figure 1.

Figure 1

Timeline of aerosol concentration detected by Aerodynamic Particle Sizer (APS)* and Mini Wide Range Aerosol Sizer (MiniWRAS)† spectrometers‡

* GRIMM Aerosol Technik, Ainring, Germany. † TSI, Shoreview, MN, USA. ‡ The x-axis has lighter grey, vertical dotted bars indicating 5-minute intervals. Important events are labelled along the timeline as darker, black dashed bars. Pre-oxygenation occurred between bipolar diathermy ending and bronchial intubation. A useful threshold for a significant rise in particle counts is up to 3 standard deviations (99.5%) above the baseline mean of the theatre preparation period with all staff present (Table 1, Activity 2). The horizontal dashed orange line indicates this threshold for the APS measurements, while the light blue dashed line (mixed into the background blue line) represents this for the MiniWRAS measurements. Clearly, only diathermy, bronchial intubation and inadvertent circuit disconnection post-tracheal incision lead to aerosolisation above this background aerosol count. The y-axis gives the number of aerosols per cm-3 (mL), with smaller particles measured by the MiniWRAS spectrometer and larger particles by the APS spectrometer.