Use of a high-flow extractor to reduce aerosol exposure in tracheal intubation

Editor—Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission is thought to be through fomites, droplets, and droplet nuclei (aerosols).¹ Aerosol-generating medical procedures are commonly performed and are associated with increased risk of infection of healthcare workers.² Some clinicians are using barriers such as transparent plastics and Plexiglas boxes to reduce aerosol spread.3, 4, 5, 6, 7 However, these barriers may limit access to the patient and mobility of the clinician.⁸ An alternative to barriers that may reduce aerosol spread is directed high flow air extraction. A high flow air extractor combines high flow suction and a high-efficiency particulate (HEPA) filter. We conducted a study to determine if high flow air extraction reduces aerosol exposure of clinicians. We designed an experimental model that determined the efficacy of removal of particles similar in size to human aerosols. We used two particles to simulate aerosols, essential oil particles ranging in size from 1 nm to 1 μm, and ISO 12103-1 A1 Ultrafine test dust (Powder Technologies Inc., Arden Hills, MN, USA) ranging in size from 1 to 20 μm. We simulated human breathing using an essential oil diffuser as a continuous aerosol source.

Human cough aerosols range in size from 0.58 to 5.42 μm with 80% in the 0.74–2.12 μm range.⁹ For coughing experiments, a manikin (Electripod ET/J10 Tracheal Intubation model; TUQI, Shanghai, China) was used (Supplementary 1a, b). We applied 500 mg of A1 Ultrafine test dust to the oropharynx and distal trachea of the manikin and simulated a cough using a medical air gun connected to the distal trachea and fired for 0.4 s. The researchers placed their hand 2–3 cm from the mouth of the manikin to simulate a covered cough. The high-flow air extractor Epurair HA-500 (Industrie Orkan Inc., Montreal, Quebec, Canada) was placed 25–30 cm above the manikin's head.

We quantified aerosols with the following sensors (Supplementary 1a, b). Two dust aerosol calibrated DustTrak DRX (TSI, Shoreview, MN, USA) units using four chambers placed near the source and the clinician's head. Two wide-range aerosol spectrometers, miniWRAS 1371 (Grimm Aerosol Technik, Ainring, Germany) each with 41 bins and calibrated to an oil aerosol were similarly placed. To determine the vertical and horizontal variation in concentrations, 10 DC1700 optical particle monitors (Dylos, Riverside, CA, USA) were placed at predetermined positions (Supplementary 1a, b). To eliminate inter-monitor variation, monitors were co-located for 10 min after the experiments and reported concentrations corrected by the deviation from the mean concentration of each monitor. The high-flow air extractor is a portable high efficiency filtration unit allowing up to 235 L s⁻¹ (500 ft³ min⁻¹) that can be used to transform a regular room into a negative pressure room. It contains a HEPA filter that removes 99.97% of all airborne pathogens of 0.3 μm or greater. The filtered air can be adapted to an existing exhaust system or vented outside. We operated the device with a calibrated booster fan to maintain a continuously measured flow of 142 L min⁻¹ for the experiments (Supplementary 2). Each experiment was completed in triplicate, and mean concentration values were used for analysis.

Our primary outcome was to determine the reduction of aerosols at the source. A 99% reduction in the aerosol concentration near the source would be consistent with the Centre for Disease Prevention and Control's (CDC) requirements for air exchanges between patient encounters.¹⁰ Secondary outcomes included reduction of aerosol concentrations at the level of the clinician's head with the high-flow air extractor ‘on’ during a cough and an obstructed cough. The effectiveness, H, was calculated by subtracting the ratio of ‘high-flow air extractor on’ to ‘high-flow air extractor off’ mean particle concentration measured by each aerosol quantification device from unity.

The high-flow extractor device was 99% effective at removing aerosols near the source, resulting in no levels detected at the clinician's head (Fig. 1 a and Supplementary 3 online video). During an uncovered cough, the high-flow extractor had a 97% effectiveness in reducing the aerosols detected near the clinician's head (Fig. 1b). In these first two scenarios, aerosols were effectively removed at source and did not contaminate the room or reach the clinician's head. However, when the cough was covered by the provider's hand there was only a 52% reduction in aerosols detected at the clinician's head; the absolute concentration was very low because of less aerosols reaching the clinician's head as a result of covering the cough (Fig. 1c). The covered cough resulted in a higher concentration of aerosols at sensors placed lateral to the patient (Supplementary 4). This was likely because aerosols were diverted away from the device's intake but subsequently reached the clinician's head. The effectiveness of the high-flow air extractor was high for larger particles (>1 μm) emitted from the simulated cough, and generally low for small particles (<1 μm) (Supplementary 5a, b).

Fig 1.

Particle concentration measurements from the two DustTrak DRX units near the source (NS) and clinician's head (HH) with the high flow extractor (HFE) turned on and off. Calculated HFE effectiveness is labelled on top of each pair of boxes/bars during (a) essential oil diffuser test; (b) simulated cough test; (c) simulated covered cough test. In (a), the boxes represent the first and third quartiles, the line in the boxes represents the median, the whiskers represent 1.5 times the inter-quartile range. Concentrations outside of the whiskers are excluded for visual clarity. In (b) and (c), the bars represent the mean concentrations during the tests.

Supplementary video related to this article can be found at https://doi.org/10.1016/j.bja.2020.07.014

The following is the supplementary data related to this article:

Supplement 3

Video depicting a sample of the experiments. If reading the pdf online, click on the image to view the video.

Our study shows that a high-air flow extractor is effective in removing aerosols during simulated continuous breathing and a simulated cough. However, simply covering a cough with a gloved hand resulted in the escape of aerosols and subsequent detection at the clinician's head.

Removal of aerosols may enhance the safety of healthcare workers and improve operational efficiencies. Currently, a minimal air exchange rate of 15–20 h⁻¹ is recommended for operating room air decontamination. At this rate 18–28 min is required to reduce airborne contaminants by 99%.¹⁰ This delay causes workflow inefficiencies and the extractor can be used to accelerate air decontamination.

A limitation of this study is the difference between airflows in the test environment and actual operating rooms. Compared with the test environment, operating rooms have higher air exchange rates (15–20 vs 0.75 h⁻¹), which may cause turbulence, interfere with the extractor exhaust plume, and decrease capture efficiency. We have shown that the high-flow air extractor is highly effective at reducing aerosol concentrations at the source. This has potentially large-scale implications for clinical practice and warrants translation into high-risk clinical areas in order to minimise clinician exposure. Furthermore, this technique is consistent with current recommendations from the CDC to augment room air exchanges.

Authors' contributions

Conceptualisation: CM, TE, VC, PF, JF

Methodology: CM, TE, VC, PF, JS, SD

Visualisation: CM, TE, VC, PF, JS, TL, BD

Software: PF, JS, TL, BD

Analysis: PF, JS, TL, BD

Original draft preparation: CM, TE, VC, PF, JS, SD, TL, BD

Review and editing of the manuscript: CM, TE, VC, PF, JS, SD, TL, BD, JF

Declarations of interest

The authors declare no that they have no conflicts of interest.

Funding

National Sciences and Engineering Research Council of Canada (Grant RGPIN-2014-06698) and the Canada Foundation for Innovation (Grant 32319) to JS.

Appendix A. Supplementary data

The following are the Supplementary data to this article:

Supplement 1.

Experiment layout and particle monitor location. (a) Bird's eye view of experimental setup. (b) Perspective view of experimental setup.

Supplement 2.

Depiction of placement of high air flow extraction device over the manikin.

Supplement 4.

The spatial spread of aerosol during each experiment. (a) continuous breathing – essential oil diffuser, (b) simulated cough, (c) covered simulated cough.

Supplement 5.

Particle concentration measurements from the two DustTrak DRX units near the source (NS) and clinician's head (HH) with the high flow extractor (HFE) turned on and off with calculated HFE effectiveness labelled on top of each pair of boxes/bars during (a) simulated cough test and (b) simulated covered cough test. There is little difference in the clearance of particle sizes PM₁ (particles with an aerodynamic diameter less than 0.1 μm) and PM_2.5, (particles with an aerodynamic diameter less than 2.5 μm).