Droplet and Aerosol Generation With Endonasal Surgery: Methods to Mitigate Risk During the COVID-19 Pandemic

Abstract

Objective: To define the aerosol and droplet risks associated with endonasal drilling and to identify mitigation strategies.

Study design: Simulation series with fluorescent 3-dimensional (3D) printed sinonasal models and deidentified cadaveric heads.

Settings: Dedicated surgical laboratory.

Subjects and methods: Cadaveric specimens irrigated with fluorescent tracer and fluorescent 3D-printed models were drilled. A cascade impactor was used to collect aerosols and small droplets of various aerodynamic diameters under 15 µm. Large droplet generation was measured by evaluating the field for fluorescent debris. Aerosol plumes through the nares were generated via nebulizer, and mitigation measures, including suction and SPIWay devices, nasal sheaths, were evaluated regarding reduction of aerosol escape from the nose.

Results: The drilling of cadaveric specimens without flexible suction generated aerosols ≤3.30 µm, and drilling of 3D sinonasal models consistently produced aerosols ≤14.1 µm. Mitigation with SPIWay or diameter-restricted SPIWay produced same results. There was minimal field contamination in the cadaveric models, 0% to 2.77% field tarp area, regardless of drill burr type or drilling location; cutting burr drilling without suction in the 3D model yielded the worst contamination field (36.1%), followed by coarse diamond drilling without suction (19.4%). The simple placement of a flexible suction instrument in the nasal cavity or nasopharynx led to complete elimination of all aerosols ≤14.1 µm, as evaluated by a cascade impactor positioned immediately at the nares.

Conclusion: Given the findings regarding aerosol risk reduction, we strongly recommend that physicians use a suction instrument in the nasal cavity or nasopharynx during endonasal surgery in the COVID-19 era.

Keywords: COVID-19; aerosol; droplet; endonasal; prevention; safety; skull base.

Figure 1.

Field contamination setup. (A, B) Fluorescent 3-dimensional (3D) model with and without face covering. (C) The 3D model or cadaveric specimen was placed on top of a tarp with 6-inch distances marked. After each 2-minute trial, the tarp was examined for debris. (D) 3D model demonstrating drilling conditions.

Figure 2.

Impactor survey setup. (A) Impactor setup with vacuum generator (black arrow) and flow meter (white arrow). (B) Opened view of Next Generation Impactor (NGI) with aluminum foils in collection chambers. Experimental setup demonstrating nebulizer conditions with 3-dimensional (3D) model (C) and cadaver head (D) with the impactor inlet just inferior and anterior to the nostrils. Experimental setup demonstrating drilling conditions with 3D model (E) and cadaver head (F).

Figure 3.

Representative images of filter foil results from impactor trials. Photographs of removable foil pieces that lined the cascade impactor capture chambers illuminated under UV light for nebulized vitamin B2 trial (positive control; A), cadaver coarse diamond drilling with vitamin B2 irrigation without suction (B), cadaver coarse diamond drilling with vitamin B2 irrigation and suction use (C), 3-dimensional (3D) model cutting burr drilling with nebulized vitamin B2 without suction (D), and 3D model coarse diamond burr drilling with nebulized vitamin B2 without suction (E). Particles filtered based on average aerodynamic diameter into 8 impactor stages are displayed: (1) 14.1 µm, (2) 8.61 µm, (3) 5.39 µm, (4) 3.30 µm, (5) 2.08 µm, (6) 1.36 µm, (7) 0.98 µm, and (8) <0.98 µm.

Figure 4.

Field contamination results. Representative grids and personal protective equipment (PPE) displaying field contamination present on tarp and provider PPE (gown and palmar and dorsal surfaces of gloves), respectively, following each trial. Each grid square represents 6-inch units with the model head oriented on the center of the left border of the grid (A). This scale and orientation were kept consistent across all images. Coarse diamond burr without suction (A) and cutting burr without suction (B) on fluorescent 3-dimensional model. Cutting burr drilling Draf III (C), cutting burr drilling clivus (D), and coarse diamond burr drilling Draf III (E) on cadaver head. All cadaver trials were with suction at the discretion of the surgeon.