Demonstration and Mitigation of Aerosol and Particle Dispersion During Mastoidectomy Relevant to the COVID-19 Era

Abstract

Background: COVID-19 has become a global pandemic with a dramatic impact on healthcare systems. Concern for viral transmission necessitates the investigation of otologic procedures that use high-speed drilling instruments, including mastoidectomy, which we hypothesized to be an aerosol-generating procedure.

Methods: Mastoidectomy with a high-speed drill was simulated using fresh-frozen cadaveric heads with fluorescein solution injected into the mastoid air cells. Specimens were drilled for 1-minute durations in test conditions with and without a microscope. A barrier drape was fashioned from a commercially available drape (the OtoTent). Dispersed particulate matter was quantified in segments of an octagonal test grid measuring 60 cm in radius.

Results: Drilling without a microscope dispersed fluorescent particles 360 degrees, with the areas of highest density in quadrants near the surgeon and close to the surgical site. Using a microscope or varying irrigation rates did not significantly reduce particle density or percent surface area with particulate. Using the OtoTent significantly reduced particle density and percent surface area with particulate across the segments of the test grid beyond 30 cm (which marked the boundary of the OtoTent) compared with the microscope only and no microscope test conditions (Kruskall-Wallis test, p = 0.0066).

Conclusions: Mastoidectomy with a high-speed drill is an aerosol-generating procedure, a designation that connotes the potential high risk of viral transmission and need for higher levels of personal protective equipment. A simple barrier drape significantly reduced particulate dispersion in this study and could be an effective mitigation strategy in addition to appropriate personal protective equipment.

FIG. 1

Aerosolization of fluorescent bone dust and droplets occurs during mastoidectomy. A, The aerosol plume created by using a high-speed otologic drill to perform a cortical mastoidectomy is visible in a darkened room under ultraviolet light. Surgeon is using a size 6 cutting bur, at 70,000 RPM, on a cadaveric specimen. See Supplemental Video 1 {Aerosolization of fluorescent droplets and bone particulate from cortical mastoidectomy is demonstrated on a cadaveric specimen under an ultraviolet light in a darkened room. The OtoTent preparation and use with the microscope is shown.}. B, Fluorescent debris (some indicated by green arrowheads) soiling a surgeon's chest, arms, and lap is shown under ultraviolet light after drilling part of a cortical mastoidectomy for 2 minutes, with size 6 cutting bur, at 70,000 RPM. C, Image showing fluorescent particulate matter scattered on the surgeon's face shield and hair covering (green arrowheads) after 2 minutes of drilling.

FIG. 2

Experimental setup. A, Octagonal grid created to define distances and locations of particulate debris from the ear canal. The inner octagon has a radius of 30 cm and the outer octagon has a radius of 60 cm. The cadaveric head specimen was placed in the center (red dotted circle). Segments of the grid are numbered (small black font), and quadrants are labeled (large blue font) for reference in the text. B, Sample aerial photo of grid under ultraviolet light with the cadaveric specimen marked by the “X”. C, Sample close-up photo of one segment of the grid with numerous fine fluorescent particles, representing bone dust or fluorescein stained droplets.

FIG. 3

Preparing the OtoTent. A, Sketch of an opened 1,060 3 M drape. The central 10 × 12.5 cm portion of the drape is backed in adhesive. B, Sketch showing how a hole is cut in the adhesive portion of the drape to allow for the microscope lens. C, Photo of the OtoTent in position on the microscope, with the edge of the drape lifted. The microscope oculars (blue arrowheads), microscope lens (yellow arrow), and cadaveric specimen (X) are marked for orientation.

FIG. 4

Positioning and using the OtoTent. A, The drape was secured at cardinal points 30 cm away from the EAC of the specimen using adhesive tape: superior, inferior, posterior, and anterior (red arrowheads). B, Photo of surgeon operating under the OtoTent. Black arrowheads indicate the positions of the hands underneath the drape. C, Photo of the underside of the OtoTent after drilling for 60 seconds. The edge of the drape is lifted up to show the fluorescent particles densely adherent to the underside of the drape (green arrowheads). The microscope lens (yellow arrow) and cadaveric specimen (X) are marked for orientation. EAC indicates external auditory canal.

FIG. 5

Heat map of the surface density of fluorescent particles found in each grid segment after each test condition. A, Simulation without the microscope shows a predominance of particles in the quadrants closest to the surgeon (quadrants 1 and 2—see Fig. 2A for quadrant labeling). There is also particulate dispersion away from the surgeon, illustrating the importance of considering strategies that offer protection to nearby operating room staff. B, The addition of the microscope still results in particulate dispersion that is highest in quadrants 1 and 2 (adjacent to the surgeon), and also still demonstrates particulate dispersion away from the surgeon (potentially toward other operating room staff). C, Simulation with the OtoTent (blue dotted lines) shows decreased particulate matter in all areas, including both the inner and outer octagons. Note the OtoTent drape was fixed at four cardinal points at a radius of 30 cm, thus enclosing the inner octagon on the grid. Note that particulate surface density is close to zero in the surrounding outer octagon, outside the OtoTent barrier.

FIG. 6

Quantifying fluorescent particles under three test conditions: no microscope, microscope, and microscope + OtoTent. in terms of particle surface density (A) and percent (%) surface area covered by particles (B). The mean of the inner semicircle (segments 1–4) and outer semicircle (segments 5–8) is shown, with standard error bars. There was no significant difference in either particle surface density or % area covered when the inner semicircle segments were compared. The OtoTent condition showed significantly decreased particle surface density and % area covered when the outer semicircle was compared to the no microscope and microscope conditions. Particulate dispersion as a function of distance from the EAC (C, D) is shown based on a subanalysis of a single triangular wedge of the octagonal grid (segments 2 and 4). For both microscope and no microscope conditions, the particulate surface density and % area covered began to decrease beyond 40 cm from the EAC but were still present at 60 cm from the EAC. In the OtoTent condition, measured particulate density and % area approach zero beyond the OtoTent, which was fixed at a 30 cm radius. Down-pointing arrow denotes the location of the perimeter of the OtoTent at 30 cm away from the EAC.

FIG. 7

Modified OtoTent (dotted blue outline) use in the operating room for a lateral skull base surgery. The setup shown here is similar, but not identical, to the experimental setup for the OtoTent. After a standard sterile microscope drape (+) was placed, a 9 cm diameter circle was cut out of the incise area of the 1,060 drape and the drape was attached to the lens mount of the Leica M525 OH4 microscope. The drape was then secured to the table with staples, and one portion of it was tucked into an otologic irrigation collection bag. Two small slits (one indicated with black arrow) were cut to accommodate the surgeon's arms. The otologic drill and suction irrigator passed underneath the drape. An additional barrier sheet (∗) was hung to partition the surgical field from anesthesiologist.