In the era of SARS-CoV-2, the risk of infectious airborne aerosol generation during otolaryngologic procedures has been an area of increasing concern. The objective of this investigation was to quantify airborne aerosol production under clinical and surgical conditions and examine efficacy of mask mitigation strategies.
Prospective quantification of airborne aerosol generation during surgical and clinical simulation.
Cadaver laboratory and clinical examination room.
Airborne aerosol quantification with an optical particle sizer was performed in real time during cadaveric simulated endoscopic surgical conditions, including hand instrumentation, microdebrider use, high-speed drilling, and cautery. Aerosol sampling was additionally performed in simulated clinical and diagnostic settings. All clinical and surgical procedures were evaluated for propensity for significant airborne aerosol generation.
Hand instrumentation and microdebridement did not produce detectable airborne aerosols in the range of 1 to 10 μm. Suction drilling at 12,000 rpm, high-speed drilling (4-mm diamond or cutting burs) at 70,000 rpm, and transnasal cautery generated significant airborne aerosols (
Transnasal drill and cautery use is associated with significant airborne particulate matter production in the range of 1 to 10 μm under surgical conditions. During simulated clinical activity, airborne aerosol generation was seen during nasal endoscopy, speech, and sneezing. Intact or VENT-modified N95 respirators mitigated airborne aerosol transmission, while standard surgical masks did not.
The COVID-19 pandemic has catalyzed an unparalleled disruption in the provision of health care around the world. Following its detection in December 2019, health policy shifted from an initial strategy of containment to mitigation.
Rhinologic cases are of unique concern in this reopening phase. Delays in elective care do appear to be associated with worse outcomes
The purpose of this study was to therefore (1) quantify airborne aerosol production following endonasal instrumentation during cadaveric surgical and clinical diagnostic conditions and (2) determine the relative efficacy of source control solutions.
The surgical simulation was Institutional Review Board approved through a formal excess tissue protocol. The clinical simulation was reviewed by the Partner’s Human Research Committee director and performed under the Quality Improvement Initiative at Massachusetts Eye and Ear; as such, it was not required to be formally supervised by the Institutional Review Board per its policies. All cadaver experiments in this study were performed in a dedicated surgical laboratory with 2 fresh-frozen head specimens at room temperature. The clinical examination room (111 sq ft) and the surgical laboratory (726 sq ft) were equipped with air exchangers operating at a rate of 6 total air changes per hour.
Aerosol sampling was performed with an optical particle sizer (OPS 3330; TSI Inc), which measures particle number, concentration, and size distribution with single particle–counting technology up to a size of 10 μm. Flow rate through the OPS 3330 is a constant 1.0 L/min via a 3-mm port. Particle size distribution is measured in 16 user-adjustable channels. Total particle counts by size over a period of timed data were collected.
The cadaver head was placed in a supine position with the nostril situated 15 cm from the optical particle sizer (OPS) intake port (
Surgical simulation: (A) Experimental setup (arrow denotes intake port). (B) Aerosol generation after 2 to 5 minutes. ***
Participants were seated upright in a clinical room examination chair with the naris placed 15 cm from the OPS intake port (
Clinical simulation: (A) Experimental setup (arrow denotes intake port). (B) Airborne aerosol generation during simulated clinical conditions. (C) Airborne particle generation under sneeze conditions with various source controls. *
Following behavioral simulation, participants then performed additional simulated sneezing every 10 seconds for 30-second replicates with the opening of the mouth positioned 15 cm from the OPS intake port while wearing (1) a standard level 1 surgical mask (Halyard Health), (2) N95 Health Care Particulate Respirator and Surgical Mask (1860; 3M), and (3) modified N95 VENT respirator (valved endoscopy of the nose and throat) as previously described,
Stata 13 (StataCorp) was used for statistical analysis to assess differences between background particle concentration and particles generated during simulated clinical and surgical activities. Nonparametric statistical techniques were utilized due to small sample sizes, with Bonferroni correction for multiple comparisons. Average background particle concentration (separate for clinical encounter and surgical laboratory encounter) was subtracted from each condition prior to data visualization as previously described.
All sampling periods were 30 seconds, and conditions were performed in duplicate with 2 cadaver heads. Sixteen background samples were obtained, as spaced between experiments, and minimal variability in background was observed. (1) Nasal suctioning with a 10Fr Frazier suction for 4 sampling periods and (2) endoscopic through biting of the middle turbinate (hand actuated) for 10 sampling periods did not produce significant detectable airborne aerosols in the range of 1 to 10 μm (
With the cadaver head in the surgical position, 3 separate drilling conditions were performed: (1) a suction drill at 12,000 rpm for ten 30-second samples, (2) a powered high-speed drill at 70,000 rpm with a 4-mm diamond bur for four 30-second samples, and (3) a powered high-speed drill at 70,000 rpm with a 4-mm cutting bur for four 30-second samples. The drill was used to remove bone at the sphenoid rostrum. In all 3 conditions, significant airborne aerosol generation in the range of 1 to 10 μm was observed (
Transnasal cautery of the inferior turbinate demonstrated significant particle generation in the range of 1 to 10 μm over background in four 30-second samples (
Participants were positioned sitting upright with the nose and mouth 15 cm from the aperture of the OPS air intake valve. All samples were collected over a period of 30 seconds and performed with 2 participants and at least 2 replicates per participant (n = 4-10). Panting and coughing generated detectable 1- to 10-μm aerosols that were not significantly greater than background (
As simulated sneezing generated the largest number of 1- to 10-μm airborne aerosols, several sneezing conditions were performed with different source control mask solutions. The surgical mask alone attenuated airborne aerosol generation (
While droplet and contact infectious transmission in SARS-CoV-2 has been largely accepted, the role of airborne transmission remains unclear. This mode is of particular concern in the health care setting given the propensity for AGPs to produce particles <10 µm.
Our surgical simulation conditions were designed to test a variety of endonasal instruments from suction and through-cutting forceps to powered devices and thermal cautery. Our findings were generally consistent with our prior study in that use of a surgical drill carried the greatest risk of generating detectable aerosols. The concomitant use of suction appeared to provide some benefit in reducing aerosol concentration; however, the lower speed of the suction drill is a confounding variable. Similarly, the microdebrider with distal tip suction did not produce detectable aerosols, even when requiring removal and active unclogging adjacent to the detector. Conversely, thermal cautery produced significant and particularly fine aerosols, which is consistent with the previous literature.
With regard to the clinical diagnostic conditions, our findings demonstrated that detectable airborne aerosols are generated during limited periods of speech, panting, cough, and sneeze. However, talking and sneezing were the only behaviors associated with a significant increase over background. Unfortunately, the most common method used to reduce sneezing—namely, topical nasal anesthesia and decongestion spray—also produced a significant number of aerosols. While the lack of significance in the other behavioral conditions could be attributed to the short testing duration and use of healthy volunteers, these results are consistent with prior physiologic reports confirming the differential risk of speech and sneeze conditions.
Our tested mask conditions focused on the ability to mitigate sneeze-associated aerosol production, as this was clearly the behavior of greatest risk. The existing literature regarding the utility of masks is complex, as studies tend to focus on discrete attributes, such as filtration efficiency, performance under steady and episodic conditions, and the relationship between mask use and infectious transmission. Epidemiologic and virologic studies have suggested that surgical masks may be equivalent to N95 respirators at protecting health care workers from infectious respiratory viruses.
As we apply these data to infection prevention and control recommendations in the outpatient otolaryngology setting, it is useful to conceptualize the protection needs of the 3
There are several limitations to this study that bear discussion. As the surgical simulation was performed in a cadaver head, it is possible that the lack of pulsatile blood supply at body temperature and physiologic mucus secretion may alter the propensity for aerosol production in the range of 1 to 10 μm. Consequently, further studies during active surgery are warranted. It is important to note that this study specifically measured optical particle size and did not use an aerodynamic particle sizer or alternative instrument to measure the aerodynamic nature of these particles, material makeup, particle volume, shape, density, or rate of settling. Particulate observed in any condition is known to be present only at the distance measured from the source of generation and was measured in real time; this does not reflect particulate desiccation or morphological changes that may occur over time, or settling rates of these particles. Future studies should investigate the aerodynamic properties of these particles to determine their likelihood of being deposited within the upper respiratory tract. With regard to the testing of the clinical diagnostic conditions, we must stress that our methodology was sensitive only to the generation of airborne droplet nuclei. The study was not designed to detect the presence of virus within these particles or their infectious transmissibility. However, in the absence of clear data on the minimum infectious dose of SARS-CoV-2, we believe that our findings should be interpreted in the most conservative context possible with respect to infectious control recommendations.
Our study represents a systematic effort to quantify the degree of airborne aerosol production associated with a variety of endonasal procedures. The surgical simulation data confirm that the use of high-speed drills and cautery produces the largest number of particles. The clinical conditions revealed that endoscopic instrumentation, speech, and sneezing all produced significant detectable airborne aerosols within only 30 seconds of measurement. An intact surgical mask failed to fully protect against sneeze-associated contamination. Therefore, surgical VENT masks, as previously described by our group, may not be sufficient in terms of <10-µm particles. However, when applied to an N95 respirator, the VENT modification retained the ability contain airborne aerosols. These results suggest that while nasal endoscopy carries a risk profile similar to established AGPs, barrier mask solutions offer the potential of effective source and engineering controls.
We thank Dr Stanley McClurg for his donation of masks to this study.