Quantifying Aerosol Generation in Maxillofacial Trauma Repair Techniques

Abstract

Study Design: Cadaveric simulation study. Objective: The novel coronavirus (COVID-19), which can be transmitted via aerosolized viral particles, has directed focus on protection of healthcare workers during procedures involving the upper aerodigestive tract, including maxillofacial trauma repair. This study evaluates particle generation at different distances from open reduction and internal fixation (ORIF) of maxillofacial injuries in the intraoperative setting to reduce the risk of contracting airborne diseases such as COVID-19. Methods: Two cadaveric specimens in a simulated operating room underwent ORIF of midface and mandible fractures via intraoral incisions as well as maxillomandibular fixation (MMF) using hybrid arch bars. ORIF was performed with both selfdrilling screws and with the use of a power drill for creating guide holes. Real-time aerosol concentration was measured throughout each procedure using 3 particle counters placed 0.45, 1.68, and 3.81 m (1.5, 5.5, and 12.5 feet, respectively) from the operative site. Results: There was a significant decrease in particle concentration in all procedures at 1.68 m compared to 0.45 m, but only 2 of the 5 procedures showed further significant decrease in particle concentration when going from 1.68 to 3.81 m from the operative site. There was significantly less particle concentration generated at all distances when using self-drilling techniques compared to power drilling for ORIF. Conclusions: Consideration of using self-drilling screwing techniques as well as maintaining physical distancing protocols may decrease risk of transmission of airborne diseases such as COVID-19 while in the intraoperative setting.

1. Introduction

Coronavirus disease 2019 (COVID-19) is a viral illness caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and is responsible for the ongoing COVID-19 pandemic. COVID-19 has been shown to have a high transmissibility with asymptomatic cases estimated to be as high as 40 to 45% of infections. [1] As a result, limiting the spread of COVID-19 has presented a novel challenge to both hospital systems and the public at large. Healthcare workers (HCWs) appear to be at increased risk of contracting and spreading COVID-19 due to close contact with infected patients, with some states reporting infection rates as high as 11% in HCWs. [2] Moreover, 55% of infected HCWs have reported the healthcare setting as their only known COVID-positive contact. [3] Particular attention has been paid to optimizing personal protective equipment (PPE) for HCWs, although PPE guidelines may vary between agencies, hospital systems, and departments. Although the COVID-19 pandemic has been ongoing for over one year at the time of this report, and despite the demonstrated efficacy of the multiple approved vaccines, there are several indications that this disease may continue to present a problem for HCWs. [4] Vaccination rollout to the general public has been relatively slow on an international level. The vast majority of countries have less than 50% of their population fully vaccinated, and only 1% of individuals in developing countries have received a single dose. [5] Genetic diversity of the virus is also growing worldwide, with dozens of mutations discovered in multiple continents that have the potential to increase virulence and transmissibility. [6,7]

Otolaryngologists are at increased risk of COVID-19 exposure as high viral loads have been found in nasal, throat, and sputum samples. [8,9] Transmission is thought to occur via direct contact with larger respiratory droplets as well as via inhalation of aerosolized viral particles that may remain in the air for hours. [10,11,12,13] The risk of airborne transmission necessitates extra precautions in aerosol-generating procedures, particularly of the head and neck. Some procedures are elective and may allow for the delay of obtaining a COVID19 test or until an individual is outside the infectious window. However, this delay may not be an option in the setting of facial trauma, where urgent and emergent surgical interventions may be indicated. Hsieh et al. [14] has previously outlined a protocol for determining respiratory PPE based on trauma severity and COVID-19 status, distinguishing extreme (powered air-purifying respirator [PAPR]) from enhanced (N95) airway precautions. Studies have also shown that surgical management of facial trauma, particularly with the use of operative drills for plating systems, can create large amounts of aerosolized particles. [15,16,17]

In this study, we performed simulated facial trauma repair on cadaveric specimens to (1) quantify and characterize aerosol particle generation during various procedures for facial bony and soft tissue trauma, and (2) compare various methods of fixation of facial fractures with respect to aerosol particle generation. Based on previously published data, we hypothesize that facial trauma procedures will generate a significant degree of aerosolized particle burden. We also postulate that self-drilling screws without power instruments will have significantly lower particle burden than open reduction internal fixation (ORIF) techniques with pre-drilling using a power drill.

2. Materials and Methods

2.1. Study Design

Our study was submitted to the University of Cincinnati Institutional Review Board (IRB) and determined to be IRB exempt. In this real-time intraoperative assessment of aerosolized particles during facial trauma repair, 2 fresh-frozen cadaver specimens were thawed to room temperature, placed in a supine position, and set up in a simulated operating room. The specimens were then draped in standard fashion with the face left exposed. A primary surgeon, a surgical assistant, and an anesthesiologist donned sterile gowns, gloves, and masks.

Five procedures were performed: (1) maxillomandibular fixation (MMF) with hybrid arch bars, (2) ORIF of zygomaticomaxillary complex (ZMC) fractures with self-drilling screws, (3) ORIF of ZMC fractures with power drilling techniques, (4) ORIF of mandibular fractures with self-drilling screws, and (5) ORIF of mandibular fractures with power drilling techniques. The cadavers were nasally intubated and extubated for each procedure with the pilot balloon inflated and the end of the endotracheal tube covered to simulate a closed loop system. Intubation and extubation times served as the start and stop times for each procedure, respectively.

2.2. Operative Techniques

MMF with hybrid arch bars. A dental cheek retractor was used to expose both the maxillary and mandibular alveolus and dentition. Stryker SMARTlock hybrid arch bars were then fixed to the maxillary and mandibular alveolus with 6 millimeter (mm) self-drilling screws using a screwdriver, and multiple wire loops were placed to position the maxillary and mandibular dentition into maximal intercuspation.

ORIF ZMC fracture. To simulate the high risk nature of intraoral mucosal exposure in an infectious COVID-19 patient, an intraoral approach to ORIF of a simulated ZMC fracture patient was used. An intraoral incision was started in the left maxillary gingivolabial sulcus and extended down to the subperiosteal plane over the anterior maxilla. This was elevated superiorly for adequate exposure of the zygomaticomaxillary buttress. The same approach to bony exposure was utilized for both the self-drilling procedure and the power drilling procedure.

In the self-drilling screws method, the zygomaticomaxillary buttress was fixed using a 6-hole 0.6 mm L-shaped titanium plate and secured into place with 6 mm self-drilling screws using a hand-operated screwdriver. Gentle saline irrigation using a bulb-irrigation syringe was performed to remove bony debris as the screws were placed.

In the power drilling technique, the zygomaticomaxillary buttress was fixed using the same 0.6 mm L-shaped titanium plate. However, a Stryker Total Performance System (TPS) drill was used with a 50 mm drill bit at 40,000 RPM to create guide holes prior to securing the plate with 6 mm screws and a hand-operated screwdriver. During the power drilling, gentle saline irrigation with a bulb-irrigation syringe was performed over the drilling site and a Frasier-tip suction device was used to remove the irrigation prior to placement of the screws.

ORIF mandibular fracture. To simulate the high risk nature of intraoral mucosal exposure in an infectious COVID-19 patient, an intraoral approach to ORIF of a simulated mandibular fracture patient was used. An intraoral incision was made in the mandibular gingivolabial sulcus over the parasymphyseal area and dissection was carried down to the subperiosteal plane over the mandible. The soft tissue was then elevated for exposure of the parasymphysis and body of the mandible. The mental nerve was identified and preserved. The same approach to bony exposure was utilized for both the self-drilling procedure and the power drilling procedure.

In the self-drilling screws method, the parasymphyseal region was fixed with a 4-hole 2.0 mm titanium plate on the inferior border. Pilot guide holes were first created with 12 mm self-drilling screws using a hand-operated screwdriver. These were then removed and replaced with 12 mm locking screws. A second 1.0 mm superior border plate was placed in the parasymphyseal region as well. Pilot guide holes were first created with 8 mm self-drilling screws using a hand-operated screwdriver. These screws were then replaced with 6 mm nonlocking screws. Gentle saline irrigation using a bulb-irrigation syringe was performed to remove bony debris as the screws were placed.

In the power drilling technique, the parasymphyseal region was fixed with a 4-hole 2.0 mm titanium plate on the inferior border. A Stryker TPS drill was used with an 85 mm drill bit at 40,000 RPM to create guide holes, and 12 mm bicortical locking screws were then placed with a handoperated screwdriver. A second 1.0 mm superior border plate was placed in the parasymphyseal region. The same power drill was used with a 50 mm drill bit at 40,000 RPM to create guide holes prior to securing the plate using 5 mm nonlocking screws and a hand-operated screwdriver. During the power drilling, gentle saline irrigation with a bulbirrigation syringe was performed over the drilling site and a Frasier-tip suction device was used to remove the irrigation prior to placement of the screws.

2.3. Data Collection

The measurement of real-time aerosol concentration was conducted utilizing one Condensation Particle Counter (CPC) (TSI-3007; Shoreview, MN) and 2 P-Trak Ultrafine Particle Counters (TSI 8525; Shoreview, MN). The CPC measures particle sizes ranging from 0.01 to 1.0 μm and the P-Trak counters measure particle sizes ranging from 0.02 to 1 μm. The 3 particle counters were placed at various distances from the surgical site to evaluate aerosol concentrations at different locations. The CPC was placed at the surgical area with a distance no more than 0.45 m from the surgeon, and the 2 PTrak counters were placed at 1.68 and 3.81 m, respectively. The particle counters automatically logged the aerosolized particle counts in cubic centimeters of air (particles/cc) at 5-second intervals. Since the particle counters rely on supersaturation of solvents, wicks were placed inside the particle counters to deliver isopropyl alcohol. The wicks for all 3 devices were submerged in 99.5% isopropyl alcohol overnight to ensure thorough saturation. The particle counters were turned on prior to the experiment and allowed to warm up for 10 minutes. They were then zero-calibrated using the provided calibration tools from the manufacturer. The times of all 3 particle counters were synchronized using a digital clock that included milliseconds. Baseline ambient particle levels were taken at the beginning and end of the procedures. Particle counts were taken at each location before, during, and after each procedure. Several minutes were taken between each procedure to allow the particle counter to return to baseline.

2.4. Statistical Analyses

Data from the particle counters was extracted using the Aerosol Instrument Manager Software version 8.1 (TSI; Shoreview, MN). Time-series data was generated to match up the variables for each procedure type tested in this study. Intraoperative aerosol counts were summated and averaged for each of the 5 procedures, and the change of average aerosol level from the perioperative ambient baseline was calculated for each procedure. Using JSAP version .13.1 (Amsterdam, Netherlands), paired sample T-tests were performed to compare aerosol levels generated by self-drilling vs. power drilling techniques, as well as aerosol levels by distance from the surgical field for each of the 5 procedures completed.

3. Results

3.1. Distance from Source

A significantly lower level of particles was measured at 1.68 m from the surgical site vs. 0.45 m from the surgical site for all 5 procedures performed (Figure 1,

Table 1. Comparison of Aerosolized Particle Count at Increasing Distances from Operative Site.

Procedure	Distance (meters)	Mean Aerosol Count (Particles/cc)	Standard Deviation (Particles/cc)	p Value
MMF	0.45	3575.075	202.065	<0.001
	1.68	2302.5	176.27
	3.81	1990.455	215.963
ORIF ZMC drill	0.45	3719.952	371.931	<0.001
	1.68	2255.86	272.841
	3.81	2626.2	268.311	1.000
ORIF ZMC hand-screw	0.45	2702.548	162.882	<0.001
	1.68	1734.274	114.848
	3.81	1332.867	71.763
ORIF mandible drill	0.45	3604.142	210.801	<0.001
	1.68	2410.542	201.522
	3.81	2932.417	179.453	1.000
ORIF mandible hand-screw	0.45	3221.617	214.076	<0.001
	1.68	1935.522	145.839
	3.81	2301.813	113.796	1.000

). For ORIF of ZMC fractures, there was an average difference of 1464.092 particles/cc (power drilling) and 968.274 particles/cc (self-drilling) between 0.45 m and 1.68 m (p < 0.001). For ORIF of mandible fractures, there was a difference of 1193.6 particles/cc (power drilling) and 1286.095 particles/cc (selfdrilling) between 0.45 m and 1.68 m (p < 0.001). To a lesser extent, further decreases in ambient particle levels were observed at 3.81 m vs. 1.68 m for 2 of the 5 procedures performed (MMF, ORIF ZMC self-drill) (Figure 1, Table 1).

3.2. Self-Drilling vs. Power Drilling

A significant reduction in the level of aerosolized particles was observed when comparing self-drilling to power drilling techniques for ORIF of both ZMC and mandibular fractures (

Table 2. Comparison of Aerosolized Particle Count Between Hand-Screw and Power Drill.

Procedure	Distance (meters)	Mean Aerosol Count (Particles/cc)	Standard Deviation (Particles/cc)	p Value
Mandible hand-screw	0.45	3221.617	214.076	<0.01
Mandible drill		3604.142	210.801
Mandible hand-screw	1.68	1935.522	145.839	<0.01
Mandible drill		2410.542	201.522
Mandible hand-screw	3.81	2301.813	113.796	<0.01
Mandible drill		2932.417	179.453
ZMC hand-screw	0.45	2702.548	162.882	<0.01
ZMC drill		3719.952	371.931
ZMC hand-screw	1.68	1734.274	114.848	<0.01
ZMC drill		2255.86	272.841
ZMC hand-screw	3.81	1332.867	71.763	<0.01
ZMC drill		2626.2	268.311

). Self-drilling procedures for both fracture types were associated with lower levels of aerosols at all 3 distances from the surgical site (0.45 m, 1.68 m, and 3.81 m) when compared to power drilling for the same fracture types. For ORIF of ZMC fractures, self-drilling resulted in an average reduction of 1017.404 particles/cc at 0.45 m, 521.586 particles/cc at 1.68 m, and 1293.333 particles/cc at 3.81 m when compared to power drilling methods (p < 0.01) (Table 2, Figure 2). For ORIF mandible, self-drilling resulted in an average reduction of 382.525 particles/cc at 0.45 m, 475.02 particles/cc at 1.68 m, and 630.604 particles/cc at 3.81 m when compared to power drilling methods (p < 0.01) (Table 2, Figure 3).

4. Discussion

Maxillofacial trauma constitutes a unique challenge to the provider with regards to potential COVID-19 exposure as timely repair may be necessary despite infection status. Several protocols and expert opinions regarding safety regulations in the setting of facial trauma and COVID-19 are available, and there is published data to suggest the high aerosolizing potential of operative facial trauma repair. [14,15,16,17,18,19,20] In this study, we quantified aerosol generation relative to distance to surgical field in the simulated repair of mandible and ZMC fractures both with and without the use of power drills. We sought to gain a better understanding of the exposure risk to surgeons as well to help inform preventative guidelines. Furthermore, we hope these findings can be generalized beyond the scope of COVID-19 as aerosolization is a major transmission modality for infectious respiratory viruses. [21]

The guidelines that currently exist on facial trauma repair are limited but have provided several useful recommendations to reduce COVID-19 transmission. Edwards et al. [20] has suggested repairing mandible/maxillary fractures in the emergency department when possible, utilizing self-drilling screws, and delaying repair of ZMC fractures, even if it may result in suboptimal esthetic outcomes. Shokri et al. [19] has discussed the importance of reducing the number of surgeon assistants, intubating early, utilizing a scalpel over bipolar cautery, favoring closed over open reduction, and minimizing intraoral dissection in favor of transcutaneous approaches. These recommendations offer a useful framework to help surgeons navigate the challenging COVID-19 pandemic. However, only a few studies have attempted to quantify the exposure risk to a surgeon performing facial fracture repairs. Calvarial plate drilling and mandibular plate screw drilling have been found to have high particle burden both adjacent to the surgical site and at the surgeon’s mouth level, which is partially mitigated by irrigation. [16] A similar cadaveric study measuring aerosolization at a single location during mandibular and midface fixation found increasing levels of particle generation with power drilling and electrocautery and decreasing levels with smoke-evacuating electrocautery devices. [15] There are plating systems that do not use power drills for screw and plate placement that have similar treatment outcomes to traditional ORIF techniques. [22] These self-drilling screws have been suggested as preferable to power drilling during the COVID-19 pandemic. [18,23] To our knowledge, there is no study to date that has quantified aerosol generation at multiple distances in an operating room during facial trauma repair, nor analyzed the degree to which self-drilling screws may mitigate this aerosol generation.

Facial injuries continue to happen during the COVID-19 pandemic despite widespread lockdowns, and surgeons who manage facial trauma are at increased risk of COVID-19 exposure. [18] It is important to quantify the transmission risk of these situations and to help determine steps a healthcare practitioner can take to reduce their risk. In this study, we found that utilizing self-drilling screws significantly reduces the amount of aerosol particles generated in both ZMC and mandibular fracture fixation as compared to power drilling. This comparative reduction in aerosolized particles remained significant at all 3 distances from the surgical site (0.45 m, 1.68 m, and 3.81 m), which attempt to simulate the distance between the patient and the primary surgeon, surgical assistant, and anesthesiologist, respectively. Our finding is consistent with prior guidelines that have called for the use of self-drilling screws when applicable to minimize aerosolization. [14,18,23] Furthermore, we found that the degree of aerosol particle generation is inversely proportional to the distance from the surgical site. This suggests that it is important to limit the surgical staff to essential personnel only around the patient with additional support staff as far away from the surgical field as can be allowed. Due to the exposure risk to surgical teams in the setting of operative facial trauma treatment, our findings are consistent with prior guidelines that have called for a conservative approach to favor nonoperative or delayed operative management whenever possible. [18,19,20]

There are several limitations to our study. As outlined by Ye et al. [15] utilizing cadaveric specimens rather than live patients may affect aerosol generation with relation to blood flow and physiologic temperature. In addition, our study measured smaller, aerosolized particles that remained suspended in the air and did not assess larger droplets that fell to the floor. It has been well-documented that COVID19, as well as several other respiratory viruses, can be transmitted via respiratory droplets. The focus of our study was on the more insidious nature of aerosolized transmission. We also did not measure actual viral particles, which may have unique physical and infectious properties not captured in this study.

5. Conclusions

Operative facial trauma procedures, including ZMC and mandibular fixation, generate aerosolized particles which can pose significant infectious risk to the surgical team during the ongoing COVID-19 pandemic. While we concur with favoring a nonoperative or delayed operative approach when possible, there remain scenarios especially in the setting of traumatic injuries where urgent operative management is necessary. In these situations, there are methods to mitigate infectious aerosol transmission. Use of self-drilling screws reduces the degree of particle aerosolization when compared to power drilling techniques and should be utilized when possible. Additionally, limiting the operative team to essential personnel only and physically distancing staff from the surgical field as much as possible is a further action that should be considered.