COVID-19 in the Clinic: Aerosol Containment Mask for Endoscopic Otolaryngologic Clinic Procedures

Abstract

Objective
To create an aerosol containment mask (ACM) that contains aerosols during common otolaryngologic endoscopic procedures while protecting patients from environmental aerosols.

Study Design
Bench testing.

Setting
Mannequin testing.

Methods
The mask was designed in SolidWorks and 3-dimensional printed. Mannequins were fitted with a nebulizer to generate aerosols. Commercial particle counters were used to measure mask performance.

Results
The ACM has 2 ports on either side for instruments and endoscopes, a port for a filter, and a port that can evacuate aerosols contained within the mask via a standard suction pump. The mask contained aerosols on a mannequin with and without facial hair when the suction was set to 18.5 L/min. Other types of masks demonstrated substantial aerosol leakage under similar conditions. In a subsequent experiment, the ACM contained aerosols generated by a nebulizer up to the saturation of the particle detector without measurable leakage with or without suction.

Conclusion
The ACM will accommodate rigid and flexible endoscopes plus instruments and prevent leakage of patient-generated aerosols, thus avoiding contamination of the room and protecting health care workers from airborne contagions.

Level of evidence
2.

Full text

Original Research
COVID-19 in the Clinic: Aerosol
Containment Mask for Endoscopic
Otolaryngologic Clinic Procedures
Otolaryngology–
Head and Neck Surgery
1–8
ÓThe Author(s) 2021
Reprints and p ermission:
sagepub.com /journalsPermissions.nav
DOI: 10.1177/01945998211024944
http://otojournal.org
Elisabeth H. Ference, MD, MPH
1
, Wihan Kim, PhD
1
,
John S. Oghalai, MD
1
, Jee-Hong Kim, MD
1
,
and Brian E. Applegate, PhD
1
Abstract
Objective. To create an aerosol containment mask (ACM) that
contains aerosols during common otolaryngologic endoscopic
procedures while protecting patients from environmental aerosols.
Study Design. Bench testing.
Setting. Mannequin testing.
Methods. The mask was designed in SolidWorks and 3-dimen-
sional printed. Mannequins were fitted with a nebulizer to
generate aerosols. Commercial particle counters were used
to measure mask performance.
Results. The ACM has 2 ports on either side for instruments
and endoscopes, a port for a filter, and a port that can evac-
uate aerosols contained within the mask via a standard suc-
tion pump. The mask contained aerosols on a mannequin
with and without facial hair when the suction was set to
18.5 L/min. Other types of masks demonstrated substantial
aerosol leakage under similar conditions. In a subsequent
experiment, the ACM contained aerosols generated by a
nebulizer up to the saturation of the particle detector with-
out measurable leakage with or without suction.
Conclusion. The ACM will accommodate rigid and flexible
endoscopes plus instruments and prevent leakage of patient-
generated aerosols, thus avoiding contamination of the room
and protecting health care workers from airborne contagions.
Level of evidence. 2.
Keywords
negative pressure mask, endoscopy, laryngoscopy, nasal
endoscopy, aerosol production, COVID-19
Received February 22, 2021; accepted May 25, 2021.
Due to the spread of SARS-CoV-2, the virus responsi-
ble for COVID-19, clinicians and hospitals face diffi-
cult decisions regarding how to provide care for
patients in clinics during procedures that may lead to the gen-
eration of aerosols. Airborne SARS-CoV-2 has been found in
hospital rooms and ventilation systems where patients with
COVID-19 have been treated.
1-5
Aerosolized particles \5
mm may remain viable in the air for at least 3 hours.
6
While
one study found that laryngoscopy alone may not generate
aerosols greater than that produced by breathing, laryngo-
scopy and nasal endoscopy are associated with increased risk
of coughing and sneezing, which are aerosol-generating
events.
7,8
Currently in many practices, patients wear a surgi-
cal mask over their mouths during nasal endoscopy, although
a regular surgical mask is insufficient to protect at close range
against all particle transmission generated by simulated aero-
sol generation.
8
In principle, virus aerosolized during clinic procedures
could infect not only the surgeon performing the procedure
but others who enter the room. The Centers for Disease Con-
trol and Prevention recommends that procedure rooms with-
out negative pressure remain vacant following any aerosol-
generating procedure before undergoing deep cleaning. This
period is typically deemed to be 6 times the room air turnover
time.
9,10
These cleaning and time requirements, compounded
by limited testing capacity with variable time to results, can
severely diminish an outpatient clinic’s capacity to treat
patients.
Prior authors have suggested negative pressure microenvir-
onments,
11
modification of Ambu,
12
nasotracheal intuba-
tion
13
face masks with negative pressure, or a modified N95
mask
8
to decrease aerosol dispersion during diagnostic nasal
endoscopy and laryngoscopy. We present a 3-dimensional
(3D) printed negative pressure respiratory aerosol contain-
ment mask (ACM) that provides N95-level protection to the
patient. The negative pressure is generated through a standard
suction commonly found in otolaryngology clinics. We mea-
sured aerosol generation in the ACM and compared it with
previously described masks with and without instrumentation.
1
Caruso Department of Otolaryngology–Head and Neck Surgery, Keck
School of Medicine of University of Southern California, Los Angeles, Cali-
fornia, USA
Corresponding Author:
Elisabeth H. Ference, MD, MPH, USC Caruso Department of
Otolaryngology–Head and Neck Surgery, 1540 Alcazar Street
Suite 204M, Los Angeles, CA 90033, USA.
Email: ference@usc.edu

Materials and Methods
The study was approved by the University of Southern Cali-
fornia Institutional Review Board (HS-20-00482).
Mask Design and Development
We created multiple design iterations by using SolidWorks
(Dassault Systemes) and printing on a 3D printer (Ultimaker)
with tough PLA (polylactic acid; Ultimaker). We tested initial
prototypes on endoscopic surgery model heads to gauge
access to the nasal cavity and ability to contain aerosols. The
design was modified as issues were identified. The main con-
siderations during the design phase were to appropriately
position the blind grommet, find a gel cushion to seal the
mask to various face shapes, and create a way to attach an
easily replaceable HEPA filter (high-efficiency particulate
air). The revision described in this article is the fifth.
The final design included a 3D printed body with 4 ports, a
gel cushion for seal and comfort of fit, and custom blind
grommets placed in 2 front ports plus a head strap (Figures 1
and 2). Each blind grommet contains 2 openings, and an endo-
scope or suction can be passed through any of the 4 openings.
All materials can be cleaned in Cidex OPA (Advanced Sterili-
zation Products). A N95-level commercially available
respirator filter can be attached to any of the 3 front ports and
replaced between patients. A suction is attached to the suction
port of the mask from a commercially available suction pump.
Testing on Model Heads vs Previously Published Designs
A test bench (Figure 1) was created to test the performance of
the ACM in a controlled environment and to compare the mask
with previously published designs. The test bench was set up in
a small room with an unused biosafety cabinet. The room air
was cleaned by closing the door and running the biosafety cabi-
net’s HEPA air filtration. Two mannequin heads, with and with-
out facial hair, were attached to a nebulizer device (DeVilbiss)
via a tube running through the back of the mannequin to the
nose. The nebulizer was loaded with 2% sterile saline at a flow
rate of 10 L/min.
14,15
Aerosols were measured by an optical par-
ticle counter (Particles Plus) at approximately 2 cm anterior to
the mask (sensor 1) and at 2 cm lateral to the mask near the area
where its edge was against the face of the mannequin (sensor 2).
The level of aerosol around the ACM was compared with
that from an Ambu mask design
12
(an Ambu mask fitted with
suction tubing leading to HEPA suction) and a commercially
available N95 mask.
8,16
The flow rate was varied for the ACM
and Ambu mask designs, but the N95 mask does not have the
ability to apply suction. The amount of aerosol was measured
at baseline for all 3 mask designs and at various flow rates for
the Ambu and ACM, between –18.5 and 16.5 L/min, by vary-
ing the valve in front of the suction pump. Particles were mea-
sured for 2 minutes with 15-second sampling intervals, and
each measurement was performed 5 times for each mask type.
Testing on Model Heads While Measuring Particle
Counts Inside the Mask
The mannequin testing was repeated for the ACM (Figure 3a)
with a 3-mm copper tube to measure particles within the mask
(sensor 1) and with a particle counter 2 cm anterior to a grom-
met through which a 4-mm rod was placed to mimic the place-
ment of an endoscope (sensor 2). Measurements were made for
1 minute with a 1-second sampling interval at a flow rate of
18.5 L/min. The tests were repeated with 1 grommet uncov-
ered, mimicking an approach that could be used to allow access
for the placement of larger instruments or nasal packing.
Statistical Analysis
Standard ttests, as fully specified in the text with a= 0.05,
were used to test for statistical significance. All statistics were
calculated with OriginLab (OriginLab Corporation, OriginPro
2021).
Results
Testing on Model Heads vs Previously Published Designs
Figure 4 is a set of box plots showing average 0.3-mm par-
ticle counts (averaged over 120 seconds) for the mannequin
Figure 1. Aerosol containment mask design: (a) SolidWorks drawing, (b) final assembly of the 3-dimensional printed mask, and (c) flow
directions.
2Otolaryngology–Head and Neck Surgery

Figure 2. (a, b, f, g) Mannequin heads with and without hair. The (c, h) aerosol containment mask, (d, i) Ambu mask, and (e, j) a commercial
N95 mask. A particle counter measured lateral (top row) and anterior (bottom row) to the mask.
Figure 3. Mask testing setup for the mannequin: (a) the ‘‘closed’’ setup and (b) the ‘‘open’’setup with the right grommet removed.
Ference et al 3

head with and without facial hair. The average was mea-
sured 8 times. The largest changes observed were in the
0.3-mm particle; hence, only the results for this size are
shown in Figure 3 for simplicity (others are in Figure 5).
A 2-tailed unpaired ttest was used to test if the mean aver-
age particle count minus the baseline particle count was sig-
nificantly different from zero (n = 8; Supplemental Table
S1, available online). A positive mean indicates leakage of
aerosols. A negative mean implies that the mask is function-
ally cleaning the air near the sensor. On the mannequin
head with no facial hair, no leakage was found under any
conditions for the ACM. At 18.5 L/min, the sensor directly
in front of the N95 filter (sensor 2) had a negative mean.
This implies that the air near this sensor is cleaner when the
suction is on. It may be that the filter is removing particles
from the air in the vicinity of the sensor or that the air flow
into the mask is drawing cleaner air into the room. The
Ambu mask shows leakage at both sensors when the suction
is 16.5 L/min but only at sensor 2 when the suction is –18.5
L/min. The N95 shows leakage at both sensors. On the man-
nequin head with facial hair, the ACM shows leakage when
the suction is 16.5 L/min but not when the suction is set to
18.5 L/min, while the Ambu and surgical N95 masks show
leakage under all conditions.
Figure 4. Particle counts (0.3 mm) with ambient baseline subtracted for masks on mannequins with and without facial hair. *Mean not signifi-
cantly different from zero. **Positive mean significantly different from zero. ***Negative mean significantly different from zero. ACM, aerosol
containment mask; IQR, interquartile range.
4Otolaryngology–Head and Neck Surgery

Testing on Model Heads While Measuring Particle
Counts Inside the Mask
In these experiments, the particle count from the nebulizer
had to be reduced as compared with the aforementioned
experiments to avoid saturating sensor 1, which was measur-
ing the count inside the mask. Nevertheless, the particle
counts exceeded any of those measured on the human volun-
teers. A baseline was acquired just prior to turning on the
nebulizer. This was subtracted from particle counts measured
with the nebulizer on, the mask suction on and off, and the
grommet opened and closed. The box plots in Figure 6 repre-
sent average particle counts measured in 5 trials for 0.3-mm
particles. The data used to build the plot are in Supplemental
Figure 5. Particle counts for all particle sizes .0.3 mm with ambient baseline subtracted for the ACM, Ambu, and surgical N95 mask on manne-
quins with and without facial hair. ACM, aerosol containment mask; IQR, interquartile range.
Ference et al 5

Table S2 (available online), with box plots of the other parti-
cle sizes in Supplemental Figure S1. Sensor 1 (within mask)
showed a significant difference in average particle count with
the suction on and off for both experiments. Sensor 2 (outside
mask) showed no significant difference with the suction on or
off for the mock endoscope experiment. Hence, in this config-
uration, even with a very high particle count within the mask,
there was no detectable leakage with the suction on or off. In
the experiment with the grommet removed, there was no sig-
nificant difference with the suction on. As expected, though,
when the suction is turned off, there is a significant increase in
particle count, as aerosols leak from the mask.
Discussion
The ACM significantly decreased the spread of aerosol particles
in mannequin testing. It outperformed previously described
masks, especially on mannequins with facial hair.
Prior studies found that regular surgical masks are insuffi-
cient in protecting against aerosol escape generated by sneez-
ing.
8
However, an N95 respirator with an incision lined with a
cut piece of surgical glove (VENT modification [valved endo-
scopy of the nose and throat]) contained aerosol spread.
8
When
trialed on the mannequin, the unmodified N95 underperformed
when compared with the devices with suction, especially on
patients with facial hair. Other barrier devices, such as a hood
or box, have been detailed but may be difficult to place, are not
conducive to rigid endoscopy, and do not contain suction.
17,18
Prior studies of endoscopic surgery found that the addition
of suction prevents the spread of aerosols. Dharmarajan et al
found that, even in a cadaver model with an endotracheal tube
in the nasopharynx attached to a nebulizer with B2 solution,
no aerosols were detected visually or with a cascade impactor
once a flexible suction was placed in the nasal cavity or the
nasopharynx.
15
Similarly, no aerosols were detected with
drilling of a cadaveric specimen or 3D sinonasal model once a
flexible suction was placed, likely because the aerosols were
directed toward the suction tip rather than exiting the nares.
15
Similarly, Workman et al did not identify aerosol contamina-
tion when utilizing the microdebrider, which is attached to
suction.
8,16
Our findings are similar in that once suction is
placed on the mask at a level sufficient to overcome the gener-
ation of the aerosols and the difficulties of fit with facial hair,
then no particles are detected leaking from the mask.
Creating negative pressure microenvironments around the
patient to contain particles has been described. Prior studies
also detailed box-like containers that can be placed around the
patient for outpatient procedures or intubation, although these
may be time-consuming in an outpatient setting.
11,19
Finally,
modifications of existing masks, such as the Ambu mask or
nasotracheal intubation masks, have been outlined.
11,12
While
the Ambu mask outperformed an unmodified N95 mask, it
was difficult to place and allowed for less access to the nasal
cavity and oropharynx as compared with the ACM.
Additionally, prior studies have reported on the creation of
3D printed devices to contain aerosols. Two studies described
a 3D printed vent that could be placed through a regular surgi-
cal mask, but the efficacy of these devices may be limited, as
Workman et al found that surgical masks contain aerosolized
particles poorly.
8,20,21
One of these articles also detailed a
complete 3D printed mask; however, it did not include suc-
tion, had only a single midline port for flexible endoscopes,
and had not been tested on a human.
21
Figure 6. Box plots of 0.3-mm averaged particle counts. Sensor 1 (within mask). **Significant difference based on suction. Sensor 2 (outside
mask). *No significant difference except with grommet removed and suction off. IQR, interquartile range.
6Otolaryngology–Head and Neck Surgery

The current study design has several limitations. The mask
material is not clear. This necessitates scope guidance via a
camera or the eye piece to drive the scope from the entrance
of the mask into the nares. Future versions of the mask could
be made with clear material through injection molding or
chemical polishing of transparent 3D printed parts. While the
mask allows access to the nose and oral cavity for diagnostic
purposes and single-instrument procedures, such as suction-
ing and hand instruments, it does not allow for insertion of
larger objects (eg, nasal packing) without removing 1 of the
grommets. Nevertheless, in a trial on the mannequin with the
grommet off, we found no significant increase in aerosols
external to the mask with the suction on (Figure 4). It may be
possible to uncover a grommet to get wide exposure while
providing good protection to the health care worker. Addition-
ally, in the Workman et al study of the N95 mask with VENT
modification, some contamination occurred after N95 respira-
tor removal.
8
We have not yet tested removal procedures,
although we believe that most aerosols would be evacuated by
the suction pump.
Studies are ongoing regarding whether a single suction
pump, such as that from an SMR cart (Global Surgical Corpo-
ration), can be split and continue to provide adequate suction
to the mask and a surgical suction. This article describes test-
ing of the mask on only a mannequin, but we have tested it on
healthy volunteers and are in the process of completing a
larger-scale clinical trial on patients presenting to an otolaryn-
gology clinic.
22
Conclusion
A negative pressure mask may allow for the passage of rigid
and flexible endoscopes without leakage of particles outside
the mask. This may help prevent contamination of the room
and protect health care workers during viral pandemics that
involve airborne contagion. A larger clinical study is ongoing.
Author Contributions
Elisabeth H. Ference, grant application, study design, product
design, patient recruitment, data acquisition and analysis, manuscript
writing; Wihan Kim, grant application, study design, product
design, data acquisition and analysis, manuscript writing; John S.
Oghalai, grant application, study design, discussion, manuscript
revision; Jee-Hong Kim, patient recruitment, data acquisition,
manuscript writing and revision; Brian E. Applegate, grant applica-
tion, study design, data analysis, manuscript revision.
Disclosures
Competing interests: None.
Sponsorships: None.
Funding source: Keck School of Medicine COVID-19 Funding
Program supported by the W.M. Keck Foundation.
Supplemental Material
Additional supporting information is available in the online version
of the article.
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8Otolaryngology–Head and Neck Surgery