Research ArticleOriginal Research

Efficacy of Various Mitigation Devices in Reducing Fugitive Emissions from Nebulizers

Lauren J Harnois, Amnah A Alolaiwat, Guoqiang Jing, James B Fink, Rajiv Dhand and Jie Li
Respiratory Care April 2022, 67 (4) 394-403; DOI: https://doi.org/10.4187/respcare.09546

Abstract

BACKGROUND: Fugitive aerosol concentrations generated by different nebulizers and interfaces in vivo and mitigation of aerosol dispersion into the environment with various commercially available devices are not known.

METHODS: Nine healthy volunteers were given 3 mL saline with a small-volume nebulizer (SVN) or vibrating mesh nebulizer (VMN) with a mouthpiece, a mouthpiece with an exhalation filter, an aerosol mask with open ports for SVN and a valved face mask for VMN, and a face mask with a scavenger (Exhalo) in random order. Five of the participants received treatments using a face tent scavenger (Vapotherm) and a mask with exhalation filter with SVN and VMN in a random order. Treatments were performed in an ICU room with 2 particle counters positioned 1 and 3 ft from participants measuring aerosol concentrations at sizes of 0.3–10.0 μm at baseline, before, during, and after each treatment.

RESULTS: Fugitive aerosol concentrations were higher with SVN than VMN and higher with a face mask than a mouthpiece. Adding an exhalation filter to a mouthpiece reduced aerosol concentrations of 0.3–1.0 μm in size for VMN and 0.3–3.0 μm for SVN (all P < .05). An Exhalo scavenger over the mask reduced 0.5–3.0 μm sized particle concentrations for SVN (all P < .05) but not VMN. Vapotherm scavenger and filter face mask reduced fugitive aerosol concentrations regardless of the nebulizer type.

CONCLUSIONS: SVN produced higher fugitive aerosol concentrations than VMN, whereas face masks generated higher aerosol concentrations than mouthpieces. Adding an exhalation filter to the mouthpiece or a scavenger to the face mask reduced aerosol concentrations for both SVN and VMN. Vapotherm scavenger and filter face mask reduced fugitive aerosols as effectively as a mouthpiece with an exhalation filter. This study provides guidance for reducing fugitive aerosol emissions from nebulizers in clinical practice.

Introduction

Prior to the COVID-19 pandemic, aerosol particle concentrations in room air were reported to be higher with nebulization than with other treatments such as noninvasive ventilation1 and bronchoscopy2 or with other patient care activities, including bathing, pouring, flushing, or changing linens.2 While using smoke to simulate aerosol dispersion, the exhaled air dispersion distance was found to be greater with nebulization than with a simple oxygen mask and noninvasive ventilation.3 As such, nebulization was considered an aerosol-generating procedure4,5 due to concerns that aerosol generated by the nebulizer might carry virus to the surrounding environment, especially with reports of SARS-CoV-2 being viable in aerosols for up to 3 h.6 In the recent systematic review and meta-analysis, nebulization was found to significantly increase the odds of health care workers contracting SARS-CoV-1 or SARS-CoV-2 virus.7 Thus, several clinical societies made recommendations against the use of nebulizers during the COVID-19 pandemic.8,9 Switching from nebulizers to other aerosol devices such as metered-dose inhalers or dry powder inhalers caused a shortage of those devices10 and inefficient drug delivery for some patients who were unable to correctly use them. More importantly, some inhaled medications such as antimicrobials, mucolytics, and prostaglandins are only available in the solution form so that avoiding the use of nebulizers limited the potential for patients to benefit from those treatments.11

Clinically, there are different types of nebulizers and interfaces (face mask or mouthpiece) available for aerosol therapy. Fugitive emissions consist of aerosol that has been exhaled from the patient (bioaerosol) and/or aerosol that escaped from the nebulizer system prior to inhalation. The latter are medical aerosols and do not carry infectious particles unless the nebulizer is contaminated by patients’ secretions. An in vitro study reported lower fugitive aerosol concentrations with use of vibrating mesh nebulizers (VMNs) than small-volume nebulizers (SVNs),12 especially when a mouthpiece was utilized, and that adding expiratory filters reduced fugitive aerosol concentrations.12 However, no in vivo data are available on the fugitive aerosol particle concentrations using different nebulizers with common interfaces.

Adding an expiratory filter to a mouthpiece during nebulization has been recommended for treatment of COVID-19 patients.13,14 Unfortunately not all patients are able to effectively use a mouthpiece, for example, patients with cognitive or neurological defects who cannot hold the mouthpiece in their mouth and form a tight seal with their lips. Consequently, reducing the concentrations of fugitive aerosols generated during the use of a face mask could promote the safe and efficient use of face masks with nebulizers. Filter face masks and 2 designs of scavengers are commercially available. The filter face mask incorporates filters at the exhalation holes on the aerosol mask, whereas the scavenger device continuously suctions the aerosol particles during aerosol-generating procedures. However, the effectiveness of those devices in reducing fugitive aerosol concentrations in vivo is still unknown. Thus, we aimed to investigate the concentrations of fugitive aerosols generated by VMNs and SVNs with the use of an interface (face mask and mouthpiece) with and without a mitigation device (filter or scavenger) among healthy volunteers. Another aim was to determine the most effective mitigation device(s) to reduce fugitive aerosol concentrations during nebulization.

QUICK LOOK

Current Knowledge

Nebulization is an aerosol-generating procedure. Due to the concerns that aerosol generated by the nebulizer might carry virus to the surrounding environment, several clinical societies made recommendations against the use of nebulizers during the COVID-19 pandemic. However, no in vivo data are available on the fugitive aerosol particle concentrations using different nebulizers with common interfaces.

What This Paper Contributes to Our Knowledge

Small-volume nebulizers produced higher fugitive aerosol concentrations than vibrating mesh nebulizers, whereas face masks generated higher fugitive aerosol concentrations than mouthpieces. Adding an exhalation filter to the mouthpiece or a scavenger to the face mask reduced fugitive aerosol concentrations for both nebulizers. Vapotherm scavenger and filtered face mask had similar effectiveness in reducing fugitive aerosol concentrations as mouthpiece and an exhalation filter.

Methods

This prospective randomized crossover trial was registered in clinicaltrials.gov (NCT04681599) and was approved by the Rush University Ethics Committee (approval No. 20121804-IRB01). Healthy adults age 18–65 y with no history of respiratory disease were included. Participants were excluded if they met any of the following criteria: had chronic lung disease such as asthma or COPD, upper-airway anatomical abnormalities, uncontrolled diabetes, hypertension, or untreated thyroid disease; were pregnant; or had a positive COVID-19 test or any COVID-19-related symptoms (including sore throat, cough, body aches or shortness of breath for unknown reasons, loss of taste or smell, and fever with temperature ≥ 100°F) within 21 d of enrollment.

Written consent was obtained from each participant prior to starting the study. The study was conducted in an ICU patient room (3.65 × 3.65 × 2.8 m3 with air exchange frequency of 6 times/h). The door remained closed throughout the study, and talking or moving around was discouraged. Participants were seated in an upright position, and 2 particle counters (Model 3889, Kanomax, Andover, New Jersey) were placed at 1 and 3 ft from participants at the mouth level, with continuous monitoring of aerosol particle concentrations from 0.3–10.0 µm in size (Fig. 1). A single investigator wearing an N95 mask stayed in the room with the participant throughout the study, whereas the participant wore an N95 mask before and between the use of different devices/interfaces. The interval between device use was 15 min, and devices/interfaces were used in a predetermined random order. A nominal dose of 3 mL of normal saline was administered and nebulization ended when no aerosol was visible.

Fig. 1.
Fig. 1.

Study setup. The study participant was seated on a sofa chair with particle counters positioned at 1 and 3 ft from the participant at mouth level. The study investigator stayed in the room with the participant, with N95 mask worn throughout the study. With permission.

Comparisons of VMN Versus SVN With Mouthpiece and Face Mask

An SVN (AirLife 002446, CareFusion, San Diego, California) was compared with a VMN (Aerogen Ultra, Aerogen, Galway, Ireland) with a mouthpiece. Per manufacturer’s instructions, an open face mask (Vyaire Medical, Mettawa, Illinois) was used for SVN and a valved face mask (Salter Labs, El Paso, Texas) was used for VMN (Fig. 2). Per manufacturer’s instructions, 8 L/min compressed air was used to drive the SVN, whereas 2 L/min air was connected to the VMN chamber.

Fig. 2.
Fig. 2.

Different devices to reduce fugitive aerosol concentrations. SVN = small-volume nebulizer. A mouthpiece with an expiratory filter: VMN (A) and SVN (E); face mask with exhalation filters: VMN (B) and SVN (F); Exhalo scavenger with an aerosol face mask: VMN (C) and SVN (G); Vapotherm scavenger with an aerosol face mask: VMN (D) and SVN (H). With permission.

Comparisons of Different Mitigation Devices to Reduce Fugitive Aerosols Generated by Nebulizer and Interfaces

Nine subjects used SVN and VMN with a mouthpiece with an expiratory filter and a face mask with a scavenger (Exhalo, McArthur Medical, Rockton, Ontario, Canada) consisting of a collection scoop designed to attach to an aerosol mask and continuous draw suction set to −100 mm Hg. Five subjects received 4 additional nebulizations using SVN and VMN with a face mask fitted with exhalation filters (Respan Products, Erin, Ontario, Canada) and a different scavenger (Vapotherm, Exeter, New Hampshire) consisting of a face tent attached to a vacuum pressure of −100 mm Hg placed over the open face mask for SVN and the valved face mask for VMN (Fig. 2).

Sample Size

This study was designed as a superiority study based on our previous clinical study that showed reduced aerosol particle concentrations when wearing a surgical mask,15 particularly in close proximity to the source. With a filter or scavenger, the aerosol particle concentrations would be expected to decrease even more. Thus, we expected that various methods to mitigate the release of aerosols into the environment would have a medium-to-large treatment effect. Using G*Power software16 to calculate the sample size in repeated ANOVA measures, with confidence level (1-α) of 95% and power (1-β) of 80%, the number of patients who needed to be enrolled was 9.

Data Collection

Aerosol particle concentration data were extracted as the mean aerosol concentration for each particle size range during the initial baseline and with each device. The mean concentration was the average of the concentrations taken from the beginning to the end of the nebulization. Additionally, participants self-evaluated their comfort while breathing with each device using a 5-point Likert scale ranging between 1 (very uncomfortable) and 5 (very comfortable).

Statistical Analysis

Continuous variables at each particle size with each device were expressed as mean ± SD or median (interquartile range) based on the distribution of variables, which was analyzed by Kolmogorov-Smirnov test. Paired t test or Wilcoxon test was used to compare the differences of aerosol concentrations between 2 devices, whereas independent t test or Mann Whitney test was used to compare aerosol concentrations at 1 and 3 ft from participants. A P value of < .05 was statistically significant. Data analysis was conducted with SPSS statistical software (SPSS 26.0; IBM, Armonk, New York). To minimize bias, the statistician who analyzed the data was blinded to the names of each device.

Results

Comparisons of VMN Versus SVN With Mouthpiece and Face Mask

Nine participants (8 females) were enrolled in the first section of the study. The baseline particle concentrations in the room were stable except for the sole male participant, whose baseline concentrations were higher than the female participants. Fifteen minutes after the use of each interface, the aerosol particle concentrations in the room air returned to each individual’s baseline level. No participants coughed during nebulization.

SVN generated higher fugitive aerosol concentrations than VMN with mask at particle sizes of 1.0–5.0 µm (Fig. 3A) and with mouthpiece at particle sizes of 1.0–3.0 µm (Fig. 3B) (all P < .05). When VMN was utilized, mouthpiece generated lower fugitive aerosol concentrations than aerosol mask with particle sizes of 0.5–3.0 µm (Fig. 3D) (all P < .05), whereas no differences were observed for SVN (Fig. 3C). Fugitive aerosol concentrations were lower at 3 ft than 1 ft from participants when VMN was utilized with a face mask at particle sizes of 0.3 µm (P = .01) and SVN with a face mask at particle sizes of 3.0 µm (P = .02) (Fig. 4).

Fig. 3.
Fig. 3.

Mean fugitive aerosol concentrations of VMN versus SVN with mouthpiece and face mask at 1 ft from participants. A and B: SVN had higher fugitive aerosol concentrations than VMN with particle sizes of 1.0–5.0 µm for mask (A) and 1.0–3.0 µm for mouthpiece (B). C and D: Mask had higher fugitive aerosol concentrations than mouthpiece with particle sizes of 0.5–3.0 µm for VMN (D) whereas no differences for SVN (C). SVN = small-volume nebulizer. VMN = vibrating mesh nebulizer. *P < .05.

Fig. 4.
Fig. 4.

Comparison of fugitive aerosol concentrations at 1 and 3 ft from participants. When an aerosol face mask was utilized with nebulizers, fugitive aerosol concentrations were higher at 1 ft from participants than at 3 ft with A: VMN at particle sizes of 0.3 µm, and B: SVN at particle sizes of 3.0 µm. * P < .05.

Comparisons of Different Mitigation Devices to Reduce Fugitive Aerosols Generated by Nebulizer with Mouthpiece and Mask

Fugitive aerosol concentrations were lower when mouthpiece was used with a filter than that without a filter at particle sizes of 0.3–3.0 µm with SVN (Fig. 5A) (all P < .05) and at particle sizes of 0.3–1.0 µm with VMN (Fig. 5B) (all P < .05). When SVN was utilized with a mask, fugitive aerosol concentrations were lower with the Exhalo scavenger at particle sizes of 0.5–3.0 µm (Fig. 5C) (all P < .05). Whereas for VMN, no significant differences of fugitive aerosol concentrations were found with versus without the use of the Exhalo scavenger (Fig. 5D).

Fig. 5.
Fig. 5.

Mean fugitive aerosol concentrations of a mouthpiece with an expiratory filter and a face mask with Exhalo scavenger at 1 ft from participants. A and B: Compared to using mouthpiece alone, adding an expiratory filter to a mouthpiece significantly reduced fugitive aerosol concentrations with A: particle sizes of 0.3–3.0 µm for SVN and B: 0.3–1.0 µm for VMN. C and D: Compared to using aerosol mask alone, using the Exhalo scavenger with the aerosol mask significantly reduced fugitive aerosol concentrations with C: particle sizes of 0.5–3.0 µm for SVN, whereas D: no differences were observed for VMN. SVN = small-volume nebulizer. VMN = vibrating mesh nebulizer. * P < .05.

Five participants continued to complete the second part of the study. Compared to the aerosol face mask alone, using a face mask with exhalation filters significantly reduced fugitive aerosol concentrations at particle sizes of 0.3–3.0 µm for both VMN and SVN (all P < .05) (Fig. 6). Similarly, using the Vapotherm scavenger significantly reduced aerosol concentrations at particle sizes of 0.3–3.0 µm (all P < .05) for VMN while at particle size of 3.0 µm for SVN (P = .043). When SVN was used, both filter mask and Vapotherm scavenger had lower fugitive aerosol concentrations than Exhalo scavenger at particle sizes of 0.3–3.0 µm (all P < .05). Compared to the mouthpiece, both filter mask and Vapotherm scavenger had similar fugitive aerosol concentrations at all particle sizes (Fig. 6). Among the 4 mitigation devices with SVN and VMN, use of VMN with mouthpiece and an expiratory filter, a face mask with Vapotherm scavenger, and the filter face mask were the most efficient in reducing fugitive aerosols.

Fig. 6.
Fig. 6.

Comparisons of Vapotherm scavenger and filter face mask to reduce fugitive aerosols generated by nebulizer and face mask at 1 ft from participants. A: Fugitive aerosol concentrations with particle sizes of 0.3–10.0 µm with the use of SVN; B: fugitive aerosol concentrations with particle sizes of 0.3–10.0 µm with the use of VMN. *P < .05. SVN = small-volume nebulizer. VMN = vibrating mesh nebulizer. When SVN with an aerosol mask was utilized, fugitive aerosol concentrations with particle sizes of 0.3–3.0 µm were lower with Vapotherm scavenger, filter mask, and mouthpiece with a filter, which had similar effectiveness to reduce fugitive aerosol concentrations and higher effectiveness than Exhalo scavenger. When VMN with an aerosol mask was utilized, fugitive aerosol concentrations with particle sizes of 0.3–1.0 µm were lower with Vapotherm scavenger, filter mask, and mouthpiece with a filter, which had similar effectiveness to reduce fugitive aerosol concentrations. Whereas slightly lower fugitive aerosol concentration with mouthpiece and filter than Exhalo scavenger was only found at particle size of 1.0 µm.

Participants’ Comfort on Different Interfaces

When SVN was utilized, participants’ self-evaluated comfort while breathing was similar among different interfaces (Fig. 7). In contrast, when VMN was utilized, there was considerable variation in the comfort while breathing; participants ranked the face mask with the exhalation filters and mouthpiece with filter as being the most comfortable interfaces and mask with and without scavengers the least comfortable, with the complaint of feeling asphyxiated when breathing via the valved face mask. During the use of VMN, the comfort was higher with the mouthpiece and a filter than the valved face mask with Exhalo scavenger (P = .047). No significant differences regarding comfort were noted while breathing with VMN or SVN.

Fig. 7.
Fig. 7.

Participant self-evaluated comfort while breathing with different devices. SVN = small-volume nebulizer. VMN = vibrating mesh nebulizer. The devices with the highest comfort scores were VMN with a filter mask, VMN with a mouthpiece and a filter, and SVN with a filter mask. Whereas the 2 devices with mean comfort score below 3.0 are VMN with an aerosol mask and VMN with an aerosol mask and Exhalo scavenger. During the use of VMN, the comfort was higher with the mouthpiece and a filter than the valved face mask with Exhalo scavenger (P = .047).

Discussion

In this first in vivo study, we found that the concentrations of fugitive aerosols at particle sizes in the inhalable range (0.5–3.0 µm) were higher with an SVN than a VMN and with a face mask than a mouthpiece for VMN at a distance of 1 ft. Adding a filter to the end of the mouthpiece further reduced fugitive aerosol concentrations in both SVN and VMN. The face mask with exhalation filters and the Vapotherm face tent scavenger were both as effective in reducing fugitive aerosol concentrations as the mouthpiece with an expiratory filter. Large particles (5.0–10.0 µm) settle by gravity close to the source, whereas particle of 0.5–5.0 µm are suspended in air and have a high likelihood of depositing in the airway after inhalation. Thus, reducing their concentrations in the patients’ vicinity is clinically meaningful.

Similar to the in vitro findings by McGrath and colleagues,12 an SVN generated higher fugitive aerosol concentrations than a VMN. This might be explained by the higher driving flow used by SVN (8 L/min) than VMN (2 L/min), which dispersed aerosols to a further distance. Indeed, we found that the differences in fugitive aerosol concentrations between SVN and VMN were greater at 3 ft from participants than at 1 ft away. Therefore, regarding the reduction of fugitive aerosols during nebulizer use, a mouthpiece would be preferred over a face mask provided that the subject can form a tight seal around the mouthpiece with their lips.

To our knowledge, this is the first study to investigate the efficacy of commercially available scavengers and filter face mask in reducing fugitive aerosol concentrations. The 2 scavengers and the filter face mask reduced fugitive aerosol concentrations when compared to a traditional aerosol face mask with nebulizer. The Vapotherm scavenger had a similar effectiveness as the properly fitted filter face mask, both of which were more effective in reducing fugitive aerosol concentrations than the Exhalo scavenger. This is probably due to the larger vacuum space surrounding the nebulizer and face mask with the Vapotherm face tent scavenger (Fig. 2). Particularly, when the aerosol mask does not perfectly fit the subject’s face, some aerosols could leak from the gap between the mask and subject’s face without being suctioned by the Exhalo scavenger. Likewise, some aerosols could leak from a filter face mask when it does not form a tight fit with the subject’s face. Moreover, the scavenger might suction the aerosol from the aerosol face mask, or the filter mask may capture the aerosol, but the impact of the scavenger or filter mask on aerosol delivery is unknown. Adding a filter to the end of a mouthpiece is recommended by groups of researchers and scientific committees,9,13,14 and our study is the first in vivo trial to demonstrate its effectiveness in reducing fugitive aerosol emissions. It should be noted that with the use of the mouthpiece and an exhalation filter aerosol could still leak or be exhaled via the subject’s nose, despite achieving a tight mouth seal.

Our results provide valuable clinical implications that should be considered when choosing the appropriate nebulizer and interface for patients with respiratory diseases that are spread by the airborne route, such as COVID-19, influenza, or tuberculosis. Especially at the current phase, there are emerging reports of using aerosol treatment for COVID-19 patients, including inhaled glucocorticoid17 or heparin,18 aerosolized vaccine,19 etc. Moreover, our findings are meaningful to help clinicians avoid secondhand inhalation of medical aerosols when providing nebulizer treatment for patients. Clinicians should consider not only fugitive aerosol concentrations but also the possibilities of contaminating the nebulizers and interfaces.13 Lower chances of contamination would reduce the risk of generating and dispersing bioaerosol to the surrounding environment. The possibility of contaminating the nebulizer depends on the structure and the use of the nebulizer. As the nebulizer cup is directly open to a face mask or a mouthpiece via a T-piece, an SVN has a higher possibility of contamination by patient’s secretions.14 Additionally, SVN can be easily soiled in the process of cleaning, air drying, or storage after use.20 In contrast, in VMN, the cup is isolated from the nebulizer reservoir; the medication cup is usually sealed with a cap and only opened for filling medication. There is little to no possibility that patient secretions contact with the mesh plate to generate contaminated aerosol.14 As such, use of VMN may be preferred over SVN for COVID-19 patients.9,13,14

If SVN is the only choice, adding a filter to the mouthpiece is recommended if patients can breathe via the mouth with a tight seal around the mouthpiece. During nebulization, removing the mouthpiece from the mouth is discouraged. If patients need to cough or talk, the SVN should be turned off. Otherwise, using a filter mask or adding a face tent scavenger with the aerosol mask is required. Furthermore, if possible, clinicians should stand at a minimum of 3 ft from patients as fugitive aerosol concentrations decrease with increasing distance from the source.21 Regardless, clinicians should always wear appropriate personal protective equipment when providing nebulization for patients to avoid inhaling the secondhand medical aerosol and protect clinicians from bioaerosols generated by patients during coughing or talking or contaminated aerosols during nebulization. Previous studies showed that coughing generated even more aerosols than the fugitive aerosols generated during nebulization,22 and coughing generated bioaerosol that contains microorganisms.23 Thus, wearing personal proctective equipment during the care for any COVID-19 patient is essential as patients might cough at any time or cough may be provoked by nebulization. As a further precautionary measure, the number of people inside the patient room should be minimized during nebulization. It should be noted that fugitive aerosol suspended in the room requires time to clear to baseline after nebulization (15 min in our ICU room) depending on the space volume, air exchange frequency, and the use of negative pressure in the room.23,24

There are several limitations to our study. Due to the lengthy process, only 5 participants volunteered to continue the additional tests with the filtered face mask and Vapotherm scavenger. Future studies with larger sample size are needed to confirm our findings with both devices, especially the cost-effectiveness in avoiding/reducing transmission is warranted. Additionally, only a limited number of mitigation devices were evaluated; future studies are needed to compare a broader range of commercial devices. Second, healthy volunteers may have different breathing patterns than patients; and cough, especially productive cough, could influence the results in patients compared to healthy volunteers. Thus, studies on subjects with varying respiratory patterns should be performed to validate our findings. Third, all the measurements were made in one ICU room at our hospital; results may vary in different hospital rooms depending on environmental factors, such as temperature and humidity in the room, and the number of air exchanges/h.23 Fourth, we only had 2 particle counters placed in 2 positions, especially the particle counter at 1 ft was placed slightly behind the participant (convenient for stabilizing the particle counter); the aerosol concentrations especially the large particles might vary at different position; future studies with more particle counter placements are needed. Fifth, similar to other studies that used aerosol particle concentrations to indirectly reflect the aerosol transmission risk,25 our study did not investigate the virus load nor its infectivity. Sixth, we found that our participants had large variance in comfort with breathing when different interfaces were employed with VMN, in contrast to similar comfort with breathing when different interfaces were employed with SVN. The feeling of asphyxia with VMN and valved face mask might be due to the low oxygen flow setting (2 L/min). Whether the comfort noted by healthy volunteers would differ from patients with respiratory diseases also needs further investigation. Lastly, the particle concentrations in the room at baseline varied under various experimental settings. Ideally, such experiments should be conducted in a particle-free environment.

Conclusions

SVN produced higher fugitive aerosol concentrations than VMN, whereas face masks generated higher fugitive aerosol concentrations than mouthpieces. Adding an exhalation filter to the mouthpiece or a scavenger to the face mask reduced fugitive aerosol concentrations for both SVN and VMN. Vapotherm scavenger and filtered face mask had similar effectiveness in reducing fugitive aerosol concentrations as mouthpiece and an exhalation filter.

Acknowledgments

We thank all the volunteers for generously sharing their time to participate in this lengthy study. We also appreciate Mr Rongshou Zheng MPH, for his help with the data analysis.

Footnotes

  • Correspondence: Jie Li PhD RRT RRT-ACCS RRT-NPS FAARC, 600 S Paulina St, Suite 765, Chicago, IL, USA. E-mail: Jie_Li{at}rush.edu

  • See the Related Editorial on Page 496

  • Dr Li discloses relationships with Fisher & Paykel Healthcare, Aerogen, The Rice Foundation, the American Association for Respiratory Care, and Heyer. She also serves as Section Editor for Respiratory Care. Dr Fink is Chief Science Officer for Aerogen Pharma. Dr Dhand discloses relationships with GSK Pharmaceuticals, Boehringer Ingelheim, Mylan, Teva, and AstraZeneca Pharmaceuticals. The remaining authors have disclosed no conflicts of interest.

  • A version of this paper was presented by Ms Harnois as an Editors’ Choice abstract at AARC Congress 2021 LIVE!, held virtually December 1, 2021.

  • This study was supported by unrestricted research funding from Aerogen. Devices for testing were supplied by McArthur Medical, Vapotherm, and Respan. The companies had no role in the study design, data collection, analysis, preparation of the manuscript, or the decision to publish the findings.

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