Evaluation of Exhaled Fugitive Particles During Mechanical Ventilation

COVID-19 has brought concerns about caregiver contamination from patient-exhaled gases and droplets to heights not seen since early days of tuberculosis treatment. Much of the focus has been on procedures and therapy associated with non-intubated patients during noninvasive ventilation, high-flow nasal cannula (HFNC), bronchoscopy, and intubation. This month’s Editor’s Choice paper by Ring et al sought to determine the effect of nebulization and breathing pattern on exhaled viral particles during mechanical ventilation using an ex vivo porcine lung system and found that neither had a statistically significant effect on the viral quantity expelled.¹ This study is especially relevant in the era of the COVID-19 pandemic, as the fear of the potential risk of fugitive aerosols has been practice-altering, despite limited data.^2,3 The authors’ ingenuity in developing a model to allow for aerosol viral quantification in an intubated and mechanically ventilated patient is appreciated.

All in vitro and ex vivo models have limitations. The main limitation of this study is that the results are translatable only to mechanically ventilated patients. The authors evaluated the spread of particles within a ventilator circuit as opposed to those dispersed into the room atmosphere, making the results of this study only translatable to patients with an endotracheal tube in place.¹ This is important to note because clinically the concern of fugitive aerosols during nebulization and cough is primarily due to spontaneously breathing patients expelling bioaerosols, open nebulizers dispersing bioaerosols, or bioaerosol dispersion when the ventilator circuit or artificial airway is open to the room. Additionally, there are several relevant variables this model does not address, including the presence of viral content in upper airways, the contribution of upper airways to the components of expelled aerosols during cough, cough induction caused by aerosolized medications passing through the upper airways instead of through an endotracheal tube, and the dispersion of exhaled viral particles during a cough without an artificial airway present.

To allow for broader clinical application, further studies to help evaluate these variables would be useful. Specifically, spontaneous breathing models open to the environment would allow for more translatability to most fugitive aerosol concerns and would allow for better assessment of the role of the upper airway in viral particle expulsion. For example, Bem et al⁴ used laser light scattering and particle counters to detect and quantify aerosols generated with HFNC and conventional oxygen therapy; these methods may be useful in conjunction with those used in the current study. Additionally, nebulization studies using traceable aerosols would allow for a mode of detection outside of a ventilator circuit and could also be considered.⁵

Although this study shares limitations associated with virtually all in vitro models, the data presented here are valuable and interesting. Many health care centers throughout the world reduced the use of nebulizers throughout the pandemic out of concern of the risks of fugitive aerosols without supportive data. While not translatable to all patients and settings, the findings reported here suggest that using a nebulizer within a ventilator circuit during mechanical ventilation is not a biohazard risk. Further studies with more comprehensive models will help generate the evidence to guide best practice for respiratory clinicians in the next respiratory pandemic.

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