Read on Twitter
1/ Nebulizers have taken a lot of flak recently, in large part due to the use of a neb by an asthmatic patient in an AUS quarantine hotel. There’s an idea floating around that this only happened because a nebulizer was used– that the nebulizer is a smoking gun.
2/ I'm going to defend nebs here. First of all, nebulizers work by nebulizing (heh) a solution containing some pharmaceutical drug of choice from a reservoir. There’s a few different ways to do this, the most common being with a jet of pressurized air from e.g. a compressor.
3/ The aerosol generated by a nebulizer is a pharmaceutical aerosol meant to be inhaled by the patient. This is a useful tool as the lungs are a great way to deliver certain drugs to the body. This aerosol is NOT the aerosol we need to be concerned with for SARS-CoV-2.
4/ The aerosol we are concerned with is the bioaerosol generated in the airways of the patient. This bioaerosol, comprised of respiratory fluid/saliva, can contain virus if originating from a carrier of SARS-CoV-2.
5/ This bioaerosol does not originate from the nebulizer; it exists with or without nebulizer use and the patient will be emitting this aerosol in varying amounts during any number of actions (talking, coughing, breathing, etc.)
6/ So where could the the nebulizer come into play? Hypothetically, it’s possible (though unlikely) that the reservoir of the nebulizer could become contaminated with virus emitted by the patient. This requires a unique set of circumstances that would result in
7/ virus-laden droplets from the patient landing in the reservoir. As best as I can tell, this has not been demonstrated to have occurred with SARS-CoV-2, but an enterprising EPI team should be able to measure this if they’re convinced nebs are the problem.
8/ If this contamination occurs, the virus that is now inside the contaminated reservoir has no way to replicate. We take a small amount of virus from the patient, deposited it inside our reservoir, and the neb may now nebulize this small amount of virus over a long duration.
9/ There is no additional virus being created here; we have only the virus emitted by the patient. By intuition, we end up with essentially the same amount of virus in our local environment.
10/ There are some other mechanistic effects that could occur with regards to coagulation of pharmaceutical aerosols from the nebulizer with bioaerosol from the patient, leading to different sizes of exhaled droplets and minor differences in droplet behaviour later on.
11/ There's no evidence of contamination of medical aerosols occurring in the lungs before exhalation ( https://www.liebertpub.com/doi/pdf/10.1089/jamp.2020.1615) and back of the envelope calcs suggest this and above effects aren't of practical concern given the number/size distributions and timescales.
12/ There’s actually some evidence that nebulized aerosols may REDUCE the emission of bioaerosols https://www.ncbi.nlm.nih.gov/pmc/articles/PMC536048/ (via deposited isotonic saline altering physical properties of the fluid lining the airways). Isotonic saline is a common ingredient in solutions for nebs.
13/ The issue here is not really the nebulizer itself – it’s that the patient is not masked while using a nebulizer. There’s a pretty easy fix here, which is to use an exhalation filter to capture fugitive bioaerosols emitted by the patient.
14/ This is the explicit recommendation of the International Society for Aerosols in Medicine, who addressed this question of nebulizer use during COVID-19 in the position paper I linked above and again here ( https://www.liebertpub.com/doi/10.1089/jamp.2020.1615).
15/ Many of our definitions of AGMPs have been influenced by SARS. A retrospective study found that medical nebulizer use did NOT result in a significant increase in risk for HCW, in stark contrast to intubation and non-invasive mechanical ventilation ( https://pubmed.ncbi.nlm.nih.gov/22563403/ ).
16/ Now of course SARS-CoV-2 is not the same virus that caused SARS, but we’ve certainly been applying (some of) the lessons from SARS to guide our decision making during this pandemic.
17/ I believe that the case in Australia tells us that we need to revisit the whole idea of what is and what isn’t an AGMP, something that has been much more elegantly discussed by @First10EM ( https://first10em.com/aerosol-generating-medical-procedure-is-a-faulty-paradigm/).
18/ Finally, we should also consider the effects that taking away a useful treatment will have on an asthmatic patient. Uncontrolled asthma is probably going to lead to more coughing, and we know coughing produces a lot more bioaerosol than breathing.
19, end/ There are other devices like DPIs and pMDIs, but these aren’t perfect solutions either. Blame is being thrown at a device, when it should be thrown at a paradigm for AGMPs that is showing cracks at the seams.
