Masks do not affect gas exchange

This article was first published in October 2020.

‘I feel short of breath.’
 
‘I can’t breathe properly.’
 
‘I find wearing it for long periods of time uncomfortable.’
 
These are the kinds of comments Melbourne-based GP Associate Professor Vicki Kotsirilos has been hearing from patients in regards to wearing a face mask.
 
She told newsGP such concerns are ‘very common’, even in patients with no history of existing lung disease.
 
‘Basically a lot of patients are experiencing difficulty wearing face masks,’ she said.
 
Recent research offers such patients reassurance.
 
Published in the Annals of the American Thoracic Society on 2 October 2020, the research found that wearing a face mask has a negligible negative effect on oxygen and carbon dioxide levels.
 
The study was performed by examining 15 physicians without lung conditions and 15 veterans with severe chronic obstructive pulmonary disease (COPD).
 
Each participant performed a six-minute walk test while wearing a surgical face mask, with arterial blood analysis performed before and immediately after the walk.
 
The researchers also tested the participants’ blood oxygen levels at five and 30 minutes while resting with a face mask on, and found there were no changes of clinical significance in either end-tidal CO₂ nor oxygen saturation at rest.
 
Subjects with severe COPD experienced decreased oxygenation as expected during the six-minute walk.
 
‘However, as a group, subjects with COPD did not exhibit major physiologic changes in gas exchange measurements after the six-minute walk test using a surgical mask, particularly in CO₂ retention,’ the authors wrote.
 
‘[T]his data find that gas exchange is not significantly affected by the use of surgical mask, even in subjects with severe lung impairment.’
 
The study’s lead author, Dr Michael Campos, says the results show that the effects of mask-wearing on gas exchange is ‘minimal at most’.
 
‘Dyspnoea, the feeling of shortness of breath felt with masks by some, is not synonymous [with] alterations in gas exchange,’ he said.
 
‘It likely occurs from restriction of air flow with the mask, in particular when higher ventilation is needed on exertion.’
 
These findings make sense to Associate Professor Louis Irving, Director of Respiratory and Sleep Medicine at the Royal Melbourne Hospital.
 
He told newsGP that wearing a face mask does not alter gas exchange in a meaningful way.
 
‘You’d be horrified if people are becoming hypoxic or hypercapneic [from wearing a face mask],’ he said.
 
However, he says people do report feeling breathless or uncomfortable when wearing a mask.
 
Associate Professor Irving says that feeling relates to increased work of breathing, rather than changes in gas levels, and this feeling is often even more pronounced in people with underlying lung disorders.
 
‘The reality is that patients with COPD, particularly if they’ve got bad COPD, do find it more uncomfortable to wear a mask and that will be unrelated to oxygen and carbon dioxide levels,’ he said.
 
‘It’s just like if you put your hand over your face and started walking up and down the corridor – it’s harder to breathe.’
 
Perception of breathlessness can be likened to a pain threshold, and is affected by fatigue, how robust a person is, and other factors.
 
Associate Professor Irving explains there is a level of work of breathing that people ‘accept as normal’ but, if that increases, they then become aware of it and that can alter perceptions of breathlessness. 
 
‘For people wearing a mask there will be an increased work of breathing and some people won’t think twice about it, because they’re too busy doing other stuff and they’re not concentrating on it,’ he said.
 
‘But there will be some people who are very aware of it and will find it almost suffocating.
 
‘If you’ve already got borderline abnormal lung function – where, as soon as you start to walk you’re aware of your breathing – having a mask on will make that even more noticeable.’
 
The authors of the research concur that there are other factors that lead to feelings of breathlessness while wearing a mask.
 
‘The discomfort felt with surgical mask use has been ascribed to neurological reactions  – increased afferent impulses from the highly thermosensitive area of the face covered by the mask or from the increased temperature of the inspired air – or associated psychological phenomena such as anxiety, claustrophobia or affective responses to perceived difficulty in breathing,’ they wrote.
 
They do note, however, that using an N95 mask may increase pCO₂ in lung-healthy users, but that this change occurs without ‘major physiologic burden’.
 
Associate Professor Irving says this research can offer reassurance to patients who feel they may be desaturating from wearing a surgical or cloth face mask.
 
‘You have to be very hypoxic before you actually feel breathless,’ he said.
 
‘When we fly from Melbourne to Sydney in a partially pressurised aircraft, it’s routine for our oxygen saturation levels to drop below 90, particularly if we exercise or have chronic lung disease,’ he said.
 
‘And people don’t feel breathless on an aircraft.
 
‘You have to be very hypoxic before you start to increase your ventilation; the PaO₂ has to be below 60 mmHg.’
 
Associate Professor Kotsirilos says the results of this research will help her when discussing the issue of face masks with her patients.
 
She says most patients understand the importance of wearing a mask to reduce transmission of SARS-CoV-2.
 
‘But it’s very common, including in patients who have healthy lungs, who don’t have existing lung disease like asthma or COPD, to ask me for letters of exemption so they can walk outdoors without needing to wear a mask,’ she said.
 
‘Then I have to educate and reassure them why they need to wear it.’

While Associate Professor Irving says it is reassuring to know that face masks do not affect gas exchange, he says it does not necessarily make them more tolerable for those who feel short of breath when wearing them.
 
‘Using an analogy, just because people don’t become hyperthermic with wearing personal protective equipment [PPE] all day, doesn’t mean that they’re not uncomfortable wearing PPE all day, and that they don’t feel hot and sweaty,’ he said.
 
‘If you’re encouraging compliance it’s not just a safety [issue], it’s an acceptability [issue].’
 
Associate Professor Kotsirilos believes the issue of acceptability will become even more problematic since a recent change in restrictions came into place in Victoria, which stipulates that masks must be fitted and people can no longer use a scarf, bandanna or face shield instead.
 
‘That will make it even more challenging for some of our patients,’ she said.
 
The authors want their research to be used to help dispel myths around mask use.
 
‘It is important to inform the public that the discomfort associated with mask use should not lead to unsubstantiated safety concerns as this may attenuate the application of a practice proven to improve public health,’ they wrote.
 
‘We believe our data will help mitigate fears about the health risks of surgical mask use and improve public confidence for more widespread acceptance and use.’
 
While Associate Professor Irving hopes the assurance of safety can help quell fears, the issue regarding discomfort also needs to be addressed.
 
‘Breathlessness can be dulled, if you can get used to it and just turn the amplifier down, or it can be amplified if people get really worried by it,’ he said.
 
‘However, we shouldn’t discount the fact that people with COPD say, “I do find it harder to breathe [with one on]”. We need to acknowledge that.’
 
He says it is also worth acknowledging that people with no underlying lung disorders may feel breathless when wearing a mask, and should be reassured about their safety.
 
‘They may find it uncomfortable to wear a mask, but that doesn’t relate to their oxygen or carbon dioxide levels,’ he said.
 
‘It isn’t causing any physiological harm.’
 
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