If Oral Breathing Does Not Determine Mask Choice for Continuous Positive Airway Pressure Delivery, What Does?

To the Editor:

As underlined by the 2020 American Thoracic Society Workshop Report, current evidence suggests that nasal masks should be the first option for the delivery of continuous positive airway pressure (CPAP) therapy for most patients with obstructive sleep apnea (1). Some patients, however, may require an oronasal mask to optimize their treatment, but evidence to support the choice is lacking. We read the study by Xavier and colleagues with interest, in particular their hypothesis that patients for whom an oronasal mask is well adapted breathe predominantly through the nose (2).

The data provided by Xavier and colleagues suggest that oral breathing is not the main pathophysiological endotype (PE) associated with the choice of an oronasal mask, because only 1 of the 12 patients investigated breathed exclusively through the mouth (2). These results therefore raise the question, If oral breathing is not the main reason for the choice of an oronasal mask, which other PEs determine the choice?

Oronasal masks are often used to prevent mouth opening, which disturbs the patient and leads to adverse effects, in particular leaks and a dry mouth. Mouth opening may therefore be the main PE that leads to the choice of an oronasal mask. In our opinion, three main factors explain mouth opening during CPAP therapy in patients with obstructive sleep apnea:

• 1.Nasal obstruction: Evidence supporting this is conflicting. Two pathophysiological observational studies in our group found that the choice of an oronasal mask was related to severe nasal obstruction (3, 4), although this was not found by Xavier and colleagues (2). This apparent discrepancy may be the result of differences in the severity of the nasal obstruction between the three studies. In the Xavier and colleagues study, only 1 of 12 patients was classified with severe nasal obstruction, and 4 of 12 were classified with moderate nasal obstruction (2). Current medical consensus is to treat nasal symptoms first to improve acceptance of the nasal mask and to switch to an oronasal mask only if nasal treatment fails and nasal mask tolerance remains poor (1).
• 2.Respiratory effort: During obstructive respiratory events, the mandible drops progressively as the respiratory effort increases, which can lead to leakage through the mouth (5).
• 3.Sleep stage: Variability in masseter tone with sleep stage could also contribute to mouth opening (5, 6).

We suggest that because oral breathing is an infrequent reason for the choice of an oronasal mask, as shown by Xavier and colleagues, clinicians should assess and manage mouth opening when possible (e.g., by treating nasal obstruction or sometimes increasing CPAP to reduce residual respiratory effort).

As interest in personalized medicine grows within the medical community, it is important to develop new tools to optimize mask selection for individual patients. We congratulate Xavier and colleagues (2) for providing new evidence regarding mask choice because this will lead to precision medicine and better patient outcomes. We fully agree with Xavier and colleagues that patients who breathe through the nose should switch to a nasal mask, but the question remains whether patients whose main problem is mouth opening should also be switched. It is our opinion that the reasons for the mouth opening should be managed first, in particular nasal obstruction and residual respiratory effort.