Protective Face Masks Add Significant Dead Space

Question What is the effect of protective face masks on pulmonary gas exchange? Is there an objective reason that explains the frequently reported breathing limitations and impairments in well-being caused by masks?\n\nMethods A lung simulator with intubation head was used to create breathing through different masks, taped and untaped mounting, mouth open and closed, quiet breathing and moderate exercise. Measurements within the trachea included capnography, pneumotachography and oximetry. From these measurements, indices of the effectiveness of carbon dioxide (CO2) elimination and oxygenation were derived and compared with non-mask reference values.\n\nResults All measurements with masks showed significant increase in end-tidal CO2 (etCO2, +17.4 mmHg on average), even more pronounced in the moderate exercise setting (+25.9 mmHg on average). The extent of the increase of etCO2 varied with different mask types and with the mouth open or closed. The Bohr dead space nearly doubled when wearing a protective face mask. Intratracheal oxygen concentration decreased marginally when wearing protective masks (−0.6 vol% on average). The inspiratory and expiratory resistance increased marginally, on average by 0.4 mbar (L s−1)−1 and 0.3 mbar (L s−1)−1, respectively.\n\nAnswer Currently available protective face masks only marginally affect inspiratory oxygen concentration and resistance to breathing. However, they significantly increase dead space ventilation. The increasing end-tidal CO2 concentration could explain the reported symptoms among mask wearers especially in those with pre-existing lung disease.\n\nThe accumulation of CO2 is related to the size of the dead space. Simple measures to minimise the dead space would be tight fitting masks and preference for nasal breathing.\n\nFootnotes \n\nThis manuscript has recently been accepted for publication in the European Respiratory Journal . It is published here in its accepted form prior to copyediting and typesetting by our production team. After these production processes are complete and the authors have approved the resulting proofs, the article will move to the latest issue of the ERJ online. Please open or download the PDF to view this article.\n\nConflict of interest: Dr. Elbl reports grants from Innosuisse (Swiss innovation agency), during the conduct of the study;.\n\nConflict of interest: Dr. Brunner reports personal fees and other from neosim AG, during the conduct of the study; other from Organis GmbH, outside the submitted work; .\n\nConflict of interest: Dr. Schier reports grants from nnosuisse (Swiss innovation agency), during the conduct of the study;.\n\nConflict of interest: Adrian Junge has nothing to disclose.\n\nConflict of interest: Dr. Junge reports grants from Innosuisse (Swiss innovation agency), during the conduct of the study;.