Background:
Face masks are recommended based on the assumption that they protect against
SARS-CoV-2 transmission, however studies on their potential side effects are
still lacking. We aimed to evaluate the inhaled air carbon dioxide
(CO
2
) concentration, when wearing masks.
Methods:
We measured end-tidal CO
2
using professional side-stream
capnography, with water-removing tubing, (1) without masks, (2) wearing a
surgical mask, and (3) wearing a FFP2 respirator (for 5 minutes each while
seated after 10 minutes of rest), in 146 healthy volunteers aged 10 to
90 years, from the general population of Ferrara, Italy. The inhaled air
CO
2
concentration was computed as: ([mask volume × end-tidal
CO
2
] + [tidal volume − mask volume] × ambient air
CO
2
)/tidal volume.
Results:
With surgical masks, the mean CO
2
concentration was
7091 ± 2491 ppm in children, 4835 ± 869 in adults, and 4379 ± 978 in the
elderly. With FFP2 respirators, this concentration was 13 665 ± 3655 in
children, 8502 ± 1859 in adults, and 9027 ± 1882 in the elderly. The
proportion showing a CO
2
concentration higher than the 5000 ppm
(8-hour average) acceptable threshold for workers was 41.1% with surgical
masks, and 99.3% with FFP2 respirators. Adjusting for age, gender, BMI, and
smoking, the inhaled air CO
2
concentration significantly
increased with increasing respiratory rate (mean 10 837 ±3712 ppm among
participants ⩾18 breaths/minute, with FFP2 respirators), and among the
minors.
Conclusion:
If these results are confirmed, the current guidelines on mask-wearing should
be reevaluated.