Inhaled CO2 Concentration while Wearing Face Masks: A Pilot Study Using Capnography

Cecilia Acuti Martellucci, Maria Elena Flacco, Mosè Martellucci, Francesco Saverio Violante, Lamberto Manzoli

None of the available evaluations of the inhaled air carbon dioxide (CO2) concentration, while wearing face masks, used professional, real-time capnography with water-removal tubing. We measured the end-tidal CO2 using professional side-stream capnography, with water-removing tubing (Rad-97™ capnograph), at rest, (1) without masks, (2) wearing a surgical mask, and (3) wearing a FFP2 respirator, in 102 healthy volunteers aged 10-90 years, from the general population of Ferrara province, Italy. The inhaled air CO2 concentration was then computed as: ((mask volume × end-tidal CO2) + ((tidal volume – mask volume) × ambient air CO2)) / tidal volume).

The mean CO2 concentration was 4965±1047 ppm with surgical masks, and 9396±2254 ppm with FFP2 respirators. The proportion of the sample showing a CO2 concentration higher than the 5000 ppm acceptable exposure threshold recommended for workers was 40.2% while wearing surgical masks, 99.0% while wearing FFP2 respirators. The mean blood oxygen saturation remained >96%, and the mean end-tidal CO2 <33 mmHg. Adjusting for age, gender, BMI, and smoking, the inhaled air CO2 concentration significantly increased with increasing respiratory rate (with a mean of 10,143±2782 ppm among the participants taking 18 or more breaths per minute, while wearing FFP2 respirators), and was higher among the minors, who showed a mean CO2 concentration of 12,847±2898 ppm, while wearing FFP2 respirators.

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