Discussion
HEAT
Surgical-type facemasks have been in use for over one hundred years, with the first major study performed by Doust in 1918 evaluating their use in the prevention of respiratory pathogen transmission (The first 90 years of surgical mask use passed with minimal concerns regarding ventilation or oxygenation. Assessments of carbon dioxide levels in masked participants were quite rare prior to the COVID-19 pandemic. A 2012 study evaluated twenty adult participants unmasked on a treadmill for 1 h followed by 1 h while masked, finding clinically insignificant increases in respiratory rate and transcutaneous carbon dioxide levels (Physiologic assessments of pediatric participants wearing surgical masks are even less common, with none identified prior to the COVID-19 pandemic. A 2021 study evaluated triple layer surgical face masks on 47 children, including many younger than 2 years of age (A later 2021 study focused on an ETCO2 endpoint and suggested masks caused physiologic harm, although the study model did not include any live subjects. Using a lung simulator and intubation head, the simulation resulted in an average ETCO2 increase of 17.4 mmHg (Publications like the above retracted study fueled increasing claims about physiologic harm caused by mask wearing. Multiple lawsuits against Ohio school districts (With the paucity of studies on the topic of surgical masking, small sample sizes focusing on one age group, and variable recorded physiological data, this study was designed to be the largest of its kind assessing the effect of surgical masks on both end tidal CO2 levels and inspired CO2 levels. It is the first study to compare both end tidal and inspired CO2 levels in masked children, and the first to compare the effects of mask dead space in children Surgical masks have a pore size of around 20 micrometers, with CO2 molecules measuring 0.32 nanometers and O2 molecules measuring even smaller. Even triple layer surgical masks like the models used in this study have high breathability, as measured by the low differential pressure of <5 mm H20/cmIncreases in mechanical dead space (or apparatus dead space) are of particular importance in pediatric patients because of their larger dead space to tidal volume ratio (Clinically, it is well known that an increase in mechanical dead space can have significant effects on PaCO2 levels, especially in the youngest of pediatric patients. In a study of infants and young children, adding a heat and moisture exchanger (HME) into the ventilation circuit increased the PaCO2 inversely proportional to weight and age. In healthy pediatric patients weighing more than 25 kg, however, the additional 22 ml of dead space from the HME had no effect (The retracted 2021 study (The argument in the 2021 Kisielinski review article (Limitations of the study include a masked observation period limited to 15 min, and the evaluation of subjects only at rest. Longer observation times and the effects of masking during exercise have been reported in other smaller studies, as noted above. In this study, ETCO2 and ICO2 levels were significantly increased from baseline within the first 5 min of masking, and pairwise comparisons between each 5-min masked period thereafter confirmed the ETCO2 and ICO2 levels were at equilibrium (