Objectives: The physiological impact of wearing personal protective equipment (PPE), in particular filtering-face-piece 3 (FFP3) masks, has increasingly been gaining importance since the outbreak of coronavirus disease 2019 (COVID-19). So far, gas exchange has been examined using transcutaneously measured partial pressure of carbon dioxide (PaCO₂), ergo-spirometry and impedance cardiography. Material and Methods: In this structured investigation, arterial blood gas analysis in a 30-year-old female resident was carried out during a 13-hour day shift on the COVID-19 Intensive Care Unit of the University Hospital of Innsbruck, Austria. An FFP3 mask (3M^TM Aura^TM) with an exhalation valve was continuously worn, except for 1 break of 20 min. Arterial blood samples were obtained before putting on the PPE, and after 5 h, 9 h and 13 h of working in the contaminated area. Results: During the multi-hour wearing time, an increase in PaCO₂ (the baseline value: 29.3 mm Hg, the max. value: 38.9 mm Hg) and a continuous decrease in partial pressure of oxygen (PaO₂, the baseline value: 102 mm Hg, the min. value: 80.8 mm Hg) was detectable. Conclusions: All measured values were within the normal range, but a trend towards an insufficient gas exchange could be suspected. Int J Occup Med Environ Health. 2021;34(6):817–9