Reduced Effective Oxygen Delivery and Ventilation with a Surgical Facemask Placed under Compared to over an Oxygen Mask: A Comparative Study

OBJECTIVES: Consensus guidelines for perioperative anesthesia management during the COVID-19 pandemic recommend that patients wear a facemask in addition to their oxygen mask or nasal cannulae following tracheal extubation, where this is practical. The effects on effective oxygen delivery and ventilation of a surgical facemask under compared to over an oxygen (O(2)) mask are unclear. DESIGN: Single-center, comparative pilot study. Setting. Endoscopy procedure room at a major academic hospital. SUBJECTS: Five healthy anesthesiologists. Interventions. Using a carbon dioxide (CO(2)) sampling line positioned at the lips, the fraction of inspired O(2) (FiO(2)), fraction of expiratory O(2) (FeO(2)), expiratory end-tidal CO(2) (EtCO(2)), and respiratory rate (RR) were measured under the following conditions: (1) a surgical facemask only, (2) a surgical facemask under an O(2) mask, (3) an O(2) mask only, and (4) a surgical facemask over an O(2) mask. Measurements and Main Results. The sampled fractional expired oxygen (FeO(2)) at the lips was significantly lower when the surgical facemask was under compared to when over the O(2) mask (27.9± 1.68 vs. 49.9 ± 6.27, p = 0.001), while there was no significant difference in inspired oxygen (FiO(2)). The sampled expiratory EtCO(2) was significantly higher when the surgical facemask was under the O(2) mask compared to when over the O(2) mask (28.3 ± 8.5 vs. 23.5 ± 7.6, p = 0.026). The RR was not significantly different when the surgical facemask was under compared to over the O(2) mask. CONCLUSIONS: Effective oxygen delivery and ventilation was reduced (lower FeO(2) and increased EtCO(2)) when a surgical facemask was placed under compared to over an O(2) mask.