P039 Impact of protective masks on gas exchange in chronic hypercapnia

Abstract Introduction Protective masks are used in the prevention of respiratory virus transmission. Mask safety is well documented in healthy individuals but is unclear in people with chronic hypercapnic respiratory failure (CHRF). Additionally, masks are often poorly tolerated in this population. This study assessed the effect of surgical masks and N95 masks in people with stable CHRF using non-invasive ventilation (NIV). Methods A randomised cross-over trial was performed. SpO2 and transcutaneous CO2 (PtcCO2) were measured in participants wearing a surgical mask, an N95 mask and no mask for 20-minute periods at rest. Secondary outcomes included heart rate, respiratory rate, the A1 scale from the Multidimensional Dyspnoea Profile (MDP) and the modified Borg dyspnoea scale (mBORG). Results 24 participants (50% female; mean (SD) age 61 (13) years) participated. The surgical and N95 masks had negligible effects on SpO2, PtcCO2, heart rate and respiratory rate across the 20-minute study period. Masks increased the mBORG (surgical mask median difference 0.75 points [95% CI 0.25 to 2.00]; N95 mask median difference 1.25 [95% CI 0.75 to 2.00]) and MDP (surgical mask median difference 1.5 points [95% CI 0.5 to 2.5]; N95 mask median difference 2.0 points [95% CI 1.0 to 3.0]). Discussion Wearing a surgical or N95 mask did not significantly affect gas exchange in patients with CHRF using NIV. However, dyspnoea and breathing discomfort did increase.