Prolonged N-95 Mask Use Did Not Result in Carbon Dioxide Retention or Clinically Significant pH Changes in One Cohort of Health Care Workers

ABSTRACT

Study Objective: Concerns over emerging infectious diseases spread via airborne or respiratory droplet transmission have highlighted the importance of respiratory protection for health care workers. During the current COVID-19 pandemic, widespread use of N95 masks by health care workers helped to prevent transmission and contraction of SARS-CoV2. It is not clear if prolonged continuous use of an N-95 during clinical duties results in any detrimental physiological effects and clinical features from increased carbon dioxide. The primary objective of the study was to evaluate for carbon dioxide retention and/or clinically significant changes in pH with prolonged use of N-95 masks. Secondary objective assessed for changes in vital signs and any unexpected subjective symptoms experienced by the study participants. Methods: 10 healthy emergency medicine residents between the ages of 27 and 31 years old provided written consent. All subjects denied history of structural lung disease (asthma, COPD, interstitial lung disease) and had been previously fit-tested for the correct size of N-95 mask. Each participant was provided a new N-95 mask and instructed to don as if they were about to enter a clinical scenario that would require this degree of respiratory protection. All subjects remained in a seated position and asked to refrain from speaking in order maximize fit of the mask. Venous blood gas samples were obtained prior to donning their mask followed by three additional intervals at, 20, 40, and 60 minutes. In addition, vital signs (heart rate, pulse oximetry, blood pressure and respiratory rate) were recorded at each of those four intervals and subjects were ask to self-record any symptoms they experienced prior to each blood draw. Each sample collected consisted of acquiring 2 ml of venous blood, which were analyzed within 30 minutes at the University of Nebraska Medical Center’s core lab. PCO2 and pH was assessed at each of the time intervals and fit with a linear mixed effect model to determine if statistically significant change over time for these measurements. Mean and standard deviations were used to describe the values at each time point. Pairwise comparisons between time points were adjusted using Tukey’s method. All analysis was done using SAS, Version 9.4 and a p-value < 0.05 was considered statistically significant. Results: The mean carbon dioxide levels at time 0 and 60 minutes were 48.9 (CI, 49.0-56.0) and 48.5 (CI 39.0- 57.0) and there was no statistically significant change across any of the time intervals (p=0.20). There was a small significant increase in the mean pH between the 20-minute assessment and baseline [(7.367, CI 7.350- 7.400) vs (7.381, CI 7.350-7.410) p=0.019], which was not clinically significant. In addition, there were no significant changes in vital signs or report of unexpected clinical symptoms by any the subjects. Conclusion: In this small cohort of subjects, there was no evidence of carbon dioxide retention or clinically significant changes in pH with prolonged use of N-95 masks. [Formula presented]