A crossover trial investigating the atmospheric content of improvised respirators.

Introduction: This study was designed to determine the respiratory safety of improvised respirators based on modified full-face snorkel masks, making comparisons with a purpose-designed mask.
Methods: This is a prospective crossover study conducted on ten recruits. Volunteers wore snorkel masks mated to an anaesthetic heat and moisture exchange filter. The system was worn at rest then during exercise. Gases were sampled from the mask at 5-min intervals.
Results: The modified snorkel was satisfactory in seven participants. For three carbon dioxide concentrations were >1%. Two participants exposed to excessive CO2 also experienced oxygen concentrations <19%. All participants exposed to unsatisfactory gas mixtures were non-white. Conclusions: Modifying snorkel masks changes the way that gases circulate through the system. These modifications increase the risk of rebreathing in some users, which may yield an unsafe gas mixture. These improvised masks cannot be recommended as a substitute for purpose-designed equipment. © The Intensive Care Society 2021.