Delivery of helium–oxygen mixture during spontaneous breathing: evaluation of three high-concentration face masks

Purpose To evaluate the efficacy of delivering a mixture of helium and oxygen gas (He–O 2 ) in spontaneous ventilation. Three high oxygen flow reservoir masks were tested: the Heliox21, specifically designed for helium; the Hi-Ox 80 mask, with an inspiratory and an expiratory valve; and a standard high-concentration face mask. Methods This prospective randomized crossover study was performed in six healthy volunteers in a laboratory setting. Volunteers breathed a mixture of 78% He/22% O 2 through each of the masks under two different breathing conditions (rest and hyperventilation: minute ventilation of 14.9 ± 6.1 and 26.7 ± 8.7 L min −1 , respectively) and four different He–O 2 flow rates (7, 10, 12, and 15 L min −1 ). Results A nasopharyngeal catheter was used to estimate He pharyngeal concentration (Fp [He]) in the airways in order to determine the percentage of contamination with room air (% air cont) at end-expiration. Under all testing conditions, the Hi-Ox 80 mask presented a significantly lower % air cont. During resting breathing pattern, a Fp [He] higher than 50% was achieved in 54% of the tests performed with the Hi-Ox 80 mask compared to 29% for the Heliox21 mask and only 17% for the standard mask. At hyperventilation, a Fp [He] higher than 50% was achieved in 17% of the tests performed with the Hi-Ox mask compared to 4% for the other two masks. Conclusion He–O 2 administration via the usual high-concentration reservoir masks results in significant dilution by room air. The Hi-Ox 80 mask minimized room air contamination and much more frequently achieved a pharyngeal He concentration higher than 50%.