title: Delivery of helium–oxygen mixture during spontaneous breathing: evaluation of three high-concentration face masks.
abstract: OBJECTIVE
  To evaluate the efficacy of delivering a mixture of helium and oxygen gas (He–O2) in spontaneous ventilation. Three high oxygen flow reservoir masks were tested: the Heliox21, specifically designed for helium; the Hi-Ox80 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% O2 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–O2 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-Ox80 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-Ox80 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.
  
  
  CONCLUSIONS
  He–O2 administration via the usual high-concentration reservoir masks results in significant dilution by room air. The Hi-Ox80 mask minimized room air contamination and much more frequently achieved a pharyngeal He concentration higher than 50%.
authors: Medical Intensive Care Unit, AP-HP Groupe Hospitalier Henri Mondor, Créteil, France. ferranroche@yahoo.es
authors: Ferran
authors: F
authors: Roche-Campo
authors: Laurence
authors: L
authors: Vignaux
authors: Fabrice
authors: F
authors: Galia
authors: Aissam
authors: A
authors: Lyazidi
authors: Frédéric
authors: F
authors: Vargas
authors: Joëlle
authors: J
authors: Texereau
authors: Gabriela
authors: G
authors: Apiou-Sbirlea
authors: Philippe
authors: P
authors: Jolliet
authors: Laurent
authors: L
authors: Brochard
mesh_terms: D000328:Adult; D018592:Cross-Over Studies; D005260:Female; D005602:France; D006371:Helium / Q000008:administration & dosage*; D006801:Humans; D008297:Male; D008397:Masks / Q000592:standards*; D010100:Oxygen / Q000008:administration & dosage*; D011446:Prospective Studies; D012119:Respiration
chemical_list: D006371:Helium; D010100:Oxygen