title: Water content of delivered gases during non-invasive ventilation in healthy subjects.
abstract: BACKGROUND
  No clear recommendation exists concerning humidification during non-invasive ventilation (NIV) and high flow CPAP, and few hygrometric data are available.
  
  
  METHODS
  We measured hygrometry during NIV delivered to healthy subjects with different humidification strategies: heated humidifier (HH), heat and moisture exchanger, (HME) or no humidification (NoH). For each strategy, a turbine and an ICU ventilator were used with different FiO(2) settings, with and without leaks. During CPAP, two different HH and NoH were tested. Inspired gases hygrometry was measured, and comfort was assessed. On a bench, we also assessed the impact of ambient air temperature, ventilator temperature and minute ventilation on HH performances (with NIV settings).
  
  
  RESULTS
  During NIV, with NoH, gas humidity was very low when an ICU ventilator was used (5 mgH(2)O/l), but equivalent to ambient air hygrometry with a turbine ventilator at minimal FiO(2) (13 mgH(2)O/l). HME and HH had comparable performances (25-30 mgH(2)O/l), but HME's effectiveness was reduced with leaks (15 mgH(2)O/l). HH performances were reduced by elevated ambient air and ventilator output temperatures. During CPAP, dry gases (5 mgH(2)O/l) were less tolerated than humidified gases. Gases humidified at 15 or 30 mgH(2)O/l were equally tolerated.
  
  
  CONCLUSIONS
  This study provides data on the level of humidity delivered with different humidification strategies during NIV and CPAP. HH and HME provide gas with the highest water content. Comfort data suggest that levels above 15 mgH(2)O/l are well tolerated. In favorable conditions, HH and HMEs are capable of providing such values, even in the presence of leaks.
authors.affiliation: Service de Réanimation Médicale, Assistance Publique-Hôpitaux de Paris, Centre Hospitalier Albert Chenevier, Henri Mondor, Université Paris 12, Créteil, INSERM U 955, Créteil, France. francois.lellouche@criucpq.ulaval.ca
authors.forename: François
authors.initials: F
authors.lastname: Lellouche
authors.forename: Salvatore Maurizio
authors.initials: SM
authors.lastname: Maggiore
authors.forename: Aissam
authors.initials: A
authors.lastname: Lyazidi
authors.forename: Nicolas
authors.initials: N
authors.lastname: Deye
authors.forename: Solenne
authors.initials: S
authors.lastname: Taillé
authors.forename: Laurent
authors.initials: L
authors.lastname: Brochard
mesh_terms: D005740:Gases; D006801:Humans; D006813:Humidity; D007362:Intensive Care Units; D011175:Positive-Pressure Respiration / Q000379:methods*
chemical_list: D005740:Gases