title: Inspiratory Tube Condensation During High-Flow Nasal Cannula Therapy: A Bench Study.
abstract: BACKGROUND
  High-flow nasal cannula (HFNC) therapy provides better humidification than conventional oxygen therapy. To allay loss of vapor as condensation, a servo-controlled heating wire is incorporated in the inspiratory tube, but condensation is not completely avoidable. We investigated factors that might affect condensation: thermal characteristics of the inspiratory tube, HFNC flow, and ambient temperature.
  
  
  METHODS
  We evaluated 2 types of HFNC tubes, SLH Flex 22-mm single tube and RT202. Both tubes were connected to a heated humidifier with water reservoir. HFNC flow was set at 20, 40, and 60 L/min, and FIO2 was set at 0.21. Air conditioning was used maintain ambient temperature at close to either 20 or 25°C. We weighed the tubes on a digital scale before (0 h) and at 3, 6, and 24 h after, turning on the heated humidifier, and calculated the amount of condensation by simple subtraction. The amount of distilled water used during 24 h was also recorded.
  
  
  RESULTS
  At 25°C, there was little condensation, but at 20°C and HFNC flow of 20, 40, and 60 L/min for 24 h, the amount of condensation with the SLH was 50.2 ± 10.7, 44.3 ± 17.7, and 56.6 ± 13.9 mg, and the amount with the RT202 was 96.0 ± 35.1, 72.8 ± 8.2, and 64.9 ± 0.8 mg. When ambient temperature was set to 20°C, condensation with the RT202 was statistically significantly greater than with the SLH at all flow settings (P < .001).
  
  
  CONCLUSIONS
  Ambient temperature statistically significantly influenced the amount of condensation in the tubes.
authors.affiliation: Medical Equipment Center, Tokushima University Hospital, 2-50-1 Kuramoto, Tokushima 770-8503, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Chikata
authors.affiliation: Faculty of Medicine, Tokushima University, 3-18-15 Kuramoto, Tokushima 770-8503, Japan.
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Unai
authors.affiliation: Emergency and Critical Care Medicine, Tokushima University Hospital, 2-50-1 Kuramoto, Tokushima 770-8503, Japan.
authors.forename: Masayo
authors.initials: M
authors.lastname: Izawa
authors.affiliation: Emergency and Critical Care Medicine, Tokushima University Hospital, 2-50-1 Kuramoto, Tokushima 770-8503, Japan.
authors.forename: Nao
authors.initials: N
authors.lastname: Okuda
authors.affiliation: Emergency and Critical Care Medicine, Tokushima University Graduate School of Medicine, 3-18-15 Kuramoto, Tokushima 770-8503, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Oto
authors.affiliation: Emergency and Critical Care Medicine, Tokushima University Graduate School of Medicine, 3-18-15 Kuramoto, Tokushima 770-8503, Japan. nmasaji@tokushima-u.ac.jp.
authors.forename: Masaji
authors.initials: M
authors.lastname: Nishimura
mesh_terms: D000072601:Cannula; D004867:Equipment Design; D006361:Heating / Q000295:instrumentation; D006813:Humidity; D010102:Oxygen Inhalation Therapy / Q000295:instrumentation*; D012121:Respiration, Artificial / Q000295:instrumentation*; D013227:Steam / Q000032:analysis*; D013696:Temperature
chemical_list: D013227:Steam
keywords: absolute humidity; environmental temperature; heated humidifier; humidification; oxygen therapy