title: FIO2 in an Adult Model Simulating High-Flow Nasal Cannula Therapy.
abstract: BACKGROUND
  High-flow nasal cannula therapy (HFNC) is widely used for patients with acute respiratory failure. HFNC has a number of physiological effects. Although FIO2is considered to be constant, because HFNC is an open system, FIO2varies according to inspiratory flow, tidal volume (VT), and HFNC gas flow. We investigated the influence of HFNC gas flow and other respiratory parameters on FIO2during HFNC.
  
  
  METHODS
  We evaluated an HFNC system and, for comparison, a conventional oxygen therapy system. The HFNC apparatus was composed of an air/oxygen blender, a heated humidifier, an inspiratory limb, and small, medium, and large nasal prongs. HFNC gas flow was set at 20, 40, and 60 L/min, and FIO2was set at 0.3, 0.5, and 0.7. We measured FIO2for 1-min intervals using an oxygen analyzer and extracted data for the final 3 breaths of each interval. Spontaneous breathing was simulated using a mechanical ventilator connected to the muscle compartment of a model lung. The lung compartment passively moved with the muscle compartment, thus inspiring ambient air via a ventilator limb. With a decelerating flow waveform, simulated VTwas set at 300, 500, and 700 mL, breathing frequency at 10 and 20 breaths/min, and inspiratory time at 1.0 s.
  
  
  RESULTS
  With HFNC gas flow of 20 and 40 L/min, at all set FIO2values, inspiratory oxygen concentration varied with VT(P < .001). As the set value for FIO2increased, the difference between set FIO2and measured FIO2increased. Neither breathing frequency nor prong size influenced FIO2.
  
  
  CONCLUSIONS
  During HFNC with simulated spontaneous breathing, when HFNC gas flow was 60 L/min, measured FIO2was similar to set FIO2at 0.3 and 0.5, whereas at 0.7, as VTincreased, measured FIO2decreased slightly. However, at 20 or 40 L/min, changes in VTrelated with deviation from set FIO2.
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: Critical Care and Emergency Medicine, Tokushima University Graduate School, 3-18-15 Kuramoto, Tokushima 770-8503, Japan.
authors.forename: Mutsuo
authors.initials: M
authors.lastname: Onodera
authors.affiliation: Critical Care and Emergency Medicine, Tokushima University Graduate School, 3-18-15 Kuramoto, Tokushima 770-8503, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Oto
authors.affiliation: Critical Care and Emergency Medicine, Tokushima University Graduate School, 3-18-15 Kuramoto, Tokushima 770-8503, Japan. nmasaji@tokushima-u.ac.jp.
authors.forename: Masaji
authors.initials: M
authors.lastname: Nishimura
mesh_terms: D000328:Adult; D000072601:Cannula; D006801:Humans; D001239:Inhalation; D008954:Models, Biological; D010100:Oxygen / Q000008:administration & dosage*; D010102:Oxygen Inhalation Therapy / Q000295:instrumentation / Q000379:methods; D010313:Partial Pressure; D013990:Tidal Volume; D012122:Ventilators, Mechanical
chemical_list: D010100:Oxygen
keywords: gas blender; gas flow; nasal prong; oxygen analyzer; oxygen therapy; spontaneous breathing