title: The effects of flow on airway pressure during nasal high-flow oxygen therapy.
abstract: BACKGROUND
  Nasal high-flow oxygen therapy increases the mean nasopharyngeal airway pressure in adults, but the relationship between flow and pressure is not well defined.
  
  
  OBJECTIVE
  To determine the relationship between flow and pressure with the Optiflow nasal high-flow oxygen therapy system.
  
  
  METHODS
  We invited patients scheduled for elective cardiac surgery to participate. Measurements were performed with nasal high-flow oxygen at flows of 30, 40, and 50 L/min, with the patient's mouth both open and closed. Pressures were recorded over one minute of breathing, and average flows were calculated via simple averaging.
  
  
  RESULTS
  With the mouth closed, the mean ± SD airway pressures at 30, 40, and 50 L/min were 1.93 ± 1.25 cm H(2)O, 2.58 ± 1.54 cm H(2)O, and 3.31 ± 1.05 cm H(2)O, respectively. There was a positive linear relationship between flow and pressure.
  
  
  CONCLUSIONS
  The mean nasopharyngeal pressure during nasal high-flow oxygen increases as flow increases. Australian Clinical Trials Registry http://www.adhb.govt.nz/achicu/hot_2_airway_pressure.htm.
authors.affiliation: Cardiothoracic and Vascular ICU, Auckland City Hospital, Auckland, New Zealand. rparke@adhb.govt.nz
authors.forename: Rachael L
authors.initials: RL
authors.lastname: Parke
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Eccleston
authors.forename: Shay P
authors.initials: SP
authors.lastname: McGuinness
mesh_terms: D000328:Adult; D045422:Continuous Positive Airway Pressure / Q000379:methods*; D005500:Follow-Up Studies; D006801:Humans; D008875:Middle Aged; D009305:Nasopharynx / Q000503:physiopathology*; D010102:Oxygen Inhalation Therapy / Q000379:methods*; D011312:Pressure; D011446:Prospective Studies; D012119:Respiration; D012131:Respiratory Insufficiency / Q000503:physiopathology / Q000628:therapy*; D016896:Treatment Outcome