title: Pressures delivered by nasal high flow oxygen during all phases of the respiratory cycle.
abstract: BACKGROUND
  Nasal high flow (NHF) oxygen therapy and CPAP are modes of noninvasive respiratory support used to improve respiratory function in multiple patient groups. Both therapies provide positive pressure, although this varies during the respiratory cycle. The purpose of this study was to measure and compare the airway pressure generated during different phases of the respiratory cycle in patients receiving NHF at various gas flows.
  
  
  METHODS
  Patients scheduled for elective cardiac surgery were invited to participate. Nasopharyngeal pressure measurements were performed using NHF with gas flows of 30, 40, and 50 L/min. All measurements were performed in random order, with the subject breathing with mouth closed.
  
  
  RESULTS
  During NHF the mean ± SD nasopharyngeal airway pressures were 1.5 ± 0.6, 2.2 ± 0.8, and 3.1 ± 1.2 at 30, 40, and 50 L/min using NHF. Analyses also determined the mean peak expiratory and mean expiratory plateau pressures.
  
  
  CONCLUSIONS
  The expiratory pressure during NHF was higher than the mean pressure previously reported for NHF. This may account in part for the disproportional clinical effects seen with NHF. (Australian Clinical Trials Registry www.anzctr.org.au ACTRN12609000305224).
authors.affiliation: Cardiothoracic and Vascular Intensive Care Unit, Auckland City Hospital, Auckland, New Zealand.
authors.forename: Rachael L
authors.initials: RL
authors.lastname: Parke
authors.forename: Shay P
authors.initials: SP
authors.lastname: McGuinness
mesh_terms: D000399:Air Pressure; D006348:Cardiac Surgical Procedures; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009305:Nasopharynx / Q000502:physiology*; D009666:Nose; D010100:Oxygen / Q000008:administration & dosage*; D010102:Oxygen Inhalation Therapy / Q000379:methods*; D011175:Positive-Pressure Respiration / Q000379:methods*; D011300:Preoperative Care / Q000379:methods*; D011446:Prospective Studies; D012119:Respiration
chemical_list: D010100:Oxygen
keywords: airway pressure; nasal high flow oxygen; noninvasive ventilation; oxygen