title: High-flow oxygen therapy: pressure analysis in a pediatric airway model.
abstract: BACKGROUND
  The mechanism of high-flow oxygen therapy and the pressures reached in the airway have not been defined. We hypothesized that the flow would generate a low continuous positive pressure, and that elevated flow rates in this model could produce moderate pressures. The objective  of this study was to analyze the pressure generated by a high-flow oxygen therapy system in an experimental model of the pediatric airway.
  
  
  METHODS
  An experimental in vitro study was performed. A high-flow oxygen therapy system was connected to 3 types of interface (nasal cannulae, nasal mask,  and oronasal mask) and applied to 2 types of pediatric manikin (infant and neonatal). The pressures generated in the circuit, in the airway, and in the pharynx were measured at different flow rates (5, 10, 15, and 20 L/min). The experiment was conducted with and without a leak (mouth sealed  and unsealed). Linear regression analyses were performed for each set of measurements.
  
  
  RESULTS
  The pressures generated with the different interfaces were very similar. The maximum pressure recorded was 4 cm H(2)O with a flow of 20 L/min via nasal cannulae or nasal mask. When the  mouth of the manikin was held open, the pressures reached in the airway and pharynxes were undetectable. Linear regression analyses showed a similar linear relationship between flow and pressures measured in the pharynx (pressure = -0.375 + 0.138 × flow) and in the airway (pressure  = -0.375 + 0.158 × flow) with the closed mouth condition.
  
  
  CONCLUSIONS
  According to our hypothesis, high-flow oxygen therapy systems produced a low-level CPAP in an experimental pediatric model, even with the use of very high flow rates. Linear regression analyses showed similar  linear relationships between flow and pressures measured in the pharynx and in the airway. This finding suggests that, at least in part, the effects may be due to other mechanisms.
authors.affiliation: Pediatric Intensive Care Department, Hospital General Universitario Gregorio Marañón, Complutense University of Madrid, Madrid, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Urbano
authors.forename: Jimena
authors.initials: J
authors.lastname: del Castillo
authors.forename: Jesús
authors.initials: J
authors.lastname: López-Herce
authors.forename: José A
authors.initials: JA
authors.lastname: Gallardo
authors.forename: María J
authors.initials: MJ
authors.lastname: Solana
authors.forename: Ángel
authors.initials: Á
authors.lastname: Carrillo
mesh_terms: D000367:Age Factors; D000403:Airway Resistance / Q000502:physiology*; D045422:Continuous Positive Airway Pressure; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008348:Manikins; D008397:Masks; D008954:Models, Biological; D010102:Oxygen Inhalation Therapy; D010614:Pharynx / Q000503:physiopathology