title: High flow through a nasal cannula and CPAP effect in a simulated infant model.
abstract: BACKGROUND
  Limited data are available to describe the CPAP effects that can be expected when using high flow with a traditional nasal cannula.
  
  
  OBJECTIVE
  To describe the relationship between the pressure generated at the airway opening and flow through a nasal cannula using a simulated  infant model. We hypothesized that positive pressure generated by a standard cannula at flows > 2 L/min would be minimal and clinically unimportant.
  
  
  METHODS
  Nares were simulated with holes drilled in a plastic fixture. A nares template for CPAP prongs served as a sizing template for the  holes. Small, medium, and large nares fixtures were constructed and connected to a lung simulator that simulated spontaneous breathing. Respiratory muscle pressure was simulated by setting a waveform and adjusting the amplitude to deliver a range of tidal volumes (V(T)) from 3 mL  to 12 mL. Lung compliance and resistance were set at 0.5 mL/cm H(2)O and 125 cm H(2)O/L/s, respectively. Nasal cannulas were inserted in the model nares. We assured that the prong occlusion of the nares did not exceed 50%. Cannula flow was adjusted from 2-6 L/min in  1-L/min increments. Data were averaged over 20 breaths. Mean airway pressure and percent change in V(T) were recorded.
  
  
  RESULTS
  The greatest effect on V(T) (mean ± SD 0.16 ± 0.10 mL) and pressure change (mean ± SD 0.7 ± 0.5 cm H(2)O) occurred  with the premature cannula. The least effect on pressure (mean ± SD 0.3 ± 0.22 cm H(2)O) and V(T) change (mean ± SD 0.01 ± 0.02 mL) occurred with the infant cannula.
  
  
  CONCLUSIONS
  Clinically important pressures were not generated by high flows with  a standard nasal cannula. The differences in spontaneous V(T) across all flows were negligible.
authors.affiliation: Children's Hospital Medical Center of Akron, Akron, OH, USA. tvolsko@chmca.org
authors.forename: Teresa A
authors.initials: TA
authors.lastname: Volsko
authors.forename: Kathy
authors.initials: K
authors.lastname: Fedor
authors.forename: Jason
authors.initials: J
authors.lastname: Amadei
authors.forename: Robert L
authors.initials: RL
authors.lastname: Chatburn
mesh_terms: D000403:Airway Resistance / Q000502:physiology; D057785:Catheters; D045422:Continuous Positive Airway Pressure / Q000295:instrumentation* / Q000379:methods; D004867:Equipment Design; D006801:Humans; D007231:Infant, Newborn; D008170:Lung Compliance; D008954:Models, Biological; D012131:Respiratory Insufficiency / Q000628:therapy; D013990:Tidal Volume