Factors influencing delivered mean airway pressure during nasal CPAP with the RAM cannula

Pediatr Pulmonol. 2016 Jan;51(1):60-9. doi: 10.1002/ppul.23197. Epub 2015 Apr 7.


Objective: To measure mean airway pressure (MAP) delivered through the RAM Cannula® when used with a ventilator in CPAP mode as a function of percent nares occlusion in a simulated nasal interface/test lung model and to compare the results to MAPs using a nasal continuous positive airway pressure (NCPAP) interface with nares fully occluded.

Study design: An artificial airway model was connected to a spontaneous breathing lung model in which MAP was measured at set NCPAP levels between 4 and 8 cmH2 O provided by a Dräger Evita XL® ventilator and delivered through three sizes of RAM cannulae. Measurements were performed with varying leakage at the nasal interface by decreasing occlusion from 100% to 29%, half-way prong insertion, and simulated mouth leakage. Comparison measurements were made using the Dräger BabyFlow® NCPAP interface with a full nasal seal.

Results: With simulated mouth closed, the Dräger interface delivered MAPs within 0.5 cmH2 O of set CPAP levels. For the RAM cannula, with 60-80% nares occlusion, overall delivered MAPs were 60 ± 17% less than set CPAP levels (P < 0.001). Further, MAP decreased progressively with decreasing percent nares occlusion. The simulated open mouth condition resulted in significantly lower MAPs to <1.7 cmH2 O. The one-half prong insertion depth condition, with closed mouth, yielded MAPs approximately 35 ± 9% less than full insertion pressures (P < 0.001).

Conclusions: In our bench tests, the RAM interface connected to a ventilator in NCPAP mode failed to deliver set CPAP levels when applied using the manufacturer recommended 60-80% nares occlusion, even with closed mouth and full nasal prong insertion conditions.

Keywords: NCPAP; mean airway pressure; nasal cannula; nasal prongs; premature infant; upper airway model.

MeSH terms

  • Continuous Positive Airway Pressure / methods*
  • Humans
  • Infant, Newborn
  • Infant, Premature
  • Lung / physiopathology*
  • Models, Biological*
  • Nasal Cavity / physiopathology
  • Pressure
  • Ventilators, Mechanical