title: High flow biphasic positive airway pressure by helmet--effects on pressurization, tidal volume, carbon dioxide accumulation and noise exposure.
abstract: BACKGROUND
  Non-invasive ventilation (NIV) with a helmet device is often associated with poor patient-ventilator synchrony and impaired carbon dioxide (CO2) removal, which might lead to failure. A possible solution is to use a high free flow system in combination with a time-cycled pressure valve placed into the expiratory circuit (HF-BiPAP). This system would be independent from triggering while providing a high flow to eliminate CO2.
  
  
  METHODS
  Conventional pressure support ventilation (PSV) and time-cycled biphasic pressure controlled ventilation (BiVent) delivered by an Intensive Care Unit ventilator were compared to HF-BiPAP in an in vitro lung model study. Variables included delta pressures of 5 and 15 cmH2O, respiratory rates of 15 and 30 breaths/min, inspiratory efforts (respiratory drive) of 2.5 and 10 cmH2O) and different lung characteristics. Additionally, CO2 removal and noise exposure were measured.
  
  
  RESULTS
  Pressurization during inspiration was more effective with pressure controlled modes compared to PSV (P < 0.001) at similar tidal volumes. During the expiratory phase, BiVent and HF-BiPAP led to an increase in pressure burden compared to PSV. This was especially true at higher upper pressures (P < 0.001). At high level of asynchrony both HF-BiPAP and BiVent were less effective. Only HF-BiPAP ventilation effectively removed CO2 (P < 0.001) during all settings. Noise exposure was higher during HF-BiPAP (P < 0.001).
  
  
  CONCLUSIONS
  This study demonstrates that in a lung model, the efficiency of NIV by helmet can be improved by using HF-BiPAP. However, it imposes a higher pressure during the expiratory phase. CO2 was almost completely removed with HF-BiPAP during all settings.
authors.affiliation: Department of Anaesthesiology, Emergency and Critical Care Medicine, University of Göttingen, 37075 Göttingen, Germany. omoerer@gwdg.de
authors.forename: Onnen
authors.initials: O
authors.lastname: Moerer
authors.forename: Peter
authors.initials: P
authors.lastname: Herrmann
authors.forename: José
authors.initials: J
authors.lastname: Hinz
authors.forename: Paolo
authors.initials: P
authors.lastname: Severgnini
authors.forename: Edoardo
authors.initials: E
authors.lastname: Calderini
authors.forename: Michael
authors.initials: M
authors.lastname: Quintel
authors.forename: Paolo
authors.initials: P
authors.lastname: Pelosi
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D008348:Manikins; D008962:Models, Theoretical; D009622:Noise; D011175:Positive-Pressure Respiration / Q000295:instrumentation* / Q000379:methods*; D013990:Tidal Volume
chemical_list: D002245:Carbon Dioxide