High flow biphasic positive airway pressure by helmet--effects on pressurization, tidal volume, carbon dioxide accumulation and noise exposure

Crit Care. 2009;13(3):R85. doi: 10.1186/cc7907. Epub 2009 Jun 5.


Introduction: 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.

Publication types

  • Evaluation Study

MeSH terms

  • Carbon Dioxide / metabolism
  • Manikins
  • Models, Theoretical
  • Noise
  • Positive-Pressure Respiration / instrumentation*
  • Positive-Pressure Respiration / methods*
  • Tidal Volume


  • Carbon Dioxide