BackgroundBias flow (BF) is essential to maintain mean airway pressure (MAP) and to washout carbon dioxide (CO2) from the oscillator circuit during high-frequency oscillatory ventilation (HFOV). If the BF rate is inadequate, substantial CO2 rebreathing could occur and ventilation efficiency could worsen. With lower ventilation efficiency, the required stroke volume (SV) would increase in order to obtain the same alveolar ventilation with constant frequency. The aim of this study was to assess the effect of BF rate on ventilation efficiency during adult HFOV.MethodsThe R100 oscillator (Metran, Japan) was connected to an original lung model internally equipped with a simulated bronchial tree. The actual SV was measured with a flow sensor placed at the Y-piece. Carbon dioxide (CO2) was continuously insufflated into the lung model (CO2), and the partial pressure of CO2 (PCO2) in the lung model was monitored. Alveolar ventilation (A) was estimated as CO2 divided by the stabilized value of PCO2. A was evaluated by setting SV from 80 to 180 mL (10 mL increments, n = 5) at a frequency of 8 Hz, a MAP of 25 cmH2O, and a BF of 10, 20, 30, and 40 L/min (study 1). Ventilation efficiency was calculated as A divided by the actual minute volume. The experiment was also performed with an actual SV of 80, 100, and 120 mL and a BF from 10 to 60 L/min (10 L/min increments: study 2).ResultsStudy 1: With the same setting SV, the A with a BF of 20 L/min or more was significantly higher than that with a BF of 10 L/min. Study 2: With the same actual SV, the A and the ventilation efficiency with a BF of 30 L/min or more were significantly higher than those with a BF of 10 or 20 L/min.ConclusionsIncreasing BF up to 30 L/min or more improved ventilation efficiency in the R100 oscillator.Electronic supplementary materialThe online version of this article (10.1186/s40635-018-0176-3) contains supplementary material, which is available to authorized users.
BackgroundTwo recent large randomized controlled trials did not show the superiority of high-frequency oscillatory ventilation (HFOV) in adults with ARDS. These two trials had differing results, and possible causes could be the different oscillators used and their different settings, including inspiratory time % (IT%). The aims of this study were to obtain basic data about the ventilation characteristics in two adult oscillators and to elucidate the effect of the oscillator and IT% on ventilation efficiency.MethodsThe Metran R100 or SensorMedics 3100B was connected to an original lung model internally equipped with a simulated bronchial tree. The actual stroke volume (aSV) was measured with a flow sensor placed at the Y-piece. Carbon dioxide (CO2) was continuously insufflated into the lung model (CO2), and the partial pressure of CO2 (PCO2) in the lung model was monitored. Alveolar ventilation (A; L/min) was estimated as CO2 divided by the stabilized value of PCO2. A was evaluated with several stroke volume settings in the R100 (IT = 50%) or several airway pressure amplitude settings in the 3100B (IT = 33%, 50%) at a frequency of 6 and 8 Hz, a mean airway pressure of 25 cmH2O, and a bias flow of 30 L/min. Assuming that A = frequencya × aSVb, values of a and b were determined. Ventilation efficiency was calculated as A divided by actual minute ventilation.ResultsThe relationship between aSV and A or ventilation efficiency were different depending on the oscillator and IT%. The values of a and b were 0 < a < 1 and 1 < b < 2 and were different for three conditions at both frequencies. A and ventilation efficiency were highest with R100 (IT = 50%) and lowest with 3100B (IT = 33%) for high aSV ranges at both frequencies.ConclusionsIn this lung model study, ventilation characteristics were different depending on the oscillator and IT%. Ventilation efficiency was highest with R100 (IT = 50%) and lowest with 3100B (IT = 33%) for high aSV ranges.Electronic supplementary materialThe online version of this article (10.1186/s40635-019-0229-2) contains supplementary material, which is available to authorized users.
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