The Science Journal of the American Association for Respiratory Care
Current concerns regarding mechanical ventilator performance have focused on the response of the ventilator to patient demand. We used a spontaneously breathing lung model to evaluate the response of the following new generation ventilators to varying inspiratory demand in both PS and PC modes: Bear 1000 (Bear Medical Systems, Inc; Riverside, CA), Drager Evita 4 (Drager, Inc; Telford, PA), Hamilton Galileo (Hamilton Medical AG; Rhazuns, Switzerland), Intermed T-Bird (Bird Products Corp; Palm Springs, CA), Nellcor Puritan-Bennett 840 and 740 (Puritan-Bennett Corp; Pleasanton, CA), Siemens 300A (Siemens-Elema AB; Solna, Sweden).
Methods: A bellow-in-a-box lung model was set at a respiratory rate of 12 breaths/min, inspiratory time of 1.0 second, and inspiratory flow rates of 40, 60 and 80 L/min. Each ventilator was set at three levels of PS and PC (10, 15 and 20 cm H2O). On all ventilators flow triggering was set as sensitive as possible without causing self-cycling. When variable pressure rise time was available on a ventilator, the fastest setting was used. A pneumotachometer (Validyne; Northridge, CA) measured flow at the airway opening of the lung model and differential pressure transducers (Validyne) were used to measure pressures at the airway opening and in the simulated pleural space. A computerized graphics program (WINDAQ; Dataq Instruments Inc; Akron, OH) was used to digitize the signals and analyze the data.
Results: Trigger pressure (PT), trigger pressure-time product (T-PTP), inspiratory trigger time delay (DT), inspiratory area as a per cent of the ideal inspiratory area (Area I%) and expiratory time delay (DE) are listed below as mean±SD for all settings.
Conclusions: There are differences between the responses of individual ventilators, but as a group these ventilators show an improved response to inspiratory demand in comparison to previous generations. For any given ventilator, there was little difference between PS and PC in terms of response of the ventilator to inspiratory demand.