Evaluation of inspiratory rise time and inspiration termination criteria in new-generation mechanical ventilators: a lung model study

S Chatmongkolchart, P Williams, D R Hess, R M Kacmarek
Respiratory Care 2001, 46 (7): 666-77

INTRODUCTION: Inspiratory rise time adjustment during pressure ventilation and inspiration termination criteria adjustment during pressure support ventilation are available on some of the newest mechanical ventilators. Both are designed to improve patient-ventilator synchrony. However, the function of these adjuncts during pressure ventilation on these ventilators has not been evaluated.

METHODS: Three inspiratory rise times (minimum, medium, and maximum) were evaluated in 5 new-generation mechanical ventilators (Hamilton Galileo, Siemens 300A, Puritan Bennett 840, BEAR 1000, and Dräger Evita 4) during pressure support and pressure assist/control. Three inspiration termination criteria settings (minimum, medium, and maximum) were also evaluated in 2 mechanical ventilators (Hamilton Galileo and Puritan Bennett 840) during pressure support. All evaluations were performed with a spontaneous breathing lung model (compliance 50 mL/cm H2O, resistance 8.2 cm H2O/L/s, respiratory rate 12 breaths/min, inspiratory time 1.0 s, and lung model peak inspiratory flow 60 L/min). Throughout the evaluation, inspiratory pressure was set at 15 cm H2O and positive end-expiratory pressure at 5 cm H2O, resulting in a peak airway pressure of 20 cm H2O.

RESULTS: Significant (p < 0.05) and important (> 10%) differences were found among the ventilators at similar rise times (minimum, medium, and maximum) and for each ventilator as rise time was varied. Also, significant (p < 0.05) and important (> 10%) differences were observed between ventilators and within each ventilator when inspiration termination criteria were varied. There were significant (p < 0.05) differences between pressure support and pressure assist/control, but most were < 10%, except those associated with expiration.

CONCLUSIONS: Major differences exist for each ventilator as rise time or inspiration termination criteria are varied and among ventilators at similar settings. Inspiration termination criteria adjustment markedly affects transition to exhalation in the Puritan Bennett 840.

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