The effect of triggering type on post-triggering pressure variations during pressure support ventilation: a simplified surrogate for dyssynchrony

Several studies comparing flow and pressure triggering using invasive and noninvasive techniques have mostly focused on the trigger phase and favored flow triggering. Recently, there have been advancements in the technology of pressure triggering to improve its performance. We sought to evaluate the effect of triggering type in old and new ventilators on patient’s synchrony in the post-trigger phase using variations in airway pressures with the set inspiratory pressure as a surrogate for dyssynchrony. Using three different ventilator types, 32 patients on pressure support ventilation were set on the two triggering types (at the same equivalent levels), each for 1 h, with all other ventilatory setting kept constant. At the end of the hour on each trigger mode, the measured peak pressure and its difference with the set inspiratory pressure [delta pressure (ΔP)], the mean airway pressure, and different ventilatory parameters and arterial blood gases were assessed. Pressure triggering resulted in a significantly higher peak pressure, ΔP, and lower dynamic compliance at any equivalent sensitivity and pressure support regardless of the level (<0.05). Moreover, at higher sensitivity levels (3 cmH2O and l/min), flow triggering produced higher mean airway pressures and oxygenation (<0.05). However, there was no significant difference as regards tidal volume, minute volume, frequency, rapid shallow breathing index, or PCO2. Despite advances in pressure-triggering technology, flow triggering results in less pressure variation and better patient’s synchrony during pressure support ventilation; in this respect, ΔP and dynamic compliance are simple noninvasive measures for dyssynchrony.