Flow triggering systems have theoretical advantages over the classical pressure-triggering systems in that they never let the patient breathe against a closed circuit. Most bench and clinical evaluations have found some advantages to the newer flow-triggering systems [13-15]. Aslanian et al. found, however, that this advantage was clinically detectable only with pressure support ventilation and not with assist-control . There were two main reasons. First, the advantage ofone system over the other was small and the expected benefit in terms of work of breathing was less than 10% of the total patient work. Second, an inadequate setting of the peak-flow during assist-control ventilation had much more weight than the trigger effect, and masked any advantage of one system over the other. Lastly, results of experimental and clinical studies generally indicate that manufacturers have brought major improvements to the triggering systems of newer-generation ventilators . The last generation of ventilators has improved the pressure-trigger systems, which now offer very similar performance to the flow-trigger systems in terms of time delay and imposed work of breathing.
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