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Effect of inspiratory flow waveform on work on endotracheal tubes: a model analysis
G Polese1, E D'Angelo, A Rossi
1Centro Regionale Fibrosi Cistica, Azienda Ospedaliera di Verona, Italy. gpolese@qubisoft.it
Objective:
This model analysis aimed to predict the impact of different inspiratory flow wave-forms, i. e., constant, sinusoidal, and two linearly decreasing flows, on the resistive work (Wres) performed on endotracheal tubes.
Design:
Model analysis.
Results:
Model analysis predicts that: (i) minimal Wres is obtained with the constant flow; (ii) for any given tidal volume/inspiratory duration (V(T)/T(I), mean inspiratory flow), Wres increases with decreasing tube size; (iii) for any given inspiratory flow waveform, Wres increases with increasing V(T)/T(I), being lowest with constant flow.
Conclusions:
These findings have major clinical implications: at any given ventilator setting, not only the size of the endotracheal tube but also the inspiratory flow waveform must be taken into account to interpret the values of Wres and hence of the total work of breathing.