Effect of inspiratory flow waveforms on the mechanical work of ventilation; a fluid dynamic analysis

Abstract In most intensive care patients, the mechanical work (MW) is increased due to airway obstruction and/or tracheal intubation. Increasing MW is known as a risk factor for ventilator induced lung injury (VILI). Moeover, minimizing of MW is crucial to facilitate weaning process. In this paper MW is compared between three different inspiratory flow waveforms. The fluid dynamic analysis is used to compute the resistive pressure drop and the resistive work. We have compared square, sinusoidal and decelerating flow waveforms under the same tidal volume. The results show that under the constant tidal volume and I:E ratio, for tidal volumes below 1 lit, an square flow profile is beneficial for minimizing MW while a sinusoidal flow profile is prefered for tidal volumes of 1 lit or higher. It is shown that for make a decision about most beneficial flow profile in terms of less MW, both tidal volume and I:E ratio is important. By the way the results suggest to use decelerating flow waveforms with higher 1:E ratio. The qualitative conclusion is that in order to lower the MW especially in patients with obstructive lung diseases, sinusoidal, square and decelerating flow became preferable respectively with increasing I:E ratio. Our study suggest the square and sinusoidal profile for tidal volumes below and equal or over 1 lit, respectively in pointwiew of less MW. This paper also encouraged the engineers to add an option to select sinusoidal flow waveform in VCV mode to lower MW when tidal volume is l lit or higher.