At a constant respiratory rate and tidal volume, the adjustment of inspiratory time governs the I:E ratio and the inspiratory flow rate (the latter also depends on the inspiratory waveform). Inspiratory time may be controlled directly or indirectly depending on the type of ventilator. In indirect methods the inspiratory flow rate or I:E ratio is adjusted. Some ventilators allow direct control of one of these variables, showing the corresponding change in the value of the variable that is not adjusted. If an inspiratory hold, pause, or plateau is required, the time that this takes is part of the inspiratory time.
Many patients undergoing mechanical ventilation can be adequately managed using an inspiratory time similar to their resting value, i.e. 0.8 to 1.5 s. However, there are factors that may result in changes to this inspiratory time being necessary for optimal ventilation.
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