I think the trigger window concept of SIMV has been a little over-complicated in our lectures. I wanted to verify I understand this right or wrong. As I understand, the trigger window is the percentage of the expiratory phase between mandatory breaths that the ventilator monitors for patient trigger. If patient trigger is detected, the vent provides a synchronized breath at the settings of the mandatory breath. For vents that run SIMV/PSV, spontaneous breaths outside the trigger window are ONLY given pressure support.

So SIMV with trigger at 25%, the timer starts at the beginning of expiration. Say there are 4 seconds between end inspiration and the beginning of the next inspiration. The patient must take a spontaneous breath in the first second of this window for the vent to deliver a synchronized breath.

Thanks for any help.