Flow-time waveform from a patient receiving intermittent mandatory ventilation with pressure support. Large tidal volume (VT) during the mandatory breath prolongs expiratory time (lengthened time constant) that exceeds the patient’s neural timing mechanism. Additional patient efforts that fail to trigger the ventilator are evident in the expiratory flow waveform.
It illustrates the impact of large tidal volumes (VT) provided during the mandatory breaths and the impact on expiratory timing. Following the large mandatory breath, expiratory time is slightly prolonged and interferes with the patient’s internal timing mechanism, so the next inspiratory effort (seen as a sudden drop in the expiratory flow, to nearly zero) occurs prior to completion of exhalation. As in previous waveforms, this example illustrates the importance of carefully evaluating the flow waveform to identify additional patient efforts.