Waveform of the week: Inspiratory time too short

Inappropriate termination during breath delivery may be the result of an inspiratory time which is too short for the patients inspiratory time constant, when utilizing PC-CMV or PC-IMV.

The above image demonstrates a I-time set too short as evidence of the inspiratory flow waveform not fully decelerating to baseline (shown by red the arrow).

Ideally the operator should titrate I-time to allow for full deceleration of the inspiratory flow waveform. When flow is allowed to fully decelerated, alveolar recruitment, alveolar ventilation, & mean airway pressure is maximized.

The below video clip shows the titration of I-time to allow for a fully decelerating flow waveform, observe the increase in Vt even when the pressure, compliance, & resistance remains constant.

Waveform of the week: Rise time too fast

Setting the rise time too fast, especially in combination with a small E.T. tube or high airway resistance may result in noticeable pressure over-shooting during the early stage of inspiration. This pressure over-shooting may lead to the inappropriate termination of inspiration by setting off the pressure limitation threshold.

Waveform of the week: Rise time too slow

Rise time setting too slow as evidence by the sloping pressure waveform.

A slow rise time may cause increased work of breathing for patients with a high inspiratory drive, decreases mean airway pressure & alveolar time which may decrease the delivered tidal volume.

The following video clip demonstrates the increase in tidal volume with the speeding up of rise time to achieve the optimal rectangular pressure waveform.