1. Even though this patient is undergoing positive-pressure mechanical ventilation, the first 4 breaths have a relatively negative pressure (ie, pressure is below PEEP, arrows A).
Even though this patient is undergoing positive-pressure mechanical ventilation, the first 4 breaths have a relatively negative pressure (ie, pressure is below PEEP, arrows A). One breath (third breath) even has an absolute negative pressure (ie, below atmospheric pressure). Only the last breath (arrow B) does not have a relatively negative pressure during ventilator-assisted inspiration. The peak flow of the breaths with relatively negative pressure (arrows A) during assisted inspiration is lower that the peak flow of the breath that is positive throughout mechanical inspiration (arrow B). The breath size of the last breath (arrow B) is also larger than all the other breaths. The breaths marked by arrows A have the same flow and the same tidal volume; these breaths are flow-targeted (peak flow 35 L/min) with descending ramp and volume-control (500 mL). The patient is ventilated with intermittent mandatory ventilation with volume control, flow-targeted ventilation, and pressure support. The last breath (arrow B) has a pressure support of 7 cm H2O and the peak flow measured is 55 L/min. The PEEP is 6 cm H2O. Note that the volume-control breaths are not patient initiated; only the pressure-support breath (arrow B) is patient initiated. Flow in the volume-control breaths (arrow A) has not returned to zero prior to breath initiation.
Marjolein de Wit Respir Care 2011;56:61-72
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