Appendix D: Theory of Breath Delivery
219
At that point, the ventilator terminates flow, allowing the patient to exhale.
Figure 169: Pressure Support Breath Waveform
PATIENT SPONTANEOUS BREATH
A spontaneous breath is a patient breath which is initiated and terminated by the
patient like a patient support breath. The only difference between these two
subtypes of breaths is that the spontaneous breath pressure is maintained at the
PEEP level (PSV=0) during the inspiratory phase. Flow is regulated by the ventilator
to meet the patient’s inspiratory flow demand and to maintain airway pressure at
the PEEP level. An inspiratory phase in this breath type continues until:
The flow decreases to a set value of the peak flow (Esens); or
The airway pressure exceeds a value 5 cmH2O above PEEP; or
Three seconds or two breath periods have elapsed; whichever occurs first.
At this point, the ventilator terminates flow, allowing the patient to exhale.
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