Dräger Babylog 8000 plus Operating Instructions Manual page 135

Theory of Operation
Ventilation Modes
Pressure Support Ventilation
(PSV)
PSV works essentially the same as A/C. In addition to
ventilator rate, the patient will also control the duration of
ventilator breaths via flow: A mandatory inspiration is
terminated when flow has decreased to 15 % of maxi-
mum inspiratory flow, at the latest after the set inspiratory
time T .
in
In order to allow the flow to decrease during a mandatory
breath, the pressure pattern must show a plateau (see
description of CMV). This is the condition where
increased lung pressure due to the filling of the lungs will
start to equalize with airway pressure and flow will start
to decrease.
The speed of this equalizing process is determined by
the time constant TC of the respiratory system. The
shorter TC, the faster the lung will be filling. This means
that a breath is terminated in PSV when the lung is nearly
filled. The resulting inspiratory time is perfectly tuned to
the patient.
The same rules as in A/C mode apply for triggering.
The shape of a ventilator breath is set in the same
fashion as in CMV, except for inspiratory time. If the
plateau is too short, a breath will end after T as in A/C.
in
If the patient fails to trigger breaths, ventilation is
performed as in CMV.
PSV is suitable for patients with sufficient spontaneous
respiration and respiratory control. Weaning may be
performed by successively decreasing support pressure.
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