Dräger Babylog 8000 plus Operating Instructions Manual page 136

Theory of Operation
Ventilation Modes
Volume Guarantee
(VG)
The ventilation mode extension VG allows for the volume
control of mandatory breaths. Babylog 8000 plus con-
trols inspiratory plateau pressure automatically, in order
to deliver the set tidal volume.
Changes in the mechanical properties of the respiratory
system are compensated; tidal volume of delivered man-
datory breaths remains constant.
VG may be used with ventilation modes A/C, SIMV, or
PSV. The diagram shows an example of SIMV with VG.
The advantage of volume control over time-cycled, pres-
sure-limited ventilation is that changes in resistance or
compliance will not have an impact on delivered tidal
volumes. If compliance increases, inspiratory pressure is
automatically reduced. Reversely, pressure increases for
a decrease in compliance: however, only up to the set
pressure limit P . By the same token, fluctuations in
insp
spontaneous breathing will be compensated: The more a
patient contributes by breathing spontaneously, the less
pressure the ventilator will apply. Using VG, Babylog
8000 plus will always apply just the pressure needed to
deliver the desired tidal volume. Pressure load for the
patient lung is therefore minimized as much as possible.
Without VG, the respiratory therapist must manually
readjust inspiratory pressure in order to deliver the
desired tidal volume. VG thus also frees the user from
routine chores.
Control is performed in the range from +3 cmH
P . The user determines the pressure the ventilator is
insp
allowed to apply via P .
insp
There are two situations where the ventilator will not be
able to deliver the target volume:
1. P is not sufficient.
insp
2. The inspiratory pressure pattern does not exhibit a
plateau because flow is set too low or T
short.
In both situations, Babylog 8000 plus will display a mes-
sage, if delivered V remains below 90% of target volu-
T
me.
The control operates in a breath-to-breath fashion. Expira-
tory tidal volume V is measured, compared to the target
T
volume, and a new plateau pressure is then calculated for
the next breath. After a change in target volume, it will
take about seven breaths before the corresponding
inspiratory pressure has been reached.
136
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