Page 19
3.10 Detailed description of TTV
plus
, HFO
MAP Compensation & Automatic
Leak Compensation in PSV modes
3.10.1 TTV
plus
TTV
plus
is based upon providing a stable expired
volume at the lowest possible pressure at the set Ti.
3.10.1.1 Detailed Description
When in TTV
plus
mode, the PIP is automatically
controlled to try and maintain the set expiratory
volume. As a safety measure, the pressure cannot
exceed the set Max PIP.
Spontaneous breath volumes are ignored for the
purposes of control.
If SIMV+PSV is used with TTV
plus
then the ventilator
can deliver machine breaths at two different PIP
levels and therefore deliver two different volumes.
No attempt is made to deliver the TTV
plus
volume for
the PSV breaths, only the mandatory breaths are
volume controlled. However the PSV breath
pressure level will change because it is defined as a
percentage of the mandatory breath ∆P (PIP minus
PEEP), which is volume adjusted.
3.11 Automatic Leak Compensation in
PSV modes
If a large leak is present in the respiratory circuit, it
may prevent the flow from being terminated in PSV
mode. If the leak flow is above the selected
termination sensitivity level the flow would not
terminate as the flow would never reach the
termination level.
An algorithm has been added that will compensate
for the leak and enables the termination levels
below leak flow to be terminated at the leak flow
level.
If the termination level is above the leak flow, the
flow is terminated at the selected termination level.
An algorithm would compensate for leak flows up to
5 l/min or 50% of the peak flow whichever happens
first. It is also only active if the leak volume is
between 10% to 50%.
3.12 HFO mean compensation
The ventilator includes a compensation algorithm
that closely maintains the set mean airway pressure
when the Delta P is increased/decreased.
In certain situations the mean airway pressure may
still increase in response to changes in Delta P as
the algorithm only has limited control over the
inadvertent mean airway pressure (10 mbar). The
feature may be disabled by the user if required.
Warning: The user should set the MAX PIP
close to measured PIP (4 to 5 mbar above
measured PIP or as per clinical
recommendation). If the flow sensor is
removed from the circuit (for suctioning or re-
calibration) and the patient circuit is
reconnected, the ventilator senses that the
Vte has dropped below the set target level. It
will then increase the pressure up to the set
MAX PIP to try and achieve the set Vte.
Note: HFO mean compensation cannot be
disabled whilst in a ventilatory mode.
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