APRV
Airway Pressure Release Ventilation
Spontaneous breathing under continuous positive airway
pressure with brief pressure release. This ventilation
mode is suitable for patients with a poor gas exchange.
The patient breathes spontaneously at a high pressure
level Phigh for an adjustable length of time Thigh. For very
short expiration times Tlow, Evita 4 switches to a low
pressure level Plow. The normal lung areas are emptied,
but the "slow" lung areas only change volume to a lesser
extent.*
In this way, the ventilation/perfusion ratio can be
improved for patients with a poor gas exchange.
The steepness of the increase from the lower pressure
level to the upper pressure level is controlled by the
setting . The effective time for the increase in pressure
cannot become greater than the set time Thigh.
MMV
Mandatory Minute Ventilation
In contrast to SIMV, the MMV ventilation mode gives
mandatory breathing only if spontaneous breathing is
not yet sufficient and has fallen below a pre-selected
minimum ventilation.
This minimum ventilation is controlled by the two set
values tidal volume VT and frequency f, and results from
the product VT x f.
Unlike SIMV, the mandatory strokes are not given
regularly but only in cases of insufficient ventilation.
The frequency of mandatory strokes is determined by the
level of spontaneous breathing: if spontaneous breathing
is sufficient, mandatory strokes are not used.
If spontaneous breathing is not sufficient, intermittent
mandatory strokes of the set tidal volume VT are applied.
If there is no spontaneous breathing at all, the mandatory
strokes are applied at the set frequency f.
____________
* Bibliography (6), (7), (8), (9), page 182
Description
Ventilation Modes
168
Thigh
Tlow
Phigh
Plow
t
Paw
Paw
Flow
T
insp
Pmax
PEEP
short
rise time
long
rise time
trigger phase
V
T
Insp. Flow
t
t
1
f
ASB
pressure support
MV
sufficient spontaneous
breathing
spontaneously
breathed MV
set
MV
mandatory MV
beginning spontaneous
breathing
no spontaneous
breathing
t
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