Dräger Evita 4 - Ventilation Modes Explained

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Description
Ventilation Modes
Ventilation Modes
Volume-controlled ventilation
with PLV and AutoFlow

AutoFlow

is a new additional function that regulates
inspiratory flow during the mandatory ventilation stroke in
the constant-volume ventilation modes IPPV, SIMV and
MMV. To explain the improvement achieved by this
function, the conventional methods are explained first:
Classic volume constant mandatory ventilation stroke
In mandatory ventilation strokes without AutoFlow

, the
»Insp.Flow« parameter restricts the inspiration flow. If the
inspiration flow is so high that the set tidal volume VT is
attained before the inspiration time Tinsp has fully
elapsed, the inspiration valve closes, and the breathing
gas supply stops. The expiration valve remains closed
until the end of the inspiration time Tinsp. This phase, the
inspiratory pause, can be identified in the curve Paw (t)
as the plateau Pplat.
This type of mandatory ventilation stroke, which for
technical reasons is found in the same form in almost all
intensive care ventilators, has two serious drawbacks:
– If the lungs are extremely non-homogeneous, the
pressure peaks can lead to the overdistension of
specific lung areas, and
– the limited inspiration flow and closed inspiration and
expiration valves during the inspiratory pause can
cause the patient to "fight" the machine, unless the
pattern of ventilation is regularly adapted to the needs
of the spontaneously breathing patient.
Manual pressure limiting with Pmax
Evita 4 can prevent pressure peaks, while maintaining the
set tidal volume VT, by means of the pressure limit Pmax.
The tidal volume VT remains constant as long as a
pressure plateau Pplat is still detectable and the flow
curve shows a brief zero flow between inspiration and
expiration.
Evita 4 performs this function by reducing the Insp. Flow
on reaching the set Pmax value. If the tidal volume VT can
no longer be attained with the selected pressure Pmax,
due to reduced compliance, the alarm "Volume not
constant" is automatically generated.
Manual pressure limiting can be performed with all Evita
models.
Paw
Flow
T
insp Te
Pplat
Insp.
pause
Pmax
(configu-
rable)
PEEP
1
f
Insp. flow
t
t