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Description
Ventilation Modes
Automatic leakage compensation
Evita 4 determines the difference between the delivered
flow on the inspiration side and the measured flow on the
expiration side.
This difference provides a measure of the amount of
leakage and is displayed by Evita 4 as the leakage minute
volume MV
. Evita 4 can compensate for this leakage
leak
in volume controlled ventilation.
Example:
Tidal volume setting V
= 500 mL, 10 % leakage in tube.
T
Leakage compensation Off
Evita 4 delivers 500 mL. This is indicated as the
inspiratory tidal volume V
. 50 mL escape as leakage
Ti
during inspiration, and 450 mL reach the lung. 450 mL
are expired, and 45 mL again escape as leakage.
A tidal volume of 405 mL is measured on the expiration
side and indicated as V
.
Te
With a ventilation rate of 10 strokes per minute, a minute
volume of 5.0 L/min is delivered on the inspiration side
and a minute volume of 4.05 L/min is measured on the
expiration side. The lung is ventilated with an MV of
4.5 L/min.
Without leakage compensation, the set V
the volume delivered by Evita 4.
Leakage compensation On
With automatic leakage compensation, Evita 4 delivers
550 mL on the basis of the measured leakage minute
volume, instead of the 500 mL set. 500 mL enter the
lung and the displayed inspiratory tidal volume V
500 mL.
The volume of 450 mL measured on the expiration
side is displayed without compensation, even when
leakage compensation is activated. The minute volume
measured on the expiration side is 4.5 L/min and is also
uncompensated.
If this were not so, the alarm for a low minute volume
could be inhibited by the expiratory leakage
compensation. Evita 4 must always emit an alarm if
the minute volume is too low.
With leakage compensation, the set V
the volume to be delivered to the patient.
This example has been simplified:
In fact, the calculated leakage correction takes into
account the pressures in the hose system. A higher
percentage volume is lost on the inspiration side than on
the expiration side because the pressure during
inspiration is higher. The displayed leakage minute
volume MV
is based on the mean pressure P
leak
172
determines
T
is
T
determines
T
.
mean
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