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Econometer
The econometer can be configured as a numerical
module on the screen. It helps the anaesthetist assess
the fresh gas balance during anaesthesia with reduced
fresh gas flow (low-flow or minimal-flow anaesthesia).
If there is a danger of fresh gas shortage, an advisory
message is displayed before the caution message
"FRESH GAS? !!" appears on the screen.
In the case of excess fresh gas flow, the Cicero EM
ventilator releases the excess gas by actuating the gas
overflow valve (V
). This valve is opened during the
2
expiration period and is automatically adapted to the fresh
gas flow.
Three measured values are used to calculate the
econometer reading:
– Valve V
opening ratio
2
= valve opening period as a percentage of the
expiration period.
– Opening pressure
Pressure in the breathing system immediately before
valve V
is opened.
2
– End-expiratory piston pressure
This value permits conclusions to be drawn on the
filling level of the breathing bag.
These three values are compressed by a specific
algorithm into the value displayed as a bar in the econo-
meter module, giving a qualitative assessment of the
fresh gas reserve. Depending on the reserve of fresh
gas, the indicator bar moves from its starting point (thick
vertical line) to the right or left between the extreme
values of fresh gas excess and fresh gas shortage,
passing through the ranges »none«, »low« and »high«.
Fresh gas surplus:
none
low
high
Tendency:
0
In the event of significant changes, tendency arrows
pointing in the relevant direction are displayed under the
bar indicator (to indicate rising or falling fresh gas
reserve). The reason for these changes may be changed
settings or leakage in the breathing system.
If the system is so stable that no major changes in
measured values are indicated for several minutes, no
tendency arrow is displayed.
Example of a good setting
with stable tendency.
Fresh gas surplus:
none
low
high
Tendency:
Good setting
but tendency dropping.
The qualitative assessment of the econometer reflects
the prevailing conditions in the breathing system most
accurately when anaesthetic ventilation for adults is
carried out with a rate of 6 to 25 strokes per minute.
The econometer is optimised for frequencies between
6 and 25 strokes per minute - but it can be used up to
40 strokes per minute if a slight instability can be
accepted.
The size of the breathing bag should be in a specific ratio
to the stroke volume in order to accept a buffer volume
for the patient expiration gas in addition to its basic filling.
The table below gives guideline values:
Ventilation volume
V
<
200 ml
T
200 ml < V
<
500 ml
T
500 ml < V
<
800 ml
T
800 ml < V
T
If the appropriate breathing bag is not available, select
the next larger bag.
With certain settings on the ventilator, the econometer
cannot generate any useful display and is therefore
automatically switched off.
For example, if the ventilation parameters are set so that
the piston only stops at the end of expiration, the pres-
sure values are no longer usable for the econometer due
to the influence of piston movement. Similar problems
arise with high ventilation frequencies or inverse T
ratio. The message »The econometer cannot display
measurement data at present« is then displayed.
Econometer temporarely disabled
Description
Econometer
Fresh gas surplus:
none
low
high
Tendency:
Good setting
but tendency rising.
Bag size
0.5 litre bag
1.5 litre bag
2.3 litre bag
3.0 litre bag
:T
I
E
The econometer is switched
off.
179
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