Influence of gas composition
The concentration delivered is dependent on the compo-
sition of the fresh gas since the viscosity and density of
the gas changes from one gas and composition to
another. The Vapor is calibrated with Air because the
concentration delivered is then in the middle of the range
for available anaesthetic gas mixtures.
When 100 % O
2
is used the concentration delivered
compared with Air rises by 15 % of the set value at most,
up to a maximum of 0.3 vol.%
When 30 % O
2
and 70 % N
2
O is used, it falls by 15 %
of the set value at most, and by not more than 0.3 vol.%.
The effect of gas composition varies slightly for different
anaesthetic agents and, for this reason, maximum effects
are given here.
When changing from one gas mixture to another, an
additional dynamic effect can occur which may result in a
further deviation in concentration until the earlier fresh
gas is flushed out of the vaporising chamber.
These deviations and their duration are all the greater,
– the lower the volume of anaesthetic agent in the Vapor
– the higher the concentration set and
– the more extreme the change of gas type.
The extent of this dynamic deviation increases as gas
flow increases, though the duration of the deviation
decreases.
The diagram shows the dependence of concentration
delivered on the fresh gas composition at a 1 vol.%
setting. Illustration of maximum measured deviations in
the entire 0.25 to 15 L/min flow range at 1 vol.% (22
°
C,
atmospheric pressure 1013 hPa, Vapor 1/4 filled).
35
Description
Influence of gas composition
0
20
40
60
Minuten
0
0,5
1
1.5
Einstel-
lung am
Handrad
Vol.% bei
1013 hPa
+ 0.2 Vol.%
+ 0.15 Vol.%
– 0.15 Vol.%
100% Air
30% O
2
70% N
2
O
100% O
2
Gaswechsel
Gaswechsel
Vol.% at
1013 hPa
minutes
Setting on
hand-
wheel
gas change
gas change
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