11-8
11.5 Influence of Gas Composition
The concentration delivered by the vaporizer is dependent on the composition of the fresh gas since the
viscosity and density of the gas changes from one gas to another. The vaporizer is calibrated with Air
because the concentration delivered is then exactly in the middle of the range for the anesthetic gas
mixtures available.
When 100% O
2
is used, the output concentration compared with Air rises by 10% of the set value and
by not more than 0.5vol.%.
When a mixture of 30% O
2
and 70% N
2
O is used, the concentration falls by 10% of the set value at
most, and by not more than 0.5vol.%.
The effect of gas composition is different for different anesthetic 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 any earlier fresh gas is flushed out of the vaporizer.
These deviations and their duration will all be greater under the following circumstances:
1. The lower the volume of anesthetic agent in the vaporizer;
2. The higher the concentration set;
3. The lower the gas flow;
4. 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 will decrease.
The following diagram shows the influence of gas composition on output concentration when carrier
gas is set to 1 vol.%.
If the humidity of gas is higher than that specified in appendix A “Product Specifications”, the output
concentration will be affected slightly.
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