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Influence of temperature
Vapor compensates for changes in temperature through
the different thermal expansion characteristics of two
different materials. The saturation concentration of the
anaesthetic agent, which rises as temperature rises, is
automatically balanced by routing a higher proportion of
the gas flow through the vaporising chamber-bypass.
This proportion is increased as temperature rises
because the material which makes the gap has a lower
thermal expansion than the material which surrounds it.
Temperature compensation changes the gap in a linear
manner. This compensation does not exactly match the
non-linear variation of the saturation concentration for the
whole temperature range, so that the concentration
delivered still remains slightly dependent on temperature.
The deviations are within the accuracy specified between
15 ° and 35 °C. The diagrams show typical dependence.
The deviations increase for temperatures outside this
range, despite continuing compensation.
Under no circumstances must the temperature of the
anaesthetic agent reach boiling point, as the concentra-
tion delivered will then become impossible to control. As
altitude increases, boiling point falls:
Boiling point of anaesthetic agent °C
Atmospheric 1013 hPa 900 hPa
pressure/
Altitude
0 m
Halothane
50.2
Enflurane
56.5
Isoflurane
48.5
Sevoflurane 58.6
The operating range of Vapor with Dräger anaesthetic
machines has been set in such a way that, in the most
critical situation of 700 hPa, 35 °C and a maximum
negative pressure of –100 mbar on the Vapor, the boiling
point of the anaesthetic agent cannot be reached.
Temperature compensation is resistant to ageing and
hysteresis, but is affected by a certain inertia:
differences in temperature between Vapor and the room
within the 15 to 35 °C range are compensated within the
concentration accuracy specified.
However, if the temperature of the Vapor before use was
outside 15 to 35 °C, a time of 15 min/°C has to be
allowed for temperature adjustment if the concentration is
to remain within the accuracy specified.
800 hPa 700 hPa
1000 m
2000 m
3000 m
46.8
43.4
39.8
53.4
50.3
46.8
45.4
42.2
38.9
53.4
52.1
48.7
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Concentration
Abgegebene
Halothane
delivered [vol.%]
Konzentration [Vol.%]
5.0
4.0
3.0
2.0
1.0
10
15
20
Concentration
Abgegebene
Enflurane
delivered [vol.%]
Konzentration [Vol.%]
5.0
4.0
3.0
2.0
1.0
10
15
20
Concentration
Abgegebene
Isoflurane
delivered [vol.%]
Konzentration [Vol.%]
5.0
4.0
3.0
2.0
1.0
10
15
20
Concentration
Abgegebene
Sevoflurane
Konzentration [Vol.%]
delivered [vol.%]
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
10
15
20
Description
Influence of temperature
Set
Eingestellte
concentration
Konzentration
[vol.%]
[Vol.%]
5.0
4.0
3.0
2.0
1.0
0.5
25
30
35
40
Temperature [°C]
Temperatur [°c]
Set
Eingestellte
concentration
Konzentration
[vol.%]
[Vol.%]
5.0
4.0
3.0
2.0
1.0
0.5
25
30
35
40
Temperature [°C]
Temperatur [°c]
Set
Eingestellte
concentration
Konzentration
[vol.%]
[Vol.%]
5.0
4.0
3.0
2.0
1.0
0.5
25
30
35
40
Temperature [°C]
Temperatur [°c]
Set
Eingestellte
concentration
Konzentration
[vol.%]
[Vol.%]
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.5
25
30
35
40
Temperatur [°c]
Temperature [°C]
33
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