Ambient Temperature; Back Pressure - Datex-Ohmeda Tec 7 User's Reference Manual

Ambient temperature

Back pressure

w w w w WARNING
Steady back pressure
Fluctuating back pressure
1175-0013-000
The effects of variation in temperature are normally negligible at commonly used
combinations of dial setting and ambient temperature.
If the vaporizer temperature is above the range shown on the performance curves, the
vaporizer output may be unpredictably high, particularly if the temperature of the
agent approaches the agent boiling point specified by the agent manufacturer.
If the vaporizer temperature is below the range shown on the performance curves, the
vaporizer output may be lower than expected.
To help avoid inaccuracies due to extreme temperatures, before using the vaporizer it
must be allowed to attain a temperature within the range shown on the performance
curves.
Pressures in excess of 400 mmHg may overcome the internal pressure
balance and cause a variation in output.
The vaporizer cannot distinguish between pressures at the outlet due to barometric
pressure and pressures in excess of barometric due to steady back pressures applied
by downstream components. The equation given in the section Barometic Pressure
therefore applies with the term P now being the absolute pressure at the outlet, that is,
barometric pressure plus back pressure. Steady back pressure reduces the % v/v.
Currently, it is unlikely that the steady back pressure imposed by commonly used
downstream components, other than some ventilators, exceeds 30 mmHg at
commonly used flowrates. Back pressures as high as 30 mmHg would reduce the
delivered % v/v, at 760 mmHg barometric pressure, to the following:
760
= 0.96 of what would otherwise be expected.
-------- -
790
790
Under normal clinical circumstances effects of this magnitude can be ignored.
Fluctuating back pressure may be imposed on the vaporizer by downstream
components and/or assisted or controlled ventilation to the patient. These fluctuating
back pressures can affect the vaporizer and increase the concentration by
intermittently altering the pressures, and consequently the flow distribution, within the
vaporizer.
The greatest effects are observed at combinations of very low flowrates and low dial
setting with large and rapid pressure fluctuations. The effects become progressively
less important as the dial setting and flowrate increase and the magnitude and rate of
cycling of the pressure fluctuations decrease.
7 Specifications
7-9