Effects Of Variables - Ohmeda Tec 3 Bedienungsanleitung

Effects of Variables
Temperature
The effects of variation of temperature are normally
negligible at commonly used combinations of dial setting
and ambient temperature.
The vaporizer responds very slowly to change in ambient
temperature and (to prevent the valve from closing
completely) as a safety feature the temperature sensitive
valve does not respond to temperatures below the range
12-15°C approx.
Should the vaporizer temperature be lower than this, then
the output can be expected to be lower than that indicated
on the dial.
At temperatures above the range shown on the
performance curves, the vaporizer output may be
unpredictably high - particularly if the temperature
approaches the boiling point of the anaesthetic agent.
To avoid inaccuracies due to extreme temperatures the
vaporizer should be allowed to attain a temperature in the
range shown on the performance curves prior to use.
Pressure
Vaporizers are graduated in v/v percentage at 760 mm Hg.
If the ambient pressure changes the v/v % wiU change so
that at an ambient pressure P mm Hg the delivered
percentage (D% v/v) -
Equation 1 D = % x 760
P
where % is the nominal setting of the vaporizer
It is genercilly accepted that the depth of anaesthesia
depends on the inspired partial pressure of agent and not
the concentration by volume of agent.
To obtain a consistent depth of anaesthesia when gross
changes of barometric pressure occur it is necessary to
chsmge the v/v % in inverse proportion to the barometric
pressure.
The vaporizer automatically does this and for practical
cUnical purposes the effects of the barometric pressure can
be ignored.
Back Pressure Steady
Low and Moderate Pressures;
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
downstrecim components. Equation 1 therefore applies
with term P now being the E±>solute pressure at the outlet
(i.e barometric pressure plus back pressure). Steady back
pressure reduces the v/v percentage.
High Pressures:
Pressures in excess of approximately 400 mm Hg should not
be imposed on the vaporizer since these may overcome the
loads imposed by internal thrust springs.
Low and Moderate Back Pressures;
Currently it is unlikely that the steady back pressure
imposed by commonly used downstream components
(other than some ventilators) vnll exceed 30 mm Hg at
commonly used flowrrates. Back pressures as high as this
would reduce the delivered v/v percentage (at 760 mm Hg
barometric pressure) to ;-
EquaUon2 760 = 0.96
790
of what otherwise would be expected. Under normal
clinical circumstances effects of this magnitude can b e
ignored.