Page 26
Tec 5 Vaporizer
August 1999
O & M Manual Part No. 1105-0100-000
7.2
Effects Of Variables
7.2.1
Anaesthetic Agent Consumption
7.2.1.1
Isoflurane, Enflurane And Halothane
The rate of consumption of anaesthetic agent depends primarily on flowrate and vapour output
concentration. As an approximate working figure, 1 millilitre of liquid anaesthetic is required to provide
200 millilitres of vapour.
The approximate hourly consumption of anaesthetic agents can be expressed as 3 x % x F, where %
represents the setting of the vaporizer output percentage and F represents the input flowrate in litres/
minute.
Example:
If a vaporizer is set to deliver 2% at 6 litres/minute total gas input flowrate then the
approximate rate of consumption = 3 x 2 x 6 = 36 ml/hour.
The figures are approximate and are intended for general guidance only.
7.2.1.2
Sevoflurane
The rate of consumption of anaesthetic agent depends primarily on flowrate and vapour output
concentration. As an approximate working figure, 1 millilitre of liquid anaesthetic is required to provide
200 millilitres of vapour.
The approximate hourly consumption of anaesthetic agents can be expressed as 3.3 x % x F, where %
represents the setting of the vaporizer output percentage and F represents the input flowrate in litres/
minute.
Example:
If a vaporizer is set to deliver 2% at 6 litres/minute total gas input flowrate then the
approximate rate of consumption = 3.3 x 2 x 6 = 39.6 ml/hour.
The figures are approximate and are intended for general guidance only.
7.2.2
Temperature
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 to 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.
7.2.3
Barometric Pressure
Vaporizers are graduated in % v/v at 760 mm Hg. If the ambient pressure changes the % v/v changes,
so that at an ambient pressure P mm Hg the delivered percentage (D% v/v) is calculated as follows:
Equation 1: D =
where % is the nominal setting of the vaporizer.
To obtain a consistent depth of anaesthesia when gross changes of barometric pressure occur, the
% v/v must be changed in inverse proportion to the barometric pressure.
The vaporizer automatically makes this % v/v change and for practical clinical purposes the effects of
barometric pressure can be ignored.
% x 760
P
