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When the vaporizer is turned from OFF after a period out of use, a brief high concentration may occur
which rapidly stabilises to the set concentration within approximately 10 seconds at 5 litres/minute.
The preceding phenomena are normal characteristics of vaporizers. In use the volume of vapour
involved is small compared to the volume of the breathing circuit.
7.2.8
Other Variables
Ambient temperature, input flowrate and duration of use can affect delivered concentration, particularly
when the vaporizers are used at extremes of the usual clinical range.
Note: Use of the vaporizer at high gas flows and high dial concentrations may affect the accuracy of
delivered concentrations. Refer to Performance Curves in Section 7.1 for full information.
The valve design and temperature compensation system of Tec 5 Vaporizers reduces the effects to
levels such that, under most clinical conditions, their effect on vaporizer performance is not clinically
significant. The nominal performance characteristics should be consulted for further details.
8.0
Checking The Calibration
The performance of most vaporizers which are in clinical use can be confirmed by observing patient
signs and consumption of anaesthetic agents. Some users may, however, wish to employ analysers
either as a routine procedure or as part of an investigation to determine whether any abnormalities of
performance have developed.
In order to help to achieve the reliability and consistency of performance of Tec 5 Vaporizers, Datex-
Ohmeda use closely specified test conditions, test methods and detailed protocol in conjunction with
training, experience and quality auditing systems. For these reasons the full programme necessary to
help to ensure that a vaporizer complies with Datex-Ohmeda specifications cannot practicably be
carried out in a field situation.
The following points must be considered when any measurements are being carried out on vaporizers
to assist in determining whether any abnormalities of performance have developed.
1.
In order to predict the concentration that the vaporizer can be expected to deliver, the detailed
nominal performance data and the preceding comments must be taken into account.
2. The method of test used must not be such that it bears little relation to normal conditions of
clinical use.
3.
Any sampling techniques used must be such as to ensure the following:
a) The sample is fully representative of the vaporizer output, which may not be a homogeneous
mixture at the vaporizer outlet.
b ) The absorption of agent by any connecting tubing is negligible.
4. If a number of vaporizers are being examined at the same time the probability of all of them being
consistently in error is so remote as to be negligible and the cause of any apparent error probably
lies in the test method employed.
5.
Consistent and reproducible analytical techniques must be used.
6. If unexpected results are obtained it is a wise precaution to repeat the observation because the
vaporizer may be more reliable than the techniques used to observe its performance.
7.
If unexpected results occur it is also worthwhile checking for sources of error such as the
flowmeter, leaks or absorption by adjacent components.
8.
Full account must be taken of any extraneous effects on the analyser which may arise from
changes in the carrier gas composition.
Page 28
August 1999
Tec 5 Vaporizer
O & M Manual Part No. 1105-0100-000
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