Performance Effects Of Variables - VisualSonics VEVO Operator's Manual

Appendix B: Specifications and Performance
Agent usage
Performance effects
of variables
Temperature
Flow
Carrier gas composition
32 VisualSonics Vevo Integrated Rail System Operator Manual
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small, and the variation in output when used with Intermittent Positive
Pressure Respiration is negligible.
The rate of consumption of anesthetic agent depends primarily on flow
rate and vapor output concentration.
The rate of evaporation of anesthetic agent may, with caution, be used as
an approximate method of checking that the delivered output is not
grossly in error, and as a means of estimating how often the vaporizer is
likely to need refilling. The approximate hourly consumption of
anesthetic agents can be expressed as follows:
3 x % x F
Where % represents the setting of the vaporizer output percentage, F
represents the input flow rate in liter/min.
Example: if a vaporizer is set to deliver 2% at 6-liter/min. total input gas
flow rate:
Approximate rate of agent consumption = 3 x 2 x 6 = 36 ml/hour.
The figures are intended only for clinical guidance and are approximate.
They will vary depending upon the type of anesthetic agent employed,
accuracy of graduation of flowmeters, etc., and will be grossly in error if
the vaporizer drain port is not fully closed.
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 changes 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 of approximately 12 - 15 ºC (54 - 59 ºF). Should the vaporizer
temperature be lower than this, the output can be expected to be lower
than that indicated on the dial.
At temperatures above 32 ºC (90 ºF), the vaporizer output may be
unpredictably high - particularly if the temperature approaches the
boiling point of the specific anesthetic agent.
To avoid inaccuracies due to extreme temperatures, the vaporizer should
be allowed to attain a temperature of 20-32 ºC (68 - 90 ºF).
The vaporizer compensates for variations in inlet flow from 300 ml to 10
liters per minute with minimal change in output concentration.
Resistance to flow within the vaporizer is minimal: 40 cm/H 2 0 (30 mm/
Hg) at 10 liters per minute.
Small effects can occur when the carrier gas composition is changed from
oxygen to air or nitrous oxide/oxygen mixture. As a general rule,
variation of output with carrier gas composition can be considered of
negligible clinical significance since the effects, if any, are normally less
than 10% of setting. Where changes do occur, the usual effect is that the
output is slightly depressed when nitrous oxide is employed compared to
V1.0