Mindray V60, Operator'S Manual

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11-9
11.6 Influence of Atmospheric Pressure
The anesthetic agent partial pressure delivered by the vaporizer is all but independent of atmospheric
pressure, so that weather-based fluctuations do not need to be taken into account and altitude-based
pressure changes in the range 70 to 106 kPa will only lead to small deviations within the accuracy
specified. For this reason, the physiological effect within the specified anesthetic agent concentration
of the vaporizer is independent of atmospheric pressure.
When measuring the output concentration of the vaporizer in partial pressure, there is no influence of
ambient pressure. When measuring in volume percent, the measured values do, however, change with
atmospheric pressure and the measured values rise, when atmospheric pressure falls below 101.3 kPa.
The following formula for conversion applies:
Concentration (% partial pressure) =
Measured value (vol.%) x atmospheric pressure (kPa)
101.3 kPa
WARNING
z
Under no circumstances should the vaporizer ever be used at atmospheric pressure and
temperature at which the anesthetic agent could start to boil, as the concentration
delivered will rise and be uncontrolled.
11.7 Influence of Fluctuations in Pressure
During ventilation, pressure fluctuations on the anesthetic vaporizer can cause a higher concentration
to be delivered than is shown on the control dial setting.
The vapor in the vaporizing chamber is compressed when pressure rises, and it expands when pressure
falls. If this effect is strong enough, small quantities of saturated vapor will be pumped backwards
through the inlet of the vaporizing chamber into the fresh gas. This is described as the pumping effect.
The higher the ventilation pressure and ventilation frequency, the more rapid the fall in pressure during
expiration. The lower the fresh gas flow, the smaller the quantity of anesthetic agent in the vaporizer,
the more obvious the pumping effect. The compensation system of the vaporizer will reduce these
effects.