Dependency On Alternating Pressure During Ventilation - Dräger Vapor 2000 Technical Documentation Manual

3.6

Dependency on alternating pressure during ventilation

Alternating pressures to which an anaesthetic vaporizer is subject during ventilation without
fresh gas decoupling may cause a higher concentration to be delivered than is set on the
handwheel.
When the pressure increases the vapour in the vaporizer chamber is compressed. When the
pressure decreases the vapour expands again. If this pumping effect becomes strong
enough, it pumps small amounts of saturated vapour backwards through the inlet of the
vaporizer chamber into the fresh gas.
This pumping effect becomes all the more pronounced:
− the higher the ventilation pressure and frequency
− the faster the decrease in pressure during exhalation
− the lower the fresh-gas flow
− the lower the pre-set concentration
− the less anaesthetic there is in the vaporizer.
The compensation device of the Vapor 2000 effectively reduces these effects.
When used on anaesthetic machines without fresh gas decoupling and at ventilation
pressures higher than 30 mbar, with concentration settings < 1 vol.% and/or fresh-gas flow
< 1 L/min the Vapor 2000 should be fully filled, in order to minimise deviations resulting from
alternating pressure.
5327.400 Vapor 2000 05/99 Function Description
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