Influence Of Fluctuations In Pressure During Ventilation - Dräger Medical Vapor 2000 Operating Instructions Manual

Theory of Operation
Influence of Fluctuations in Pressure During Ventilation
For effective O flushing on Dräger anesthesia delivery
2
systems a negative pressure is produced at the Vapor outlet
which may be up to 100 cm H O.
2
100 cm H O negative pressure has the same effect as raising
2
the altitude by 1000 m or a drop in boiling point of about
o
3.5 C (see page 67). As a protection against excessive
pressure, e.g. if the fresh gas hose is kinked, the Vapor has a
self-resetting pressure relief mechanism which vents the fresh
gas to the atmosphere at high pressures.
Influence of Fluctuations in Pressure
During Ventilation
When ventilation is performed or when the O flush is
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operated without fresh gas de-coupling, 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 in the literature as the pumping effect.
This pumping effect is greater,
— the higher the ventilation pressure and ventilation
frequency,
— the more rapid the fall in pressure during expiration,
— the lower the fresh gas flow,
— the lower the concentration set,
— the smaller the quantity of anesthetic agent in the vaporizer.
The compensation system of the Vapor will reduce these
effects.
When using anesthesia delivery systems without fresh gas de-
coupling and with ventilation pressures greater than 30 cm
H O, Vapor should be filled completely, if concentration set is
2
<1 vol.% and/or fresh gas flow is <1 L/min, to keep deviations
due to fluctuations in pressure as low as possible.
Continuous monitoring of the inspiratory side of the breathing
system will easily show when an overdosage is likely to occur.
The concentration set on the Vapor can then be slightly
reduced.
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