Low-Resistance
Vaporizers
Some vaporizers
are designed to have a low internal resistance to gas flow so that
they may be used within the breathing circuit, the gas flow being
driven through them by the patient's breathing. They may be used
in a non-rebreathing draw-over
apparatus, or as in-circuit
vaporizers in a circle absorber
system.
Vaporizers used in draw-over applications
are usually of the simple bottle or bowl
type (e.g. the Ohio 8 bottle, Goldman or Stephens), but more
accurate, low resistance draw-over vaporizers, such as the Penlon
Oxford Miniature Vaporizer (OMV) and Ohmeda Draw-Over Tec vaporizers,
have been manufactured.
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Oxford
Miniature Vaporizer
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The OMV is particularly
versatile, since the same vaporizer can be used to vaporize a number
of agents with only the dial scale being changed.
Some precision vaporizers (such as
the Fluotec 2) have a sufficiently low internal resistance that
they may be used in draw-over applications (ventilation being assisted
or controlled if necessary), but the resistance of the majority
of precision vaporizers is much to high for them to be used in this
way.
Low resistance vaporizers may also
be used in place of precision vaporizers if necessary. However,
the inaccuracy and, frequently, restricted output of the bowl-type
vaporizers makes them less satisfactory than a precision vaporizer
in most situations. In addition, the inlet and outlet may need to
be adapted to fit the normal 23 mm vaporizer connectors.
Measured-flow
vaporizers
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