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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.

Oxford Miniature Vaporizer

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   

Comments on this article should be addressed to Dr Guy Watney
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