Effects of carrier gas composition on the output of six anaesthetic vaporizers.

The effect of carrier gas composition on the output of six anaesthetic vaporizers was studied using oxygen, nitrous oxide, helium and argon as the carrier gases. Vaporizer output was measured with an MGA 200 mass spectrometer and a Riken refractometer and, in addition, the pressure decrease across each vaporizer was determined simultaneously. A change in carrier gas composition produced both a transient and a steady state change in vaporizer output. The possible reasons for the changes in steady state output are discussed in relation to the construction of each vaporizer. The addition of nitrous oxide to the carrier gas produced changes of clinical significance only when the vaporizers were used at extreme dial settings and flow rates.