The uptake of halothane given in constant concentration (1 per cent) was shown to be more rapid in a mixture with 70 per cent N2O than in one with 10 per cent N2O. This demonstrates that the uptake of a gas is influenced by the constituents of the mixture of which it is a component. Changes in the concentration of other components which are sufficient to produce a significant concentration effect will produce alterations of uptake rate of companion gases given in constant concentration ("second gas effect"). This acceleration of uptake was interpreted to be a result of additional inspiratory inflow secondary to the absorption of N2O at a higher concentration. This absorption produces the concentration effect on the rate of uptake of the N2O itself, also observed in this study. Second gas effects presumably occur as well for the other gases in the inspiratory mixture, including the usual respiratory gases.
(C) 1964 American Society of Anesthesiologists, Inc.