An instrument for the accurate and continuous measurement of halothane concentrations in nitrous oxide-oxygen...

An instrument is described which measures continuously both the halothane concentration and the composition of the carrier gas when the vaporizer is situated outside the breathing circuit. The instrument is an adapted katharometer in which the out-of-balance voltage is used to measure the concentration of one compound in a three-component mixture, and the total voltage reduction across the constant-current-supplied bridge is used to indicate the proportions of the other two components. Halothane concentrations can be determined with an inaccuracy of 0.1% for concentrations up to 6%. Nitrous oxide (N2O) concentration in the nitrous oxide-oxygen mixture, serving as carrier gas, can be determined with an accuracy of 1% over the whole range up to 100% N2O. The 99% response time of the instrument is approximately 1 min.