Fig 1. Simplified schematic piping diagram of the Siemens KION anesthetic machine used for the experiment. The designation of internal and external circuitries were coined exclusively for the purpose of clarifying the source of anesthetic in the washout. Fresh gas entered the KION at the gas distribution block. In internal circuitry , the fresh gas traversed the inspiratory fresh gas valve and was diverted through the auxiliary gas outlet to the analyzer. In external circuitry , fresh gas also traversed the inspiratory fresh gas valve but was directed into the ventilator/patient cassette and was analyzed after passing through the circle circuit. In both parts, the carbon dioxide absorber was removed from the circuit during the washout.