[A mistake in the filling of a vaporizer detected by an infrared analyser of halogenated anesthetic agents].

An anaesthetic pitfall related to an incorrectly filled vaporizer, without harmful effects on the patient, is reported. A halothane specific vaporizer has been accidentally partially filled with enflurane. The incident was suspected when the Datex Normac infrared analyser, calibrated for halothane, displayed an inspired concentration of 0.83% v/v, whereas the Dräger Vapor 19 vaporizer dial was set to deliver 0.4% v/v with a fresh gas flow of 2.7 l.min-1 to a circle system. The analyser uses infrared gas spectrometry, in the 3.3 to 3.5 microns band which contains the absorption peaks of halothane, enflurane, isoflurane and methoxyflurane. The four agents have different transmittances, with halothane the greatest. The agent selection control changes the gain to correct for the selected agent. The measurements are only accurate when only one agent is present at a time. In the reported case, the displayed concentration was very high because the high gain of halothane (12.0) was applied to enflurane (enflurane gain: 2.24). An in vitro experiment measuring the values of different enflurane/halothane mixtures, carried out with the involved vaporizer, showed that it contained, at the time of the incident, a mixture of 20% enflurane and 80% halothane. It may therefore be possible to detect a vaporizer filling error when the values "measured" by the analyser are not in concordance with those set on the vaporizer. Filling an enflurane vaporizer with halothane is more dangerous, as it results in a high halothane output with a Normac "enflurane" inspired concentration remaining very low. The indexed pin safety system remains the best means of avoiding wrong vaporizer filling.