A reflection filter for isoflurane and other anaesthetic vapours

A new way of saving anaesthetic vapours is described. The method is analogous to the heat-moisture exchanger principle: the vapour is trapped in a filter during expiration and is returned to the patient during the subsequent inspiration. Fresh vapour is supplied on the patient side of the filter. A small container with 60 ml of a hydrophobic zeolite (an inorganic material) was used as filter. In model lung tests, this reduced the isoflurane consumption by 51% at a tidal volume of 300 ml, by 57% at 600 ml and by 51% at 930 ml. Neither isoflurane nor halothane yielded any degradation products when brought in contact with the zeolite.