A comparison of keyed and non-keyed vaporizer filling modes and volatile agent wastage.

Two hundred and forty bottles of enflurane were collected after their contents had been emptied into vaporizers equipped with keyed or non-keyed filling ports. The volume of agent remaining, the residual volume, was measured. There was a greater (p < 0.001) residual volume in 'empty' bottles which had been used to fill keyed compared with non-keyed enflurane vaporizers. Five hundred and fifty two bottles of isoflurane were also collected after they had been used to fill keyed vaporizers. There was no significant difference between the residual volume remaining in bottles of isoflurane and enflurane used to fill keyed fillers; however, the difference was statistically significant if the residual volume was expressed as a proportion to the volume of agent contained in the full bottle. The results show that volatile anaesthetic agent wastage is increased by the use of keyed fillers. Isoflurane wastage caused by utilisation of keyed fillers could be reduced by a factor of 2.5 by supplying isoflurane in 250 ml rather than 100 ml bottles.