No this is an urban myth
anaesthetic gas CANNOT be used int his way -at all let alone safely
comes up every y or two - watch out for words such as 'halothane or something' and ' killer truth serum gas'
The Royal College of Anaesthetists used to have an FAQ on this
but the intellects on the council voted to take it off, [ as they said it was infra dig for their very important reputations [= reflected badly on their reputations in that they were responding to such stupid suggestions]
In case anyone asks
the moscow kidnappings were terminated by direct order of Putin by pumping in an aerosolized synthethetic opiate in as a mist/smoke and there was no one on site to maintain airways so around 32 died
[ on a technical note they bussed them into the local hospital before they gave narcan and around thirty died on the way ]
see:
https://en.wikipedia.org/wiki/Moscow_theater_hostage_crisis
(oops I seem to have more knowledge of this than is )n wiki)
09 21 Beeb still carrying it, dimwitted tree-huggers !