The drugs which are used usually don't matter one bit.  Most anaesthetic
drugs are short acting, and most come out into the milk in only tiny
amounts.  The anesthetists are not thinking.  This is knee jerk reaction.
When in doubt stop breastfeeding.  Where is the proof that it is necessary
to stop breastfeeding for 24 hours.  Here is an article which suggests it is
not necessary.  Also see Hale.

Spigset O. Anaesthetic agents and excretion in breastmilk. Acta
Anaesthesiologica Scandinavica. 1994;38:94-103 (only 5 years old, your
anesthetists are a little behind in their reading)

Jack Newman, MD, FRCPC