We have dragged Reason from her Throne and set in her place the Empress of Dreams [liber Endvra]
Amor, sola lex
(referring to the version of the AO included in the core set)
Ithaqua's ability read:
Each time an investigator uses either a unique item or a spell, he loses 1 stamina
A fellow geek asked (link) whether using a Heal spell during Final Battle with one Stamina left would result in the investigator being devoured or healed (at -1 Stamina).
This is the official answer from Dane that solves all conflicts derived from Ithaqua's ability:
Q:When playing with Ithaqua, does an item’s entire effect resolve before Icy Winds takes effect?
A:Yes, the item’s entire effect resolves first, then Ithaqua’s Icy Winds ability resolves.