The correct is Итого операционных расходов или Итого операционные расходы.
What part of the speech is Итого
Adverb "in all, altogether, totally".
Use cases:
"Итого, поездка удалась" = "Altogether it was good journey".
"У нас было итого десять долларов" = "We had 10$ in total".
As was said above, in blanks, tables and programs it can be just substitute for "In total: ..." and rules for cases just do not apply to content of '...'.
Because of "итого" is adverb, "общие доходы" и "итого доходов" are not interchangable grammatically.