You should never really run out of Mana. The only 2 Mana hogs on a SCH are Succor and Adoloquium. Succor is limited in its uses, as is Adoloquium.

So you really should never have to care about using too much Mana since 90% of your healing should be coming from Physick/Lustrate/Embrace and only 1 of those costs Mana.