I think when referring to the 'max' dose of levo.. it's the point when the levo is actually harming the pt.. as opposed to supporting the pt.
I just used levo... at 0.4mcg/kg/min on a pt recently (52cc/hr). The pt weighted roughly 130+ kg.
After the 0.4mcg/kg/min mark.. we would have been shutting down here peripheral vasculature completely.
As someone stated before... after a certain point.. it becomes terminal. You start to see the discoloration of the fingers and toes.. and eventually they begin to mottle.
If you've maxed out on levo and are not in a 'terminal' situation.. you simply need to add other pressor support.
In my case.. we added vasopressin.. and our next option would have been a straight epinephrine drip.
Luckily the pt responded... and 2 days later i was halfed on the levo gtt.. and the vasopressin was off.