How long can he be barfing before I have to take him in for fluids? He's only kept down a bit of breast milk today, spit up all the formula (I supplement) and pedialyte. I don't know how much he's gotten in him total. He's be barfing since noonish.

First up I would look up online the signs of de-hydration in babies. I would not want to subject a baby to the risks of the ER-other infections and so on-if it wasn't really warranted.

Breastmilk is the best thing there is for him right now. Forget the formula, nurse him a couple of times and hour.

I have always read up that most people worry when little ones spit up milk but that in many cases the spit up looks like more than what it really is. Maybe a teaspoon size full?

I think I would try to get an estimate of what you can even if its a rough estimate before doing the ER deal like suggested above.

Does your baby have a cold? If so, a lot of what you may think is vomit is most likely mucus. My son "vomited" a lot when he was young, and this is what my doctor told me was going on.

However, when in doubt, give your baby's doctor a call! Better to be safe than sorry. :)

My son had a bad case of vomiting and throwing up for about 24 hours - he was around 9/10 months old. All he would drink was formula and he couldn't keep it down. We tried the pedialyte and he wouldn't drink it so we started mixing the pedialyte with the formula.
Anyway, pediatrician said keep checking for wet diapers and as long as he still had them everything was ok.