It's very nice if you're going to do it. Are you going to join up with some non-profit organization or you'd set up your own clinic in Vietnam? Vietnamese people in general is very friendly. I can't say the same thing about local officials. Setting up a healthcare facility is not that easy. There are endless hoops that you'd have to jump through. I admire you're doing it for a good cause but if I were you, I would be very careful. You don't want it to ruin your life, emotionally and financially.
Vietnam ranks the worst corrupt country in the region, keep that in mind.