You should check the blood flow,I mean which veins are still in use,for that they inject some stuff to see the veins.In Bangsaen at Burapha university hospital they have an english speaking specialist,but pretty busy.First you need an appointment there,after that he will give you an appointment for vein screen(I had to wait 6 weeks),i don't remember how much I paid.To make an appointment you need a thai speaker.It is government hospital but very ok