My dr said there's no point in doing more symoathetic blocks because I've had minimal relief. She wants to try a bier block. Anyone have experience with these?

On a side note i told the pain dr that my ot thinks I have an injury to my scaphoid ligament and asked if she got the chart notes requesting an Mri. She pretty much said that she and the hand specialist knew what they were seeing and a mri would be a waste of time?? I got frustrated and little tears came to my eyes and I said that I really wasn't content with an rsd diagnosis cause I don't want to think I have some forever thing (she just got done telling me there was little more they could do) when there is a question about an injury and my bone scan disnt show soft tissue so how could they know?

So she said she would read the notes and think on it. But we needed to do the bier block first.
Just wanted to hear some experiences of what this is like. Kind of scares me as I've had a interscalene block get into my blood stream and it was a horrible experience. And this is intentionally injecting anesthetic into my blood stream? Can they be sure the tournicate is efficient in preventing that?