My CRPS is in my left hand and wrist after surgery for broken wrist. surgery was Dec. 28,'12 and I was diagnosed Feb. 1st.
So, my nerve blocks are "stellate ganglion" done through the front/side of my neck through to the spine. I was scared to death at first.
They inject different formulations of anesthesia to the nerve area affecting the limb (pain signals from brain to limb or vice-versa). The proceedure itself is only 1/2 hr. or less & done with light sedation or not.
The effects seem to last approx 9-14 days but some of my blocks are done closer together so have overlapped.
There are some temporary side effects that differ depending on the person and other factors.
I went to youtube and found videos of the proceedure, one using flouroscope (x-ray) and one using ultrasound. After a horrible experience by one Dr. using just x-ray on my 1st one I then found a new Dr. who uses both types of guidance.

There is a lot of good advice here, hope this helps.