The most common complication is post-sympathectomy neuralgia

Neural Blockade in Clinical Anesthesia and Management of Pain

By Michael J. Cousins, Phillip

"The most common complication is post-sympathectomy neuralgia.... The reported incidence has varied widely between studies, from around 30% to 50%. Whether the sympathectomy is achived by open surgical resection or percutaneous techniques does not seem to influence the incidence."

Vascular Surgery: Principles and Practice

by Robert W. Hobson, Samuel E. Wilson, Frank J. Veith - 2004 - Medical - 1600 pages
Postsympathectomy neuralgia is a constant and annoying feature of sympathectomy, and the patient should be forewarned.