The indications for neurolytic or surgical sympathectomy are uncertain. There is no clear correlation between the degree or duration of pain relief and the actual period of sympathetic blockade and the same patient may show variable responses on different occasionsv (Loh et al 1980). Some patients demonstrate unexpected responses such as contralateral or delayed blocks and some are made worse (Purcell-Jones &Justins 1988, Evans et al 1980, Kleiman 1954)
http://www.springerlink.com/content/7013w45630522h6k/
and
http://ceaccp.oxfordjournals.org/content/10/3/88.full
and
http://ceaccp.oxfordjournals.org/content/10/3/88.full