Barring a suggestion from someone with more precise medical knowledge, it seems like this must refer to anesthetic applied to a "puncture channel" (i.e. a place where a surgical device has passed through tissue or a place where a wound has been created from something passing through the tissue, such as a nail or bullet, etc.). Langenscheidt suggestions "puncture channel" or "entry wound" for "Stichkanal," and there are numerous hits on Google of authoritative Web sites that talk about anesthesia applied to or used with such channels or wounds:

Among others:
http://www.klinik.uni-frankfurt.de/zrad/diagnostik/pub/vogl_...
http://www.wjgnet.com/1007-9327/9/94.asp
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&d...

Staying very close to the original is also often best in medical contexts like this, so that's my suggestion.