Well, there's this:

Mortality Associated with Implantation and Management of Intrathecal Opioid Drug Infusion Systems to Treat Noncancer Pain, Coffey RJ, Owens ML, Broste SK, et al, Anesthesiology 2009;111:881-891, full text at http://www.rsds.org/2/library/articl...L_BrosteSK.pdf