The use of ketamine in complex regional pain syndrome: possible mechanisms.

Complex regional pain syndrome is a neuropathic pain syndrome that is characterized by: severe pain beyond the area of injury; autonomic dysregulation; neurogenic edema; movement disorder; and atrophy and dystrophy. Ketamine is an open-channel NMDA blocker that only acts on those receptors whose Mg(2+) block has been lifted. It is effective in the treatment of the syndrome when standard treatments have failed. Different protocols are utilized depending on the severity of illness. There have been no serious ketamine-induced complications from these protocols, owing to careful psychological screening and the liberal use of midazolam and lorazepam to counter any psychomimetic effects and clonidine to block possible 'Olney's' lesions.