With CRPS, we believe there are changes in the central nervous system at work. These changes wind up the pain signals from your body. Normally, bumping your leg or touching a cold item would cause a small amount of pain. In someone with CRPS, those stimuli cause intense, severe pain. This type of amplification of pain is believed to be due to activation of one of the nerve cell receptors, namely NMDA receptor. Ketamine Is a potent anesthetic that works on these receptors, blocking them from firing, which decreases the pain.