This is a method, developed in the past few years, for reducing pain after surgery. It would appear to be particularly suitable for any operation intended to reduce pain. What follows is my attempt to interpret the medical texts I have read.
A general anesthetic works on the brain and the central nervous system. Among other effects, it stops the brain 'hearing the screams' from the nerves in tissues damaged by surgery. A local anesthetic or powerful analgesic, on the other hand, works by stopping the nerves from 'screaming'. This difference is important. If you have only a general anesthetic during surgery, the nerves are generating signals of extreme pain, and this leaves the local nervous system in a highly excited, hyper-sensitive, state after the surgery. Because of this, a minor stimulation, such as touch, is felt as pain. This can persist for weeks.
Pre-emptive analgesia consists of giving a powerful pain-killer to the patient before surgery starts, in addition to the general anesthetic. This prevents the nerves from becoming too excitable. To be fully effective, the analgesia needs to be continued for some days after surgery, while the damaged tissue starts to repair itself. Research has shown that this procedure can significantly reduce pain after some surgical operations.