 PREVENTIVE ANALGESIA. Preventive analgesia PA is an antinociceptive treatment which prevents the establishment of the altered processing of the sensory input, that amplifies and chronic postoperative pain. The PA concept was formulated by Crile at the beginning of the century on the basis of clinical observations. There are two terms in English which refer to the same concept: preemptive analgesia, which consists of a treatment that is given before the surgical incision and maintained for intervention to avoid an altered sensory processing that amplifies and chronic postoperative pain. Is usually to compare the same way and the same drug management before and after the incision; and preventive analgesia consists of a longer lasting analgesic effect which that would theoretically be expected after administration of a certain drug on the basis of its pharmacological properties. 